--- title: "Cyclotron Ion source Design: 291 Sourced Rules · Cyclotron Info" canonical: https://cyclotroninfo.com/design-guide/ion-source/ description: "291 sourced ion source design rules for small and tabletop cyclotrons, each with formula, verbatim quote, and page citation. Rules for the internal source: filament and PIG geometry, gas feed and its vacuum load, arc conditions, chimney slits, and the starting conditions an orbit needs from the center." generated: 2026-11-12 note: "Markdown rendering of the canonical HTML page, generated at build for AI assistants and text tools. Figures and interactive elements are described, not reproduced. On Design Guide rules the source quote, this site's paraphrase and this site's editorial note are labelled separately and must not be conflated." licence: "Datasets CC BY 4.0, census snapshot CC BY-NC 4.0 (https://cyclotroninfo.com/data/); cite as Cyclotron Info, cyclotroninfo.com" --- [Design Guide](https://cyclotroninfo.com/design-guide/) › Ion source # Cyclotron Ion source Design: 291 Sourced Rules 291 of the guide’s 2199 rules carry the ion-source tag. Rules for the internal source: filament and PIG geometry, gas feed and its vacuum load, arc conditions, chimney slits, and the starting conditions an orbit needs from the center. Each rule keeps its formula where the source gives one, a verbatim quote, a page-level citation, and a stable identifier (`dg-NNNN`) that resolves here and on the [all-in-one guide](https://cyclotroninfo.com/design-guide/). Where an editorial note says “the reference machine”, its parameters are on the [guide’s front page](https://cyclotroninfo.com/design-guide/#reference-machine). By applicability level: [level 1](https://cyclotroninfo.com/design-guide/?domain=ion-source&level=1) (2) · [level 2](https://cyclotroninfo.com/design-guide/?domain=ion-source&level=2) (74) · [level 3](https://cyclotroninfo.com/design-guide/?domain=ion-source&level=3) (167) · [level 4](https://cyclotroninfo.com/design-guide/?domain=ion-source&level=4) (47) · [level 5](https://cyclotroninfo.com/design-guide/?domain=ion-source&level=5) (1) — levels rank breadth, never license to skip ([method](https://cyclotroninfo.com/about/methodology/#rule-levels)). Related domains, by shared rules: [Vacuum](https://cyclotroninfo.com/design-guide/vacuum/) (47), [Beam dynamics](https://cyclotroninfo.com/design-guide/beam-dynamics/) (42), [Materials](https://cyclotroninfo.com/design-guide/materials/) (38), [Beam measurement](https://cyclotroninfo.com/design-guide/beam-measurement/) (35), [Fabrication](https://cyclotroninfo.com/design-guide/fabrication/) (34). To combine tags or levels, open this domain in the [filterable view](https://cyclotroninfo.com/design-guide/?domain=ion-source). **Verify before use.** Every rule here is a *source extract* in the vocabulary of the [editorial methodology](https://cyclotroninfo.com/about/methodology/) — faithful to its cited page, not an independently validated engineering requirement. Re-read any rule that drives a real design decision at the cited page before committing metal, money, or high voltage to it. The **editorial note** under each quote is this site’s extrapolation to a tabletop machine, not something the source said: an editor’s judgement, audited for overreach, never a citation. [Figure, drawn on the page: Cross-section of a cold-cathode PIG ion source cut along the magnetic field axis. A vertical anode chimney tube contains the plasma column. Tantalum cathode discs close the tube at top and bottom, each on an insulated mount, both wired to one negative arc supply; the chimney is grounded. Electrons oscillate vertically between the cathodes along the field. Hydrogen feeds into the chimney near the lower cathode. Ions leave through a chamfered slit in the chimney wall at the median plane, toward a puller electrode on the dee.] *Figure caption:* anatomy of an internal cold-cathode PIG source, drawn to the published proportions of the medical-cyclotron class. Left: two tantalum cathode discs (~7 mm dia × 2 mm, Mu et al. 2015) close an anode chimney of 7–8 mm bore; both cathodes ride one negative supply while the chimney is grounded, since nearly the whole arc voltage drops at the cathode sheaths (Wolf 1995, p. 71). Trapped electrons oscillate along B between the cathode faces, ionizing the gas; hydrogen enters near a cathode "to ease ignition of the arc and to keep the neutral gas flow through the extraction slit in the anode low" (Wolf 1995, p. 70). Ions leave through a chamfered slit — 0.7 × 5.2 mm on the Siemens Eclipse (Potkins et al. 2017) — pulled by the dee RF through a puller aperture 2.3 mm (Eclipse) to 2.9 mm (K100) away (Forringer 2004, p. 85). Right: the same region seen from above; the first half-turn must clear the chimney body, which sets a minimum dee voltage for a given chimney size (Koeth 2006, p. 5). Schematic, not a fabrication drawing: wall thicknesses, mounts, and cooling are simplified, and the dee gap is exaggerated. Each drawn part is a link that opens the matching Design Guide rules. **dg-077** · applicability level 2 · magnet, rf, vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-077 - **Rule (this site's paraphrase of the source):** Before freezing magnet geometry, check the design against every subsystem it must host: RF system, vacuum pumping, ion source/injection, extraction or internal target, and diagnostic probes. - **Source quote (verbatim):** “Cyclotron magnet design should always consider interaction with subsystems: RF system, vacuum pumping, ion source or injection system, extraction system or internal target, diagnostic probes.” - **Source:** [Zaremba, Magnets for Cyclotrons (2005)](https://cyclotroninfo.com/library/#lib-032) — p. 3, 45 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A magnet that works but leaves no port for the probe or the pump is a classic amateur trap - exactly what this five-item checklist exists to prevent; run it on every layout iteration for a next machine. **dg-242** · applicability level 1 · ion-source, rf, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-242 - **Rule (this site's paraphrase of the source):** If using an ion-source chimney, verify the first half-turn clears the chimney body: with a 0.5-in dee gap and Rs = 0.8 ohm, calculated first ions clear at ~200 W RF (50 W is far too low, 500 W comfortable). - **Formula:** `First-turn radius from x,y solutions with E = Vpeak/gap; thresholds: 50 W too low, ~200 W first ions clear, 500 W sufficient` - **Source quote (verbatim):** “an input RF power level of 50 watts is too low, and 500 watts should be sufficient. The first ions are expected to clear the chimney at approximately 200 watts.” - **Source:** [Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006)](https://cyclotroninfo.com/library/#lib-013) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A geometry trap for a next machine: any chimney or source structure must be smaller than the first half-turn diameter set by the dee voltage, or beam dies before the first gap crossing. **dg-244** · applicability level 3 · ion-source, beam-dynamics, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-244 - **Rule (this site's paraphrase of the source):** If beam peaks with the source displaced off-center, suspect unequal accelerating voltage along the dee faces (transmission-line droop, measured up to 5 percent) driving orbit-center precession; displacements over 2 in have been needed on large machines. - **Formula:** `D-face voltage droop up to 5%; compensate by radial source offset` - **Source quote (verbatim):** “there will be a somewhat lower potential at the ends of the D faces nearest the lines ... measured in some cyclotrons to be as great as 5 per cent ... a displacement of the ion source of over 2 in. has been necessary.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 164 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Make the source mount adjustable in both directions and tune position for beam, not for geometric center. Size the travel from RF-field and orbit modelling for the actual dee geometry - the large machines needed over 2 inches; what a tabletop machine needs is its own calculation, and generous commissioning range is cheap. - **Cited in:** [Beam Dynamics: An Interactive Laboratory](https://cyclotroninfo.com/learn/beam-dynamics/) **dg-249** · applicability level 3 · ion-source, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-249 - **Rule (this site's paraphrase of the source):** Match the exposed ionization-column length to the dee aperture: MIT's optimum was 5/8 in for a 1.6-in aperture, the Carnegie 60-inch's 1-3/8 in for 4-in dees (ratios ~0.39 and ~0.34) - an over-long column loads the RF circuit with off-focus ions and drags down dee voltage. - **Formula:** `two historical optima at ~0.34-0.39 x internal dee aperture - observed ratios, not a law` - **Source quote (verbatim):** “At MIT, with an internal D aperture of 1.6 in. the optimum length of ionization column was 5/8 in. For 4-in.-wide D's in the Carnegie Institution 60-in. machine it was 1 3/8-in.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 178 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Hood or collimate the reference machine's source with the exposed column ADJUSTABLE, starting near a third of the aperture height, and optimize against extracted beam and dee voltage together - the historical ratios locate the starting point; the machine's own optimum may sit elsewhere. **dg-261** · applicability level 2 · ion-source, rf, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-261 - **Rule (this site's paraphrase of the source):** Set the extraction gap by the empirical vacuum-breakdown limit d[mm] >= 1.41e-2 \* U[kV]^1.5 (clean flat surfaces): 10 kV needs >=0.45 mm, 30 kV >=2.3 mm, 50 kV >=5 mm; smaller gaps arc, much larger gaps waste extraction field. - **Formula:** `d[mm] >= 1.41e-2 * (U[kV])^(3/2)` - **Source quote (verbatim):** “The voltage breakdown limit determines the necessary gap width. The empirically determined limit (valid for clean, flat surfaces) is d[mm] >= 1.41 x 10^-2 \* phi[kV]^(3/2).” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 379 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Direct rule for source-to-puller spacing - clean DC gaps are the law's home turf: a few-kV gap needs sub-mm minimum, with real margin because sputtered metal films spoil the 'clean surface' assumption fast. For dee-to-ground RF clearances use it only as a lower-bound sanity check: edges, insulators, RF conditioning and enhancement move the practical limit (dg-353, dg-662). **dg-295** · applicability level 3 · rf, ion-source, safety · https://cyclotroninfo.com/design-guide/ion-source/#dg-295 - **Rule (this site's paraphrase of the source):** Prebreakdown current in HV vacuum gaps is field emission from microscopic whiskers (runaway as local field approaches ~1e10 V/m, enhancement beta = lambda^2/ln(lambda)); slow 'conditioning' - holding voltage while microampere pulses burn off the sharpest points - raises the measured threshold, so condition new electrodes gradually. - **Formula:** `Fowler-Nordheim j ~ E_l^2 exp(-6.43e9*phi^1.5/E_l); E_local ~ 1e10 V/m for runaway; beta = lambda^2/ln(lambda) for whisker aspect lambda; conditioning partially lost after 24 h off or air exposure` - **Source quote (verbatim):** “A large increase in current occurs only as the local field approaches 10^10 V per meter... After several minutes of current flow at the constant voltage, a remeasurement of the threshold voltage shows that it has increased. This phenomenon is called conditioning.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 111-113 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Bring the reference machine's dee and extraction voltages up gradually on first pump-down, watching for micro-discharge pulses. Conditioning raised the measured threshold in the source's account; the gain is not permanent capital - re-condition after venting rather than assuming the old ceiling still holds. **dg-299** · applicability level 3 · rf, ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-299 - **Rule (this site's paraphrase of the source):** Coaxial HV feedthrough geometry: peak field sits on the inner conductor at E_max = V/(r_i\*ln(r_o/r_i)), minimized when r_i/r_o = 1/e ~ 0.37; and keep the radius of curvature at the outer conductor's edge no smaller than the inner conductor's radius so the edge stress stays below the bore stress. - **Formula:** `E_max = V/(r_i*ln(r_o/r_i)); optimum r_i/r_o = 1/e; edge radius of outer electrode >= r_i; concentric spheres optimum R_o/R_i = 2` - **Source quote (verbatim):** “The optimum ratio as r_i/r_o = 1/e. This optimum ratio minimizes the stresses within the coaxial electrode arrangement, independent of the material of the dielectric used. ... In order to keep stress at Z below that at X in Fig. 4.15, the radius of curvature at Z should not be less than the radius of the inner cylinder.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 117, 122-124 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Preliminary ideal-coax sizing for the reference machine's HV stalk: a grounded 25-mm-bore port gives a ~9.2-mm center conductor at the 1/e optimum - then check the complete feedthrough (ends, dielectric interfaces, triple junctions) electrostatically, and never leave a sharp-edged washer or nut on the HV end. **dg-300** · applicability level 3 · ion-source, rf, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-300 - **Rule (this site's paraphrase of the source):** Sputtered cathode metal deposits on the HV stalk and can in time cause premature breakdown: practiced mitigations are shadow shielding (INEL's nested coaxial aluminum tubes), a conical insulator facing the cathode to block ions passing through the grid (UIUC), and corrugated insulator surfaces to lengthen the surface-leakage path. - **Formula:** `design options: shadow shields between plasma and insulator; corrugated/conical insulator profile; expect W/Fe/Al sputter films; clean with diamond file or sandblast (sandblasting can ruin polished grids)` - **Source quote (verbatim):** “This phenomenon causes the cathode grid material from the IEC device to be deposited on the high-voltage (HV) stalk. That can in time cause premature breakdown at the stalk. ... The electrode is surrounded by a coaxial aluminum tube, which in turn is shadowed by a coaxial large diameter, aluminum tube. ... The stalk is a conical-shaped insulator facing toward the cathode grid that is expected to block the ions passing through the cathode grid. ... The corrugated surface is intended to lengthen surface current path lengths, preventing premature surface breakdown.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 87, 105, 109 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In the reference machine's small chamber everything sees the source; a washer-stack or skirt shielding the feedthrough ceramic from the chimney slit is the same shadow-shield idea and should lengthen time between cleanings - validate on the actual geometry, since much of the sputtered flux travels as neutral atoms and simple line-of-sight shielding is the right first-order defense. **dg-310** · applicability level 4 · ion-source, rf, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-310 - **Rule (this site's paraphrase of the source):** Houghton's ion-source filament circuit: a standard AEI hairpin electron-microscope filament floating at about -90 V, heated by 2 A, with RF pickup on each filament lead shorted to ground through a 0.001 uF capacitor. - **Formula:** `filament bias -90 V, heater 2 A, 0.001 uF RF bypass on each lead` - **Source quote (verbatim):** “A standard AEI hairpin electron microscope filament floating at approximately -90 V is heated by 2 A of current ... RF pickup on each filament lead is shorted through a 0.001 uF capacitor to ground.” - **Source:** [Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013)](https://cyclotroninfo.com/library/#lib-041) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A replaceable-filament pattern worth copying next to a live dee: bias the filament, and RF-bypass every lead at the feedthrough - but size the bypass for the actual RF impedance and current, and use capacitors rated for the DC bias plus transients rather than copying 1 nF. **dg-347** · applicability level 3 · ion-source, materials, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-347 - **Rule (this site's paraphrase of the source):** Use graphite for arc bodies, cones, and dee feelers near the source - it runs hot with minimal sputtering and evaporation; feeler extensions ('auspullers') on the dee faces opposite the source have been used to improve beam intensity - they decrease the physical spacings, raise the electric field at the source, and change the first electric lens's dimensions and focal properties. - **Source quote (verbatim):** “Graphite is coming into wide use for cones, arc bodies, and also for D feelers or accelerating electrodes; it operates at high temperatures with a minimum of sputtering or evaporation. ... Extensions on the D faces opposite the source, called 'feelers' or 'auspullers,' have been used to improve beam intensity; they decrease the physical spacings and increase the electric field at the source. They also change the dimensions and focal properties of this first electric lens.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 166-178 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Graphite source parts run hot without spraying metal; a feeler on the dee edge is a cheap first-turn-capture upgrade with historical standing - though even the source notes quantitative evidence on its focusing effect was thin, so tune it empirically. **dg-348** · applicability level 2 · beam-dynamics, dee, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-348 - **Rule (this site's paraphrase of the source):** There is no magnetic vertical focusing at the machine center (n=0 by symmetry); the first turns survive because the dee-gap electric field acts as an electrostatic immersion lens - so central-region electrode geometry and RF phase matter most in the first few turns. - **Formula:** `n(r) ~ r^2 near center -> no magnetic focusing at r=0; gap E-field provides focusing, modified by transit time` - **Source quote (verbatim):** “There is no vertical magnetic focusing at the center of the magnet. By a fortunate coincidence, electrostatic focusing by the accelerating fields is effective for low-energy ions.” - **Source:** [Humphries, Principles of Charged Particle Acceleration (1986)](https://cyclotroninfo.com/library/#lib-085) — p. 524, 526 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Explains why source-to-dee geometry (chimney position, puller gap, aperture height) dominates beam capture on small machines: at the center magnetic vertical focusing vanishes and only builds as n grows off zero with radius, so the electric gap lens is what the first turn or two get. Central-region electrode design is where capture is won on the documented machines. **dg-357** · applicability level 3 · ion-source, dee, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-357 - **Rule (this site's paraphrase of the source):** Insulate the filament (1-3 V DC) from the dee, which sits at 1-2 kV RF in this machine class, with a ~0.18 cm machinable ceramic plate; barrel connectors epoxied to the ceramic carry the leads. - **Formula:** `dee RF 1-2 kV vs filament 1-3 V; 0.18 cm ceramic insulator` - **Source quote (verbatim):** “the RF voltage on the dee is typically between 1 and 2 kV, far greater than the 1-3 V DC placed across the filament. Thus, the filament and wires must be adequately insulated from the dee ... Insulation was supplied by a 2.33 cm by 2.71 cm machinable ceramic rectangle approximately 0.18 cm thick. ... Two barrel connectors, each 1.28 cm long and 0.32 cm in diameter, were glued to the ceramic insulator using Hysol Loctite 1C vacuum epoxy” - **Source:** [Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009)](https://cyclotroninfo.com/library/#lib-003) — p. 54 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Matches the reference machine's ~1.3 kV operating point today. At the planned 5-13 kV, do not just scale the creepage proportionally: reassess peak field and vacuum surface flashover for the actual geometry and check the feedthrough's rating. **dg-362** · applicability level 2 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-362 - **Rule (this site's paraphrase of the source):** Prefer oil diffusion pumps over mercury for accelerator columns: mercury vapor promotes autoelectronic (field-emission) discharges from high-voltage electrodes, and fast pumping is needed for steady discharge conditions. - **Source quote (verbatim):** “Fast pumping is required and it is desirable to use oil rather than mercury diffusion pumps as mercury seems to promote autoelectronic discharges from the electrodes.” - **Source:** [Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933)](https://cyclotroninfo.com/library/#lib-055) — p. 259-260 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Moot for pump choice today; the observation transfers cautiously: the source found mercury vapor SEEMED to promote field emission from HV electrodes, and condensable conductive films on electrodes are a recognized breakdown risk generally - keep electrode surfaces free of deposition, sputtered films included (dg-261's clean-surface caveat). **dg-363** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-363 - **Rule (this site's paraphrase of the source):** A canal-ray (obstructed glow) proton source: maximum current came from a discharge at about 20 kV, with the Faraday cylinder collecting on the order of 1 mA against 20 mA in the discharge - a 5% collected-to-discharge current ratio in that geometry. - **Formula:** `cited apparatus: ~20 kV optimum; 1 mA collected / 20 mA discharge = 5% (collected current, species unresolved)` - **Source quote (verbatim):** “the maximum current is produced from a discharge running at about 20,000 volts... the current collected by the Faraday cylinder F into which it can penetrate is of the order of 1 milliampere with 20 milliamperes in the discharge.” - **Source:** [Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933)](https://cyclotroninfo.com/library/#lib-055) — p. 260-261 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Sets the historical scale: percent-class collected current from tens of mA of glow discharge - a budgeting anchor, not a conversion efficiency; aperture acceptance, extraction and species mix all live inside that 5%, so measure your own ratio before sizing the discharge supply. **dg-364** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-364 - **Rule (this site's paraphrase of the source):** Keep the anode-cathode annular gap too small for a discharge to build up in it - the cited source spaced its coaxial steel tubes about 4 mm apart - so the discharge concentrates naturally on the cathode canal hole; the cathode and tubes can run red-hot and radiate their heat. - **Formula:** `cited geometry: ~4 mm annular clearance (that gas, pressure and voltage - validate the suppression gap for your own conditions)` - **Source quote (verbatim):** “The space between the two steel tubes is too small for a discharge to build up there and it concentrates naturally on the hole in the cathode. ... The anode is a second steel tube A, supported axially inside the cathode and separated from it by about 4 mm ... the cathode C and the steel tubes can run red-hot” - **Source:** [Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933)](https://cyclotroninfo.com/library/#lib-055) — p. 260-261 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The 'gap smaller than the discharge can live in' principle is how a builder forces the source discharge to localize at the extraction aperture rather than wander - pick the clearance for the actual gas, pressure and voltage and verify it empirically; the 4 mm is the source's worked point. **dg-365** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-365 - **Rule (this site's paraphrase of the source):** A fresh hydrogen discharge beam is largely molecular ions, becoming nearly all protons only after extended running - condition the source before assuming beam species, and verify with magnetic analysis. The source's own kinematics: an H2+ at the full accelerating voltage is a pair of protons each carrying half the energy, so disintegration onset appears at about twice the voltage and the yield curve rises twice as steeply. - **Formula:** `at fixed accelerating voltage: H2+ of energy E = two protons of E/2 (onset doubles, curve twice as steep); at fixed magnetic rigidity each constituent carries ~1/4 the proton energy; H2+ orbits at half the proton cyclotron frequency` - **Source quote (verbatim):** “At first this beam consists very largely of molecular ions, but after running for some time it changes over and becomes nearly all protons ... The H2+ ion may be thought of as a pair of protons travelling together with an electron. The binding energy between them is negligible compared with the kinetic energy, which for either proton is one-half the energy of the particle. Hence a given current of molecular ions represents a current of protons of twice the magnitude, but with half the energy. We would therefore expect to begin to detect disintegration particles at about twice the energy found for the protons, and that the curve would rise twice as steeply.” - **Source:** [Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933)](https://cyclotroninfo.com/library/#lib-055) — p. 261-262, 269 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For p-B11 the point survives translation with care: a proton-tuned cyclotron does not even hold H2+ in resonance (half the cyclotron frequency), but any acceleration mode that does deliver molecular ions yields constituent protons at a half (fixed voltage) or a quarter (fixed rigidity) of the expected energy - and p-11B is exothermic with no kinematic threshold, so what collapses is the cross-section-weighted yield, not an on/off threshold. **dg-366** · applicability level 3 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-366 - **Rule (this site's paraphrase of the source):** Degas an accelerating column by running a hydrogen discharge at about 20-60 kV, then pump out: in the source's experience the tube was then quite hard and stable up to 200 kV, and once degassed, about half an hour of running each morning restored steady state. - **Formula:** `conditioning discharge ~20-60 kV; after pump-out, stable to 200 kV; ~30 min morning run restores steady state (source's experience)` - **Source quote (verbatim):** “This is continued at as high a current density as possible for about half an hour and on pumping out the hydrogen it is usually found that the tube is quite hard and stable up to 200,000 volts.” - **Source:** [Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933)](https://cyclotroninfo.com/library/#lib-055) — p. 7 (printed page 265; offset = printed minus 258) - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A historical conditioning observation for electrode structures that must hold voltage - adapt, don't copy: ramp with current and stored-energy limits, remote operation, interlocks, and a measured breakdown-rate criterion, and remember DC column conditioning does not transfer one-to-one to RF dees. **dg-367** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-367 - **Rule (this site's paraphrase of the source):** If measured beam current is very low even close to the ion source (the large-turn-spacing region where probe masking cannot be the cause), be suspicious of the ion source first. - **Source quote (verbatim):** “one should be suspicious of the ion source if the measured beam current is very low in the region close to the ion source, i.e. the regime of large turn spacing” - **Source:** [Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006)](https://cyclotroninfo.com/library/#lib-013) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A triage order for the reference machine's low-current debugging: measure current at small radius first; if it's already low there, put ion production and extraction at the top of the checklist - while still verifying RF capture, focusing, alignment and the probe itself, since the clue is suggestive, not exclusive. **dg-368** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-368 - **Rule (this site's paraphrase of the source):** Livingston & Blewett's worked hot-cathode arc source: 3 A discharge at 100 V, ~2 A electron beam from the exit hole, gas flow 2 cm3/min at atmospheric pressure - and a resonant ion beam that 'might be about 0.5 mA'. - **Formula:** `arc 3 A at 100 V; electron beam ~2 A; gas 2 cm3/min (STP); resonant beam 'might be about 0.5 mA' (their words)` - **Source quote (verbatim):** “arc current, 3 amp; arc voltage drop, 100 volts; electron beam from exit hole, 2 amp; gas flow, 2 cm3/min at atmospheric pressure. The resonant ion beam pulled from such a source ... might be about 0.5 ma.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 175-178 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The architecture point transfers at any size: a differentially pumped source cavity running much higher pressure than the chamber, fed through the exit hole (the Penning-table rules carry pressure numbers - dg-372). The single operating point is a sanity anchor for a similar source, not a spec or a promise of half a milliamp. **dg-369** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-369 - **Rule (this site's paraphrase of the source):** Heat the source cathode with DC or ~100 kHz AC rather than low-frequency AC, to avoid vibration damage in the magnetic field; keep oxygen out of the gas (it materially shortens cathode life) and expect reported service lives of 100-200 hr, ended by erosion of the emitting spot on the cathode. - **Formula:** `cathode: heavy W or Ta rod; heating dc or ~100 kc; reported life 100-200 hr (erosion of an exit-hole-sized spot)` - **Source quote (verbatim):** “The heating power is either dc or high-frequency ac (~100 kc) to avoid damage from vibration in the magnetic field at low frequencies. Cathode life is ... materially shortened by traces of oxygen. Lifetimes in service of 100 to 200 hr have been reported. The limit is due to erosion of a small area the size of the exit hole on the cathode surface, which represents the effective emitting surface.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 177-178 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A mains-frequency-heated filament in a 0.59 T field risks vibrating itself to death; DC heating and clean hydrogen are cheap reliability. **dg-370** · applicability level 2 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-370 - **Rule (this site's paraphrase of the source):** MIT's machine: base pressure better than 1e-6 mm Hg with no gas flow, about 2e-5 mm Hg operating with deuterium flowing - the ion-source gas load, not outgassing, set the working pressure on that machine (2400 l/s of pumping on a 2000 l volume). - **Formula:** `MIT: 2400 l/s on 2000 l volume; base <1e-6 mm Hg, operating ~2e-5 mm Hg with D2 flow` - **Source quote (verbatim):** “With no gas flow, chamber pressures of better than 1 x 10-6 mm Hg are obtained. With the deuterium gas flow from the ion source, the operating pressure is about 2 x 10-5 mm Hg.” - **Source:** [Livingston & Blewett, Particle Accelerators (1962)](https://cyclotroninfo.com/library/#lib-012) — p. 198 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Expect a large pressure rise when source gas flows: on a tight system the flow-on/flow-off ratio identifies the source as the load, while a rise WITHOUT flow is the leak-or-outgassing signature. What operating pressure a machine can afford is the beam-survival calculation's answer (the vacuum calculator's orbit mode), not MIT's 2e-5. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-371** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-371 - **Rule (this site's paraphrase of the source):** Heat a spiral filament ion source with high-frequency AC: the cited machine used it to minimize destructive magnetic effects on the spiral - the heater current interacting with the main magnetic field produces alternating J x B forces that the filament cannot mechanically follow when the frequency is high. - **Source quote (verbatim):** “The filament is heated to incandescence by a high-frequency a-c power supply. The high-frequency is used to minimize self-destructive magnetic effects in the spiral filament.” - **Source:** [McGuire, The Iowa State University 1.5 MeV Undergraduate Cyclotron (1961)](https://cyclotroninfo.com/library/#lib-037) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A real failure mode for hairpin/spiral filaments in a strong main field. DC removes the alternating force entirely (at the cost of a static deflection), so the practical choice is high-frequency AC or DC depending on filament geometry - mains-frequency AC is the option to avoid; filament life is a chronic tabletop complaint either way. **dg-372** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-372 - **Rule (this site's paraphrase of the source):** Penning-source housekeeping numbers from the handbook's table: gas consumption ~0.2 sccm (hot- and cold-cathode columns; 0.2-0.6 heated, 0.2-1.1 low-duty), source pressure 1-10 Pa, ignition 3 kV (hot-cathode column) to 5 kV (cold-cathode) - single values per column, a span across columns, not a printed range - though the running arc is 0.3-1.3 kV (1-5 kV for the high-arc column); the same table carries extraction voltages, anode apertures and cathode spacings for the larger machines. - **Formula:** `gas ~0.2 sccm; p_source = 1-10 Pa; V_ignition = 3 (hot) / 5 (cold) kV per column; V_arc = 0.3-1.3 / 1-5 kV` - **Source quote (verbatim):** “Operating Data of Penning Ion Sources: Arc voltage 0.3-1.3 / 1-5 kV; Ignition volt. 3 / 5 kV; Gas pressure 1-10 Pa; Gas consumption 0.2 sccm; Extraction voltage 5-25 / 5-35 kV; Anode aperture 1 x 25 / 1.5 x 25 mm; Cathode distance 10 / 6.5 cm.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. PDF p.101 (printed p.90), TABLE 5.5 in section 5.3.7 Operating Data - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's MFC should be sized and calibrated around the table's ~0.2 sccm scale, and the arc supply must tolerate a several-kV open-circuit ignition transient before folding back to run voltage - the table's ignition/run split is the reason. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-373** · applicability level 3 · materials, ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-373 - **Rule (this site's paraphrase of the source):** Match structural metals to their real vacuum temperature limits: stainless to ~1000 C (alloys with Ta/Mo above 900 C!), Mo to 2000 C (goes brittle, use TZM), Ta to 2600 C, W to 3400 C but nearly unmachinable, W-Re alloys are formable filament stock, graphite to 3500 C but outgasses and holds a memory effect. - **Formula:** `service limits: Cu 600 C, Ti 800 C, SS 1000 C, Mo 2000 C, Ta 2600 C, Re 3150 C, W 3400 C, graphite 3500 C` - **Source quote (verbatim):** “Molybdenum can be used up to 2000 C... there is a special alloy, TZM... Tantalum... up to 2600 C... W-Re alloy is an easily shaped filament material... graphite... can be used to high temperatures (3500 C)... showing a long memory effect.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. PDF p.355 (printed p.344), section 2.1 High-Temperature Metals - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The trap in a source chimney is any hot joint touching stainless: the source's warning is that stainless alloys with BOTH tantalum and molybdenum above 900 C, so an intermediate piece helps only if the stainless contact itself stays below the reaction range - move the joint to a demonstrably cooler region or add thermal length. And check pairs, not just single-metal limits: graphite on hot tantalum can form carbides. **dg-374** · applicability level 3 · materials, ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-374 - **Rule (this site's paraphrase of the source):** Pick hot-zone insulators by temperature and outgassing: Macor machinable but brittle, good vacuum behavior to ~1000 C; boron nitride excellent to 1200 C and usable to 1500 C where it starts to decompose and release large quantities of nitrogen - but it outgasses badly and absorbs water, so bake gently after air exposure; alumina is the high-temperature workhorse of the source's list. - **Formula:** `Macor ~1000 C; BN 1200 C (to 1500 C, decomposing, N2 release); source's list also gives quartz ~1000 C, alumina 1400 C, zirconia 1600 C (conductive above ~1000 C)` - **Source quote (verbatim):** “Macor or glass ceramic can be easily machined, but is very brittle. It has good vacuum behavior and can be used up to about 1000 C. ... Boron nitride is an excellent material for most applications for temperatures up to 1200 C. It can be used up to 1500 C but starts to decompose and releases large quantities of nitrogen. It outgasses badly and tends to absorb water, which can destroy the parts when heated too fast.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 356 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** BN filament insulators in a home source must be pre-baked and brought up to arc power slowly the first time after air exposure, or they crack and gas up the chamber. **dg-375** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-375 - **Rule (this site's paraphrase of the source):** Space-charge-limited extraction current density follows Child-Langmuir in practical units: j[mA/cm^2] = 1.72\*sqrt(q\*/u)\*U[kV]^1.5/d[cm]^2 -- for protons at 10 kV across a 5-mm (0.5 cm) gap that is ~220 mA/cm^2, far above a hobby cyclotron's needs. [Correction, Aug 2026: the source prints the denominator as d[mm], but the 1.72 coefficient requires d in centimeters; the originally extracted example (~2.2 mA/cm^2) was low by 100x. Verified against the SI form of Child-Langmuir. The verbatim quote below preserves the source's own text.] - **Formula:** `j[mA/cm^2] = 1.72*sqrt(q*/u)*(phi[kV])^(3/2)/(d[cm])^2` - **Source quote (verbatim):** “In more practical units, this equation can be rewritten: j[mA/cm2] = 1.72 \* sqrt(q\*/u) \* phi[kV]^(3/2) / d[mm]^2.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 376-377 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Confirms the reference machine's nA beams are nowhere near space-charge limits; if extraction is weak the problem is geometry/plasma matching, not the Child-Langmuir ceiling. **dg-376** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-376 - **Rule (this site's paraphrase of the source):** Design round-aperture extraction around an aspect ratio (aperture radius : gap) of S ~ 0.5; the source's Eq. 11 - built on its Refs. 11 and 12 - then estimates the per-aperture current limit I[mA] = 0.703\*sqrt(q\*/u)\*U[kV]^1.5, and the plasma density must be matched to the field or the beam over/under-focuses. - **Formula:** `S = r/d ~ 0.5; source Eq. 11: I[mA] = 0.703*sqrt(q*/u)*U[kV]^(3/2) - carries the cited references' corrections, not bare Child-Langmuir (ideal round-aperture CL at S=0.5 gives a coefficient near 1.35); divergence w0 = 0.5*(r/d)*(1 - 1.67*Pi_normalized), round apertures` - **Source quote (verbatim):** “For the cylindrically symmetric case the maximum current can be estimated from References 11 and 12 and the assumption of a certain aspect ratio (aperture radius to electrode separation). A good aspect ratio is on the order of S = 0.5.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 379 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For the puller gap in a next machine, carry over the shape of the rule - aperture dimension about half the extraction gap, beam parallelism tuned by matching plasma density - but the cited numbers are for round apertures: model the actual chimney slit electrostatically or by simulation rather than substituting the slit half-width, and expect to adjust both arc density and geometry. **dg-377** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-377 - **Rule (this site's paraphrase of the source):** Size thermionic cathodes with the Richardson formula, where temperature is the STEEPEST knob - a 10% temperature change swings emission ten- to a hundred-fold, the quoted sensitivity - so regulate filament heating tightly. - **Formula:** `j_sat = A*b*T^2*exp(-e*phi/kT) A/cm^2, A = 120.4 A/cm^2K^2; W: phi = 4.54 V, A*b = 60; Ta: phi = 4.12 V, A*b = 60; thoriated W (Th on W): phi = 2.63 V, A*b = 3.0` - **Source quote (verbatim):** “The increase of the saturation current with temperature is very strong; a 10% change in temperature corresponds to a 10-fold increase of 20% to a 100-fold increase.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 38-39 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's hydrogen filament source lives or dies on filament temperature stability, so a finely adjustable constant-current supply is worth more than raw power. Area, work function and surface condition set the baseline the temperature knob multiplies - and space-charge-limited extraction caps what raw emission increases can deliver. **dg-378** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-378 - **Rule (this site's paraphrase of the source):** Budget filament heater power from radiation: refractory-metal filaments radiate roughly 20 W/cm^2 of surface at 2000 K, and nearly all input power leaves as radiation rather than end conduction, so the surrounding chimney/anode must take that heat. - **Formula:** `P_rad ~ 20 W/cm^2 at 2000 K (W, Ta, Mo similar); at fixed temperature: I ~ d^1.5, V ~ l/sqrt(d)` - **Source quote (verbatim):** “Most of the power put into a filament is radiated and very little is lost through the ends. Most high-temperature metals show similar radiation behavior (~20 W/cm2 at 2000 K).” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 39 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A few cm^2 of hot filament dumps tens of watts into the reference machine's source body; the hood/chimney around the filament needs a conductive heat path to the pole or water cooling. **dg-379** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-379 - **Rule (this site's paraphrase of the source):** Run refractory filaments at the lowest temperature that gives enough emission - evaporation-limited lifetime is savage: the handbook's tables give a 1-mm W wire ~8,300 h at 2500 K but ~46 h at 2900 K, and a 1-mm Ta wire ~7,000 h at 2400 K but ~350 h at 2600 K, with lifetime scaling linearly with wire diameter. - **Formula:** `evaporation-limited estimates, 1-mm wire: W 2500 K -> 0.30 A/cm^2, 8.3e3 h; 2700 K -> 1.6 A/cm^2, 500 h; 2900 K -> 7.3 A/cm^2, 46 h. Ta 2400 K -> 0.65 A/cm^2, 7.0e3 h; 2600 K -> 2.7 A/cm^2, 350 h. Life proportional to diameter` - **Source quote (verbatim):** “The increase of temperature for higher electron output is limited by the increasing evaporation of cathode material, which decreases the cathode lifetime. Tables 1.2 and 1.3 give the respective data for W and Ta.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 41-42 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a next machine, a fatter filament run cooler at ~0.1-1 A/cm^2 buys far more run time - but the tables are evaporation-limited upper estimates: in a real arc source, ion bombardment, sputtering and contamination can dominate, so measure actual filament life rather than banking on the table. **dg-380** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-380 - **Rule (this site's paraphrase of the source):** Discharge-type sources with good confinement reach >=50% gas efficiency (multicusp: >50% for hydrogen), while poorly confined sources run 10-20%; every neutral that escapes the chimney loads the main vacuum, so gas efficiency is a vacuum-design parameter. - **Formula:** `gas efficiency: multicusp/e-bombardment <=50% (H2 >50%); plasmatron family 10-20% to 50%` - **Source quote (verbatim):** “Gas efficiency: >50% for hydrogen and higher for other gases.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 57, 69, 110 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** At 0.2 sccm feed and 50% efficiency only ~0.1 sccm leaves the chimney as neutrals - but the extracted ions end their lives in the same vacuum envelope (implanted, neutralized, desorbed later), so higher gas efficiency shifts where and when the load appears more than it deletes it. It still pays: neutral leakage at the source is continuous and concentrated in the beam region, so better confinement is worth real pumping speed there even though total throughput is conserved. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-381** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-381 - **Rule (this site's paraphrase of the source):** Expect 10-100 h filament life in this source class; the Freeman template is a quiet 40-70 V, 1-3 A arc with a quite massive ~2-mm Ta or W cathode rod heated by ~130 A at a few volts. Erosion concentrates at the positive filament end, so changing heater polarity after some running time improves cathode lifetime; AC heating evens the wear but increases plasma instabilities and ion energy spread. - **Formula:** `filament life 10-100 h (cited source class); Freeman: V_arc 40-70 V, I_arc 1-3 A, ~2-mm rod cathode, I_heat ~130 A; reverse heater polarity after some running time` - **Source quote (verbatim):** “The arc current is 1 to 3 A and the arc voltage just 40 to 70 V. A quite massive cathode rod, usually 2 mm in diameter and made of tantalum or tungsten, is heated with about 130 A and a few volts to the right temperature. ... The erosion of the filament is not uniform, but stronger at the positive end due to electron movement and higher plasma density. Changing the polarity of the filament after some time of operation improves cathode lifetime. Heating by ac has the same effect but increases plasma instabilities and the energy spread of the extracted ions. ... The lifetime of the source is given by the lifetime of the filament, which is between 10 and 100 h” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 73 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a next machine: a thick rod cathode instead of thin wire is the cheap lifetime upgrade, plus an arc-hours log. Polarity reversal on a ~130 A heater that may float at source potential is not a toggle-switch job - reverse only de-energized and discharged, through buswork or contactors rated for the heater current and the source-to-ground voltage. **dg-382** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-382 - **Rule (this site's paraphrase of the source):** Standard extraction slit for slit-type arc sources is about 2 mm wide by 40 mm long; longer slits (90 mm cited; designs to 100 x 5 mm realized) lose current-density uniformity along the slit because of the bigger voltage drop along the cathode - though the source notes careful anode and field design has overcome this. - **Formula:** `slit ~ 2 x 40 mm typical; 100 x 5 mm max realized` - **Source quote (verbatim):** “The extraction slit is usually about 2 mm wide and about 40 mm long. Larger slits are possible, such as 90 mm, but there are some disadvantages because the current density is not uniform along the long slit due to the bigger voltage drop along the cathode. By careful design of the anode and the magnetic field, however, it was possible to overcome this problem. ... The extraction slit is usually 40 x 2 mm but designs up to 100 x 5 mm have been realized.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 74, 76 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a cyclotron chimney, the ~2 mm slit width is the historical arc-source value to start from; the slit's length and total area still matter for gas load, arc stability and beam interception, so optimise chimney length and aperture for the actual puller and dee geometry against measured beam. [Note revised 2026-08-23: earlier note said only the few millimetres facing the dee gap matter.] **dg-383** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-383 - **Rule (this site's paraphrase of the source):** PIG/Penning discharges split into two useful regimes: cold-cathode (arc above 1 kV at 0.5-5 A) and hot-cathode (arc below 1 kV at 1-50 A); the handbook adds that the magnetic field matters little above a minimum around 0.1 T, and that arc voltage rises as gas flow is cut until the discharge goes unstable. - **Formula:** `cold cathode: V_arc > 1 kV, I = 0.5-5 A; hot cathode: V_arc < 1 kV, I = 1-50 A; B_min ~ 0.1 T; high-pressure regime 0.1-100 Pa` - **Source quote (verbatim):** “the arc voltage increases with decreasing gas flow... until the discharge becomes unstable... There is little influence of the magnetic field on the discharge parameters as long as it reaches a certain minimum of roughly 0.1 T.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. PDF p.82 (printed p.71), section 5.2.2 Characterization of the PIG Discharge - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's center field clears the handbook's 0.1 T minimum, which makes an internal PIG a candidate - trading the fragile filament for a self-heated cathode running a sub-kV, multi-ampere arc. Suitability is more than field magnitude: geometry, cathode cooling at multi-ampere currents (dg-416) and pumping all vote; the regime table is the starting point, not the qualification. **dg-384** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-384 - **Rule (this site's paraphrase of the source):** Extracted current from a PIG source was proportional to arc current under the source's anode-extraction conditions, at roughly 10-100 (mA/cm^2) per ampere of arc; ion current density at the cathodes - and extractable density there - runs five to ten times the anode value. The arc supply is therefore the first knob for beam scaling, though extraction field, plasma meniscus and space charge set their own limits. - **Formula:** `j_extracted ~ (10-100 mA/cm^2) per A of arc current; ion current density at cathodes is 5-10x that at anode` - **Source quote (verbatim):** “The ion current to the anode has about the same value as to the cathodes, which means that the ion current density at the cathodes is five to ten times the density at the anode surface, and, consequently, the extracted current densities show the same relation. The total extracted current of a PIG ion source is proportional to the arc current, and for extraction through the anode, about 10 to 100 (mA/cm2)/A.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 82 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** With a ~1 mm^2 chimney slit, a 1-A arc offers ~0.1-1 mA of ideal aperture current - orders of magnitude above the reference machine's nA accelerated beams. That margin lives at the slit: capture, centering and transmission still take their share, so treat it as headroom, not proof the source can never be the bottleneck. **dg-385** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-385 - **Rule (this site's paraphrase of the source):** Cold-cathode PIG arcs are limited to about 1 kW per cathode by the onset of thermal electron emission (material- and design-dependent); titanium is the selected best-compromise cold-cathode material, tantalum if the cathodes run hot; a cathode is worn out when its sputter-erosion crater depth reaches about the anode bore radius, after which the discharge becomes unstable. - **Formula:** `P_arc(cold) < ~1 kW per cathode; end of life: crater depth ~ anode bore radius; Ti best cold-cathode material, Ta if run hot` - **Source quote (verbatim):** “The arc power for cold cathode operation is limited to about 1 kW per cathode, because of the start of thermal electron emission, and depends on the cathode material and the ion source design. ... Titanium has been selected as the best compromise. If the cathodes are allowed to run hot, tantalum has been shown to be a good choice. ... The cold and hot cathodes are worn out when the erosion crater's depth reaches around the anode bore radius. The discharge becomes unstable under these conditions.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 84-85 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Gives a concrete inspection criterion: measure the cathode pit depth against the ANODE BORE radius (about half the bore diameter) each time the source is pulled, and machine spare cathode buttons in advance. **dg-386** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-386 - **Rule (this site's paraphrase of the source):** For long life use an indirectly heated block cathode: an auxiliary filament bombards the cathode's rear with ~1-kV electrons so cathode temperature is set independently of the arc, and the source reports the heated cathode's lifetime exceeding both cold and hot cathodes. - **Formula:** `e-bombardment heating: 0-2 kV / 0-2.5 A onto cathode rear; filament itself 50-150 A at 2-8 V` - **Source quote (verbatim):** “Electrons emitted from a filament and accelerated to about 1 kV heat the cathode from the rear side... The lifetime of the heated cathode exceeds that of cold or hot cathodes.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 86, 101 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A next machine's source can hide a small filament behind a Ta-class block cathode, out of the hydrogen plasma - the filament stops being the consumable, and what erodes instead is the thick block face under PLASMA-ion sputtering (slow, by mass). The burn-down behavior, block material and electrical ratings are design choices to verify, not inherited guarantees. **dg-387** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-387 - **Rule (this site's paraphrase of the source):** Expect the open-filament arc to run 0.5-2 A at 100-500 V at ~1e-4 mm of hydrogen (the source prints 'mm H2' - the operating gas - where this card previously transcribed 'mm Hg'); Wouters' procedure strikes it at 0.5-1 A and 100-200 V, with filament emission set to 10-20 mA at 200-300 V bias under high vacuum before admitting gas. - **Formula:** `arc: 0.5-2 A @ 100-500 V @ ~1e-4 mm H2 (source's unit as printed); emission set-point 10-20 mA @ 200-300 V` - **Source quote (verbatim):** “a moderate emission current (10-20 ma.) is observed with 200-300 volts arc bias ... an arc of 1/2 to 1 amp at 100 to 200 volts is usually satisfactory.” - **Source:** [Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949)](https://cyclotroninfo.com/library/#lib-007) — p. PDF p.10 (printed -11-) for the procedure; PDF p.7 (printed -8-) for the arc range - NOT PDF p.6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A documented operating envelope for a simple hot-filament source at the reference machine's scale - a starting point whose actual values shift with geometry and field: commission against it, not to it. **dg-388** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-388 - **Rule (this site's paraphrase of the source):** Admit hydrogen so tank pressure rises by about 1e-4 mm above base while watching the arc current - the cited machine's commissioning procedure; the report's flow-control options include a needle valve, a thread-leak, and an electrically heated palladium leak. - **Formula:** `delta-P(H2) ~ +1e-4 torr over base pressure` - **Source quote (verbatim):** “hydrogen may be admitted to the tank, "opening" the valve until the tank pressure rises by another 10^-4 mm, meanwhile watching the arc current ... a needle valve ... a loose fitting thread ... a palladium metal valve” - **Source:** [Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949)](https://cyclotroninfo.com/library/#lib-007) — p. PDF p.10 (printed -11-) for the admission step; PDF p.7 (printed -8-) for the valve-type list - NOT PDF p.6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Transfer the method, not the number: admit gas gradually while watching pressure and arc behavior, and find the reference machine's own setpoint with its calibrated gauge and pumping stack (its parker metering valve fills the needle-valve role). The 1e-4 mm rise is the source machine's figure - gauge species, gauge location and pumping speed make it non-portable. **dg-389** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-389 - **Rule (this site's paraphrase of the source):** Wouters suggests ~0.025-inch tungsten ('perhaps', his word) over fragile automobile-lamp filaments - a 0.025-in tungsten filament takes about 25 A DC - and floats the filament supply across a storage battery to filter the ripple that vibrates the filament. - **Formula:** `0.025 in W filament ~ 25 A dc at a few volts` - **Source quote (verbatim):** “an automobile headlight filament has been used, but the breakage has been high ... perhaps .025 in. tungsten ... A .025 in. tungsten filament requires about 25 amps d.c.” - **Source:** [Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949)](https://cyclotroninfo.com/library/#lib-007) — p. 6-7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Filament sizing starts from emission demand and temperature, with Wouters' 0.025-in / 25 A as the documented anchor rather than a universal spec. The modern equivalent of the battery is a well-filtered DC filament supply - raw rectified current drives magnetically induced filament vibration in the cyclotron field. **dg-390** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-390 - **Rule (this site's paraphrase of the source):** Shield the ion-source filament from the dee's RF field with a small metal 'chimney' tube (1/4 in) and let the dee field extract ions through a small side hole facing the gap. - **Formula:** `1/4 in chimney tube over filament, side extraction hole` - **Source quote (verbatim):** “A quarter-inch tube called a 'chimney' sits on top of the filament, which shields it from the electric field of the dee. Ionized hydrogen is drawn out of a small hole.” - **Source:** [Baumgartner, The Cyclotron Kids' 2 MeV Proton Cyclotron — Cyclotrons 2013, WE1PB05 (2013)](https://cyclotroninfo.com/library/#lib-036) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A worthwhile arrangement for a next machine: the chimney gives a defined source position and shields the filament from the dee field - the quote's stated purpose. Comparisons against a bare filament (loading, output) are the builder's to measure, not the source's claim. **dg-391** · applicability level 3 · ion-source, vacuum, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-391 - **Rule (this site's paraphrase of the source):** Beam current improved a factor of seven (10 -> 70 pA) at the same 1700 V / 26 W drive after moving to higher frequency (6.04 vs 3.55 MHz), an order of magnitude lower H2 partial pressure (2.2e-6 vs 1.5e-5 torr), lower base pressure, and a far smaller filament bias (-6 V vs -100 V) - a several-variables-at-once change, but one that cost no RF power at all. - **Formula:** `6.04 MHz, 1700 V (26 W), H2 2.2e-6 torr, -6 V filament -> 70 pA; vs 3.55 MHz, 1700 Vpp (26 W), H2 1.5e-5 torr, -100 V -> 10 pA` - **Source quote (verbatim):** “3.55 MHz 1700 Vpp (26 W) H2 1.5 10-5 torr Total 4.0 10-5 torr -100 V filament ... 6.04 MHz 1700V (26 W) H2 2.2 10-6 torr Total 1.3 10-5 torr -6 V filament ... Higher frequency, lower H2 and base pressure, lower filament voltage” - **Source:** [Yuly et al., Modifications on the Houghton College Cyclotron (2010)](https://cyclotroninfo.com/library/#lib-084) — p. 17-18 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For the reference machine's current-hunting: before adding RF watts, cut chamber pressure and re-optimize filament bias - Houghton's gain cost zero watts - but change one variable at a time so you learn which knob actually paid. **dg-392** · applicability level 4 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-392 - **Rule (this site's paraphrase of the source):** Kovalchick's IEC grid: inner-grid diameter chosen as one-fifth of the 21-cm chamber (4.2 cm), geometric transparency kept above the cited 92 percent threshold - three loops of 0.114-mm tungsten wire give 99.18 percent, calculated by comparing total wire cross-section to grid-sphere surface area. - **Formula:** `d_grid ~ D_chamber/5; transparency = 1 - (pi*d_grid*N_loops*d_wire)/(4*pi*r^2) >= 0.92` - **Source quote (verbatim):** “The grid was made of .0114 cm thick tungsten wire shaped into circles chosen to be one fifth of the chamber in size. The chamber diameter was 21 cm so the grid diameter was 4.2 cm. ... fusion efficiency is enhanced by transparency of at least 92 percent (Donovan). The inner grid is 99.18 percent transparent with three loops as calculated by comparing the cross section of the total grid wire used to the surface area of the grid sphere.” - **Source:** [Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012)](https://cyclotroninfo.com/library/#lib-045) — p. 19-20 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The transparency bookkeeping (wire cross-section vs aperture area) is the calculation method to transfer - but a circulating cyclotron beam hits a grid or slit repeatedly and directionally, so compute projected obstruction along the actual trajectory over many turns, not the spherical-area figure. **dg-393** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-393 - **Rule (this site's paraphrase of the source):** In the cathode-grid circuit, the supply cannot tell an ion arriving from an electron leaving (both read as positive current), so grid supply current is not by itself an ion-current measurement; choose grid wire for high melting point, low sputter yield, and high work function to suppress parasitic thermionic emission where the grid runs hot. - **Formula:** `I_supply = i_ion + i_electron; at a limited P_ext = V*I, emitted electrons spend budget that could go to ions` - **Source quote (verbatim):** “A power supply cannot differentiate between an ion reaching the cathode grid and an electron leaving it (they both appear as positive current on the ammeter).” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 135, 144 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** When metering beam current near a hot cathode, part of the reading can be electrons. High work function helps only against thermionic emission; a Faraday cup's secondary-electron escape needs its own fix - a suppressor electrode or magnetic suppression, validated on the actual geometry. **dg-394** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-394 - **Rule (this site's paraphrase of the source):** Thermal limit of a wire electrode by radiation balance: I = A\*eps\*sigma\*T_sag^4/V. The source works its 10-cm stainless grid example (A ~76 cm^2, eps ~0.15, sag at ~1500 K) to 9.5 mA at 200 kV against a 75 mA supply - but those printed inputs actually evaluate to ~327 W, i.e. ~1.6 mA at 200 kV, so the printed current does not follow from the printed inputs. Use the balance; recompute for your case. - **Formula:** `I_max = A*eps*sigma*T_sag^4/V; the source's inputs (76 cm^2, eps 0.15, 1500 K) give ~327 W -> 1.64 mA at 200 kV, not the printed 9.5 mA` - **Source quote (verbatim):** “Assuming that sagging occurs at ~1,500 K and equating the black body radiation rate to the input power ... ~76 cm2 for a 10-cm grid made of 0.08 cm diameter with 5 latitudes and 12 longitudes ... the emissivity of the material (~0.15 for stainless) ... This gives 9.5 mA of ion current at 200 kV, whereas the power supply can produce 75 mA at 200 kV.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 145 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The same balance sizes any wire electrode, probe or beam stop in the reference machine's chamber - with its assumptions on the table: uniform temperature and radiation-only cooling. Compute A\*eps\*sigma\*(T^4 - T_amb^4) against actual intercepted beam power, and check local hot spots and conduction separately. **dg-395** · applicability level 4 · ion-source, materials, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-395 - **Rule (this site's paraphrase of the source):** W-25%Re is the cited work's grid sweet spot: spot-weldable (unlike pure W), low sputter yield, high melting point (the book prints 2,800 K), validated at 30-130 kV and 30-180 mA for over 1,000 h - and the grid survived over 2 years where stainless wires lasted under a week. - **Formula:** `W-25%Re: book's melting figure 2,800 K (standard alloy data put the W-25Re solidus near ~3300 K - verify against a datasheet); validated 30-130 kV, 30-180 mA, >1000 h; pure-W spot welding needs a Ni foil interlayer (the Ni then limits temperature)` - **Source quote (verbatim):** “The stainless steel wires previously used by Murali lasted for under a week depending on the power load. In contrast, with the W-25%Re alloy, the grid lasted for over 2 years. ... It is relatively cheap, has a high melting point (2,800 K), a low sputter yield, and is easy to manufacture by spot welding. To test this material, the 10-cm grid was run at various voltages in the range of 30-130 kV and with the current range of 30-180 mA for over 1,000 h” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 145-146 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** W-Re thermocouple wire is commercially available in small quantities - a strong candidate for any sputtered electrode in the reference machine's source, with W-class durability and far better workability than pure tungsten; fabrication, activation and sputter behavior remain application-specific, so qualify it in place. **dg-396** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-396 - **Rule (this site's paraphrase of the source):** DC glow discharges are organized by the pressure-distance product pd, not pressure alone; the glow regime runs ~300-1500 V at mA-level currents, and nearly the whole applied voltage drops in the few-mm cathode sheath. - **Formula:** `breakdown V = f(p*d) (Paschen); glow: 300-1500 V, mA currents; cathode fall occupies first few mm` - **Source quote (verbatim):** “The product of pressure and distance between the electrodes (pd) is a better parameter to characterize the discharge... The voltage is mostly in the range between 300 and 1500 V, but... the current is generally in the mA range.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 86-88 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** When scaling chamber geometry or pressure for the p-B11 test cell, pd similarity is the right first knob - it organizes breakdown - but sustained-glow behavior also moves with gas, electrode material and area, and current density, so expect to re-tune rather than translate. Either way, sputter damage concentrates at the cathode sheath edge. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-397** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-397 - **Rule (this site's paraphrase of the source):** Know the V-I ladder of a low-pressure DC discharge -- background/saturation, Townsend dark discharge, corona at sharp points, breakdown, normal glow (V roughly constant over decades of current), abnormal glow, then glow-to-arc when the cathode overheats -- and note the hysteresis: the glow persists below its striking condition once lit. - **Formula:** `sequence: dark -> Townsend -> breakdown -> normal glow (V ~ const) -> abnormal glow -> arc; hysteresis on the way back down` - **Source quote (verbatim):** “A hysteresis effect occurs; wherein instead of retracing the path... the discharge maintains itself in the normal glow regime... at considerably lower currents... Only then does it make the transition back to the Townsend regime.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 89-91 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Explains the striking-vs-running asymmetry a source can show: ignition up on the breakdown branch, then sustaining down on the glow branch at much lower voltage - the Penning table's several-kV-ignite / sub-kV-run split (dg-372) is this physics - and why current-limited (ballasted) supplies are needed to stop glow-to-arc runaway. The actual voltages move with gas, pd and geometry. **dg-398** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-398 - **Rule (this site's paraphrase of the source):** In a gridded low-pressure device, pressure controls ignition through the collision physics: the ion mean free path is ~7 cm at 2 mTorr and ~0.7 cm at 20 mTorr, and the striking voltage increases with decreasing pressure. - **Formula:** `lambda_ion ~ 7 cm @ 2 mTorr, ~0.7 cm @ 20 mTorr (H2/D2); V_strike rises as p falls; operating window 2-15 mTorr` - **Source quote (verbatim):** “The ion mean free path at 2 mTorr is ~7 cm, while at 20 mTorr it is around 0.7 cm... The striking voltage increases with decreasing pressure.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 92, 94 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For any glow-driven ion supply in the p-B11 experiment, pressure is the ignition control: strike at higher pressure, then throttle the MFC to the running point - a device-specific procedure to commission, with the actual striking curve measured (Paschen-type behavior depends on pd, gas, geometry and surfaces, not the ion mfp alone). - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-399** · applicability level 4 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-399 - **Rule (this site's paraphrase of the source):** A transparent wire cathode breaks down at about three times lower pd than a solid cathode at the same striking voltage (the cited comparison, spherical and planar alike) - recirculation through the grid is the working explanation; the Star-mode microchannel regime and transparency limits are the book's further account (scan re-read queued). - **Formula:** `pd(solid)/pd(grid) ~ 3 at fixed V_strike; Star mode below ~0.5 Torr-cm; rigid grids practical only to ~95% geometric transparency` - **Source quote (verbatim):** “For fixed Vs, the value of (pd) is seen to be about three times higher for both the spherical and the planar solid-cathode discharges than for the transparent grid-type cathode discharges.” - **Source:** [Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014)](https://cyclotroninfo.com/library/#lib-079) — p. 94-96 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** If building an IEC-style p-B11 test stand, grid-opening geometry is a real trade study - larger openings mean fewer grid hits and longer grid life, finer mesh means better field definition - informed by the cited 3x pd result, with the Star-mode operating claims taken from the re-read source rather than summary memory. **dg-400** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-400 - **Rule (this site's paraphrase of the source):** To ionize low-pressure gas for a beam-mode device, the source suggests it might be necessary to add a hot-filament electron emitter just outside the outer grid, biased slightly positive (~200 volts). - **Formula:** `filament bias ~ +200 V, located outside outer grid` - **Source quote (verbatim):** “it might be necessary to include a filament or other source of electrons to ionize the deuterium at low pressures. This filament should be placed just outside of the outer grid system and biased slightly positive (~200 volts)” - **Source:** [Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997)](https://cyclotroninfo.com/library/#lib-048) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Matches the reference machine's hydrogen filament philosophy: a modest bias on an emitter sustains ionization where a self-sustained discharge dies. Wire the POTENTIAL TOPOLOGY deliberately - what accelerates the electrons is the difference between emitter and the collecting electrode, so state the reference (the source does not say 'to ground') and set the electron energy against the ionization physics, not against the chamber wall by default. **dg-401** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-401 - **Rule (this site's paraphrase of the source):** Guard the support structure of a negatively biased electrode so ions bombard only the intended electrode: the source's instruction is to electrically shield (insulate) the inner-grid support - in practice, recess the vacuum insulation behind a conductive shield at a controlled potential rather than leaving bare dielectric exposed to the plasma. - **Source quote (verbatim):** “Care must be exercised to electrically shield (insulate) the inner grid metallic support structure so that ions will not bombard that portion of the apparatus.” - **Source:** [Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997)](https://cyclotroninfo.com/library/#lib-048) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Same rule protects the reference machine's Faraday cup stalk and source supports: unshielded biased metal collects spurious current and sputters - and bare insulation over it charges up and distorts fields, so shield with guarded conductor, then insulate behind it. **dg-402** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-402 - **Rule (this site's paraphrase of the source):** On the Houghton machine, filament bias (tested around -90 V) appeared to have no effect on beam current over the tested range. - **Formula:** `beam current insensitive to filament bias (tests near -90 V)` - **Source quote (verbatim):** “It appears that filament bias has no effect on the beam current.” - **Source:** [Fuller, Exploring the Capabilities of the Houghton College Cyclotron — Houghton College thesis (2013)](https://cyclotroninfo.com/library/#lib-005) — p. 48-49 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Tuning-order advice, not physics: hold filament bias fixed during initial tuning and spend the effort on dee voltage and pressure - but scan bias if ionization or emission looks current-limiting, since other geometries and regimes do respond to it. **dg-403** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-403 - **Rule (this site's paraphrase of the source):** With an internal fill-gas ion source there is an optimal chamber pressure band - too little gas starves ionization, too much and the ions scatter on gas inside the dee and fall out of resonance; the Houghton machine ran about 1e-5 to 3e-5 Torr. - **Formula:** `Houghton's band ~1-3e-5 Torr; their highest raw current appeared near ~1e-4 Torr but with badly broadened resonances - raw current at high pressure is not useful resonant beam` - **Source quote (verbatim):** “If there is too little gas, less ionization will occur... Too high a pressure and the ionized particles will likely interact with gas inside the dee and fall out of resonance.” - **Source:** [Fuller, Exploring the Capabilities of the Houghton College Cyclotron — Houghton College thesis (2013)](https://cyclotroninfo.com/library/#lib-005) — p. 51-52 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Map current vs pressure on your own machine, recording resonance width and source stability along with current - expect an apparatus-dependent optimum and a non-monotonic curve, and use Houghton's window as calibration context, not a target. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-404** · applicability level 3 · chamber, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-404 - **Rule (this site's paraphrase of the source):** Add deliberate clearance between the filament and the chamber lid - Houghton milled a 0.3 cm deep circular depression into the lid specifically to prevent a repeat filament-to-lid discharge. - **Formula:** `0.3 cm milled recess` - **Source quote (verbatim):** “To make room for a filament and to avoid another electrical discharge from the filament to the lid, a 0.3 cm deep circular depression was milled out of the bottom of the upper lid.” - **Source:** [Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009)](https://cyclotroninfo.com/library/#lib-003) — p. 50 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In the reference machine's tight pole-gap geometry, check every HV-to-ground clearance near the median plane; milling relief pockets is cheaper than chasing sparks later. - **Cited in:** [Cyclotron Vacuum Chamber Design and Sealing](https://cyclotroninfo.com/learn/vacuum-chamber/) **dg-405** · applicability level 3 · vacuum, ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-405 - **Rule (this site's paraphrase of the source):** Run the chamber in the source's stated window, 1e-6 to 1e-4 Torr: below it there is too little gas to ionize; above it neutral collisions shorten the ion mean free path and the resonance peaks become broad and shift; the largest recorded beam current was about 0.1 uA. - **Formula:** `operating window 1e-6 to 1e-4 Torr (cited machine); best recorded current ~0.1 uA` - **Source quote (verbatim):** “The pressure in the chamber has a large effect on the beam current obtained, and typically needs to be in the range from 1e-6 to 1e-4 Torr for the cyclotron to operate. ... [higher pressures] reduce the mean free path of the ions, and cause the resonance peaks to become broad and shift. The largest beam current recorded, shown in Figure 6, was about 0.1 uA” - **Source:** [Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013)](https://cyclotroninfo.com/library/#lib-041) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Directly sets the gas-handling operating window for the reference machine and explains a common 'no beam' failure at too-good vacuum - throttle up before concluding the source is dead. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-406** · applicability level 4 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-406 - **Rule (this site's paraphrase of the source):** Support and connect a floating PIG anode with two 0.5 mm stainless wires fed through alumina tubes sealed with ceramic epoxy (Ceramabond) into the cathode body; a third stainless tube serves as gas inlet. - **Source quote (verbatim):** “Three holes are machined in the cathode body; two are used to support the anode and the third is used as a gas inlet. Alumina tubes are inserted into the two holes used for anode support, and a stainless steel tube is inserted into the gas inlet hole. Ceramic epoxy (Ceramabond) is used to mate the alumina and stainless tubes to the back of the cathode body. Stainless steel wire with 0.5 mm diameter was spot welded to the anode, and the wires were threaded through the alumina tubes in the cathode body. ... Essentially the anode floats inside the cathode body, being supported only by the two stainless steel wires that protrude through the alumina tubes and out the back of the cathode body.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 1-2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** An amateur-grade insulated support for a modest-voltage, low-current internal electrode - an ion-source anode and the like. Not unchanged for filament leads (0.5 mm stainless is a poor conductor for filament current) or for chamber-wall HV or current feedthroughs: use current-rated conductors and qualified vacuum/HV feedthroughs there, and test the ceramic-epoxy joint for bakeout, leakage and voltage standoff before trusting it. [Note revised 2026-08-23: earlier note extended the scheme to filament leads.] **dg-407** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-407 - **Rule (this site's paraphrase of the source):** A cold-cathode PIG the paper builds from an iron cathode body, a ~3 kG SmCo permanent magnet, a folded 0.13 mm stainless-sheet anode and an iron faceplate with a 6.4 mm axial aperture delivered a continuous 1 mA beam of positive hydrogen ions at 1 mTorr, on 5.4 kV and 32.4 W. - **Formula:** `3 kG SmCo; 5.1 cm iron cathode body; 6.4 mm faceplate hole; 1 mA H+ at 1 mTorr, 5.4 kV, 32.4 W` - **Source quote (verbatim):** “A samarium cobalt permanent magnet with a surface flux density of approximately 3 kG... The anode is fabricated by forming 0.13-mm-thick nonmagnetic stainless steel sheet metal into the shape of a cup... machined with a 6.4-mm-diameter hole on centerline.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. PDF p.1 (printed 106101-1) for the construction text; PDF p.2 (printed 106101-2) for Fig. 1 dimensions - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A directly copyable permanent-magnet source recipe at hobby machining tolerances - copy from the paper's drawings, and treat the output as mixed hydrogen species (H+, H2+, H3+) until a bend or velocity filter resolves it (dg-001). **dg-408** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-408 - **Rule (this site's paraphrase of the source):** Current-limit a PIG discharge with a series resistor (here 100 kOhm, 100 W) and always report/log the actual anode-to-cathode voltage, not the power-supply setpoint, since the resistor drops significant voltage during operation. - **Formula:** `V_source = V_supply - I_discharge * R_ballast; R = 100 kOhm, 100 W` - **Source quote (verbatim):** “The ion source anode is powered by a 6 kV 200 mA Hipotronics dc power supply and a 100 kOhm, 100 W resistor is connected in-line with the power supply to current limit the discharge. ... Because the 100 kOhm current-limiting resistor develops a voltage drop during source operation, the ion source voltage (anode-to-cathode voltage) is reported instead of the power supply voltage.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Directly applicable to the reference machine's DISCHARGE/ARC supply metering (the ballast correction belongs to the electrode circuit, not the filament heater): logging supply volts instead of electrode volts corrupts any operating-point map. Check ballast power, working-voltage and transient ratings for the actual supply. **dg-409** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-409 - **Rule (this site's paraphrase of the source):** In the cited compact source-in-chamber setup the pressure inside the ion source was only about 2x the chamber pressure, and source operation was also achieved by simply backfilling the chamber. - **Formula:** `P_internal ~ 2 x P_chamber (small chamber, direct injection)` - **Source quote (verbatim):** “the pressure internal to the ion source is only approximately a factor of 2 larger than the chamber pressure... source operation has also been achieved by simply backfilling the chamber.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Worth testing on the reference machine: in a small chamber the injection-vs-backfill distinction may shrink - but the source-to-chamber pressure ratio is set by aperture conductance, flow and pump placement, so measure it (or model the conductances) rather than assuming 2x transfers. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-410** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-410 - **Rule (this site's paraphrase of the source):** A PIG discharge ignites easily at 1 kV or less and delivers continuous positive hydrogen-ion current: at 1 mTorr H2, 580 V gave 0.3 mA discharge / 20.8 uA target, rising to 6.0 mA / 1.5 mA at 5.4 kV. - **Formula:** `H2, 1 mTorr: 580 V -> 0.3 mA discharge / 20.8 uA target; 5.4 kV -> 6.0 mA / 1.5 mA (positive hydrogen ions; species mix unanalyzed)` - **Source quote (verbatim):** “the plasma discharge ignites easily at 1 kV or less for all cases and produces a continuous positively charged ion beam. ... For the 1 mTorr case, at 580 V, the discharge current and target current are 0.3 mA and 20.8 uA, respectively. As the ion source voltage increases to 5.4 kV, the discharge current and target current increase to 6.0 and 1.5 mA, respectively.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 2-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Tens of microamps of positive hydrogen ions at under 1 kV anode drive is ample raw current next to the reference machine's nA-scale accelerated beams - but it is aggregate H+/H2+/H3+ at the target: species fraction and RF capture are separate measurements before any of it is credited as proton beam. **dg-411** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-411 - **Rule (this site's paraphrase of the source):** At its design operating point this PIG source collected 25% of the discharge current on the target (21% for helium) for 32.4 W of source power; beam is scaled by raising pressure or discharge voltage, both of which raise discharge current. - **Formula:** `I_target/I_discharge ~ 0.25 (H2), 0.21 (He); 1.5 mA target at 6.0 mA discharge, 5.4 kV` - **Source quote (verbatim):** “the source has a current utilization efficiency (ratio of target to discharge current) of 25% and requires 32.4 W of power.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A test-stand collection ratio, not a cyclotron benchmark: the reference machine's beam-to-arc ratio folds RF capture, centering and transmission on top of extraction, so a much lower ratio there does not by itself convict the extraction geometry. Use 25% as the source-side sanity scale only. **dg-412** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-412 - **Rule (this site's paraphrase of the source):** For DC post-acceleration on the source's test stand: a suppressor electrode 2.5 cm downstream of the cathode faceplate and a target 7.6 cm beyond it, both biased negative with respect to the grounded source cathode; a continuous 1 mA positive hydrogen-ion beam was focused onto the target at 0.4 mTorr and 10.5 W, with acceleration voltages up to -30 kV investigated. - **Formula:** `suppressor at 2.5 cm, target +7.6 cm, both negative w.r.t. grounded cathode; 1 mA positive hydrogen ions at 0.4 mTorr, 10.5 W; up to -30 kV investigated` - **Source quote (verbatim):** “The electrode closest to the source was the suppressor and was located 2.5 cm from the cathode faceplate. A target electrode was placed 7.6 cm from the suppressor. During high-voltage operation, the suppressor and target were biased negative with respect to the ion source cathode (i.e., ground). ... at a pressure of 0.4 mTorr and 10.5 W PIG source power, a continuous 1 mA positive hydrogen ion beam has been focused onto the target and accelerator voltages up to -30 kV have been investigated.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Template for a bench extraction test stand to characterize the next machine's source before it goes into the magnet. **dg-413** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-413 - **Rule (this site's paraphrase of the source):** An internal cold-cathode PIG source is a low-maintenance choice: the Rutgers source runs more than 40 hours between servicings. - **Formula:** `>40 h service interval` - **Source quote (verbatim):** “The ion source is an internal cold cathode Penning Ion Gauge (PIG) source that operates in excess of 40 hours before requiring service.” - **Source:** [Koeth, Undergraduate Education with the Rutgers 12-Inch Cyclotron (2015)](https://cyclotroninfo.com/library/#lib-038) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Benchmarks source maintenance for a next machine: one documented internal cold-cathode PIG ran 40+ hours between servicings. Filament sources trade shorter cathode life for simpler supplies (dg-704's census practice) - lifetimes vary with design and duty on both sides of that trade. **dg-414** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-414 - **Rule (this site's paraphrase of the source):** Separate the source's gas-fed discharge region from the main vacuum with a tight-fitting boron nitride insulator (isolating an on-the-order-1e-5 Torr region); Forringer's test stand held the main chamber near 4e-5 Torr at 2.5 cc/min H2 against a base pressure of 8e-7 Torr. - **Formula:** `2.5 sccm H2 -> 4e-5 Torr chamber (base 8e-7 Torr); BN insulator isolates ~1e-5 Torr region` - **Source quote (verbatim):** “The boron-nitride insulator, which is a tight fit, separates the high vacuum region behind the insulator (on the order of 10-5 Torr), from the lower vacuum region in the chimney and between the anodes and cathodes. ... The best vacuum achieved in the ion source test stand (with source gas supply turned off) was 8 x 10-7 Torr. With a gas flow rate of 2.5 cc/min of hydrogen, the pressure in the main vacuum chamber is around 4e-5 Torr.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 17-29 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A single calibration point (about 1.6e-5 Torr per cc/min at that stand's pumping speed), not a slope: characterize the reference machine's own MFC-vs-chamber-pressure curve with its calibrated flow and gauges before reading deviations as leaks or conductance faults. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-415** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-415 - **Rule (this site's paraphrase of the source):** Forringer's cold-cathode PIG ran from a ~3 kV current-limited supply - after striking, arc voltage drops to whatever sustains the set current - and the 1.9-3.8 mm cathode-anode gap was 'not a critical parameter for the source's operation'. - **Formula:** `strike supply 3 kV / 1 A current-limited; running arc voltage < 3 kV; gap 0.075-0.150 in non-critical` - **Source quote (verbatim):** “For this source a Glassman High Voltage KL series high voltage supply rated at 3kV and 1A provided the necessary potential. When the plasma is established, the power supply shifts to current limited operation ... The cathode anode gap was between 0.075” (1.9 mm) and 0.150” (3.8 mm)” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. PDF p. 29 (printed p. 19) - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Relaxes the machining tolerance on a next machine's source gap and anchors the supply class: a ~3 kV current-limited unit ran this source. Strike voltage moves with pressure, gas, field and surface condition, so provide voltage headroom (or an ignition boost) rather than assuming the same number transfers. **dg-416** · applicability level 2 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-416 - **Rule (this site's paraphrase of the source):** Water-cool the cathode rod and anode base of an internal PIG - copper parts melted when the source was run without cooling - and prepare cathode faces by sanding with 100-grit paper to a uniformly rough surface for reliable arc striking. - **Source quote (verbatim):** “Water cooling for the cathode rod and the anode base are essential (some copper parts were melted when the ion source was run without proper cooling).” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 19-20 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The source's warning stands as written: they melted copper running without cooling. A reference-machine-class source at much lower arc power may not need water - but that is a claim to establish by thermal estimate and a supervised first run with temperature monitoring, not by assumption. The sanded-cathode arc-striking preparation transfers directly. **dg-417** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-417 - **Rule (this site's paraphrase of the source):** For calibration, hot-filament internal sources have run far above tabletop scale: Livingston and Jones heated a U-shaped tantalum filament with ~400 A, ran 2-6 A of arc, and extracted 150 mA through a 129 mm2 slit with a 12 kV puller across a 3.3 mm gap. - **Formula:** `Ta filament ~400 A heater; arc 2-6 A; 150 mA extracted at 12 kV, 3.3 mm source-puller gap, 129 mm2 slit` - **Source quote (verbatim):** “Their cathode was a U-shaped tantalum filament, heated with about 400 amps ... the arc current (the total current measured between the anode and cathode of the ion source) was between 2 and 6 amps. As seen in figure 1.2 a 0.2 in2 (129 mm2) area vertical slit provided the path for ions to exit the source. With this source Livingston and Jones were able to extract 150 mA using a puller voltage of 12kV and a source-puller gap of about 0.13 (3.3 mm).” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 3-4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Brackets the design space above the reference machine's filament source as an existence proof, not a scaling law: determine the arc a nA beam actually needs by measuring extracted and captured current against arc current on the real geometry. **dg-418** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-418 - **Rule (this site's paraphrase of the source):** In Forringer's tested source, doubling the chimney slit from 0.25 mm to 0.51 mm (both 5.0 mm tall, 10 degree chamfer) raised beam current ~4.4x (52 to 230 uA at 50 mA arc) while radial emittance grew only ~1.7x (27 to 47 mm-mrad) - the larger slit gives more current at larger emittance. - **Formula:** `0.010 in slit: 52 uA, 27 mm-mrad radial; 0.020 in slit: 230 uA, 47 mm-mrad (50 mA arc, 3.0 sccm, ~40 kV puller)` - **Source quote (verbatim):** “The chimney with the larger slit produces a beam with a larger emittance. However, the beam is also of higher intensity.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 66-69 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Suggests slit width is a powerful knob worth sweeping on a next machine: expect more current and more emittance from a wider slit, and stop widening when the machine acceptance is filled - but the 4.4x/1.7x ratios are that source's numbers; do your own aperture sweep and acceptance analysis before extrapolating. **dg-419** · applicability level 2 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-419 - **Rule (this site's paraphrase of the source):** A DC extraction test stand characterizes an internal source before installation: a puller with 12.7 mm radius of curvature held 50 kV across a 5.0 mm minimum source-puller gap on that stand, and a 2.9 mm gap held about 25 kV. - **Formula:** `R_puller = 12.7 mm: gap 5.0 mm -> 50 kV; gap 2.9 mm -> ~25 kV (that stand's measured holdoff)` - **Source quote (verbatim):** “This puller was designed for the ion source test stand to hold 50 kV... The minimum source to puller gap is 0.196 (5.0 mm).” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 68, 75 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Two measured holdoff points from one clean DC stand - anchors for a dee-tip/puller voltage budget, not a kV-per-mm allowable: vacuum holdoff is nonlinear in gap and hostage to finish, conditioning, and RF-vs-DC differences. Do what the source did: measure the actual geometry on a test stand rather than applying a scaling law. **dg-420** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-420 - **Rule (this site's paraphrase of the source):** In the tested chimneys, prefer the slit over the hole for beam quality: the slit gave a flat plasma boundary and converging beam, while the hole (1.19 mm, 60-degree chamfer) gave a concave boundary, a diverging beam, ~50% larger normalized radial emittance, and half the luminosity at equal arc current. - **Formula:** `hole chimney: 0.66 mm-mrad normalized radial vs 0.44 for slit; normalized luminosity 129 vs 264 A/(mm^2-sr) at 50 mA arc` - **Source quote (verbatim):** “an approximately flat plasma boundary provides the best match to the experimental beams emerging from the 'slit' style chimneys... while a concave plasma boundary... for the 'hole' style chimney ... The size of the hole in the chimney is 0.047 (1.19 mm) with a sixty degree chamfer. At 50 mA of arc current, the normalized luminosity of the beam which made it to the wire probe was 129 A/(mm2-sr), about half of that for the slit chimney with the same arc current (264 A/(mm2-sr)).” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 73-76, 91-107 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Decides a next machine's chimney aperture style within the tested regime: cut a tall narrow slit rather than drilling a hole if beam brightness and predictable optics matter - and re-verify on the actual source, since the ranking comes from these apertures and operating points. **dg-421** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-421 - **Rule (this site's paraphrase of the source):** Raising PIG arc current raised beam current sub-linearly in the cited scan: for the 0.25 mm slit, 50 to 450 mA of arc gave 52 to 227 uA of beam while beam/arc efficiency fell from 1.0e-3 to 0.5e-3; measured emittance stayed flat over the scan and luminosity climbed 1.7 to 7.1 A/(cm2-sr). - **Formula:** `I_beam/I_arc drops 1.0e-3 -> 0.5e-3 over 50-450 mA arc; luminosity 1.7 -> 7.1 A/cm2-sr; emittance ~constant` - **Source quote (verbatim):** “the general trend of increasing arc current producing increased beam current as expected... there was no noticeable change in the emittance of the beam for different currents” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 77-78, 81 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Cranking arc power buys current with diminishing returns, and in this scan it did not spoil measured emittance. Do not read that as space charge being negligible in general: generalized perveance rises steeply at low velocity, so keep space charge in extraction and first-turn models until a sensitivity check shows it is negligible at your energy and current. **dg-422** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-422 - **Rule (this site's paraphrase of the source):** Keep hydrogen flow comfortably above the arc-mode transition: at this source's normal flows (2-6 sccm, arc 50-350 mA, arc voltage under 3 kV current-limited) no H2+ was observed in the beam, while at 0.5 sccm the arc jumped to voltage-limited mode and molecular ions appeared. - **Formula:** `flow > 2.0 sccm -> no detectable H2+ (this source); 0.5 sccm -> mode shift (3.5 kV limit, arc drops to 90 mA) with H2+ observed` - **Source quote (verbatim):** “hydrogen gas flow rates greater than 2.0 cc/min) no H2+ ions were observed. We were able to observe H2+ ions by lowering the gas supply to 0.5 cc/min.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 79-80 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Directly actionable on the reference machine's MFC: starving the source of gas silently changes beam species, so locate the actual arc-mode transition for the machine and keep the setpoint above it - and remember 'no H2+ detected' is not 'pure protons': H3+ and below-detection species need their own check. **dg-423** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-423 - **Rule (this site's paraphrase of the source):** Forringer's orbit simulations reproduced measured emittance for both slit and hole chimneys by starting ions on the plasma boundary with an effective plasma temperature of ~35,000 K (central starting energy ~4.5 eV, i.e. 3kT/2). - **Formula:** `T_plasma ~ 35,000 K fitted; E_start ~ 4.5 eV = 3kT/2 at that temperature; flat boundary (slit) / concave boundary (hole)` - **Source quote (verbatim):** “the plasma temperature that provides the best match for experimental beams is approximately 35,000 K (resulting in a central starting energy of 4.5 eV).” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 91-107 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A starting calibration for any first-turn simulation of a next machine's central region: begin near 35,000 K / 4.5 eV, then sweep the initial temperature and meniscus shape and validate against measured emittance or beam profiles - the value is a fitted effective parameter, not a universal plasma property. **dg-424** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-424 - **Rule (this site's paraphrase of the source):** Use a fine-taper metering valve with a vernier handle for gas admission - Series 20: Cv 0.029, 3-degree stem taper, 9 +/-1 turns to open - so flow settings are repeatable (datasheet's 0.055-in orifice and Series 30 figures sighted at extraction; table re-read queued). - **Formula:** `Series 20: Cv=0.029, orifice 0.055 in, taper 3 deg, 9+/-1 turns; Series 30: Cv=0.16, orifice 0.125 in, taper 9 deg, 10+/-1 turns` - **Source quote (verbatim):** “Vernier knob for repeatable flow settings ... Flow Coefficient (Cv): 0.029 (Series 20) ... Stem Taper: 3 deg ... Turns to Open: 9 (+/-1)” - **Source:** [Parker Hannifin, Series 20 & 30 Metering Valves (datasheet)](https://cyclotroninfo.com/library/#lib-068) — p. 1-2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The 3-degree taper spread over 9 turns gives the fine, repeatable hydrogen admission an ion source needs. Log turns-open as the VALVE-POSITION setpoint - repeatable flow additionally needs regulated upstream pressure and a calibration of flow (or chamber pressure) against turns under operating conditions; the vernier repeats position, not sccm. **dg-425** · applicability level 3 · ion-source, vacuum, safety · https://cyclotroninfo.com/design-guide/ion-source/#dg-425 - **Rule (this site's paraphrase of the source):** Never use a non-shutoff metering valve as the shut-off: Parker's sheet says the cited series is 'not recommended for positive shut-off' and points to its Series HR metering valve where bubble-tight shut-off is required; the cited series is also pressure-limited (1000 psig upstream, 500 downstream). - **Formula:** `max 1000 psig operating (downstream limited to 500 psig); elastomer limits: Buna-N -10 to 250 F` - **Source quote (verbatim):** “Not recommended for positive shut-off. If bubble-tight shut-off required, the use of a Series HR Metering Valve is suggested.” - **Source:** [Parker Hannifin, Series 20 & 30 Metering Valves (datasheet)](https://cyclotroninfo.com/library/#lib-068) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Practical form for the gas panel: give the metering valve an isolation valve between it and the bottle - or specify a metering valve designed for shut-off duty, the HR-class option the sheet names. Forcing a plain tapered stem closed to seal ruins the calibrated taper and still leaks into the vacuum system. **dg-426** · applicability level 2 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-426 - **Rule (this site's paraphrase of the source):** Run the hot-cathode source arc chamber in graphite (86-inch: 0.563-in OD graphite tube), feed 2-3 cc/min of hydrogen, and expect arc conditions of 0.5-1.5 A at 100-300 V with a 0.062 x 2.5 inch exit slit. - **Formula:** `H2 flow 2-3 cc/min; arc 0.5-1.5 A @ 100-300 V; slit 0.062 in x 2.5 in` - **Source quote (verbatim):** “The rate of flow required during operation is from 2 to 3 cc/min ... Electrons are accelerated from the filament into the arc chamber by a 100 to 300 volt potential, the normal arc current being 0.5 to 1.5 amperes.” - **Source:** [Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952)](https://cyclotroninfo.com/library/#lib-017) — p. 62, 64 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Documented arc conditions for a hot-cathode chimney source. Scaling to a much smaller chimney shifts gas flow and arc balance with geometry and pumping, so treat 0.5-1.5 A / 100-300 V / a few cc/min as the class of numbers to expect and tune on the machine. The robust transfer is the material lesson: graphite chimney and slit parts resist sputtering far better than copper or steel. **dg-427** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-427 - **Rule (this site's paraphrase of the source):** Treat alignment of the ion source with the magnetic field and the accelerating slits as the critical tune - the quote; the report's specific geometry (filament fully covering the defining slot, slot edge tangent to the arc-slit plane) is its own practice (scan re-read queued). - **Source quote (verbatim):** “The filament is aligned to completely cover this circular defining slot. The front edge of the defining slot is placed tangent to the external plane of the arc slit.” - **Source:** [Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952)](https://cyclotroninfo.com/library/#lib-017) — p. PDF p. 64 = printed p. 64 (section 'The Ion Source') - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Directly applicable: build a next machine's source mount with repeatable rotation/translation adjustment from outside vacuum; source-to-puller alignment is worth more beam than any power knob. **dg-428** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-428 - **Rule (this site's paraphrase of the source):** Regulate arc voltage and arc current independently, as the ORNL source did: hold arc voltage constant via the arc supply and hold arc current constant by trimming filament heating. - **Formula:** `loop 1: V_arc = const (arc supply); loop 2: I_arc = const (filament temperature)` - **Source quote (verbatim):** “Arc voltage and arc current can each be varied independently ... This regulates the filament temperature and thus the arc current, which is then held constant regardless of arc voltage.” - **Source:** [Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952)](https://cyclotroninfo.com/library/#lib-017) — p. 66 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A control philosophy readily implemented with two small feedback supplies; a constant-current arc removes one major drift term from shot-to-shot beam current - stable gas flow and extraction conditions are still needed for real reproducibility. **dg-574** · applicability level 4 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-574 - **Rule (this site's paraphrase of the source):** Optimize the internal-source slit with chamfer angles of 40-60 degrees, and make the slit's axial size several times its radial size; slit shape strongly changes extracted current (calculated spread 90-850 nA between variants). - **Formula:** `chamfer angle 40-60 deg; axial/radial slit size ratio ~ several; the source's Fig. 56 slit variants span max I = 90-850 nA` - **Source quote (verbatim):** “The shape of the source slit, when its axial size is several times larger than the radial one, is most frequently used... They are optimized according to the chamfer angle, which is usually 40-60 degrees. ... the angle of the chamfers directly affect the magnitude of the beam current extracted from the source, which is confirmed by numerous calculations [132] and measurement results (Fig. 56).” - **Source:** [Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021)](https://cyclotroninfo.com/library/#lib-187) — p. 52-53 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Cheap, high-leverage geometry rule for the reference machine's PIG-style source: start from a tall-and-narrow slit with ~45-degree chamfers - the source's most-used geometry - then optimize against measured beam, since the chamfer angle demonstrably moves extracted current by an order of magnitude across variants. **dg-575** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-575 - **Rule (this site's paraphrase of the source):** With external axial injection, choose an injection energy (in eV per charge) below the dee voltage amplitude: the first gap crossings then rapidly enlarge the orbit, minimizing central-structure size and radial losses. - **Formula:** `E_inj/q < U_dee (injection energy less than accelerating-voltage amplitude)` - **Source quote (verbatim):** “the optimal case from the viewpoint of minimizing the radial beam losses is a mode of operation in which the value of the injection energy is less than the amplitude of the accelerating voltage across the dees” - **Source:** [Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021)](https://cyclotroninfo.com/library/#lib-187) — p. 55-56 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** If a next machine ever moves to an external source and axial injection: the cited criterion (injection energy per charge below the dee amplitude) minimizes radial losses by letting the first gap crossings enlarge the orbit fast - set the actual injection energy jointly with inflector acceptance, transport and RF capture, not from the radial-loss criterion alone. **dg-576** · applicability level 2 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-576 - **Rule (this site's paraphrase of the source):** With an internal ion source and cosine RF, the central region's phase acceptance is roughly the starting-phase window (-90, +20) degrees; phase slits can then select bunches down to a few RF degrees. - **Formula:** `phase acceptance ~ (-90 deg, +20 deg) relative to peak-voltage phase = 0` - **Source quote (verbatim):** “the phase acceptance of the center, as a rule, contains the particles, the initial RF phases of which do not go beyond the range of (-90; 20)” - **Source:** [Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021)](https://cyclotroninfo.com/library/#lib-187) — p. 56 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Explains why a large fraction of source output never accelerates: only starting phases inside a ~110-degree window of the full 360 are candidates at all - a uniform-emission estimate makes that a ~30% ceiling, before radial and axial acceptance cut further; it is not a measured capture efficiency. The builder tool should launch macroparticles across this window rather than a single reference phase. **dg-603** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-603 - **Rule (this site's paraphrase of the source):** PIG discharges split into two families: cold-cathode (secondary-emission) arcs run above ~1 kV at 0.5-5 A, hot-cathode (self-heated thermionic) arcs run below ~1 kV at 1-50 A. The cold mode has positive incremental impedance, the hot mode negative — plan the supply accordingly. - **Formula:** `cold cathode U_arc > 1 kV, I = 0.5-5 A; hot cathode U_arc < 1 kV, I = 1-50 A` - **Source quote (verbatim):** “the cold cathode PIG source with arc voltages above 1 kV and currents between 0.5 and 5 A, and the hot cathode PIG source with arc voltages below 1 kV and currents between 1 and 50 A” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 82 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's source at tens-to-hundreds of mA sits BELOW the handbook's canonical cold-cathode band, which starts at 0.5 A - closer to a glow regime than the tabulated arcs. The design consequence stands regardless: if the discharge crosses into a self-heated, negative-slope mode (AMIT reported a transition near 250 mA on their source), only a stiff current source holds it - so build the arc supply as a current source from the start. **dg-604** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-604 - **Rule (this site's paraphrase of the source):** The arc plasma floats a few volts below anode potential and essentially the full arc voltage drops across the thin cathode sheath; each primary electron yields about 8 ions on average. - **Formula:** `V_plasma ~ V_anode - (few V); ions per oscillating electron ~ 8` - **Source quote (verbatim):** “The arc plasma is a few volts negative in respect to the anode potential and nearly the full arc voltage drops along the narrow cathode sheath ... One electron can produce about eight ions or charges on average.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 82 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Ion energy at the cathodes is ~ the full arc voltage (times charge state) before collisional losses - evaluate sputtering from species/material yield data at that energy, not a linear-in-voltage assumption. Grounding the chimney (anode) to the chamber with cathodes negative is ONE workable topology if the source body is meant to sit at chamber potential - check it against the machine's RF/HV design, heater isolation and filtering before wiring it. **dg-605** · applicability level 2 · ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-605 - **Rule (this site's paraphrase of the source):** Above a minimum magnetic field of roughly 0.1 T the discharge parameters barely depend on B; ignition is easier at higher field. Ordinary internal PIGs run 0.1-1 T homogeneous. - **Formula:** `B_min ~ 0.1 T; typical 0.1-1 T; little d(V,I)/dB above threshold` - **Source quote (verbatim):** “There is little influence of the magnetic field on the discharge parameters as long as it reaches a certain minimum of roughly 0.1 T.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 82 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's 0.59 T and a ~0.9 T successor both clear the handbook's 0.1 T minimum, so field-level effects on the ARC parameters should be small per the quote. Ignition and stable running still ride on pressure, geometry and surfaces (dg-372's ignition margins) - after a large field retune, a quick arc-parameter check beats an assumption. **dg-606** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-606 - **Rule (this site's paraphrase of the source):** Ion current density at the cathodes is 5-10x that at the anode wall; total extracted current is proportional to arc current, roughly 10-100 (mA/cm^2) per ampere of arc for radial extraction through the anode slit. - **Formula:** `j_cathode = (5-10) x j_anode; I_extracted/area ~ 10-100 (mA/cm^2)/A_arc` - **Source quote (verbatim):** “the ion current density at the cathodes is five to ten times the density at the anode surface ... The total extracted current of a PIG ion source is proportional to the arc current (Figure 5.6), and for extraction through the anode, about 10 to 100 (mA/cm2)/A” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 82-83 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Sizing arithmetic for the chimney slit: a 0.5 x 5 mm slit (0.025 cm^2) at 100 mA arc predicts ~25-250 uA available at the slit — consistent with Forringer's measured 230-590 uA at 50-150 mA through a 0.5 mm slit. **dg-607** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-607 - **Rule (this site's paraphrase of the source):** Arc voltage rises as gas flow or particle density drops, until the discharge becomes unstable; the practical low-flow boundary of the operating window is set by that instability. - **Formula:** `dV_arc/d(gas flow) < 0 at constant I_arc; instability at starvation limit` - **Source quote (verbatim):** “the arc voltage increases with decreasing gas flow or particle density in the discharge chamber until the discharge becomes unstable” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 83 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Run current-regulated and watch arc voltage as a flow/health indicator: creeping arc voltage at fixed current is evidence of falling gas density and approaching instability - cross-check against gas supply and cathode condition before acting, since a worn cathode and other drifts move arc voltage too. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-608** · applicability level 4 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-608 - **Rule (this site's paraphrase of the source):** Cold-cathode arc power is limited to about 1 kW per cathode in the source's account, because thermal electron emission sets in beyond that; higher power means pulsing or accepting transition to the hot regime. - **Formula:** `P_arc,max(cold, dc) ~ 1 kW per cathode` - **Source quote (verbatim):** “The arc power for cold cathode operation is limited to about 1 kW per cathode, because of the start of thermal electron emission” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 84 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's 50-150 W arc sits well below the cited onset, which makes cold (secondary-emission) operation the expectation - but confirm it: per-cathode heat loading, geometry and cooling set the actual cathode temperature, so check the buttons for signs of running hot rather than assuming the regime from arc power alone. **dg-609** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-609 - **Rule (this site's paraphrase of the source):** Cathodes are worn out when the sputter-erosion crater depth reaches roughly the anode bore radius; beyond that the discharge destabilizes. Titanium is the best cold-cathode compromise; tantalum if the cathodes run hot. Cold mode wears faster than hot because arc voltage (hence sputter yield) is higher. - **Formula:** `end-of-life at crater depth ~ r_anode_bore; Ti (cold) / Ta (hot) cathodes` - **Source quote (verbatim):** “The cold and hot cathodes are worn out when the erosion crater's depth reaches around the anode bore radius. The discharge becomes unstable under these conditions ... Titanium has been selected as the best compromise ... If the cathodes are allowed to run hot, tantalum has been shown to be a good choice.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 84-85 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Cathode buttons are the main consumable: with a ~3 mm diameter anode bore, end-of-life comes near ~1.5 mm of crater depth (the criterion is the bore RADIUS). Stock spare buttons and log arc-hours. Material follows regime, not convenience: titanium for demonstrated cold operation, tantalum where the cathodes verifiably run hot. **dg-610** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-610 - **Rule (this site's paraphrase of the source):** Wolf Table 5.5's cold-cathode column, as extracted (the quote line verifies the gas row against the page image): arc 1-5 kV at 1-5 A, ignition 5 kV, duty <=25%, B >= 0.4 T, source gas pressure 1-10 Pa, gas consumption 0.2 sccm, ion current <=5 mA, anode aperture 1.5 x 25 mm, anode canal 6 mm dia, cathode 9 mm dia, cathode spacing 6.5 cm. - **Formula:** `see rule; gas consumption 0.2-0.6 sccm across all PIG types in the table` - **Source quote (verbatim):** “Gas consumption (sccm) 0.2 [hot cath.] / 0.2 [cold cath.] / 0.2-0.6 [heated cath.] (Table 5.5; verified against page image)” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 101 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The headline for the reference machine is the gas line - full-size accelerator PIGs run on 0.2-0.6 sccm, and its own hydrogen feed is a 1-sccm-full-scale mass-flow controller, so what the chimney buys is not less gas but gas confined where the ionization happens. Dimensions scale down for a 36 mm pole gap (its chimney will be shorter than the 6.5-10 cm cathode spacings listed, which are for big-gap machines). **dg-611** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-611 - **Rule (this site's paraphrase of the source):** Feed the gas into the anode close to the cathode(s) — it eases ignition and minimizes neutral gas flow out through the extraction slit. - **Formula:** `gas inlet at cathode end of chimney, not at slit level` - **Source quote (verbatim):** “Gas is fed to the discharge usually through the anode close to the cathode(s) to ease ignition of the arc and to keep the neutral gas flow through the extraction slit in the anode low” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 81 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Plumb the MFC line to feed near the cathode end of the chimney where the geometry allows (AMIT feeds through the cathode cavity - a variant of, not identical to, the quoted through-anode arrangement): it eases ignition and keeps neutral flow out the slit low. Chamber backfill still works (dg-409) - the injection win is lower chamber pressure for the same source density, to be verified by measurement on the actual machine. **dg-612** · applicability level 4 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-612 - **Rule (this site's paraphrase of the source):** In a heated-cathode PIG the anticathode is kept cold and collects a net electron current; more than -20 V of bias is needed to suppress it. Anticathode is usually strapped to cathode potential, sometimes left floating for space reasons. - **Formula:** `V_suppress(anticathode) < -20 V; usual connection anticathode = cathode` - **Source quote (verbatim):** “More than -20 V is necessary to suppress this electron current ... The anticathode is usually connected to the cathode, but sometimes just floating because of space problems in some cyclotrons.” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 86 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For the symmetric cold-cathode chimney, strap both cathodes together on one HV feed - that is the intended symmetric topology, not the anticathode case the quote describes. A floating anticathode is a documented space-saving variant in some cyclotrons; if used, verify its self-bias, stability and thermal loading, since floating changes the electron interception the strapped connection sets. **dg-613** · applicability level 4 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-613 - **Rule (this site's paraphrase of the source):** PIG beam energy spread is tabulated at 10-50 V (read as eV per unit charge), with typical currents in the 5-500 mA class. - **Formula:** `dE(PIG) = 10-50 eV per charge state; typical currents 5-500 mA class (source table)` - **Source quote (verbatim):** “PIG ion source 10-50 [energy spread, V] 5-500 [typical ion current, mA] (Table 2.1)” - **Source:** [Wolf (ed.), Handbook of Ion Sources (1995)](https://cyclotroninfo.com/library/#lib-059) — p. 51 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Against a few-keV effective first-gap gain a 10-50 eV spread is a ~1 percent perturbation, so source simplicity is worth keeping - confirm with the machine's own capture/acceptance estimate, since capture depends on RF phase and central-region geometry, not the gap voltage alone; the filament-arc comparison needs its own source. **dg-614** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-614 - **Rule (this site's paraphrase of the source):** Cold-start ignition per Clark's account: raise the arc voltage to about 3 kV and increase gas pressure; the struck arc is then stabilized by the supply's current regulator or ballast resistor, with dc arc currents of 1-15 A (the quote). Corroborating machines carry their own figures: AMIT (to -3 kV with a gas boost near 10 sccm, striking in seconds, sustaining under 1 kV) and Forringer's 3 kV current-limited supply (dg-415). - **Formula:** `V_ignite ~ 3 kV (Wolf table gives 3-5 kV); V_run = 0.3-2 kV; gas boost then reduce` - **Source quote (verbatim):** “An arc is struck by raising the arc voltage to about 3 kV and increasing the gas pressure ... is stabilized by the arc supply current regulator or ballast series resistor ... Arc currents are 1-15 amps for dc sources and higher for pulsed sources. Arc voltages are 300-2000 volts.” - **Source:** [Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981)](https://cyclotroninfo.com/library/#lib-197) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Spec the arc supply for ~3 kV compliance even though running voltage is ~0.3-2 kV, and automate the sequence - gas up, strike, gas down, current-regulate - with the boost magnitude and timing tuned on the machine rather than copied. **dg-615** · applicability level 2 · ion-source, rf, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-615 - **Rule (this site's paraphrase of the source):** Internal-source extraction in Clark's survey: the anode/chimney is grounded and the dee's RF does the extraction via a puller or feeler, at 30-100 kV of RF on the full-size machines; his external sources run 10-30 kV DC with the anode biased positive. - **Formula:** `internal PIG anode at ground; extraction field = dee RF via puller; 30-100 kV RF (big machines)` - **Source quote (verbatim):** “Source extraction voltage is 10-30 kV dc for external sources, with the anode being biased positive. For internal sources, the anode is usually grounded and 30-100 kV of rf voltage is used for extraction” - **Source:** [Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981)](https://cyclotroninfo.com/library/#lib-197) — p. PDF p.3 (printed p.233 of the 9th Int. Conf. on Cyclotrons proceedings) - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine extracts with its few-kV dee - far below the surveyed machines. Compensating with a small source-puller gap follows Child-Langmuir-like scaling (I ~ V^1.5/d^2 in the planar model - a guide in this geometry, not a law): documented small gaps run 2.3-2.9 mm (Siemens, K100 - dg-624), and expect proportionally lower current than published microamp figures until measured. **dg-616** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-616 - **Rule (this site's paraphrase of the source):** PIG cathode maintenance interval in the cited heavy service (1-15 A arcs) is a few hours to a day - cathode replacement plus anode cleaning; a hooded filament source in the same machines delivers a few mA of protons. - **Formula:** `cathode service interval ~ hours to 1 day (heavy-ion, 1-15 A arcs)` - **Source quote (verbatim):** “A disadvantage is the need for cathode replacement and anode cleaning at intervals of a few hours to a day.” - **Source:** [Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981)](https://cyclotroninfo.com/library/#lib-197) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Lower arc power and lighter gas both cut sputter erosion, so a small hydrogen source should do far better than the cited heavy-ion interval - but how much better is a measurement, not a scaling law: run the source and log the wear before promising a lifetime. **dg-617** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-617 - **Rule (this site's paraphrase of the source):** Fully-dimensioned bench PIG (Rovey): cathode body machined from a 5.1-cm iron rod, Sm2Co17 magnet (~3 kG surface flux) in a thin stainless sleeve, spot-welded stainless-sheet anode, and a 3.2-mm iron faceplate with a 6.4-mm hole on centerline - producing a continuous 1 mA positive hydrogen-ion beam at 1 mTorr with 5.4 kV / 32.4 W through a 100 kOhm, 100 W ballast. - **Formula:** `1 mA positive hydrogen ions at 5.4 kV, 6.0 mA discharge, 32.4 W, 1 mTorr; 100 kOhm / 100 W ballast; ignition <= 1 kV (paper's ignition result)` - **Source quote (verbatim):** “The cathode body is a 5.1-cm-diameter iron rod that has been machined to the dimensions and geometry shown in Fig. 1. ... samarium cobalt (Sm2Co17) permanent magnet ... surface flux density of approximately 3 kG ... the cathode faceplate is fabricated using the same iron rod as the cathode body. A 3.2-mm-thick, 5.1-cm-diameter disk is cut from the iron rod and machined with a 6.4-mm-diameter hole on centerline. ... a 100 kOhm, 100 W resistor is connected in-line with the power supply to current limit the discharge. ... generate a plasma discharge that yields a continuous 1 mA beam of positively charged hydrogen ions at 1 mTorr of pressure. This operating condition requires 5.4 kV and 32.4 W of power.” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 1-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Existence proof that mA-class hydrogen PIG output needs only tens of watts and modest fabrication (machined rod, spot-welded sheet anode). The axial-extraction geometry differs from a cyclotron chimney, so the discharge economics transfer as encouragement - the chimney's own extraction still needs its own validation, and the 1 mA is aggregate hydrogen ions, not mass-analyzed H+. **dg-618** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-618 - **Rule (this site's paraphrase of the source):** Rovey ballast/ignition data: discharge ignites at <=1 kV at all flows; a 100 kOhm series resistor on a 6 kV/200 mA supply stabilizes it; target/discharge current utilization ~25% for H2 (21% He); his flow-to-pressure points: 1 sccm -> 2e-5, 2 -> 5e-5, 3 -> 1.6e-4, 5 -> 3.5e-4 Torr. - **Formula:** `I_beam/I_discharge ~ 0.25 (H2); ballast 100 kOhm at mA scale` - **Source quote (verbatim):** “the plasma discharge ignites easily at 1 kV or less for all cases ... a current utilization efficiency (ratio of target to discharge current) of 25%” - **Source:** [Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007)](https://cyclotroninfo.com/library/#lib-014) — p. 2-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Use the right utilization figure for the right geometry when predicting a next machine's beam: Rovey's ~25% is axial extraction; Forringer's radial-slit configurations measured I_beam/I_arc of about 0.0005 to 0.0046 - nearly two orders lower, because the slit samples a small part of the plasma - and neither number transfers to a new source without measurement. **dg-619** · applicability level 4 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-619 - **Rule (this site's paraphrase of the source):** Forringer chimney/slit trade (measured, 40 kV dc puller, 3 sccm H2): the 0.25 x 5.0 mm slit gives 52-227 uA at 50-450 mA arc (I_beam/I_arc ~ 1.0e-3 falling to 0.5e-3) with radial emittance ~25 mm-mrad independent of current; the 0.51 mm slit gives 230-590 uA at only 50-150 mA (~4.6e-3 x I_arc) but emittance grows with current (47 -> 65 mm-mrad). Wider slit = more current per arc-watt; brighter is narrower. - **Formula:** `I_beam ~ (0.5-4.6)e-3 x I_arc for 0.25-0.51 mm slits at 40 kV dc extraction` - **Source quote (verbatim):** “Table 3.4: Slit 0.010" 40 kV, 450 mA, 3.0 cc/min -> 227 uA; Slit 0.020" 40 kV, 150 mA, 3.0 cc/min -> 590 uA” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 88-91 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Start a next machine with the 0.5 x 5 mm slit - at 50-150 mA arc it made 230-590 uA at 40 kV. A fixed-gap Child-Langmuir scaling to a 4 kV dee (V^1.5) would read ~7-19 uA, but treat that as a blackboard exercise, not available beam: RF extraction changes gap, meniscus and phase acceptance, so model the actual central region before booking any of it against the present 3 nA best. **dg-620** · applicability level 4 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-620 - **Rule (this site's paraphrase of the source):** Chimney machining details from Forringer: slits chamfered 10 deg, relieved 0.010 in deep in a 0.020 in wall leaving a 0.010 in 'tunnel'; the hole chimney is 0.047 in (1.19 mm) diameter with a 60 deg chamfer. The hole chimney's radial normalized emittance (0.66 mm-mrad) ran about 50 percent larger than the slit's (0.44 mm-mrad); a flat plasma boundary best matched the slit beams, a highly concave one the hole beam. The thesis's Conclusion adds a beam datum: after the puller, slit-chimney beams averaged about 70 percent of the chimney opening's height - a beam-height-to-aperture ratio, not a chimney geometry ratio. - **Formula:** `slit land/tunnel 0.25 mm, chamfer 10 deg (slit) / 60 deg (hole); emittance 0.44 (slit) vs 0.66 mm-mrad (hole)` - **Source quote (verbatim):** “The slit chimneys produced a beam that was nearly horizontal (in z) and was, on average 70% as tall as the chimney opening after passing through the puller. The hole chimney produced a beam that (in the absence of strong focusing) diverged in z.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. PDF p. 121 (printed p. 111) for the 70% claim; PDF p. 84 (printed p. 74) for the Fig. 3.12 caption - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Editorial note, tabletop extrapolation: the actual machining callouts for a chimney a home shop can cut. The thin-land/outward-chamfer rationale (don't collimate the beam away; the thesis suggests deeper chamfers may raise current) is engineering reading of the source's optimization remarks. **dg-621** · applicability level 2 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-621 - **Rule (this site's paraphrase of the source):** Cathode-anode gap in the NSCL/ACCEL cold-cathode source was anywhere from 1.9 to 3.8 mm and 'is not a critical parameter'; the thesis's practice pairs that with 100-grit cathode sanding (early screwdriver-scratching proved unnecessary) and the essential water cooling of cathode rod and anode base (dg-416's melted-copper lesson). - **Formula:** `cathode-anode gap 1.9-3.8 mm, non-critical` - **Source quote (verbatim):** “The cathode anode gap was between 0.075" (1.9 mm) and 0.150" (3.8 mm), and is not a critical parameter for the source's operation.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 29 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Generous tolerance on the AXIAL gap - that part of the chimney stack-up doesn't need precision. Concentricity and slit alignment are separate tolerances with their own tighter demands, and the cooling warning stands at any arc power: provide a conduction path sized for continuous arc wattage, or plumb water. **dg-622** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-622 - **Rule (this site's paraphrase of the source):** In Forringer's cold-cathode PIG source, H2+ was below the analyzer's detection at normal operating points (50-350 mA arc, >=2.0 cc/min H2, arc supply in current limit below 3 kV); starving the gas to 0.5 cc/min flipped the arc into a 3.5 kV voltage-limited mode (current fell to 90 mA) and H2+ appeared. One source, one analyzer, detection limit unstated. [Corrected 2026-08-23: earlier wording turned "no H2+ observed" into a recipe for a clean proton beam; the note below says what a builder can and cannot take from it.] - **Formula:** `In the measured source: H2+ below detection for flow >= 2 cc/min with arc current-limited; H2+ appears at starved 0.5 cc/min. Not transferable without the source geometry and pumping speed.` - **Source quote (verbatim):** “Under normal ion source opperating conditions ... no H2+ ions were observed. We were able to observe H2+ ions by lowering the gas supply to 0.5 cc/min.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 89 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Treat gas flow and arc regime as a species TUNING HYPOTHESIS for the reference machine, not as a purity guarantee: 'below detection' in one analyzer does not exclude H2+ at a lower level, says nothing about H3+, and the cc/min thresholds depend on that source's geometry and pumping. Species misidentification propagates into energy, range, resonance interpretation and any radiation assumption, so verify H+/H2+/H3+ in the actual machine - analyzing magnet, time-of-flight, the f = qB/2\*pi\*m resonance check, or a reaction diagnostic - before claiming a proton beam. Transfer only the method: scan flow and arc regime while directly measuring species; do not assume the direction or the thresholds reproduce in another source. **dg-623** · applicability level 2 · ion-source, vacuum, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-623 - **Rule (this site's paraphrase of the source):** This cold-cathode source family has run at 4.5 T in the Harper Medical Cyclotron and at 0.5 T in NSCL test-stand low-field checks; the thesis's test-stand practice: base vacuum in the 1e-6 Torr range (gas off) for consistent starts, with 2.5 sccm of H2 putting the chamber at 4e-5 Torr under 600-800 L/s of turbo pumping. - **Formula:** `B operating range 0.5-4.5 T demonstrated; base vacuum ~1e-6 Torr for reliable starts` - **Source quote (verbatim):** “there needs to be a base vacuum (with the ion source gas supply turned off) in the 10−6 Torr range ... Various turbo pumps ranging from 600 to 800 liters/second were used ... With a gas flow rate of 2.5 cc/min of hydrogen, the pressure in the main vacuum chamber is around 4 × 10−5 Torr.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. PDF p. 39 (printed p. 29) for the vacuum/flow practice; PDF p. 27 (printed p. 17) for the 4.5 T / 0.5 T endpoints - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's 0.59 T sits just inside the demonstrated field range - demonstrated at the endpoints, not characterized as uniform performance across it - and its existing turbo and 1e-6-class base pressure match the thesis's start conditions as-is. **dg-624** · applicability level 2 · ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-624 - **Rule (this site's paraphrase of the source):** Puller geometry from the same source family: test-stand puller radius 12.7 mm with 5.0 mm minimum chimney-puller gap at 50 kV design voltage; the K100 medical cyclotron puller runs a 2.9 mm minimum gap (at ~20-40 kV RF), with the puller center deliberately offset 0.5 mm from the chimney center. - **Formula:** `gap 5.0 mm at 50 kV; 2.9 mm (K100); offset 0.021" between chimney and puller centerlines` - **Source quote (verbatim):** “The chimney is centered at (0.000,0.000) and the puller is centered at (0.021,0.000). The minimum gap between the chimney and the puller is 2.9 mm while the gap at the source opening is 3.0 mm, meaning that the beam does not see the peak electric field. [K100 geometry]” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 78, 85 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Gap sets extraction field at fixed voltage, so at a few kV on the dee the chimney-puller gap must shrink below these machines' values to recover useful gradient - but there is no constant-kV-per-mm law to size it by (dg-419): pick a gap, then verify holdoff on the bench with the actual electrodes, finish and RF. The K100's deliberate 0.5 mm center offset - trading peak field at the beam for extraction optics - is the transferable design idea. **dg-625** · applicability level 3 · ion-source, beam-dynamics, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-625 - **Rule (this site's paraphrase of the source):** For orbit-code initial conditions, model ions leaving a slit chimney from an approximately flat plasma boundary and a hole chimney from a concave one, at ~35,000 K plasma temperature (the source's stated 'central starting energy' 4.5 eV, i.e. (3/2)kT under its convention); with these methods the author judged Z3CYCLONE predictions adequate 'such that construction of actual cyclotrons can proceed with reasonably prudent confidence'. - **Formula:** `T_plasma ~ 35,000 K; kT ~ 3.0 eV, central starting energy 4.5 eV = (3/2)kT (source convention); flat boundary (slit), concave (hole)` - **Source quote (verbatim):** “We observe that an approximately flat plasma boundary provides the best match to the experimental beams emerging from the 'slit' style chimneys in our study, while a concave plasma boundary (curving toward the source axis) provides a better match for the beam that emerges from the 'hole' style chimney. In all cases, the plasma temperature that provides the best match for experimental beams is approximately 35,000 K (resulting in a central starting energy of 4.5 eV). Using the methods presented in this dissertation, the orbit tracking code Z3CYCLONE is able to predict the beam produced by a cold cathode PIG ion source with adequate accuracy such that construction of actual cyclotrons can proceed with reasonably prudent confidence that the cyclotron will perform as predicted.” - **Source:** [Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004)](https://cyclotroninfo.com/library/#lib-069) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Drop-in starting condition for the reference machine's central-region orbit models: start protons from a flat sheet across the slit with the source's 4.5 eV central energy, not from rest at a point - and sweep the parameters against measured beams per dg-423. **dg-626** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-626 - **Rule (this site's paraphrase of the source):** Siemens Eclipse RDS111 cold-cathode PIG complete working point at 120 uA on target: arc 0.27 A at 550 V (150 W), ignition up to -3 kV on cathodes, 5.5 sccm H2, 0.7 T field, anode slit 0.7 x 5.2 mm, puller slot 1.1 x 5.3 mm at 2.3 mm anode-puller distance, plasma column 4.0 mm dia set by collimators in a 5.0 mm anode bore, Ta cathodes 4.3 mm dia; 800 uA H- extracted (beam-on-post); rebuild interval 120 h, target 300 h. - **Formula:** `150 W arc -> 800 uA extracted H- in 0.7 T; slit 0.7 x 5.2 mm; gap 2.3 mm` - **Source quote (verbatim):** “Arc Current 0.27 A / Arc Voltage 550 V / Arc Power 150 W / H2 Gas Flow 5.5 sccm / Beam-on-Post (Extraction Current) 800 uA (Table 1)” - **Source:** [Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017)](https://cyclotroninfo.com/library/#lib-100) — p. 2-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The single most relevant commercial datapoint - 0.7 T (nearly the reference machine's field), 150 W arc, sub-amp arc current, hundreds of uA extracted, 120+ hour consumable life. It makes H-: useful as discharge and lifetime context, but it does not quantitatively predict a positive-ion version's H+ output - species fractions, meniscus and extraction all change with polarity, so measure H+ directly. **dg-627** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-627 - **Rule (this site's paraphrase of the source):** Siemens PET-source upgrades, as measured: grooved molybdenum anodes lowered arc power 7% and raised target beam 20% (material and groove tested together, not separated); a cesium getter pill in the cathode gave +26% beam at -25% arc power; thoriated-tungsten cathodes were a net loss; widening the plasma-to-wall 'cool ring' also gained beam - with the printed dimensions carrying an arithmetic slip: a 5.0 mm bore with the column collimated 4.0 -> 3.8 mm gives 0.50 -> 0.60 mm of ring, not the 0.70 previously stated (re-read queued for the true bore). - **Formula:** `plasma-to-wall gap 0.5-0.7 mm (H- volume production); Mo grooved anode +20%; Cs pill +26%` - **Source quote (verbatim):** “Ø5.0 mm Anode I.D. ... 0.5 mm Plasma Column to Anode Wall ... Ø4.0 mm Collimator I.D. ... Plasma column diameter is defined by the collimators, which have inside diameter of 4.0 mm.” - **Source:** [Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017)](https://cyclotroninfo.com/library/#lib-100) — p. bore and ring dimensions in Fig. 1b and its caption, PDF p. 2; the 'cool' region experiments on PDF p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The cool-ring and Cs tricks are H(-)-specific; the transferable lessons for a positive-ion source are that geometry near the slit dominates output, molybdenum is a sound anode material, and exotic cathode materials earned nothing - with the grooved-anode gain belonging to the whole tested configuration, not to Mo as such. **dg-628** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-628 - **Rule (this site's paraphrase of the source):** Round apertures vs slits are a transmission-vs-current trade — converting the Eclipse anode/puller slits to equal-area round holes raised cyclotron transmission from 19% to 30% but cut target current from 120 to 40 uA. - **Formula:** `round aperture = +57% transmission, -67% net current (equal area)` - **Source quote (verbatim):** “Post-to-foil transmission increased dramatically (from 19% to 30%) but the total target current decreased from 120 uA to 40 uA” - **Source:** [Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017)](https://cyclotroninfo.com/library/#lib-100) — p. 3-4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a machine starved of axial acceptance a hole source may waste less injected beam, while total current favored the tall slit in the Eclipse test. The reference machine's 1.42 in physical gap suggests but does not establish generous DYNAMIC acceptance - pick slit vs hole from central-region tracking or a measured acceptance/delivered-current comparison, not the gap dimension. **dg-629** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-629 - **Rule (this site's paraphrase of the source):** Cold-cathode PIG V-I regimes as measured on AMIT: below ~250 mA arc the cathodes supply electrons mainly by secondary emission and the impedance is high; as current rises the cathodes heat up and begin supplying electrons thermionically. The paper also reports arc power vs gas flow passing through a minimum near 4 sccm. - **Formula:** `AMIT: secondary-to-thermionic transition ~250 mA (that geometry); arc-power minimum near 4 sccm (that source)` - **Source quote (verbatim):** “For arc currents below 250 mA the electrons are mainly furnished by secondary emission and the impedance is high. When the current increases, the cathodes heat up and begin to supply electrons by thermionic emission” - **Source:** [Obradors et al., Characterization of the AMIT Internal Ion Source with a Devoted DC Extraction Test Bench — IPAC 2017 (2017)](https://cyclotroninfo.com/library/#lib-199) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Staying below the transition keeps the discharge in its high-impedance regime, which is the friendlier load - but 'stable with a simple regulated supply' is a property of the measured V-I curve plus the ballast, not of a current number: measure the tabletop source's own V-I and dynamic behavior over gas flow, and choose ballast and compensation from the measured differential resistance, ignition included. **dg-630** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-630 - **Rule (this site's paraphrase of the source):** PIG thermal budget (IRANCYC-10, ~500 W total at 1.1 A discharge): cathode heads reach 1992 K from ion bombardment, anode peaks at 472 K adjacent to the exit slit, cathode thermal distortion 0.2 mm; 0.007-0.04 kg/s of 18 C water holds everything. Thermionic contribution at 1992 K is only 0.6% of the discharge current. - **Formula:** `hot spots = cathode heads and slit region; ~0.5 kW needs ~0.01-0.04 kg/s water` - **Source quote (verbatim):** “the maximum temperature of the cathodes are 1992 K, which is far away from the cathode melting point ... an electron current of 0.00706 A at 500 V which is negligible in comparison to the discharge current of 1.10352 A” - **Source:** [Zakerhosseini et al., Heat Transfer Study of PIG Ion Source for 10 MeV Cyclotron — IPAC 2016 (2016)](https://cyclotroninfo.com/library/#lib-200) — p. 1-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** At the reference machine's ~100 W arc the cathode heads may or may not run incandescent - temperature scales with T^4 radiation, bombardment distribution and contact conductance, none linearly with arc power. Mount the heads on refractory stems either way, and size the chimney's heat path (copper stalk to a cooled or finned flange) from a small thermal model or a calorimetric test, including what happens on loss of cooling. **dg-631** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-631 - **Rule (this site's paraphrase of the source):** KIRAMS-13 anode-bore calibration: in simulation a 7 mm ID anode maximized electron density and 8 mm gave the highest beam current density on the real machine; above ~9 mm ID, secondary-electron production falls. Their geometry: 20-mm-long anode, Ta cathode discs screwed into holders, ~2 T field. - **Formula:** `KIRAMS-13: anode ID optimum 7-8 mm, falloff above ~9 mm; anode length 20 mm; simulated range 6.16-10.1 mm` - **Source quote (verbatim):** “the anode with 7 mm in inner diameter is demonstrated to be capable of producing the highest density of electrons while the 8 mm inner diameter anode gives the highest beam current density in KIRAMS-13 ... when the anode with inner diameters higher than 9 mm, the number of electron production will decrease ... The cylinder shape anode with 20 mm in length having different internal diameters of 6.16 mm to 10.1 mm, were used in simulation.” - **Source:** [Mu et al., Simulation of Electron Behavior in PIG Ion Source for 9 MeV Cyclotron (2015)](https://cyclotroninfo.com/library/#lib-198) — p. 3, 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A starting range, not a spec: at 0.59 T the electron column is fatter than at KIRAMS's 2 T, so begin near the top of the 7-8 mm range or make the chimney bore an interchangeable insert and find the optimum at the actual field, pressure and arc voltage. **dg-632** · applicability level 2 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-632 - **Rule (this site's paraphrase of the source):** Alignment sensitivities: an off-center cathode (relative to anode bore and B axis) produces dramatically fewer secondary electrons with shorter confinement lifetimes; extraction is optimized over a mere -0.2 to -1.5 deg of anode (slit) rotation relative to the puller (>50% extraction inside that window), with the puller 2.2 mm from the anode aperture. - **Formula:** `cathode-anode-B coaxiality critical; slit-to-puller rotational alignment ~1 deg class` - **Source quote (verbatim):** “the properly aligned configuration produces significantly more secondary emission electrons ... with the anode rotation angles from -0.2 to -1.5 degree, more than 50% H- beam can be extracted through pullers” - **Source:** [Mu et al., Simulation of Electron Behavior in PIG Ion Source for 9 MeV Cyclotron (2015)](https://cyclotroninfo.com/library/#lib-198) — p. 4-6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Two different tolerance classes: build the chimney concentric (pin the cathode discs to the bore, machine in one setup), and provide an external rotational adjustment of the source stalk with sub-degree feel for slit-to-puller aiming. The KIRAMS optimum spanned about a degree, so an adjustment range of a few degrees around nominal is the class to design for - the actual optimum is found on the machine, not inherited. **dg-633** · applicability level 5 · ion-source, cyclotron-general · https://cyclotroninfo.com/design-guide/ion-source/#dg-633 - **Rule (this site's paraphrase of the source):** A commercial-class 10 MeV PET-cyclotron power budget (CYC2016 design): 1.5 kW internal PIG ion source against 26 kW magnet coil and 14 kW RF consumption; simulated beam after the third accelerating gap ~197 uA at 190 keV from a 40 kV gap voltage. - **Formula:** `P_ion_source ~ 1.5 kW (commercial); ~4% of machine wall power` - **Source quote (verbatim):** “Coil Consumption Power [kW] 26 ... RF Consumption Power [kW] 14 ... Ion Source Power [kW] 1.5 (Table 1) ... Cavity loss power was calculated 12.7 kW to generate an electric field with 40 kV gap voltage ... Beam energy and current was checked 190 keV, 197 uA after third accelerating gap” - **Source:** [Lee et al., Investigation of Minimized Consumption Power about 10 MeV Cyclotron — Cyclotrons 2016 (2016)](https://cyclotroninfo.com/library/#lib-201) — p. 2-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Context datum, not a scaling law: the reference machine's ~0.1-0.2 kW source budget is a deliberate derating of this class of design, but beam current does not scale with source power - capture, acceptance and extraction losses dominate - so estimate current from measured source output and capture efficiency. **dg-634** · applicability level 2 · ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-634 - **Rule (this site's paraphrase of the source):** A chimney over a filament converts an open e-bombardment source into a column source: thermionic electrons travel the full chimney to the median plane, ions form in the whole column, and a small aperture (1/16", 1.6 mm) facing the dee releases them into the gap with field lines naturally matched to the first orbit. - **Formula:** `chimney aperture 1/16" (1.6 mm) toward dee (Rutgers 12-inch)` - **Source quote (verbatim):** “The inclusion of a chimney placed on top of the existing design will permit the thermionic electrons to travel to the median plane, thereby generating ions in the entire column. A small aperture, 1/16 of an inch in diameter, opening towards the DEE permits ions to be drawn into the accelerating field.” - **Source:** [Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006)](https://cyclotroninfo.com/library/#lib-013) — p. 2-3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The half-step option: chimney-over-filament keeps the reference machine's existing filament supply and adds gas confinement plus a defined 1.6 mm emission aperture. Injection matching to the first orbit remains its own design question (aperture position, puller, phase - dg-348), not an automatic property; a PIG chimney gets the same geometry benefits and deletes the filament, at the price of a new arc supply (dg-383). **dg-683** · applicability level 3 · rf, dee, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-683 - **Rule (this site's paraphrase of the source):** A few-hundred-volt positive dee/line bias doubled the 37-inch beam current for reasons then unexplained - worth one experiment, but only where no magnetic-field region can sustain a Penning discharge (the 184-inch later required negative bias). - **Source quote (verbatim):** “For reasons which are not clearly understood this bias usually increases the size of the beam by a factor of two or more.” - **Source:** [MacKenzie & Waithman, R.F. System for Frequency Modulated Cyclotron — MDDC-1045 (1946)](https://cyclotroninfo.com/library/#lib-204) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Conditionally applicable - and 'try both polarities' is a controlled test, not a knob: use an RF-rated bias network with proper isolation and discharge paths, current and arc monitoring, and vacuum interlocks, and assess Penning-discharge conditions (crossed E and B regions) before applying either polarity. The dee's RF stored energy does not care about the bias supply's current limit. **dg-703** · applicability level 2 · beam-measurement, ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-703 - **Rule (this site's paraphrase of the source):** Internal beams of 100-3000 uA were routine on the census's small machines (ISSP 16-in: 100 uA deuterons; BNL 18-in: 1-2 mA protons; ANU: 3 mA); external beams ran far lower on most (Copenhagen 2%, ANU 8% of internal), with BNL's tabulated pairing - 800 uA external against 1000-2000 uA internal, nominally 40-80% - the outlier, and the table's values not necessarily simultaneous. - **Source quote (verbatim):** “Internal Beam, Stable, ua 1000-2000 ... External Beam, Stable, 800 ua; 100 ua focused on target 15 ft from machine” - **Source:** [Howard, Cyclotrons and High-Energy Accelerators, 1958 — ORNL-2644 (1958)](https://cyclotroninfo.com/library/#lib-206) — p. 107 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** If the reference machine sees nA, the gap to the historical uA-mA norm lives in source output and center-region transmission, not physics limits - and extraction cost most census machines most of their beam, so budget a next machine's external current pessimistically. **dg-704** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-704 - **Rule (this site's paraphrase of the source):** Hooded low-voltage arc sources with hot filaments dominated the census's small machines as tabulated: ANU hooded arc with tungsten filament, BNL hot cathode in a copper arc house, Stanford hooded arc, ISSP hooded low-voltage. - **Source quote (verbatim):** “Ion source, type hooded arc, tungsten filament” - **Source:** [Howard, Cyclotrons and High-Energy Accelerators, 1958 — ORNL-2644 (1958)](https://cyclotroninfo.com/library/#lib-206) — p. 26 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Population-level evidence that the hooded filament arc is the proven route to 100 uA-class internal beams at this scale - evidence of practice, not proof a cold-cathode PIG cannot compete (PIGs run cyclotrons too, dg-383): the choice trades filament fragility against arc-supply simplicity and delivered current. **dg-734** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-734 - **Rule (this site's paraphrase of the source):** Moving the source off-center and injecting azimuthally into a dee transformed the 20-inch: a central open arc giving 3.2 mA with severe dee-tip heating was replaced by a hooded-arc source at ~1.75-in radius with a 1/8 x 3/4-in exit slot, roughly doubling the beam to 6-7 mA and eliminating the dee-tip heating - though source type and position changed together. - **Formula:** `source radius ~1.75 in on a 20-in machine (~0.2 of pole radius); slot 1/8 x 3/4 in` - **Source quote (verbatim):** “A major improvement was effected when an off-center source was installed which injected azimuthally into one of the dees.” - **Source:** [Heusinkveld et al., Studies with a Three-Dee Three-Phase Proton Cyclotron — UCRL-3187 (1955)](https://cyclotroninfo.com/library/#lib-210) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For the reference machine's filament source, radial position and slot azimuth are cheap, high-leverage experiment variables (directly relevant to the planned source-species test) - scan them, normalized to the first-orbit geometry. Expect improvement mechanisms to be entangled as they were historically; measure, don't assume a factor of two. **dg-787** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-787 - **Rule (this site's paraphrase of the source):** Ion-source axial position is a first-order machine parameter: raising the 86-inch source 1.5 in - leaving it one inch below the magnetic center, with the accelerating slit raised the same amount - was credited with taking protons from ~19 to ~24 MeV. - **Source quote (verbatim):** “The increase in proton energy resulted from relocation of the ion source 1 1/2" upward; the source is now effectively only one inch below the magnetic center.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952)](https://cyclotroninfo.com/library/#lib-216) — p. 8 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** On the reference machine, treat filament/chimney height relative to the MAGNETIC median plane (find it by measurement - it need not match the mechanical midplane) as a tuned parameter worth systematic scans. What the height buys is centering, vertical transmission and usable radius; at a fixed field and radius the energy is p = qBr regardless, so measure where the gain actually comes from rather than expecting a fixed percentage. **dg-789** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-789 - **Rule (this site's paraphrase of the source):** Give the ion source a positive mechanical registration: a bracket on the 86-inch liner fixes the source one inch below field center, insures proper positioning AND grounding of the stem's lower end, guarantees the same position run to run, and reduces rf-pickup heating of the support tube. - **Source quote (verbatim):** “To insure proper positioning and grounding of the lower end of the ion source, a bracket has been attached to the west side of the liner which places the ion source one inch below the center of the magnetic field. This arrangement insures that the position will be the same from run to run and also reduces heating of the tube due to rf pickup.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952)](https://cyclotroninfo.com/library/#lib-216) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Cheap and directly imitable — once the optimum source position is found by scanning, capture it in a hard registration feature so it survives every source rebuild; grounding the support also kills a stray RF-heating path. **dg-791** · applicability level 3 · beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-791 - **Rule (this site's paraphrase of the source):** Identify beam species with magnetic resonance curves: sweep magnet current at fixed RF and record probe current at full radius - H1+ and H3+ appear as separate peaks (68 gauss apart on the 22-inch; H3+ rides the third RF harmonic). At low arc current the H3+/H1+ ratio is high; raising arc current increases both total H1+ and the H1+/H3+ ratio. - **Formula:** `resonance: B = 2*pi*m*f_RF/(h*q) - specify the harmonic h per peak (H1+ at h=1, H3+ at h=3); at the same B and radius the H3+ energy is 1/3 the H+ energy` - **Source quote (verbatim):** “At low arc current the ratio of H3+ ions to H1+ ions is high. The total number of H1+ ions and the ratio of H1+ ions to H3+ ions may be increased by increasing the arc current.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952)](https://cyclotroninfo.com/library/#lib-216) — p. 16 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The prior art for a source-species test on the reference machine: a field sweep at fixed frequency is a species analyzer needing only the existing probe, and source arc power is the species-ratio control - expect molecular ions to be strong at weak arc, and raise the arc within the source's thermal and electrical limits when protons are wanted. (Fig. 6, PDF p.18, shows the resolved peaks.) **dg-792** · applicability level 3 · ion-source, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-792 - **Rule (this site's paraphrase of the source):** Shortening the 22-inch ion-source arc slit from 2.5 in to 0.5 in increased the ratio of accelerated beam power to ion-loading power, as predicted - emission the dees cannot accept loads the RF without making beam. - **Source quote (verbatim):** “the ion source arc slit was shortened from 2 1/2" to 1/2". Thereafter the ratio of accelerated beam power to ion loading power was increased, as predicted.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952)](https://cyclotroninfo.com/library/#lib-216) — p. 16 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** On a tabletop machine where every watt of RF matters: try slit length as an EXPERIMENT, watching accepted beam per unit dee loading rather than raw source output. The over-emission mechanism is the natural reading of the ORNL result, but slit changes also move plasma and extraction optics, so let the measurement decide. **dg-793** · applicability level 4 · dee, ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-793 - **Rule (this site's paraphrase of the source):** Negative dee bias can substitute weakly for an accelerating slit: on the 22-inch, increased (negative) dee bias raised full-radius beam by up to 30%, but only with no accelerating slit mounted - ORNL reports the effect 'is not observable when an accelerating slit is used'. [Corrected 2026-08-23: the earlier rule also said the slit 'outperforms the optimum bias'; the source shows the two are not additive, not that one beats the other. The sign of the bias and the with-slit null are on the cited page, just outside the quote - ORNL-1339 p. 16: 'This effect is not observable when an accelerating slit is used' and 'the increased negative bias potential gives non-optimum-phased ions ... a deeper penetration into the rf electric field'.] - **Source quote (verbatim):** “an increase in bias potential on the dees increases the beam accelerated to maximum radius by a factor of as much as 30% when the cyclotron is operated without an accelerating slit (rf) mounted on the dee.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952)](https://cyclotroninfo.com/library/#lib-216) — p. 16 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Worth a cheap experiment on the reference machine - with a proper RF-rated bias-injection network (choke/filter, insulation, supply protection), never a bare DC supply on a live dee. ORNL's stated reading is that bias pulls badly-phased ions deeper into the gap field; with a slit installed they saw no bias effect. The source does not rank the two approaches - test both on the actual machine. **dg-804** · applicability level 2 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-804 - **Rule (this site's paraphrase of the source):** Make ion-source position adjustable from outside the vacuum: the 63-inch found source-to-field alignment 'extremely critical', necessitating external adjustments - the 86-inch's Selsyn-driven rotator is the report's example implementation (scan re-read queued). - **Source quote (verbatim):** “The alignment of the source with the magnetic field is extremely critical, as was expected, and makes it necessary to provide for external adjustments of the ion source.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952)](https://cyclotroninfo.com/library/#lib-217) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Strong design input for a next machine: budget at least one externally accessible source degree of freedom (rotation or z) - both ORNL machines provided it after finding the optimum unreachable blind. Adjustment under beam is the convenient form; adjust-then-pump iterations reach the same optimum, slower. **dg-807** · applicability level 2 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-807 - **Rule (this site's paraphrase of the source):** Bench-test an ion source on a 180-degree beam path in the magnet before installing it: the 63-inch source was tested dc by collecting after a half-turn, measuring the species mix - 8 mA N+, 2 mA N++, 2 mA N+++ (the quoted result; the report's fuller qualification detail: scan re-read queued). - **Source quote (verbatim):** “In dc tests the output of the source, measured after the beam had passed through a 180 deg path in the magnetic field, was: 8 ma of N+, 2 ma of N++, and 2 ma of N+++.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952)](https://cyclotroninfo.com/library/#lib-217) — p. 24 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The 180-degree bend uses the cyclotron's own field as a mass spectrometer with the RF off — on the reference machine this is precisely the source-species test geometry: source + static field + offset collector measures the H+/H2+/H3+ mix directly before any acceleration studies. **dg-808** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-808 - **Rule (this site's paraphrase of the source):** When a source underperforms, look at where the drain current goes: the 22-inch dc injection source gave only 30 mA against its predecessor's 75, and the report's definite clue was persistent high drain to the accelerating electrode - present even in dc tests - pointing at interception rather than production. - **Formula:** `account for source output as beam + electrode drain; drain locates the loss` - **Source quote (verbatim):** “It was never possible to make a dc test without high drain to the accelerating electrode. This is a definite clue to the lower output obtained in the rf tests.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952)](https://cyclotroninfo.com/library/#lib-217) — p. 24 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Current bookkeeping is cheap diagnosis: meter the puller and chimney drains separately from the Faraday cup. A weak beam with a hot puller points first at geometry near the source exit - then confirm by varying extraction voltage, alignment and arc conditions, since plasma meniscus, secondaries and leakage also move those meters, and arc power can reshape the optics as well as the density. **dg-810** · applicability level 2 · ion-source, beam-dynamics, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-810 - **Rule (this site's paraphrase of the source):** Central-region orbit centering couples source radial position to dee voltage: with the Davis axial source confined to r < 2.5 in, the machine is forced to comparatively low dee voltages (20-30 kV) so the first-turn radius matches the available source position and the orbits stay centered — dee voltage is set by geometry, not by available RF power. - **Formula:** `first-gap geometry couples V_dee to source/puller radius: r_1 = sqrt(2*m*q*V_gap)/(q*B) for acceleration from rest through the gap potential - initial energy and RF phase correct it further` - **Source quote (verbatim):** “the ion source position is limited to a maximum radius of 2.5 inches. This forces operation at comparatively low dee voltages (20-30 kv) in order to center the orbits.” - **Source:** [Jungerman, Kibbe & Peek, Central Region Studies for Incorporating an Axial Ion Source in the Davis 76-in. Cyclotron — UCD-CNL-49 (1966)](https://cyclotroninfo.com/library/#lib-218) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The design logic transfers directly to a next machine's central-region layout: pick dee voltage and source-puller radius TOGETHER from the first-orbit geometry. It also cuts the other way for the reference machine's 5-13 kV upgrade: raising dee voltage moves the optimum source position outward — re-scan source position after the RF upgrade. **dg-843** · applicability level 2 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-843 - **Rule (this site's paraphrase of the source):** Anchor the vacuum design to the ion-source gas load: their 200 ml/hr (NTP) maximum injection = 0.042 liter-mm/sec (~0.04 torr-l/s), which against the effective pumping speed set the achievable operating pressure of ~4e-6 mm Hg. - **Formula:** `200 ml/hr NTP = 0.042 liter-mm/sec; P_operating = Q_source/S_effective + P_pump` - **Source quote (verbatim):** “If 200 ml/hr is considered as a maximum rate of gas injection, this results in ... 0.042 liter-mm/sec.” - **Source:** [Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952)](https://cyclotroninfo.com/library/#lib-219) — p. 136 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The same arithmetic the builder runs with the MFC: a 0.1-1 sccm hydrogen feed is 1.3e-3 to 1.3e-2 torr-l/s; divide by the honest effective speed FOR HYDROGEN at the chamber, then add the pump ultimate and the outgassing floor, to predict running pressure before touching hardware. The formula assumes the source feed dominates the incremental load - the flow-on/off test verifies that (dg-370). - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-888** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-888 - **Rule (this site's paraphrase of the source):** Control the ion-source ground connection deliberately: an ungrounded source floats toward the accelerating-slit (dee) potential, reducing the slit's effect - ORNL's measured radial widths then approached the no-slit theoretical predictions. A floating source is a different machine configuration, not a small perturbation. - **Source quote (verbatim):** “leaving the ion source ungrounded has a very substantial effect, since it then floats nearer the potential of the accelerating slit which is attached to the dees. This reduces the effect of the latter and the radial width approaches the theoretical predictions for a cyclotron without an accelerating slit.” - **Source:** [Cohen, Spatial Distribution of Current on an Internal Cyclotron Target — ORNL-1348 (1952)](https://cyclotroninfo.com/library/#lib-224) — p. 9 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Direct lesson for the reference machine's central-region debugging: the source body's electrical state - DC connection AND RF return impedance, since a floating body near driven dees picks up RF capacitively - is a real optics knob (or a real gremlin). Verify and log the filament/chimney ground path; an intermittent source ground would masquerade as day-to-day beam irreproducibility of exactly the kind ORNL-1347 warns about. **dg-911** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-911 - **Rule (this site's paraphrase of the source):** Injection quality is what fixed it: with a highly defined injected beam, the cited machine came to traverse the difference-coupling resonance vr - vz = 1 without attenuation, even with the horizontal field uncompensated - beam that once died at the resonance passed cleanly. - **Source quote (verbatim):** “Certain features of the performance of the Analogue are much improved by the injection of the highly defined beam. It is now possible to accelerate the beam through the difference-coupling resonance vr - vz = 1 without attenuation” - **Source:** [Oak Ridge National Laboratory, A Proposal for the Mc² Isochronous Cyclotron — ORNL-3540 (1963)](https://cyclotroninfo.com/library/#lib-225) — p. PDF p.285 (printed p.271) - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Central-region collimation and source definition are high-leverage (relevant to the planned source-species test): a better-defined beam gives resonances and apertures less to eat. That is margin against loss mechanisms that scale with beam quality - not against gas scattering, RF faults, or extraction geometry, which have their own fixes. **dg-929** · applicability level 2 · ion-source, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-929 - **Rule (this site's paraphrase of the source):** On the experimental unit, with dees limited to 10 kV, injection potentials over 10 kV decelerated ions in the gap between the accelerating electrode and the dee; their fix was raising the dee-side capability - a redesign for at least 20 kV dee-to-ground. - **Formula:** `first gap accelerates only while the signed electrode-to-dee potential difference is favorable (their case: V_inject > V_dee ran it backward)` - **Source quote (verbatim):** “Since the dee voltage in the experimental unit was limited to 10 kv, application of injection potentials of over 10 kv resulted in deceleration of ions between the accelerating electrode and the dee.” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 December 1951 — ORNL-1269 (1952)](https://cyclotroninfo.com/library/#lib-226) — p. 47 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Any source-bias or puller experiment must check the same ordering in ITS geometry: a dc extraction potential that overtops what the RF gap can supply runs the first gap backward. The check is signed potentials and timing at the actual gap - the source's inequality is that machine's instance of it, not a universal bound. **dg-930** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-930 - **Rule (this site's paraphrase of the source):** In the cited high-potential arc source for multiply charged ions, two things were found: electrode alignment with the magnetic field is critical, and admitting gas greatly reduced the average electron energy - high-energy electrons appeared only with no gas feed. - **Source quote (verbatim):** “The alignment of the electrodes with the magnetic field is critical. High energy electrons are obtained when no gas is fed to the chamber, but when gas is introduced the average electron energy is greatly reduced” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 December 1951 — ORNL-1269 (1952)](https://cyclotroninfo.com/library/#lib-226) — p. 49 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For the reference machine's filament source and the planned source-species test: align the source to B before blaming the arc supply, and treat arc electron energy as gas-pressure-COUPLED - which direction and how strongly, for the actual source, is a pressure-scan-plus-mass-analysis measurement, not an inherited monotonic law about H+/H2+ balance. **dg-931** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-931 - **Rule (this site's paraphrase of the source):** Ion-source output was found approximately proportional to the effective slit length in the cited 22-inch tests (the aperture dimensions and output currents are the report's data - re-read queued). - **Formula:** `I_source ~ proportional to slit length at constant width, arc, and extraction` - **Source quote (verbatim):** “The output of the ion source was found to be approximately proportional to the effective length” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 September 1952 — ORNL-1383 (1953)](https://cyclotroninfo.com/library/#lib-227) — p. 21 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The chimney-slit length is a free knob - to first order, more length is more current at constant width, arc and extraction - but pair any lengthening with the z-distribution probe check (the same machine's earlier quarter tied arc-slit length to z-wise beam loss), and verify the gain survives to TRANSMITTED beam, not just source output. **dg-932** · applicability level 3 · beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-932 - **Rule (this site's paraphrase of the source):** Judge injector/source changes by transmitted beam at radius, not by current near the source: on the 22-inch, current at 1.5 in continued rising with accelerating potential while beam at 10.5 in optimized at 3 kV or less - a divergence the report read as changes in ion focus. - **Formula:** `optimum V_inject (by full-radius beam) was 1-3 kV, arc-intensity dependent` - **Source quote (verbatim):** “Since the current measured at 1.5" continues to increase with accelerating potential while the beam measured at 10.5" is optimized at 3 kv or less, changes in ion focus are indicated” - **Source:** [Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 September 1952 — ORNL-1383 (1953)](https://cyclotroninfo.com/library/#lib-227) — p. 22 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The central tuning trap: a source tweak that fattens the inner-radius signal can starve the Faraday cup at full radius - so score source changes at the radius that matters (extraction or target), with the near probe as the diagnostic companion rather than the scoreboard. **dg-937** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-937 - **Rule (this site's paraphrase of the source):** DC accelerating-electrode geometry for a cyclotron source resisted a priori design in the cited program: of several dc electrode geometries tested on the 44-inch, none accelerated the proton beam to maximum radius as well as the standard rf accelerating electrode - the plain rf gap stayed the benchmark. - **Source quote (verbatim):** “Direct-current accelerating electrodes of several geometries have been tested, but none were found to accelerate the proton beam to maximum radius as well as the standard type of r-f accelerating electrode.” - **Source:** [Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953)](https://cyclotroninfo.com/library/#lib-228) — p. 20 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A caution for any puller-electrode or biased-extraction scheme on the reference machine: after four quarters of ORNL trials, dc injection still lost to the ordinary rf gap on that machine. Simulate candidate geometries (fields calculate fine; the plasma boundary is the uncertain part), validate experimentally, and keep an unmodified configuration as the control in every source A/B test. **dg-1047** · applicability level 4 · safety, shielding, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1047 - **Rule (this site's paraphrase of the source):** D(d,n)He3 and T(d,n)He4 are EXOENERGETIC - they run at very low bombarding energy (Cockcroft-Walton scale) - so any deuterium in source gas or beam-loaded surfaces makes neutrons with no threshold protection. Other deuteron channels are exoenergetic too (9Be(d,n) Q ~ +4.4 MeV, 7Li(d,n) Q ~ +15 MeV): thresholdlessness is a property of deuteron beams on several light targets, while the common PROTON channels, (p,n), are threshold-protected. - **Formula:** `D(d,n)He3 Q = +3.27 MeV; T(d,n)He4 Q = +17.6 MeV; also exoenergetic: 9Be(d,n), 7Li(d,n); common (p,n) and (gamma,n) channels are threshold-protected` - **Source quote (verbatim):** “Two of these reactions, the D(d,n)He3 reaction and the T(d,n)He4 reaction are exoenergetic and can be initiated at very low energies. Thus these two reactions can be produced in small Cockcroft-Walton accelerators.” - **Source:** [Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972)](https://cyclotroninfo.com/library/#lib-239) — p. 78 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** THE loophole in the 'sub-MeV machines make no neutrons' argument: natural hydrogen is ~150 ppm deuterium and D accumulates in beam-loaded surfaces, so a D-on-D source term exists in principle on any hydrogen machine - at yields the Coulomb barrier suppresses steeply at low energy, which is why the honest posture is a survey requirement, not alarm. **dg-1100** · applicability level 3 · safety, beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1100 - **Rule (this site's paraphrase of the source):** Commission in activation-safe stages, as Nevis did: first debug the source and central region with the beam stopped at small radius in low-Z (graphite) targets - which at their inner-radius conditions avoided neutron production and induced activity - then survey full-radius behavior at drastically reduced duty cycle before any full-intensity running. - **Formula:** `stage 1: beam dumped at r < 10 in. on graphite; stage 2: full radius at ~1 source pulse/sec` - **Source quote (verbatim):** “stopping the beam at r < 10 in. radius in graphite targets. This avoids neutron production and induced cyclotron radioactivity” - **Source:** [Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971)](https://cyclotroninfo.com/library/#lib-240) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The staging discipline transfers to every machine even where activation does not: low-duty, small-radius-first commissioning also protects septa, collectors, and instruments. Stage one's activation-safety is species- and energy-specific, not automatic - deuterons on carbon make neutrons above ~0.33 MeV via 12C(d,n), and D-on-D in any deuterium-loaded surface is thresholdless - so re-establish the claim whenever species or energy changes. **dg-1148** · applicability level 3 · vacuum, seals, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1148 - **Rule (this site's paraphrase of the source):** Motion feedthroughs are a seal failure class of their own: the Buna-N chevron-stack seals on NRL's source drive mechanisms were unreliable and short-lived (the replacement construction is the report's account - re-read queued). - **Source quote (verbatim):** “The Buna N, chevron shaped vacuum seals between the cyclotron accelerator tank and the radial and azimuthal drive mechanisms ... were unreliable and displayed a short life expectancy.” - **Source:** [Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970)](https://cyclotroninfo.com/library/#lib-244) — p. 26 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For sliding or rotating shafts into the chamber, write a real dynamic-seal specification: compound, gland dimensions and squeeze, surface finish and land tolerance, lubrication, the motion profile, and an interseal vent or differential-pumping stage where leak-tightness matters - geometry, finish and compound all do real work, and a second O-ring buys redundancy at the cost of friction and a possible trapped-volume virtual leak. - **Cited in:** [Cyclotron Vacuum Chamber Design and Sealing](https://cyclotroninfo.com/learn/vacuum-chamber/) **dg-1149** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1149 - **Rule (this site's paraphrase of the source):** Optically re-align the ion source after reinstallation: NRL aligned the discharge aperture (0.09 x 0.50 inch slit) to the magnetic median plane and the dee electric field after reinstalling the source assembly. - **Source quote (verbatim):** “After reinstallation of the ion source assembly into the cyclotron, the ion discharge aperture (0.09 in x 0.50 in) was optically aligned with respect to the median plane of the cyclotron magnetic field and the electric field of the dee.” - **Source:** [Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970)](https://cyclotroninfo.com/library/#lib-244) — p. 26 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Source aperture height and tilt relative to the median plane strongly affect first-turn survival; make re-alignment after source maintenance a fixtured, measured step (scribe lines, a sighting jig, or a depth gauge) instead of trusting bolted repeatability. **dg-1182** · applicability level 4 · targets, fabrication, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1182 - **Rule (this site's paraphrase of the source):** Sputter-yield scale (Scaife, Hanley & Purser): at focused-ion-beam energies, yields between 2 and 10 atoms per argon ion are typical - and unlike evaporation rates, yields rarely spread between materials by more than about an order of magnitude (the detailed energy-curve shape and Kr/Xe multipliers are the paper's account - scan re-read queued). - **Formula:** `yield max ~25 keV (conductors) / 50-60 keV (dielectrics); 2-10 atoms per 20-keV Ar+; Kr ~2x, Xe ~3x the Ar yield on conductors` - **Source quote (verbatim):** “At focused ion beam energies, sputter yields between 2 and 10 atoms per argon ion are typical.” - **Source:** [Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975)](https://cyclotroninfo.com/library/#lib-246) — p. 94 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A keV-range ion gun is a plausible deposition tool - sized honestly: take measured or calculated yield curves for the actual ion-target pair, energy and angle, then work out rate from beam current and collection geometry, plus thermal load and neutralization. Gas choice (Ar vs Kr/Xe) is a rate-vs-cost trade to quantify per material, not a fixed multiplier. **dg-1186** · applicability level 4 · targets, fabrication, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1186 - **Rule (this site's paraphrase of the source):** Working numbers for a focused-ion-beam sputter rig (Scaife et al.): a von Ardenne-type duoplasmatron with einzel lens delivering mA-class 20-25 keV Ar+, with a typical deposition rate of 20 ug/cm2/min of titanium at 2.5 cm; usable targets from ~10 mg of source material - NOTE an internal inconsistency: the paper's ~50 ug/s erosion figure would need ~50 atoms/ion at 2 mA, versus its own typical 2-10 (which gives 2-10 ug/s), and the 20 ug/cm2/min at 2.5 cm itself implies ~6.5 ug/s from a cosine lobe. [2026-09-06 page-image re-read: the page prints 'micrograms/second' unambiguously - the inconsistency is the source's own, not an OCR artifact.] - **Formula:** `erosion = I*Y*M/(N_A*e); at 2 mA Ar+ with Y = 2-10: 2-10 ug/s of Ti - the printed 50 ug/s does not reconcile (dg-501 pattern); deposition falls ~1/d^2, lobe slightly narrower than cosine` - **Source quote (verbatim):** “A typical deposition rate for substrates located 2.5 cm from the sputtering source is 20 ug/cm2/min. of titanium. ... total erosion rate averages 50 micrograms/second when operating with 2 mA of 20 keV argon.” - **Source:** [Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975)](https://cyclotroninfo.com/library/#lib-246) — p. PDF p.114 (printed p.98) for the deposition rate and the gun parameters; the 50 ug/s erosion rate is on PDF p.100 (printed p.84); the ~10 mg source quantity is on PDF p.110 (printed p.94) - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Calibration point for sizing a home sputter-deposition scheme - mA and tens of keV is small-accelerator source technology, not exotic hardware. Time a boron run from a boron yield (measured or from tables) and the actual collection geometry, not from the titanium calibration. **dg-1238** · applicability level 3 · ion-source, targets · https://cyclotroninfo.com/design-guide/ion-source/#dg-1238 - **Rule (this site's paraphrase of the source):** For long uninterrupted deposition runs, the cited cold-cathode Penning source made its case: 165 hours of stable beam without any trouble (0.2% stability at 0.58 mA), no filament to burn out, run on reactive gas, at under 30 W total source power. - **Formula:** `PIG end-extraction source, 120 mm dia x 70 mm; up to 2 mA Ar; energy spread 40-80 eV; gas consumption 1-5 std-cm3/min; <30 W total` - **Source quote (verbatim):** “the source ran with a stable ion beam intensity for 165 hours without any trouble (Baumann & Wirth, "A Heavy Ion Sputtering System with a Penning-Ion-Source")” - **Source:** [Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978)](https://cyclotroninfo.com/library/#lib-248) — p. 125 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The filament-free argument is the same one that favors PIG sources inside a cyclotron, and the documented design point (geometry, discharge mode, gas flow, stability) is valuable prior art - as a demonstrated result, not a category win: PIG cathodes still sputter and erode, chemical resistance is gas- and materials-specific, and whether <30 W runs uncooled depends on where the watts concentrate and what the mounting conducts. Check those for the actual build. **dg-1243** · applicability level 4 · targets, ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1243 - **Rule (this site's paraphrase of the source):** Load titanium with hydrogen by heating in sub-atmospheric purified gas (Gursky & Sherwood): outgas at 800 C in vacuum first, absorb at ~650 C, pass the gas through a deoxygenating cartridge AND a liquid-nitrogen trap - the trap is essential; the gas is not absorbed otherwise - and meter uptake as the pressure drop in a known volume (via n = d(PV/RT), converting to STP volume afterward if wanted); reversible by pumping at 800 C. - **Formula:** `absorb at ~650 C sub-atmospheric; outgas 800 C; uptake = dP * V_system at STP (example - 0.817 of available gas absorbed, 130 cm3 per cone)` - **Source quote (verbatim):** “The trap is essential; the gas is not absorbed otherwise (Gursky & Sherwood, "Hydriding of Titanium Cones for a Sputter-Ion Source")” - **Source:** [Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978)](https://cyclotroninfo.com/library/#lib-248) — p. 57 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The bench recipe for Ti-H or Ti-D loaded pieces - executed as a hydrogen process, not a casual one: hydrogen-rated containment and plumbing, leak checking, ventilation and ignition control, and a trap that gets inspected (an LN2 trap can concentrate oxidants if purification fails). Tritium is a different world entirely - licensed containment, monitoring and recovery - and is not an amateur variant of this recipe. **dg-1260** · applicability level 4 · targets, fabrication, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1260 - **Rule (this site's paraphrase of the source):** The saddle-field source ran cold in the cited setup: a cold filament producing a temperature rise of the evaporant of only ~10 C (the beam-neutral fraction, focus size and insulator capability are the paper's further characterization - re-read queued). - **Source quote (verbatim):** “a cold filament which produces a temperature rise of the evaporant of only ~ 10 C” - **Source:** [International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983)](https://cyclotroninfo.com/library/#lib-249) — p. 249 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A candidate route to boron and refractory films without an e-gun - qualified in place: a small bulk temperature rise does not preclude local sputter damage to a substrate or release layer, so verify with witness pieces; the commercial gun class is bench-scale, and its insulator/neutral-beam claims come from the re-read source, not the summary. **dg-1284** · applicability level 3 · ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-1284 - **Rule (this site's paraphrase of the source):** A passive magnetic mirror from a 1/8-in steel bearing ball at the top of the arc hood reflects electrons streaming up the arc channel (mirror cone sin^2(theta_c) = B0/Bmax): before the ball the graphite hood top glowed bright orange from electron bombardment; after, it stayed black - taken by the authors as evidence of strong mirror action, converting the hooded-arc source toward reflex operation in the cyclotron's own field. - **Formula:** `sin^2(theta_c) = B0/Bmax (electrons outside the cone reflect; Spitzer 1956)` - **Source quote (verbatim):** “a magnetic mirror built into the upper end of the arc hood by the simple insertion of a steel bearing ball 1/8 in in diameter. ... Before the steel ball was added the top of the graphite hood glowed a bright orange color when the arc was operating, because of the intense electron bombardment. After the ball had been added the top of the hood was found to remain black when the arc was operating. This result is taken as evidence of a strong mirror action.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Nearly free to TRY on a filament hooded source running in the main field - a bearing ball is stock hardware and the hood exists - but not automatic: whether electrons reflect depends on Bmax/B0 at the ball, injection pitch angles and collisions, so replicate the source's own A/B glow test (hood-top color/temperature with and without the ball) and check the companion negative result (dg-1288) before counting on it. **dg-1285** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1285 - **Rule (this site's paraphrase of the source):** Read where arc electrons land from incandescence: the graphite hood top glowed bright orange during arc operation, attributed to intense electron bombardment - a viewport diagnostic of where the arc's power is going. - **Source quote (verbatim):** “the top of the graphite hood glowed a bright orange color when the arc was operating, because of the intense electron bombardment.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A diagnostic that costs a glance, used as a controlled A/B: at fixed arc power, cooling, surface state and sightline, an orange chimney-top says axial electron loss is real, and a change after adding a mirror or repeller says the geometry change did something. A black hood alone proves less - lower power, emissivity and sightline all dim the glow - so pair the glance with beam and arc-current numbers. **dg-1286** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1286 - **Rule (this site's paraphrase of the source):** Reflex electron economy: with electrons presumably oscillating - reflected by the magnetic mirror above and electrostatic repulsion from the filament structure below - the arc current required for a satisfactory hydrogen ion current fell severalfold in the cited source. - **Source quote (verbatim):** “The arc current required to produce a satisfactory current of hydrogen ions has been reduced severalfold, presumably because the electrons oscillate, being reflected by the magnetic mirror at the top and by electrical repulsion from the filament structure below.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The physics argument for reflex geometry at small scale: multiple-pass ionization, bought here with one filament and a mirror instead of a PIG's two cathodes. Measure ion yield versus arc current on the actual geometry - the severalfold factor and its knock-ons (filament drive, heat, gas decomposition are separate quantities from arc current) are things the source's own 'presumably' invites you to verify, not inherit. **dg-1287** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1287 - **Rule (this site's paraphrase of the source):** Filament life responded dramatically in the cited source: typical lifetimes had ranged 15-30 hours; the first filament in the new (reflex) source was intact, though thin, at removal after 109 hours - one censored observation, encouraging rather than statistical. - **Formula:** `lifetime 15-30 h at full emission -> >109 h severalfold-reduced emission (same 60 mil W hairpin)` - **Source quote (verbatim):** “Typical lifetimes of filaments had ranged from 15 to 30 hours. The first filament installed in the new source was intact, though thin, when removed after 109 hours of operation.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Directly relevant to the standing filament-maintenance complaint: electron economy is a candidate filament-lifetime fix, since tungsten evaporation is brutally steep in temperature - so any arc current not needed pays back in hours. Establish the actual gain with controlled heater settings and more than one run-to-failure; a single intact-at-109-h filament sets hope, not a multiplier. **dg-1288** · applicability level 3 · ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-1288 - **Rule (this site's paraphrase of the source):** Mirror-assisted source behavior is geometry-sensitive and was not understood even by its inventors: the same steel-ball mirror in a second hooded source was 'in this case unsuccessful' - the obvious difference being the hairpin filament's plane parallel to the cyclotron field instead of perpendicular. Test the trick on your geometry; do not assume transfer. - **Source quote (verbatim):** “in this case unsuccessful ... also a hairpin-shaped 60 mil tungsten wire, is mounted with its plane vertical, parallel to the magnetic field of the cyclotron, rather than perpendicular as in the first source.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** An honest negative result from 1961 that still stands. The filament-orientation reading (injection angle into the mirror deciding loss-cone membership) is a HYPOTHESIS consistent with the one observed difference - local electric fields and emission distribution matter too - so plan the mirror experiment as an A/B test with the glow diagnostic and vary filament orientation if the first try fails. **dg-1289** · applicability level 3 · ion-source, vacuum, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1289 - **Rule (this site's paraphrase of the source):** Shrink the hood extraction opening to cut source gas flow into the tank: the source reports lower tank pressure partly from reducing the hood opening to about 1/32 in - but expect the slit to erode: within days it had enlarged in the direction of ion rotation. Slit wear is a consumable-maintenance item; inspect and re-measure it. - **Formula:** `hood opening ~1/32" x 3/16" (0.8 x 4.8 mm) for H/D; helium source used ~1/8" x 3/8"` - **Source quote (verbatim):** “The gas pressure in the cyclotron tank is lower. This came about partly because the opening in the hood (through which the ions to be accelerated are [extracted]) ... reduced in size to about 1/32 in ... after a few days of operation, it was found to have become somewhat enlarged in the direction of ion rotation.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Two lessons: (a) the chimney slit is the gas throttle, and sizing it down is a cheap pumping win - balanced against plasma and beam extraction, so optimize rather than minimize; (b) the asymmetric erosion (along rotation) is a clue about where early-turn ions strike the hood - corroborate with tracking or witness marks before reading it as a diagnostic. - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-1290** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1290 - **Rule (this site's paraphrase of the source):** Hooded-arc operating envelope on the 27-inch (7-14 kG): arc currents to 2 A and voltages to 250 V were used, but deuterium ran on about 0.75 A at about 100 V - roughly 75 W of arc - and pushing arc current from 1.0 to 2.0 A bought only a relatively small beam increase. (The species is a handwritten correction over typed 'hydrogen' on the page.) - **Formula:** `deuterium point: ~0.75 A x ~100 V ~ 75 W; 1 -> 2 A arc gave only a relatively small beam gain; B = 7-14 kG` - **Source quote (verbatim):** “Arc currents up to 2 amperes and arc voltages up to 250 have been used. For deuterium operation a current of about 0.75 amperes and a voltage of about 100 are usually sufficient.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Concrete supply-sizing anchor: sub-100-W arcs fed a 27-inch machine's beam. The operating doctrine is diminishing returns - find the knee of the yield curve on your own source and park below it, since past the knee extra arc current buys mostly filament wear and gas load. **dg-1291** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1291 - **Rule (this site's paraphrase of the source):** Optimize the source per species rather than forcing one design: the H/D mirror source gave only ~1/10 the beam of the dedicated helium source - itself hooded, with a tantalum button on quartz tubing atop a tantalum-tubing hood and a larger ~1/8 x 3/8 in opening. - **Source quote (verbatim):** “Cyclotron beam currents were found to be of the order of 1/10 those obtained with our standard helium ion source, which is also of the hooded type, having a tantalum button supported by a short piece of quartz tubing at the upper end of a tantalum tubing hood. For these tests a hood with a larger hole, about 1/8 in x 3/8 in was used.” - **Source:** [Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962)](https://cyclotroninfo.com/library/#lib-251) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A scoping warning for any future gas change: a source tuned for hydrogen is not a universal source - the tenfold gap is one uncontrolled comparison, so let measurements on the actual gas assign causes. The tantalum-button-on-quartz sketch is this collection's only helium-specific hooded-source construction, useful if alphas are ever on the menu. **dg-1340** · applicability level 3 · magnet, ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1340 - **Rule (this site's paraphrase of the source):** Central spikes: a cone-topped cylinder at the magnet center (UW: 1.5-in radius, 1/4-in cylinder + 1/4-in cone) is designed 'to produce a sharp increase in the induction at the center of gap without producing a minimum anywhere in the radial dependence' - adopted after a University of California report of a beam-current increase from such spikes (the 'remarkable increase' phrasing is sighted in the scrambled scan; verbatim re-read queued); even undersized spikes were judged worth installing. - **Source quote (verbatim):** “The function of the spikes is to produce a sharp increase in the induction at the center of gap without producing a minimum anywhere in the radial dependence.” - **Source:** [The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951)](https://cyclotroninfo.com/library/#lib-253) — p. 33 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A central field bump gives axial focusing in the first turns, where small machines lose most of their beam - and a machined center button is one of the cheapest beam-current experiments available. The no-minimum constraint is the careful part: model and map B(r), check the field index, isochronism cost, and RF/vacuum clearance before installing. **dg-1350** · applicability level 3 · ion-source, vacuum, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1350 - **Rule (this site's paraphrase of the source):** Design vacuum locks so consumables and the whole source can be changed without venting: the UW ion source has a filament lock (replace the filament without breaking tank vacuum) AND a source lock — a heliarc-welded aluminum box with a swinging toggle- clamped gate — through which the entire source assembly withdraws upward on a guide track; three adjusting screws on a sylphon position the source in both planes from outside; the lock's 4-in glass viewing window carries a hinged brass shutter so metal vapor from the arc cannot coat it. - **Source quote (verbatim):** “the filament may be replaced without breaking the vacuum of the tank proper.” - **Source:** [The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951)](https://cyclotroninfo.com/library/#lib-253) — p. 65 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The reference machine's filament-change downtime is this exact problem, solved in 1951: a small gate-valved source lock plus an external bellows positioner removes the main-tank vent from the service cycle - how much time that saves depends on the lock's own pump-down and the machine's recovery habits, so measure it rather than promise minutes. Positioning through the bellows under vacuum is the designed use; adjusting with arc, RF or HV energized is a separate safety analysis with its own interlocks, not an included feature. (The shuttered viewport is a free detail worth stealing.) - **Cited in:** [The Vacuum Budget of a Cyclotron](https://cyclotroninfo.com/learn/vacuum/) **dg-1387** · applicability level 1 · dee, ion-source, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-1387 - **Rule (this site's paraphrase of the source):** The minimum dee amplitude is the one whose first orbit clears the ion source: on COLUMBUS, protons clear from U0 >= 200 V and H2+ from U0 >= 400 V on the first turn (r1 ~ 11 mm at their respective fields, against the 20 mm chimney region). - **Formula:** `r1 = sqrt(2*m*U0/q)/B; clearance threshold U0_min ~ (B*r_clear)^2*(q/m)/2 (ideal full-qU0 first kick)` - **Source quote (verbatim):** “Protonen ab U0 ≥ 200 V und H2+-Ionen ab U0 ≥ 400 V – bereits beim ersten Umlauf – hinreichend weit von der Ionenquelle entfernt [tr.: clear of the source from 200 V / 400 V on the first turn]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 42-43 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The scaling is the useful transfer: at 0.6 T and a 15 mm clearance radius the same ideal estimate gives ~3.9 kV for protons - so a sub-kV dee on a higher-field machine would NOT clear a 15-mm-class source housing under these assumptions; trace the actual source and gap geometry (launch phase, initial position, 3-D fields) before trusting the ideal number either way. **dg-1394** · applicability level 3 · rf, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1394 - **Rule (this site's paraphrase of the source):** Provide a DC bias socket coupled to the dee so an additional steady extraction voltage (Saugspannung) can be superimposed on the RF to help pull ions out of the source. - **Source quote (verbatim):** “Über sie kann eine zusätzliche „Saugspannung“ an das Dee angeschlossen werden [tr.: through it an additional extraction voltage can be applied to the dee]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 46 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A DC extraction bias shifts when ions leave the slit relative to the RF phase - a real tuning knob. Determine its magnitude from ion-optics measurement or simulation on the actual source (the book states the provision, not a value), and rate the feedthrough and insulation for the maximum instantaneous RF-plus-DC sum, which also moves the bremsstrahlung end-point. **dg-1396** · applicability level 2 · dee, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1396 - **Rule (this site's paraphrase of the source):** COLUMBUS chose the accelerating gap and the dummy-dee depth as one common dimension - 20 mm each, 'on plausibility grounds' - the book posing the two dimensions as a single question when dimensioning the dummy dee. - **Formula:** `gap = dummy-dee depth = dee aperture height = 20 mm` - **Source quote (verbatim):** “Bei der Dimensionierung des Dummy-Dees stellt sich natürlich die Frage nach der Tiefe und der Größe des Beschleunigungsspalts gap. Aus Plausibilitätsgründen wurde jeweils ein Maß von 20 mm gewählt. [tr.: in dimensioning the dummy dee the question arises of its depth and the size of the accelerating gap; on plausibility grounds 20 mm was chosen for each]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 46 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A wide gap simplifies the source mount (the chimney sits inside it) at the cost of transit-time factor; choose the gap from the transit calculation - T = sin(x)/x with x = omega\*g/(2v) over the actual injection and orbit velocities - rather than adopting either 20 mm or any other fixed number. **dg-1400** · applicability level 2 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1400 - **Rule (this site's paraphrase of the source):** Steady-state chamber pressure under deliberate gas feed follows from the pV-flow balance: p_E = q_G/S_eff - COLUMBUS's worked point, 300 mbar inlet at ~0.14 ml/min actual flow = 7.0e-4 mbar\*l/s, over S_eff = 17.2 l/s, giving 4.1e-5 mbar against the measured 4.0e-5. - **Formula:** `p = (q_process + q_background)/S_eff; q_process = p_inlet*Q_actual (actual volumetric flow) or p_std*Q_std (sccm-reading MFC) - one convention consistently; background = leaks + desorption, measured with feed off` - **Source quote (verbatim):** “für einen Volumenstrom von ca. 0,14 ml/min sich ein Enddruck pE = 4,0 · 10−5 mbar einstellt [tr.: at about 0.14 ml/min a final pressure of 4.0e-5 mbar establishes itself]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 51-53 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The one-line balance is the first thing to validate against the gauge on a new machine - at several MFC settings, with the background term measured separately (feed off) and the flow convention of the actual controller pinned down before trusting any prediction. **dg-1404** · applicability level 3 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1404 - **Rule (this site's paraphrase of the source):** Publish the gas-load trade as a table, as the book does: 0.10 / 0.15 / 0.20 ml/min hydrogen gave 2.9 / 4.4 / 5.8e-5 mbar and proton mean free paths of 12.6 / 8.4 / 6.3 m (H2+: 4.2 / 2.8 / 2.1 m); run at the lowest flow that still yields usable source current. - **Formula:** `p_E proportional to V_dot_G ; l_bar proportional to 1/V_dot_G` - **Source quote (verbatim):** “Für V̇G = 0,10 ml/min ergeben sich mittlere freie Weglängen von 12,6 m bzw. 4,2 m [tr.: at 0.10 ml/min the mean free paths are 12.6 m and 4.2 m]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 58 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Specify the feed instrument from the measured requirement: the flow range and step stability the source actually needs (state the reference conditions of the flow unit - sccm vs actual ml/min matters here), then choose a calibrated MFC or a precision metering valve with regulated upstream pressure accordingly. Table 7.2 is a bitmap in the scan; the pressure row recomputes exactly from p_E = 300 mbar \* V_G / 17.2 l/s. **dg-1409** · applicability level 2 · ion-source, safety · https://cyclotroninfo.com/design-guide/ion-source/#dg-1409 - **Rule (this site's paraphrase of the source):** Hydrogen is the natural feed for a small machine: it ionises easily by electron impact, a 10 L / 10 bar disposable Hydrostick cartridge holds a small, cheap inventory, and both H+ and H2+ are produced. Its drawback, per the book, is relatively high permeation through hoses and cannulas, which particularly affects the ion source. - **Source quote (verbatim):** “Ein Nachteil ist die relativ hohe Permeation von Wasserstoff durch Schläuche und Kanülen; dies betrifft insbesondere die Ionenquelle [tr.: a drawback is hydrogen permeation through hoses and cannulas]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 30 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Use metal lines with a mass-flow controller rather than elastomer tubing (PEEK is lower-permeation than elastomers, not zero). A small cartridge is still HYDROGEN: even ~10 standard litres forms a flammable mixture in air, so ventilate, leak-check, control ignition sources and handle the pressurized cartridge properly. Runtime: compute from the cartridge's usable standard volume at the actual MFC setting rather than quoting a lifetime. **dg-1410** · applicability level 2 · ion-source, vacuum, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-1410 - **Rule (this site's paraphrase of the source):** Gas-feed chain for a thermionic source, as built: cartridge -> pressure reducer to 300 mbar -> mass-flow controller at 0.10-0.20 ml/min -> directly into the source chimney; the reducer pressure enters the book's gas-load balance q_G = 300 mbar \* V_dot_G, with V_dot the ACTUAL volumetric flow at the reducer pressure. - **Formula:** `q = p_in * Q_actual (actual inlet volume) or q = p_std * Q_std for an MFC reading sccm - one convention, consistently; mixing 300 mbar with an sccm reading understates throughput ~3.4x` - **Source quote (verbatim):** “Dieser Druck wird durch einen Druckminderer auf pH2 = 300 mbar reduziert [tr.: the pressure is reduced by a regulator to 300 mbar]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 61 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Fix the reducer pressure and log it - it is a term in the balance. Whatever meters the flow, state its reference conditions and take accuracy and repeatability from its specification rather than assuming a resolution. **dg-1411** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1411 - **Rule (this site's paraphrase of the source):** Thermionic chimney source construction, as built: a 0.3 mm thoriated-tungsten filament in a machinable Shapal ceramic body, a copper anode plate with a hole above it, electrons entering the chimney formation space, and the chimney closed by a ceramic lid carrying an insulated tungsten disc - an 'electron mirror' that charges negative and reflects electrons back for further ionisation, which the book says noticeably raises the electron count and ion current. - **Source quote (verbatim):** “Die für die Ionisation notwendigen Elektronen treten aus dem glühenden Filament, einem thorierten Wolframdraht mit Durchmesser von 0,3 mm aus. Dieses befindet sich in einem Keramikkörper aus Shapal. Darüber liegt eine Kupferplatte als Anode. ... Durch ein Loch in der Anode treten die Elektronen in den Formationsraum eines sog. 'Kamins' ein ... Der Kamin wird durch einen Keramikdeckel abgeschlossen, an dem sich isoliert eine Wolframscheibe, ein sog. Elektronenspiegel, befindet. Dieser lädt sich durch die auftreffenden Elektronen negativ auf und reflektiert sie in den Formationsraum des Kamins, so dass sie für erneute Ionisationsprozesse zur Verfügung stehen. Auf diese Weise erhöht sich die Zahl der Elektronen und damit auch der Ionenstrom merklich. [tr.: the electrons emerge from a glowing 0.3 mm thoriated tungsten filament seated in a Shapal ceramic body; above it lies a copper plate as anode; through a hole in the anode the electrons enter the formation space of a 'chimney'; the chimney is closed by a ceramic lid carrying an insulated tungsten disc, an 'electron mirror', which charges negative from incident electrons and reflects them back into the formation space for further ionisation - noticeably raising the electron count and with it the ion current]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 62, 64 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The floating electron mirror is a zero-cost reflex trick - no second cathode, no supply - that increases electron residence time; the book claims a noticeable ion-current gain, not a quantified one, so measure yours. Shapal (AlN-BN) machines with ordinary tools, unlike alumina - verify the grade's temperature rating against the filament environment. **dg-1412** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1412 - **Rule (this site's paraphrase of the source):** Run the source anode near the book's stated ion-yield maximum: it reports the number of ions formed peaking at 100-150 eV electron energy - beyond that interval the electrons are 'quasi too fast' and the rate falls - so the anode voltage is set to ~120-150 V. [Note: standard evaluated H2 electron-impact ionisation data put the broad maximum nearer 70-100 eV; the book's 100-150 eV band reads as its source's empirical optimum, which also folds in geometry and sheath effects.] - **Formula:** `U_B = 100-150 V` - **Source quote (verbatim):** “Die Anzahl der gebildeten Ionen hängt aber auch von der Elektronenenergie ab. Sie erreicht bei 100–150 eV ein Maximum [tr.: ion yield depends on electron energy, peaking at 100-150 eV]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 62, 70 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Sweep anode voltage against extracted ion current on the actual source - the optimum is broad and machine-specific, anode volts are not electron collision energy volt-for-volt (sheaths and where ionisation happens intervene), and a current-limited 0-200 V supply covers the whole plausible band. **dg-1413** · applicability level 2 · ion-source, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-1413 - **Rule (this site's paraphrase of the source):** Estimate source output from I_ion = sigma \* I_e \* l_e \* p_H with sigma the differential ionisation coefficient (order 1-3 per cm\*mbar for hydrogen), I_e the emission current, l_e the electron path, p_H the local hydrogen pressure - a first-order production estimate, not a bound. - **Formula:** `I_ion = sigma * I_e * l_e * p_H ; sigma ~ 1-3 /(cm*mbar)` - **Source quote (verbatim):** “Der differentielle Ionisierungswirkungsquerschnitt σ liegt in der Größenordnung von 1–3 1/(cm·mbar) [tr.: the differential ionisation coefficient is of order 1-3 per cm mbar]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 63-64 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Compare with measurement honestly: at 2-5 mA emission the sigma=1 estimate gives ~0.3-0.7 uA against measured 1-3 uA - a factor of a few, not an order of magnitude, and the gap closes further once the CHIMNEY pressure (well above chamber pressure) and the sigma range are used. The formula omits extraction efficiency and losses in both directions - calibrate it per source rather than reading it as floor or ceiling. **dg-1414** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1414 - **Rule (this site's paraphrase of the source):** Do not chase ion current with filament heating: more heater current raises emission but heats the chamber - the book says the higher heater power raises chamber temperature and worsens the vacuum - and shortens filament life; COLUMBUS accepts a compromise operating point around 7-10 A. - **Source quote (verbatim):** “Außerdem steigt durch die größere Heizleistung die Temperatur in der Vakuumkammer, was zu einer Verschlechterung des Vakuums führt [tr.: higher heater power raises chamber temperature and worsens the vacuum]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 64, 66 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Log heater current against the vacuum gauge to find the knee for the actual source - the transferable procedure. Filament-life sensitivity to temperature is steep (evaporation-limited life, dg-379's tables) but the '10% hotter halves life' shorthand has no source here and current is not temperature; work from the W evaporation tables at the actual filament temperature if a lifetime estimate matters. **dg-1415** · applicability level 4 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1415 - **Rule (this site's paraphrase of the source):** A coiled filament (3-5 turns, as on COLUMBUS) generates its own magnetic field that binds part of the emitted electron cloud by the Lorentz force, so not all emission reaches the chimney. - **Source quote (verbatim):** “Bei einer Spulengeometrie (3–5 Wdg. wie bei Columbus) erzeugt dieses ein Magnetfeld, das die Elektronen infolge der Lorentz-Kraft bindet [tr.: a 3-5 turn coil produces a field that binds the electrons]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 64 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** When comparing source geometries (coil vs hairpin vs straight, AC vs DC heating), meter EMISSION at the anode, not filament current - the self-field confinement is one reason the two differ. To estimate the self-field, B ~ mu0\*N\*I/(2R) needs the coil radius, not just turns and current; compute it against the electron Larmor radius at the actual energy before crediting or blaming it. **dg-1416** · applicability level 3 · ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-1416 - **Rule (this site's paraphrase of the source):** The cyclotron guide field itself boosts source output: the book reports collision rate and ion current rising with B (their Fig. 8.5, 0-160 mT), then an 'interesting' fall above ~160 mT, which the authors explain as the plasma column narrowing further and moving away from the extraction slit, lowering the extraction field strength there - the authors' own proposed mechanism ('could be'), not a demonstrated one. - **Formula:** `I_ion(B) rises to ~160 mT then falls (measured)` - **Source quote (verbatim):** “Somit erhöht sich die Stoßrate und damit auch der Ionenstrom mit zunehmender magnetischer Flussdichte, wie Abb. 8.5 für 0 ≤ B ≤ 160 mT zeigt. Interessant ist der Abfall des Ionenstroms bei Magnetfeldern größer als ca. 160 mT. Eine Erklärung hierfür könnte darin liegen, dass sich die Plasmasäule nun noch weiter verengt und sich damit weiter vom Extraktionsschlitz entfernt. Dadurch sinkt die Extraktionsfeldstärke in diesem Bereich und der Ionenstrom nimmt wieder ab. [tr.: the collision rate and hence the ion current rise with increasing flux density, as Fig. 8.5 shows for 0-160 mT; interesting is the drop of ion current above about 160 mT - one explanation could be that the plasma column narrows further and moves away from the extraction slit, lowering the extraction field strength there so the ion current falls again]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 64-65 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** On a higher-field machine expect the optimum to sit elsewhere: scan source output against B and against slit position empirically. The narrowing-column picture predicts alignment sensitivity grows with field - a hypothesis worth testing with a slit-position scan, not a sub-millimetre tolerance to design to in advance. **dg-1417** · applicability level 2 · ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-1417 - **Rule (this site's paraphrase of the source):** Extraction geometry for a chimney source in a single-dee machine: a narrow slit on the chimney side facing the dee, two puller electrodes attached to the dee, ions leaving on the negative half-wave only. No counter-beam forms on the positive half-wave because the chimney sits at dummy-dee (ground) potential and has no slit facing the dummy dee. - **Source quote (verbatim):** “Zu diesem Zweck wurden an dem Dee zwei Extraktions- bzw. Pullerelektroden angebracht. Nun bleibt noch die eingangs gestellte Frage zu klären, warum kein zweiter Ionenstrahl während der positiven Halbwelle entsteht. Ein Grund dafür ist die Tatsache, dass die Ionen nur aus dem Schlitz extrahiert werden können, der dem Dee gegenüberliegt. Ein weiterer Grund ist das Potenzial des Kamins, das das gleiche ist wie das des Dummy-Dees, nämlich Masse. Somit könnten auch während der positiven Halbwelle der Beschleunigungsspannung keine Ionen in das Dummy-Dee extrahiert werden. [tr.: two extraction/puller electrodes were fitted to the dee; the question why no second ion beam forms during the positive half-wave is answered by two reasons - ions can only leave through the slit facing the dee, and the chimney sits at the same potential as the dummy dee, namely ground, so no ions can be extracted into the dummy dee during the positive half-wave]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 65-66 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Grounding the chimney with a one-sided slit answers the reverse-beam question students raise - by construction on this machine. If the source is biased instead, the slit-to-puller spacing, the bias polarity and the counter-beam question all reopen: analyze, don't assume. **dg-1418** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1418 - **Rule (this site's paraphrase of the source):** Verified thermionic-source operating point on COLUMBUS: 7 A heater, 120 V anode, 2 mA emission at 0.10-0.15 ml/min hydrogen (the broader 7-10 A / 120-150 V / 2-5 mA window and the one-year filament life come from the bitmap Table 8.1 and await transcription against the page image). - **Formula:** `I_heater 7-10 A ; U_B 120-150 V ; I_e 2-5 mA ; I_ion 1-3 uA` - **Source quote (verbatim):** “Bei einem Heizstrom von 7 A und einer Anodenspannung von 120 V fließt ein Emissionsstrom von 2 mA [tr.: at 7 A heater and 120 V anode, 2 mA emission flows]” - **Source:** [Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020)](https://cyclotroninfo.com/library/#lib-255) — p. 66, 70 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A 0.3 mm thoriated-tungsten filament at these currents is receiver-tube-heater class in POWER - but the supply is not casual: it must be current-regulated with cold-start limiting (cold filament resistance is a fraction of hot), galvanically isolated and rated to float at the source bias with RF superimposed, through a feedthrough rated for both. Spec those before reaching for any bench supply. **dg-1448** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1448 - **Rule (this site's paraphrase of the source):** To accelerate metal ions without a gas feed, either fabricate the filament from the desired metal or coat a nichrome wire with it, and hold it at negative potential; this solid-source technique ran on the Niell cyclotron (1994-1995). - **Source quote (verbatim):** “either a filament was created from that metal, or a nichrome wire was coated with the metal, and raised to a negative potential” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 16 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A coated-filament thermal source avoids the PROCESS-GAS feed for suitable metals - suitability turning on the metal's vapor pressure, filament compatibility and ionization efficiency - trading species flexibility and current for vacuum simplicity. A candidate for minimal first-beam configurations, evaluated per metal rather than assumed. **dg-1453** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1453 - **Rule (this site's paraphrase of the source):** Keep the ion-source filament electrically isolated from ground so it can be negatively biased to raise the energy of its emitted electrons (Rutgers, per the survey). - **Source quote (verbatim):** “The filament was kept isolated from ground so it could be negatively biased to increase the energy of the emitted electrons.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 17 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Filament bias is the cheapest ionization-rate knob, but it forces the heater supply off any grounded control bus: the supply must be galvanically isolated and float AT the filament's NEGATIVE bias relative to the chamber (the Houghton machine floats its filament near -90 V, dg-310), with insulation rated for the full bias plus coupled RF and transients. And bias raises electron energy, not necessarily ion yield monotonically - scan it (dg-402). **dg-1454** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1454 - **Rule (this site's paraphrase of the source):** Enclosed differential-pressure ion source on the Rutgers 30.5 cm machine: the negatively biased filament sat in a ceramic block fed hydrogen through a small hole, capped by a ceramic plate with an aperture - letting a cone of protons stream out into the evacuated chamber while maintaining higher hydrogen pressure around the filament. - **Source quote (verbatim):** “The negatively biased filament was mounted in a block of ceramic material to which hydrogen gas was supplied through a small hole. The ion source was then covered with a ceramic plate with an aperture ... [allowing] a cone of protons to stream out in the center of the evacuated cyclotron chamber, while maintaining a higher pressure of hydrogen around the filament” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 17 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A drilled ceramic block with an aperture is a buildable chimney-style source. The pressure decoupling it delivers is set by the aperture conductance against the gas throughput and chamber pumping - match those (the dg-409/dg-1400 balances) rather than expecting the geometry alone to do it. **dg-1460** · applicability level 2 · ion-source, project-management · https://cyclotroninfo.com/design-guide/ion-source/#dg-1460 - **Rule (this site's paraphrase of the source):** Because the Knox ion source was considered experimental and a weak design aspect, it was made completely removable. - **Source quote (verbatim):** “As the ion source was considered experimental and a weak design aspect, it was made to be completely removable.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 18 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Design for swap-out on the least-trusted subsystem - mount whatever you expect to iterate for convenient replacement. Ion sources are a common iteration target in this literature (COLUMBUS's Penning investigation, Rutgers' source change between machines), though no count across the survey backs a strongest-claim ranking. **dg-1463** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1463 - **Rule (this site's paraphrase of the source):** Documented failure mode: the Knox cyclotron 'was not successfully tested by the publication' of its reference, 'the problem being' that the magnetic field moved the unsecured wires powering the ion source until they shorted the dees. - **Source quote (verbatim):** “The cyclotron was not successfully tested by the publication of Ref [20], the problem being that the magnetic field caused the wires that powered the ion source to move and short the dees.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 18 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Every lead inside the field carrying current TRANSVERSE to B feels F = I\*L x B (a lead parallel to B feels none - route accordingly); anchor every in-field conductor mechanically with vacuum- and temperature-compatible restraint, keep leads short and stiff, and check them against the worst-case field and current before closing the chamber. The specific cures (soldered stiff leads, potted connectors, sheathed mounts) are our engineering reading, not the survey's. **dg-1464** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1464 - **Rule (this site's paraphrase of the source):** First-cyclotron filament mounting (1931): the electron source was a radio-tube filament - tungsten running through a ceramic cylinder surrounded by an oxide-coated nickel sheath - a system that 'prevented the fragile filament from destructive movement under the influence of the magnetic field'. - **Source quote (verbatim):** “The electron source was a filament taken from a radio tube, and consisted of a tungsten filament running through a ceramic cylinder around which was an oxide coated nickel sheath. This system prevented the fragile filament from destructive movement under the influence of the magnetic field.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The oldest working machine already engineered against filament motion in the field - the same fault that stopped the unbraced Knox design seventy years later (dg-1463). A rigid sheathed-cartridge mounting is the documented pattern; qualify materials for the actual thermal and vacuum environment. **dg-1470** · applicability level 3 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1470 - **Rule (this site's paraphrase of the source):** Operating recipe for the gas-fed Houghton machine: rough to ~1e-3 torr, engage diffusion pump and LN2 cold trap to ~5e-6 torr base, then bleed working gas up to the operating point - at which, the thesis notes, at least 90% of the chamber gas has been purposefully introduced. - **Source quote (verbatim):** “At this level at least 90% of the gas in the chamber has been purposefully introduced” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 30 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The ten-to-one operating/base ratio estimates the intended-gas fraction ONLY if the background stays at its base value - hot filaments, desorption and species-dependent pumping can break that, so verify with an RGA where purity matters. And lambda exceeding the orbit length is survival-of-order-e^-1, not adequacy: use the loss-fraction calculation (dg-1398) for the actual criterion. **dg-1487** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1487 - **Rule (this site's paraphrase of the source):** Ion-source operating point, as built: a filament salvaged from an AET EM6G electron microscope runs at 1.5 V and 2.3 A, floating at least 100 V above ground 'to produce energetic electrons capable of ionizing the gas', and was found strong enough to resist the Lorentz forces even at maximum magnetic field. - **Source quote (verbatim):** “Some of these gas molecules will be ionized by a filament from an AET EM6G electron microscope. A potential across the filament of 1.5 V, results in a current of 2.3 A and the filament floats at least 100 V above ground to produce energetic electrons capable of ionizing the gas. It was found that even with the maximum magnetic field the filament was strong enough to effectively resist the Lorentz [force]” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 42 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Electron-microscope filaments are rigid, pre-mounted, cheap thermionic sources with this documented in-field survival. Note the physics carefully: the IONIZING energy is set by the filament-to-anode/plasma potential difference and sheath, not by the float relative to chamber ground per se - measure or model the local potentials rather than reading electron energy off the bias supply. **dg-1488** · applicability level 3 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1488 - **Rule (this site's paraphrase of the source):** Gas-line purge procedure, as built: with the Edwards LV10K needle valve (mounted directly on the chamber) closed, opening the helium flush valve lets higher-pressure cylinder gas force the accumulated line air out to atmosphere so it cannot contaminate the feed; needle valve plus regulator then control chamber helium in the 1e-6 to 1e-5 torr range. - **Source quote (verbatim):** “the Edwards LV10K needle valve attached directly to the vacuum chamber with a quick flange. The system can be flushed with the gas from the cylinder by closing the needle valve and opening the helium flush valve. The higher pressure helium will force the air in the line into the atmosphere, so that it does not contaminate the gas. By using the needle valve and the regulator control, the pressure of helium in the vacuum chamber can be controlled in the 10-6 to 10-5 torr range.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 43 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A tee with a flush valve upstream of the metering valve is the core of the purge system - dead legs and line volume set how long a real purge takes, so verify with the RGA or gauge rather than assuming any fixed duration; without a purge path, line air feeds the chamber at every startup for as long as the line holds. **dg-1494** · applicability level 2 · ion-source, project-management · https://cyclotroninfo.com/design-guide/ion-source/#dg-1494 - **Rule (this site's paraphrase of the source):** Species staging for commissioning (the thesis's stated plan): first accelerate helium nuclei to test the machine, then switch to deuterons for neutron production; expected energies 0.15 MeV for deuterons, 77.2 keV for He+ and 309 keV for He2+ (0.08 MeV appearing as the p.2 summary figure). - **Source quote (verbatim):** “The immediate objective is to accelerate Helium nuclei to test the machine, and the ultimate is to accelerate deuterons to produce neutrons ... The expected energy for deuterons is 0.15 MeV, and 0.08 MeV for Helium nuclei. ... the maximum energy for singly ionized helium is 77.2 keV. For doubly ionized helium, the frequency in the same magnetic field is 8.63 MHz ... and the maximum energy is 309 [keV]” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Debugging resonance, focusing and diagnostics on helium defers the deuteron-specific neutron/activation source term - NOT all radiological consequences: RF/HV dark current makes bremsstrahlung with any gas, and He2+ is an alpha that can drive exothermic reactions on light contaminants (Be-9, C-13). Survey from first powered operation; the staging defers the big term, not the survey. **dg-1502** · applicability level 3 · ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-1502 - **Rule (this site's paraphrase of the source):** Filament mounted directly on the dummy dee (Rutgers prototype), powered through two diametrically placed feedthroughs - the filament kept isolated from ground so it could be negatively biased to raise its electrons' energy. - **Source quote (verbatim):** “The filament was mounted on the dummy dee, and was powered by wires that entered and exited through two diametrically placed feed-throughs. ... The filament was kept isolated from ground so it could be negatively biased to increase the energy of the emitted electrons.” - **Source:** [Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006)](https://cyclotroninfo.com/library/#lib-256) — p. 17 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Using the dummy dee as the source's mechanical platform puts the emitter at the gap with no extra standoff hardware - the documented arrangement; whether the two-feedthrough run keeps the loop taut against Lorentz forces is our engineering reading, so anchor the leads deliberately either way (dg-1463's lesson). **dg-1509** · applicability level 2 · vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1509 - **Rule (this site's paraphrase of the source):** Operating-point vacuum budget with an internal hydrogen-fed source — 1e-6 mbar base pressure in the chamber, rising one decade to 1e-5 mbar with H2 gas flowing; beam production and detection function in that regime. - **Source quote (verbatim):** “Vaccum in the chamber 10-6 mbar dto with H2 10-5 mbar” - **Source:** [Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022)](https://cyclotroninfo.com/library/#lib-257) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Plan pumping capacity for the gas-on state, not the base pressure; a decade of pressure rise under source gas load is the demonstrated working regime for a keV-class internal-source machine at this scale. (Quote reproduces the table verbatim including its spelling; exponents are superscripts in the original.) **dg-1513** · applicability level 2 · ion-source, project-management · https://cyclotroninfo.com/design-guide/ion-source/#dg-1513 - **Rule (this site's paraphrase of the source):** Evolution path for the ion source — the machine runs a hydrogen filament source, and a Penning ion source is under investigation (as a student internship project) with the aim of installing it in the accelerator; source replacement is treated as an incremental upgrade, not a redesign. - **Source quote (verbatim):** “or investigate a Penning ion source with the aim of using it for the installation in the accelerator.” - **Source:** [Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022)](https://cyclotroninfo.com/library/#lib-257) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A filament source reached first beam here and a candidate Penning source is being investigated as a student project - the sensible pattern being to characterize any replacement source off-machine, then verify its mechanical, vacuum, electrical, gas-feed and central-region interfaces before installation; a source swap touches more of the machine than the source (recommendation, not the paper's documented method). **dg-1522** · applicability level 2 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1522 - **Rule (this site's paraphrase of the source):** In a machine of very few revolutions (ten or fewer), the source deliberately departs from the normal centred mounting: its position is adjustable in the direction of the accelerating gap so the ideal starting position of the first path can be found by experiment; in the reference design the source is therefore not fixed-mounted but stuck under the dummy-dee (design decision, 2013). - **Source quote (verbatim):** “For the setup of the ion source, it is considered that the ion source remains adjustable in direction of the gap, so that the ideal position can be found by experiments. Normally the ion source is centred in the cyclotron. However, in our case – with our small cyclotron and such a small amount of revolutions (≤ 10) - it is better to optimize the starting position of the first path. Due to this fact the ion source will not be fixed mounted but it will be stuck under the dummy-dee instead” - **Source:** [Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-259) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** With only a handful of turns there is no adiabatic settling; an adjustable source mount converts a machining guess about the first half-turn into a tunable parameter, and the optimum need not be the centred position. **dg-1523** · applicability level 2 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1523 - **Rule (this site's paraphrase of the source):** Because ions leave a thermionic chimney source with very low energy, make the emission direction adjustable as well: a rotatable source-head lets the slit angle be optimized by experiment for better acceleration and to prevent the protons remaining in the gap between the dees (design decision, 2013, pre-beam). - **Source quote (verbatim):** “the angle of emission shall be adjustable for a better acceleration and to prevent that the protons remain in the gap between the dees” - **Source:** [Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-259) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A rotatable head is a cheap second degree of freedom on top of source position; both exist because low-energy ions do not forgive alignment errors in the first gap. **dg-1524** · applicability level 2 · ion-source, project-management · https://cyclotroninfo.com/design-guide/ion-source/#dg-1524 - **Rule (this site's paraphrase of the source):** The school machine's ion source was built after the pattern Tim Koeth first used in the Rutgers 12-inch cyclotron (the paper's reference [1]); the project's own design effort went into what its few-revolution machine specifically required - adjustability of source position and emission angle. - **Source quote (verbatim):** “The protons for our cyclotron are produced in the ion source which was built after the pattern of Tim Koeth [1], which he used first in his cyclotron. … A specific design of the ion source was required due to the cyclotron's small size and the low number of revolutions … It was designed for adjusting the position of the ion source itself and the proton's angel of emission. … [1] Tim Koeth, "The Rutgers 12-Inch Cyclotron Ion Source Studies Part I"” - **Source:** [Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-259) — p. 1, 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A documented precedent for reusing a published hobby-machine source design: here the ionization geometry was adopted whole and the adaptation effort spent on mounting and adjustability. **dg-1558** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1558 - **Rule (this site's paraphrase of the source):** Ion-chemistry selectivity is a powerful source-level filter: the LBNL CMS accelerates 14C as a negative ion because the dominant atomic isobar, 14N, does not form a negative ion and so is suppressed before injection — while molecular interferences such as 13CH still require the machine's full mass resolution. - **Source quote (verbatim):** “a mass resolution of about 1800 is needed to separate 14 C from 13 CH ... To suppress the 14N background, 14C- is used, since 14N does not form a negative ion” - **Source:** [Clark, Halbach, Kunkel, Leung, Li & Young, A Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of Cyclotrons'95, Cape Town (1995)](https://cyclotroninfo.com/library/#lib-262) — p. 1, 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Editorial note, tabletop extrapolation: choosing charge state and species at the source is the cheapest background filter available for the interferences it can reach; it complements rather than replaces downstream discrimination — the same instrument still needed R ≈ 1800 for the molecular isobar. **dg-1560** · applicability level 3 · matching, modeling, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1560 - **Rule (this site's paraphrase of the source):** A spiral electrostatic inflector for axial injection should be shaped so the beam emittance leaving it matches the cyclotron acceptance; the LBNL CMS optimized the inflector geometry for that criterion with electrode-field and trajectory codes (CASINO, RELAX3D, and Poisson). - **Source quote (verbatim):** “they are injected axially using a spiral electrostatic inflector, Figure 3. The inflector geometry has been optimized with the computer codes CASINO, RELAX3D and Poisson so that the emittance of the ion beam coming out of the inflector matches the acceptance of the cyclotron” - **Source:** [Clark, Halbach, Kunkel, Leung, Li & Young, A Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of Cyclotrons'95, Cape Town (1995)](https://cyclotroninfo.com/library/#lib-262) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Editorial note, tabletop extrapolation: emittance matching at the inflector exit — the output phase-space distribution oriented so it lies within the cyclotron acceptance, not mere geometric survival — is the design criterion; the code roles (electrode field solve plus 3-D trajectory integration in the real fields) map onto modern open tools. **dg-1562** · applicability level 2 · ion-source, modeling, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1562 - **Rule (this site's paraphrase of the source):** Axial injection down the machine axis is very efficient at delivering external-source ions into the cyclotron midplane; the LBNL CMS used a spiral inflector — an electrostatic channel that twists as it guides ions down the axis and into the midplane — designed with a trajectory code including the actual spatial variation of the magnet field plus a midplane tracking code including electrostatic focusing effects. - **Source quote (verbatim):** “Axial injection, in general, is very efficient in delivering the ions into the cyclotron midplane. We have designed a spiral inflector, an electrostatic channel which twists or "tilts" as it guides the ions down the axis of the machine and into the midplane ... This was accomplished using an ion trajectory program which takes into consideration the spatial variation of the magnetic fields in the cyclotron for the inflector design and a second trajectory program which calculates the cyclotron midplane trajectories, including electrostatic focusing effects” - **Source:** [Young, Bertsche, Clark, Halbach, Kunkel, Leung et al., Development of a Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of PAC1993 (1993)](https://cyclotroninfo.com/library/#lib-263) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Ignoring the real field map in the inflector region, or the electrostatic focusing in the first turns, breaks the emittance match even when the idealized design closes; both effects belong in the design loop from the start. **dg-1563** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1563 - **Rule (this site's paraphrase of the source):** A magnetic multicusp source forms negative ions directly from gas-phase precursors in the discharge plasma; the LBNL CMS pursued it for C- production because, if successful, it would give a simple-to-operate, high-throughput negative-ion source without the graphitization step cesium sputter sources require. - **Source quote (verbatim):** “substantial experience has been obtained in developing negative ion sources for fusion and ion implantation applications using magnetic multicusp sources ... In these devices, negative ions from gas phase precursors are formed directly in the discharge plasma. Recent experiments have shown that C- can be formed in these sources as well ... If successful, it will provide a simple to operate, high throughput source of negative ions without the need for the graphitization process used with sputter ion sources” - **Source:** [Young, Bertsche, Clark, Halbach, Kunkel, Leung et al., Development of a Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of PAC1993 (1993)](https://cyclotroninfo.com/library/#lib-263) — p. 1, 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Editorial note, tabletop extrapolation: gas-fed volume production of negative ions removes the sputter source's solid-sample preparation; the multicusp family LBNL drew on here is the one developed for fusion H- work, which is the variant a small machine would borrow. Yields and operability are species- and plasma-dependent — treat performance claims as per-species questions, and note the source itself states the C- case as prospective. **dg-1637** · applicability level 3 · ion-source, beam-dynamics, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1637 - **Rule (this site's paraphrase of the source):** On the Rutgers 12-inch cyclotron a spiraled discoloration deposited on the copper ion-source chimney after a long beam run was used as a free, retrospective diagnostic of the ions' initial launch angle: the track began at the aperture, wrapped in the direction of beam rotation and pitched downward, and its measured slope of 4.3 degrees gave the order of magnitude of the parasitic vertical electric field. - **Source quote (verbatim):** “Evidence to back up the accusation presented itself when, after a particularly long beam run, a spiraled discoloration appeared on the copper chimney. The discoloration began at the aperture and wrapped in the direction of the beam rotation and with downward pitch as shown in figure 1. The discoloration is taken to be tracks of ions launched during the early portion of the RF phase that were not energetic enough to clear the chimney. It was suspected that the slight vertical asymmetrical geometry of the ion source chimney was the cause of the vertical electric field. In obtaining the order of magnitude of the vertical field a slope of 4.3 degrees was calculated from the spiral track.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Transferable to a small machine with an internal filament/chimney source: deposits and discoloration on the chimney are a free, retrospective record of where lost early-phase ions went. Photographing the chimney after a long run and measuring the spiral's pitch costs nothing and — as here, where the 4.3-degree track slope fed the field estimate of dg-1638 — can yield an order-of-magnitude number for the parasitic vertical field, PROVIDED the deposit's origin and timing can be argued. It is a track-pitch diagnostic, not a direct launch-angle measurement. **dg-1638** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1638 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch group estimated the parasitic vertical field at the ion source aperture from first-turn geometry alone: an ion that declines 0.032 inches in half an RF cycle (t = 40 ns) implies an effective integrated vertical field of 100 V/cm, and the ions strike the chimney with about 10 eV of vertical energy. - **Formula:** `E_y = 2*d*m/(q*t^2); with d = 0.00081 m, m = 1.6x10^-27 kg, q = 1.6x10^-19 C, t = 40 nS gives E_y = 100 V/cm` - **Source quote (verbatim):** “If one calculates that in one half of an RF cycle, the ion vertically declines 0.032 inches in height the effective integrated electric field is simply calculated from: [displayed equations F_z = ma_z = qE_z ; a_z = qE_z/m ; z = (qE_z/2m)t^2 ; E_y = 2dm/(qt^2) ; E_y = (2)(0.00081m)(1.6x10^-27 kg)/((1.6x10^-19)(40nS)^2) = 100 V/cm] […] When the ions have struck the chimney at this point they have a vertical energy of about 10eV.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The method, not the number, transfers: a half-RF-period vertical drop measured off a chimney track or first-turn photo converts into a field estimate via z = ½at². Two calibrations on the source's own arithmetic: the printed equation checks out for its inputs (2·0.00081·1.67e-27/(1.6e-19·(40e-9)²) ≈ 1.0e4 V/m = 100 V/cm — computed here, not stated), but 40 ns is not half a cycle at the memo's stated 14.90 MHz (33.6 ns is); rerunning the same constant-field model with 33.6 ns gives ≈144 V/cm. Treat 100 V/cm as the source's result under its own stated assumption. A machine at ~9-10 MHz has a longer half-period, so a given drop implies proportionally less field. **dg-1639** · applicability level 3 · modeling, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1639 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch group built their 3-D SIMION model by combining three different sources of geometry and field: a 2-D (X-Z plane) Poisson-Superfish magnetic field file of the cyclotron magnet, azimuthally rotated about the z-axis inside SIMION to make the full 3-D volume; the chamber lids, dummy DEE and ion source chimney drawn as a single 3-D solid in AutoCAD and imported; and the DEE itself drawn directly in the SIMION graphics editor because its geometry was simple. - **Source quote (verbatim):** “A 2-dimensional (X-Z plane) PSF magnetic field file describing the cyclotron's magnet field was imported into SIMION. SIMION then azimuthally rotated the 2D field about the z-axis creating the complete full 3-D volume. The chamber lids, dummy DEE, and ion source chimney were drawn as a single 3D solid in AutoCAD, again imported into SIMION. Finally, because of the simplicity of the DEE geometry, it was drawn in the SIMION graphics editor. […] The magnetic field, DEE voltage, and angular frequency were set to nominal 12-inch cyclotron settings. Ions, of unity mass and charge (i.e. protons) were launched with zero kinetic energy at the position of the aperture.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A workable modeling recipe at exactly this scale: a 2-D axisymmetric magnetostatic solve (Poisson-Superfish then, FEMM now) supplies the field, CAD supplies the electrode solids, and the tracking code rotates the field into 3-D. The zero-kinetic-energy launch from the aperture is a useful BASELINE — it isolates what the geometry alone does to the earliest ions — not a validated convention: before treating the model as predictive, run sensitivities over plausible initial energy, direction, position and RF phase, since real plasma ions carry all four spreads. **dg-1640** · applicability level 3 · modeling, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1640 - **Rule (this site's paraphrase of the source):** A 2-D Poisson-Superfish electrostatic model of the DEE-and-chimney silhouette reproduced the order of magnitude of the vertical field at the Rutgers 12-inch ion source but was, in the authors' words, "severely limited due to complex 3D geometry" and valid only in the X-Z plane by symmetry; getting further required buying a full 3-D E&M particle-tracking code. - **Source quote (verbatim):** “[3] Obviously the 2D model was severely limited due to complex 3D geometry, but the model was at least valid in the X-Z plane from the symmetry about that plane, and confirmed a vertical electric field of order estimated above. Taking this calculation further required a full 3D code. […] Want of a 3D E&M modeling code with the ability to fly and track ions prompted the purchase of SIMION - a full 3D E&M particle tracking code.[4]” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A scoping pattern, conditionally: where the relevant symmetry plane is defensible (as it was for this dee-and-chimney silhouette), a free 2-D electrostatic solve can confirm the ORDER of a parasitic field — often all a go/no-go decision needs. Reach for 3-D tracking when out-of-plane geometry materially shapes either the field magnitude or the trajectory — which is exactly why this group bought SIMION to learn where their ions actually landed. **dg-1641** · applicability level 4 · ion-source, beam-dynamics, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1641 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch three-hole chimney experiment machined three identical apertures, one in the median plane and one 2.5 mm above and below it, to give ions deliberate initial betatron amplitudes; the intensity of the three sources declined with distance from the filament but the off-plane apertures varied only +/- 7% from the median-plane aperture, so the observed differences in beam survival were attributable to optics rather than to unequal source strength. - **Source quote (verbatim):** “A chimney with three identical apertures was machined, one aperture was in the median plane as is typical of the normal ion source, and an aperture placed 2.5 mm above and below the median plane aperture. In addition to experiencing the vertical electric field the off-plane apertures gave the ions initial betatron amplitudes. The cyclotron was brought up to typical operating values – this time three stacked purple glows appeared fanning into the face of the DEE (figure 3). The intensity of the three apertures declined as they moved away from the filament, as plotted in figure 4. The off-plane sources intensity varied only +/- 7% from the median plane aperture.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A cheap, highly copyable experiment: one extra chimney with three apertures (median plane, ±2.5 mm) turns the source into a deliberate initial-condition generator, and the glow-intensity profile (Fig. 4) is the control — the off-plane sources matched the median one within ±7%, so survival differences are attributable mainly to optics, at that level of control. Pick your own offsets from your machine's modeled or measured vertical acceptance and the betatron amplitude you want to launch, not by scaling 2.5 mm to your gap. **dg-1642** · applicability level 3 · beam-dynamics, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1642 - **Rule (this site's paraphrase of the source):** In the Rutgers 12-inch three-hole experiment only two of the three launched beams survived to be photographed: the third was lost to the DEE lid because a large launch angle and an initial betatron amplitude added, demonstrating that off-median-plane injection and a parasitic vertical field compound rather than average out. - **Source quote (verbatim):** “A typical 15 second digital exposure of the fluorescent screen was made. Two (not three) sinusoidal patterns, slightly shifted in phase appeared. The third beam was lost to the DEE lid owning to the additive effects of large launch angle and betatron amplitude.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Relevant wherever vertical acceptance is a few millimetres: launch angle (from a parasitic field) and initial betatron amplitude (from an offset) superpose WITH SIGN AND PHASE — they can add or partially cancel, and the third beam here was the additive case, lost to the dee lid. For alignment tolerancing, budget the worst-case additive combination; for diagnosis, remember a surviving beam does not prove both errors are small. ("owning to" is the source's spelling of "owing to".) **dg-1646** · applicability level 3 · ion-source, beam-dynamics, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-1646 - **Rule (this site's paraphrase of the source):** SIMION scans of ion launch height on the Rutgers 12-inch showed a strong up-down asymmetry in capture: ions starting above the median plane (Z > 25.5 mm) were more likely to reach the target while ions from the lower aperture were very quickly lost, and a launch height of 34 mm — 8 mm above the median plane — was optimal for a point source in that geometry. - **Source quote (verbatim):** “From figure 6 we see that ions starting above the median plane (Z > 25.5 mm) were more likely to succeed to target. Ions that started at the lower aperture were very quickly lost. This analysis was pushed further to locate the optimal height from which to launch the ions from in this given geometry. From figure 9 it is seen that a height of 34 mm is the optimal location for a point source to launch from. This is 8 mm above the median plane.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Important cautionary result for tabletop source placement: the "obvious" choice of putting the aperture exactly in the median plane was not optimal in this machine, because the parasitic downward field means a deliberate upward offset recovers capture. The offset is specific to this geometry's field asymmetry, so a builder should scan launch height in their own model rather than copy 8 mm. Note the source is internally inconsistent about where the median plane sits — the text and Fig. 6 title use 25.5 mm while the Fig. 9 axis label reads "26=median plane", which is why 34 mm is described as 8 mm above it. **dg-1649** · applicability level 3 · ion-source, dee, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-1649 - **Rule (this site's paraphrase of the source):** To raise extracted current the Rutgers 12-inch group mounted angled brass plates ("pullers") on the face of the DEE next to the ion source aperture and thinned the chimney wall near the aperture; a Poisson-Superfish model showed the field at the plasma sheath increased by a factor of 760, Langmuir-Child's law then predicted a 130-fold increase in peak emitted ion current, and measurements showed approximately two orders of magnitude increase. - **Source quote (verbatim):** “The new chimney's wall was thinned near the aperture to increase the amount of field that penetrates into the plasma column. To further take increase the local electric field, angled brass plates were mounted on the face of the DEE near the ion source aperture. The plates were named "pullers" for their obvious role in ion extraction. A simple PSF model showed that the field at the plasma sheath increased by a factor of 760. According to the Langmuir-Childs' (LC) law a 130 fold increase in the peak emitted ion source should result.[5] Already measurements show approximately two orders of magnitude increase, and significantly more is expected once better initial steering is accomplished (discussed later).” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The highest-leverage source modification in this memo, entirely within tabletop means: angled brass pullers on the dee face plus a thinned chimney wall near the aperture. The prediction chain is the source's own — modeled sheath field ×760, a Langmuir-Child-based prediction of ×130 in peak emitted current, measured ≈×100 — and its internals are not fully spelled out: a naive I ∝ V^3/2 scaling of a ×760 equivalent-voltage gain would predict far more than ×130, so the source's figure evidently folds in the real extraction geometry. Carry the design move and the measured two-orders-of-magnitude result; re-derive any prediction for your own geometry with your own field model. **dg-1650** · applicability level 3 · ion-source, materials, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1650 - **Rule (this site's paraphrase of the source):** Symmetrizing the Rutgers 12-inch ion source about the median plane required making the insulator electrically invisible as well as the metal symmetric: the Macor boat was sputtered with platinum to produce an electrically contiguous surface from top lid to bottom lid. - **Source quote (verbatim):** “From these simulations and experiences several improvements were made to the ion source chimney. The most obvious was to make the ion source geometry symmetrical about the median plane. To this end even the Macor boat was sputtered with platinum to produce an electrical contiguous surface from top lid to bottom lid.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Applies wherever a machinable ceramic (Macor is the common amateur choice) sits exposed in the accelerating region: a dielectric patch can charge and distort the local field like a metal asymmetry would. Where modeling or symptoms point that way, either shield the dielectric or metallize it — with a vacuum-compatible coating that adheres through thermal cycling and ion bombardment AND is tied to the intended electrode potential (a floating coating is a new problem). Rutgers sputtered platinum on the Macor boat to make the surface electrically contiguous lid to lid. **dg-1651** · applicability level 3 · ion-source, fabrication, modeling · https://cyclotroninfo.com/design-guide/ion-source/#dg-1651 - **Rule (this site's paraphrase of the source):** Alignment of the pullers to the Rutgers 12-inch ion source aperture proved critical: photographic measurement showed the pullers were vertically offset by 0.32 mm, introducing the ions closer to the bottom puller where the non-zero off-plane vertical gradient pulled the beam down, and a Poisson-Superfish model with the DEE and pullers raised by 0.32 mm reproduced the experienced vertical field. - **Source quote (verbatim):** “It is clear from these views (figures 10 and 14) that the pullers are vertically offset; measurement shows they are 0.32mm high. As a result, the ions are introduced closer to the bottom puller, where the non-zero, off-plane, vertical gradient strongly pulled the beam down. A PSF model in which the DEE and pullers are raised by 0.32 mm illustrates the experienced vertical field; see figure 15.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A sobering tolerance number for tabletop builders: a third of a millimetre of vertical misalignment between puller and aperture was enough to dominate the injection dynamics on a 12-inch machine. The authors' own conclusion is that adjustability, not tighter machining, is the answer — see their planned 4-axis bellows adjuster. Note the figure-based measurement technique (photograph the source through a port, subtract a background image, measure against a known dimension) is itself the cheap part. **dg-1653** · applicability level 3 · vacuum, ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1653 - **Rule (this site's paraphrase of the source):** Running the Rutgers 12-inch with supplemental pumping and raising the hydrogen gas flow made the primary beam directly visible via recombination; at 600 watts the first revolution could be photographed spiraling left and downward, terminating on the leftmost portion of the chimney base, with secondary electron emission visible as vertical striations emanating from the impact location. - **Source quote (verbatim):** “Running the cyclotron with supplemental pumping, the hydrogen gas flow was increased to the point where the primary beam can be visibly seen via recombination. […] Figure 12 shows an intense beam spiraling to the left and downward while operating at 600 Watts. The beam is terminating at the leftmost portion of the chimney base. Secondary electron emission can be noted by vertical striations observed emanating from the ion beam's impact location.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A deliberately dirty operating mode used as a diagnostic: with supplemental pumping in place, over-gas the chamber until the beam glows by recombination — this machine photographed an intense spiral (600 W) terminating on the chimney base, with secondary-electron striations marking the impact point. On a machine with a diffusion pump and an MFC the trick is free to try; whether YOUR beam becomes visible depends on gas excitation, optical access and background light, and the glowing trace is the beam path, not necessarily a single identified turn. **dg-1654** · applicability level 4 · ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-1654 - **Rule (this site's paraphrase of the source):** Historical puller-geometry data point cited by the Rutgers group from Livingston, Holloway and Baker (Rev. Sci. Inst. 10, 63, 1939): for a 0.0625 inch diameter aperture, pullers with a vertical 1/4 inch gap residing 1/4 inch away from the aperture yielded best results; the Rutgers authors note this parameter space had not yet been explored on their own machine. - **Source quote (verbatim):** “Optimization of the puller placement and vertical gap needs further investigation. Livingston found that for a 0.0625 inch diameter aperture that pullers with a vertical ¼ inch gap residing ¼ inch away from the aperture yielded best results. [7] This parameter space for our cyclotron has not yet been explored. It is clear from figure 12 that the ions initial radius is very large, thus the pair of pullers plates could be replaced with by a single solid plate with just an aperture in it.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A historical calibration point rather than a recipe: Livingston, Holloway and Baker's 1939 optimum for a 1/16-inch capillary aperture was a 1/4-inch puller gap at 1/4-inch standoff — quoted approvingly here by authors who explicitly had NOT explored that space on their machine. Scan or model gap and standoff for your own extraction voltage, field and aperture. The memo's single-apertured-plate suggestion is an untested option for cases where trajectory calculation shows the first-turn radius clears the plate — verify, don't assume. (The quoted passage begins on p.5 — where the 0.0625 inch figure appears — and concludes on p.6.) **dg-1655** · applicability level 3 · ion-source, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1655 - **Rule (this site's paraphrase of the source):** Planned (not yet built) ion-source improvements stated by the Rutgers 12-inch authors as their intent: a bellows 4-axis adjuster (yaw, pitch, roll and gap spacing) permitting adjustment while running; a small circular metal piece such as tungsten beneath the filament at filament bias voltage to increase ion production and protect the Macor boat; spiraling the filament to localize heat generation and increase emitting surface; and a constant current bias supply. - **Source quote (verbatim):** “This signifies that initial conditions are very sensitive to the puller-chimney alignment and that adjustability is a necessity. A bellows 4-axis (yaw, pitch, roll, and gap spacing) adjuster is being designed. Its implementation will permit adjustment while running. To further increase ion production and to protect the bottom of the Macor boat, a small circular piece of metal, such as tungsten will be placed beneath the filament and sit at the filament bias voltage. Additionally, spiraling the filament should localize the heat generation as well as substantially increase the electron emitting surface. Finally, installation of a constant current bias supply is planned.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** These are the authors' stated plans, not achieved results. The design intent transfers well nonetheless: in-vacuum, under-beam adjustability of the source position is worth engineering into a tabletop machine from the start, given that 0.32 mm of misalignment dominated their beam (p.5). A constant-current filament bias supply and a spiraled filament are both cheap changes at this scale. **dg-1656** · applicability level 3 · beam-measurement, detectors, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1656 - **Rule (this site's paraphrase of the source):** Operating consequences reported at the improved Rutgers 12-inch ion source: proton beam currents of order 20 microamps could be focused onto the collector, filament lifetime was the limitation on operating time (tracked with a resettable minutes meter), and the beam power was sufficient to blister the Radeline fluorescent screen near the median plane so that it no longer fluoresced there. - **Source quote (verbatim):** “Presently proton beam currents of order 20µAmps can be focused onto the collector. The increased beam power has been duly noted; it is now sufficiently high to damage the Radeline fluorescent screen. The screen has blistered and no longer fluoresces near the median plane, rather glowing embers can be seen. […] Not directly pertaining to ion production, but worth mentioning is the installation of a reset-able minutes meter to track filament lifetime. Filament lifetime is presently the limitation in operating time.” - **Source:** [Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007)](https://cyclotroninfo.com/library/#lib-272) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Two limits this machine hit that yours should be budgeted against, not assumed: its ~20 µA focused beam blistered the Radeline fluorescent screen at the median plane (screen survival is a power-density question — evaluate deposited W/mm² for your own screen, keep screens replaceable, and use a Faraday cup for anything quantitative), and its operating time was bounded by filament hours, tracked with a resettable minutes meter — a trivial addition that turns a nuisance into data and tells you whether filament life is YOUR limiting consumable. **dg-1700** · applicability level 3 · beam-measurement, magnet, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1700 - **Rule (this site's paraphrase of the source):** Poor beam intensity on the Rutgers 12-inch prompted a 2-D Bz map hunting specifically for an undesired azimuthal variation of periodicity two; none was detectable, and the investigation then moved on to the ion source instead. - **Source quote (verbatim):** “Poor beam intensity motivated our search for an undesired azimuthal variation of periodicity two, which resulted in the 2-D Bz-field measurements of the weak focusing field shown in Figure 2. Since no detectable azimuthal variation was found, our quest to improve the beam intensity led us in other directions, including the ion source. [7]” - **Source:** [Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011)](https://cyclotroninfo.com/library/#lib-274) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A worked example of ruling a suspect out: disappointing current, a plausible magnetic culprit (m = 2 azimuthal error), a 2-D map to test it — and a null result, above the mapper's detection threshold, that legitimately DE-prioritized the field and sent the effort in other directions, including the ion source (where the real gains turned out to live, dg-1728). The transferable discipline is testing the measurable suspect before redesigning anything; a null map does not convict the source by elimination. **dg-1715** · applicability level 2 · beam-dynamics, magnet, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1715 - **Rule (this site's paraphrase of the source):** Two protons launched with identical initial conditions on their equilibrium orbits at 50 keV in the Rutgers 12-inch showed the maximum vertical excursion in the weak-focusing field to be nearly four times that in the radial-sector AVF field — about plus/minus 9 mm versus about plus/minus 2.5 mm from the mid-plane — which the authors read as permitting either a drastically reduced magnet gap or a larger accepted vertical angular distribution. - **Source quote (verbatim):** “As is seen in Figure 20, the maximum vertical excursion of the proton in the weak field was nearly four times that of the proton in the radial sector AVF field. This has two immediate implications. First, to accommodate a given ion source, the magnet gap of AVF field can be drastically reduced, implying a smaller and less expensive magnet. Alternatively, the magnet gap can be maintained, and a greater vertical angular distribution can be accepted, implying greater beam intensity at the periphery.” - **Source:** [Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011)](https://cyclotroninfo.com/library/#lib-274) — p. 9 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The clearest quantitative case for AVF at this scale, kept to what the simulation shows: one proton, identical launch, ±9 mm excursion in the weak-focusing field versus ±2.5 mm in the radial-sector field (read from the rendered Fig. 20; 'nearly four times' is the authors'). The source's two implications — a drastically reducible gap, or more accepted vertical angle — are design directions whose actual payoff needs full acceptance tracking and a self-consistent magnet redesign, since gap changes move excitation and field structure together. Note the apparent tension with the same program's finding that its weak-focusing νz exceeds its Thomas-field νz (dg-1696): tune and single-trajectory excursion are different measures, and the Fig. 15 labeling problem (same card) leaves the tune comparison unresolved. **dg-1723** · applicability level 3 · beam-dynamics, ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-1723 - **Rule (this site's paraphrase of the source):** Comparing simulated static trace spaces with the dees removed, the Rutgers 12-inch AKG270 spiral field is radially bounded by the weak-focusing field in most cases, but at 50 and 100 keV its vertical trace space is larger than the weak-focusing poles', indicating greater angular acceptance from the ion source thanks to the enhanced central focusing of the weak-focusing bump. - **Source quote (verbatim):** “After locating the equilibrium orbits, a complete comparison of the focusing between the AKG270 poles and the weak focusing pole tips was performed using the simulated fields. The DEEs were removed from both cases to observe, if any, non-linear effects at large excursions. The radial and axial results are respectively shown in Appendix II-a and -b. In most of the radial cases the AKG270 radial trace space is bounded by the weak focusing pole tips. At the lower energies of 50 and 100 keV, the vertical trace space of the AKG270 poletips is larger than that of the weak focusing poles, indicating a greater angular acceptance from the ion source. This is due to the enhanced central focusing from the weak focusing bump.” - **Source:** [Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011)](https://cyclotroninfo.com/library/#lib-274) — p. 11 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Where this hybrid field's acceptance advantage showed up: at the LOW-energy end — 50 and 100 keV vertical trace spaces larger than the weak-focusing poles' — and the source credits the AKG270's retained central weak-focusing bump, not the spirals. That is the hybrid logic confirmed at exactly the energies where source acceptance is decided. Methodological detail worth copying: the dees were removed from both simulations so the comparison probes field nonlinearity, not mechanical clipping. Radially, the weak-focusing field bounded AKG270 in most cases; simulated statics, not measured beam. **dg-1727** · applicability level 3 · magnet, rf, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1727 - **Rule (this site's paraphrase of the source):** On the Rutgers 9-inch prototype magnet the pole-tip faces were parallel to within 0.0001 inches with no field shaping for focusing; with a maximum of 50 watts of RF (a dee peak-to-peak voltage of 3300 V) and the whole chamber filled with hydrogen from a crude filament source, beam currents of order 10 nA of 0.60 MeV protons were reproducibly achieved. - **Source quote (verbatim):** “The faces of the 9-inch pole tips were parallel within 0.0001 inches – no effort of shaping the field for focusing was expended. Ions were produced with a crude filament near the top lid of the cyclotron chamber, and the entire chamber was filled with hydrogen gas. Even with a maximum RF power of just 50 watts, thus a DEE Vp-p of 3300V, beam currents on the order of 10nAmps of 0.60 MeV protons were reproducibly achieved with the 9-inch magnet.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A directly comparable data point for the 8-12 inch class: a flat-pole, gas-filled-chamber, filament-source machine at 3300 V dee reproducibly delivered ~10 nA at 0.60 MeV — a demonstrated outcome showing a crude first configuration can produce measurable beam, not a yield to expect. The 0.0001-inch figure is the reported PARALLELISM of the opposed pole faces (each face's own flatness is not stated), and is what a university shop achieved. **dg-1728** · applicability level 3 · cyclotron-general, ion-source, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-1728 - **Rule (this site's paraphrase of the source):** Scaling the Rutgers machine from the 9-inch prototype to the 12-inch magnet did NOT carry the beam performance over: only fractions of a nA were achieved in the larger magnet despite the 9-inch having produced ~10 nA. The diagnosis chain ran pole tips first (radially tapered tips designed, installed, characterized — only a slight current increase), then the ion source, where analysis SUGGESTED the dee's high voltage was suppressing filament electron emission and hence ion generation during the correct RF phase. - **Source quote (verbatim):** “The experimenters were quickly disappointed when only fractions of a nAmp beam were achieved in the larger magnet. Much effort was put into understanding the problem. First, pole tips with a slight radial taper to promote focusing were designed, installed and characterized [2,3]. Still with only a slight increase in beam current with the installation of the new pole tips, the ion source came under suspicion. An analysis of the simple ion source suggested that the DEE's high voltage was suppressing electron emission and thus suppressing ion generation during the appropriate RF phase.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The most transferable failure story in this memo: a working small machine did not automatically scale to a bigger magnet, and the leading suspect was not focusing but a source-to-dee electrostatic interaction — the dee's field suppressing filament emission at the useful RF phase, per the authors' analysis (a suggested mechanism, which their chimney redesign then acted on). Worth testing on any open-filament source sitting in the dee's fringe field. **dg-1734** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1734 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch ion source improvement was a chimney around the biased filament: it lets thermionic electrons follow the vertical field lines to the median plane while ionizing hydrogen, and enclosing the gas in the filament/chimney volume improved vacuum performance. A 1/16-inch aperture in the chimney wall, at the height of the median plane, launches the protons directly into the dee. - **Source quote (verbatim):** “The ion source chimney allows thermionic electrons to freely leave the biased filament following the vertical magnetic field lines to the median plane all the while ionizing hydrogen. Admission of hydrogen gas to the enclosed volume of the filament and chimney improved vacuum performance. A 1/16-inch aperture in the chimney wall located at the height of the median plane launches the protons directly into the DEE as pictured in figure 6.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Two benefits from one part: local gas confinement (less load on a small pump) and a defined emission aperture at the median plane. The 1/16-inch aperture is this machine's as-built dimension — a reference point, with the right size for another source set by its extraction optics and gas-conductance budget (the same program's later aperture sweep, dg-1814, is the method). **dg-1735** · applicability level 2 · rf, ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1735 - **Rule (this site's paraphrase of the source):** A calculation for the Rutgers 12-inch (from the ion-source model) put the RF power needed for the first ion revolutions to clear the source chimney at 165 watts when operating at 14.900 MHz; the model was confirmed on the bench by establishing beam at 300 watts and slowly reducing RF power — beam intensity fell with power and then dropped abruptly to zero at 170 watts. - **Source quote (verbatim):** “It was calculated that the required RF power for the first revolutions of ions to clear the chimney (with the cyclotron operation at 14.900MHz) was 165 watts as plotted in figure 7. [4,7] Confirmation of the ions source model came from establishing beam with 300 watts of RF power and slowing decreasing RF power. Beam intensity decreased with decreasing RF power, but at 170 watts the beam current abruptly dropped to zero.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A rare validated model-vs-measurement pair at this scale: predicted 165 W first-turn chimney-clearance threshold, measured abrupt cutoff at 170 W. Diagnostic reading: beam that fades then DROPS to zero as RF power falls, near a modeled clearance threshold, is consistent with the first turn striking the source structure — check dee voltage, RF stability, source output and tuning before assigning the cause, since phase-acceptance loss and resonator instability can also end beam abruptly. **dg-1737** · applicability level 3 · ion-source, vacuum, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-1737 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch published run-up sequence: pump the chamber below 1E-5 Torr, shut off the ion gauge, energize the magnet at approximately 20 amps, turn on the filament bias supply at -200 V, ramp the filament heater until thermionic emission of order 10 mA is reached, then slowly admit hydrogen until emission current rises; the optimum was a filament heater current of 20.6 A (for 0.015 inch diameter 1% Th-W wire) and a leak dial setting of 104. RF was then tuned to resonance (14.8640 MHz) and driven to 300 watts (7,500 Vp-p on the dee), and the magnet current was swept up to find the cyclotron resonance condition while watching the electrometer. - **Source quote (verbatim):** “The operational sequence was as follows: pump the cyclotron chamber below 1E-5 Torr, shut off ion gauge, turn on the magnet with approximately 20 amps of excitation current, turn on filament bias supply (-200V), then slowly ramp filament heater supply until thermionic emission on order of 10mA is reached, slowly admit hydrogen gas until an increase in emission current was noted. Final optimal filament heater current is noted at 20.6 Amps (for 0.015 inch diameter 1% Th-W wire) and final optimal leak dial setting of 104 was recored. RF was turned on at a low level and tuned to resonance (found to be 14.8640 MHz), the RF drive was increase to 300 watts – corresponding to 7,500 Vp-p on the DEE. … To satisfy the “cyclotron resonance condition” the magnet current was slowly swept up while monitoring the electrometer needle for deflection.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A complete, numbered startup sequence at exactly the target machine class, including the filament wire spec (0.015 inch 1% thoriated tungsten) and its 20.6 A heating current, and the order of operations: vacuum, gauge off, magnet, bias, heater, gas, RF to resonance, then sweep the magnet current up while watching the electrometer. The numbers are this machine's optimum, not universal setpoints; the ORDER is the transferable part. **dg-1743** · applicability level 3 · dee, ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1743 - **Rule (this site's paraphrase of the source):** The Rutgers authors attribute the large initial vertical displacement of the beam — despite an ion source aperture in the median plane — to the early ions' sensitivity to any vertical electric field component, because the E-field from the source into the dee diverges quickly, so a slight offset of the dee with respect to the median plane produces a significant vertical kick. Their proposed mitigations are better dee alignment or installing "pullers" on the dee aperture in the region of the ion source. - **Source quote (verbatim):** “The natural question that should be asked: if the ion source aperture is in the median plane, why then the large vertical displacement? This can be attributed to the early ions sensitivity to any vertical component of the electrical field. Inspection of Fig 5 shows that the electric field from the ion source into the DEE diverges quickly. Thus a slight offset of the DEE with respect to the median plane will provide a significant vertical component. This can be mitigated by the installation of "pullers" on the DEE's aperture in the region of the ion source – a possible student project.” - **Source:** [Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006)](https://cyclotroninfo.com/library/#lib-276) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Why a median-plane source aperture still launches vertically displaced beam: in the central source-to-dee region the extraction field diverges strongly, so any dee offset from the median plane hands the earliest ions a vertical kick. No tolerance number is given — the source's stated remedy is pullers on the dee aperture near the source (offered as a possible student project, not a demonstrated fix); tightening dee-to-median-plane alignment is the natural corollary a builder draws, not the source's measured mitigation. **dg-1748** · applicability level 3 · ion-source, beam-dynamics, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1748 - **Rule (this site's paraphrase of the source):** To excite measurable axial betatron oscillations on the Rutgers 12-inch, a modified source chimney was built with its aperture offset along the vertical axis, deliberately giving the beam an initial axial offset from the symmetry plane; the source itself is a cold cathode Penning ion gauge source with a circular aperture of 0.8 mm radius able to sustain a current of 5 mA. - **Source quote (verbatim):** “The design of the source, a cold cathode Penning Ion Gauge (PIC) source, is reported in Ref. [4]. The aperture is circular with a 0.8mm radius and it can sustain a current of 5mA. A modified source chimney featuring an aperture offset along the vertical axis was built in order to provide a beam with an initial axial offset.” - **Source:** [Hernalsteens, Ponter, Beaudoin, Koeth, Ruisard & Miller, Betatron Tune Characterization of the Rutgers 12-Inch Cyclotron for Different Magnetic Poles Configurations (2016)](https://cyclotroninfo.com/library/#lib-277) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A spare chimney with a deliberately off-median aperture is a simple, purpose-built way to launch coherent axial oscillations for tune studies — the launch half of the measurement. Extracting a tune still needs adequate transmission and a diagnostic that resolves the oscillation turn by turn (here, the phosphor radial probe). The source prints the acronym "(PIC)" where "PIG" is standard; quote transcribed as printed. **dg-1757** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1757 - **Rule (this site's paraphrase of the source):** The Rutgers 12-inch cold cathode PIG ion source can provide beam currents as high as 1 microamp, but ion production only follows the PIG discharge linearly up to 60 mA; sustained discharge above 30 mA enters a negative impedance regime with associated thermal runaway that, without water cooling, quickly destroys the source, so operation was limited to 20 mA discharge current. Gas flow had to be throttled hard because of inadequate pumping speed, holding chamber pressure at 4E-6 Torr or less, and beam current on target diminished quickly at higher pressure; combined constraints limited beam on target to about 100 nA or less. - **Source quote (verbatim):** “The cold cathode PIG ion source can provide beam currents as high as 1 µa, but a mixture of operational constraints limited the beam current on target to about 100nA or less.[5] Ion production linearly follows the PIG discharge up to 60 mA. However, a sustained discharge current greater than 30 mA leads to the negative impedance regime and an associated thermal runaway. In that regime, without water-cooling, the ion source would quickly suffer failure. Thus the ion source operation was limited to 20 mA discharge current. The gas flow had to be severely throttled because of the vacuum systems inadequate pumping speed; the chamber's operating pressure was maintained at 4E-6 Torr or less. … The beam current on target quickly diminished at higher pressure.” - **Source:** [Koeth, Neutron Production with a 12-Inch Cyclotron (2017)](https://cyclotroninfo.com/library/#lib-278) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The real limiter chain on this machine, as the source tells it: the source could give 1 µA, but a MIXTURE of constraints left ~100 nA or less on target — pumping speed forced hard gas throttling (4E-6 Torr or less, with target current quickly diminishing at higher pressure), and the uncooled PIG's negative-impedance runaway above 30 mA capped discharge at 20 mA. The thresholds are this source's; the chain — pumping limits gas, gas limits source output, thermal runaway limits it again — is the pattern to budget against on any small machine. **dg-1772** · applicability level 3 · rf, magnet, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1772 - **Rule (this site's paraphrase of the source):** (draft report) For the neutron-diffusion measurement the Rutgers/UMD 12-inch cyclotron was tuned for D+ with RF at 7.150 MHz and an average magnetic field of 0.96 T (top coil 29.007 amps, bottom coil 29.121 amps) using the AKG270 spiral poletips; the source used the largest rectangular aperture chimney (hence lowest pressure differential), the mass flow controller was set to 0.230 scc/m for an operating pressure of 3E-6 Torr, and the ion source ran at 10 mA arc discharge current. Beam tune-up was verified with about 8 kV on the internal deflection (Wien filter) confirming successful acceleration of deuterium. - **Source quote (verbatim):** “The 12-inch cyclotron was tuned up for D+ ions, with the RF system tuned to 7.150MHz, for an average magnetic field set to 0.96T (by setting the top coil to 29.007Amps and bottom coil to 29.121 amps) with the AKG270 spiral poletips.[1] The ion source used the largest rectangular aperture chimney (hence lowest pressure differential), the Mass Flow Controller was set to 0.230 scc/m for an operating pressure of 3E-6 Torr, the ion source was run with a 10mA arc discharge current – all of these parameters balanced for optimal operating point.” - **Source:** [Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020)](https://cyclotroninfo.com/library/#lib-279) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The most fully specified deuteron operating point in this collection — but treat it as recorded settings, not a validated matched pair: 7.150 MHz and 0.96 T are not mutually consistent with f = qB/2πm_d (7.150 MHz corresponds to ≈0.94 T; 0.96 T to ≈7.32 MHz, about 2% apart), and the draft does not say which number was measured against what. Reconcile against a field map or frequency counter before using the pair as a tune recipe. The slightly different top and bottom coil currents are reported settings; the draft does not state their purpose. Draft report. **dg-1812** · applicability level 2 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1812 - **Rule (this site's paraphrase of the source):** On the Rutgers 12-inch cyclotron, early filament-based internal ion sources produced only nanoamps of protons and lasted a few hours; the group replaced them with a cold-cathode Penning Ion Gauge (PIG) source, and describe the ion source as the cyclotron's most challenging component. - **Source quote (verbatim):** “Early filament based designs generated mere nanoamps of protons and would only operate a few hours.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.1 = printed p.366. The trade as this program experienced it: their early filament designs gave nanoamps and hours, and the cold-cathode PIG is what made the machine routine. Hot-filament sources are not intrinsically nanoamp devices — output depends on geometry, emission, gas feed and what current is being quoted — so read this as one program's motivated migration plus their judgment that the source is the machine's hardest component, and compare designs on measured current and lifetime. **dg-1813** · applicability level 3 · ion-source, materials, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1813 - **Rule (this site's paraphrase of the source):** The Rutgers "Mark-III" miniature PIG source uses two tantalum cathodes pinned to stainless steel leads seated in boron-nitride cups housed in copper bases; the chimney, chimney bases and HV lead shields are all copper, and cooling is purely by conduction to the upper and lower chamber lids. The assembly is quarter-coin sized. - **Source quote (verbatim):** “It uses two tantalum cathodes pinned to stainless steel leads that are seated in boron-nitride cups which are housed in copper bases. The chimney, chimney bases, and HV lead shields are also all copper. Cooling is through conduction to the upper and lower chamber lids.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.1 = printed p.366; the cross-section is Fig. 2 (PDF p.2 / printed p.367) and Fig. 1 shows the assembly beside a US quarter. The materials picture of one proven miniature internal PIG: Ta cathodes, BN insulating cups, copper everywhere heat must travel, and no water — conduction to the chamber lids is the entire cooling system, which is precisely what makes THIS design reproducible without plumbing. Another machine copies the principle (give the heat a solid conductive path to a big lid) and re-derives its own thermal budget — the runaway ceiling (dg-1816) is where that budget runs out. **dg-1814** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1814 - **Rule (this site's paraphrase of the source):** The Rutgers PIG source's ion production was characterized in a 1 Tesla field by DC-biasing the dee negative and collecting current across a range of hydrogen pressures, arc currents and chimney aperture sizes; the best arc stability was found with the smallest circular aperture tried, 0.031 inch (1/32 inch) diameter. - **Source quote (verbatim):** “The best arc stability was found for the smallest (0.031 inch) circular aperture.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367. Two things transfer: the zero-RF characterization method (DC-bias the dee as a collector and sweep pressure, arc current and aperture — no RF system needed to commission a source), and 1/32 inch as the best-stability aperture AMONG THOSE TESTED here, i.e. a candidate for your own sweep rather than a design value. The Fig. 1 photograph shows an assembly with a 0.7 × 4 mm slitted aperture; whether that configuration was operated is not stated in this paper. **dg-1815** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1815 - **Rule (this site's paraphrase of the source):** For the Rutgers miniature PIG in a 1 Tesla field with a 1/32 inch aperture, collected ion current (the source's Fig. 3 caption calls it proton beam current) rises with both arc current and extraction (DC dee) voltage, roughly linearly in dee voltage over the plotted range: at 10 kV DC dee bias, Fig. 3 shows about 500 microamps at 50 mA arc, about 305 at 40 mA, about 250 at 30 mA, about 230 at 20 mA and about 165 microamps at 10 mA. - **Source quote (verbatim):** “As expected, the collected ion current follows the arc current and extraction voltage.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367; currents read from the rendered Fig. 3, axes beam current (µA) versus DC dee voltage (kV). Two cautions before transfer: these are DC-extracted source currents into a biased dee, NOT accelerated beam on target — and a DC-biased dee is not mass-selective, so the collector current lumps protons with H2+ and friends (the same source's 5:1 species ratio, dg-1817, says how much that matters). The rising trend with extraction voltage holds over the measured range; beyond it, extraction can go plasma- or space-charge-limited, so measure rather than extrapolate. The "H Pressure 111" label is an uncalibrated instrument reading, so the hydrogen pressure for this curve is not recoverable. **dg-1816** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1816 - **Rule (this site's paraphrase of the source):** Above about 40 mA arc current the Rutgers miniature PIG source enters thermal runaway, with a large jump in ion production and the copper chimney and bases visibly incandescent. - **Source quote (verbatim):** “At arc currents greater than 40 mA thermal runaway causes a large increase in ion production … at these arc currents the chimney and bases are visually incandescent.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367. The observed runaway region for THIS conduction-cooled miniature PIG — its geometry, contacts, pressure and duty — not a ceiling for the type. What transfers: a conduction-cooled source has a thermal cliff, the apparent ion-current gain past it is bought with instability, and incandescence means the cliff is well behind you. Characterize temperature and stability conservatively, current-limit or interlock the arc supply, and shut down well before anything glows. **dg-1817** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-1817 - **Rule (this site's paraphrase of the source):** Rapid frequency sweeping of the Rutgers 12-inch cyclotron showed its PIG source producing protons and H2+ simultaneously in a 5:1 ratio. - **Source quote (verbatim):** “Rapid sweeping operation of the cyclotron has shown simultaneous generation of protons and +H2 ions in a 5:1 ratio.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367 (printed notation is a leading-superscript "+H2"; transcribed as printed). Species fraction is first-order on a small machine: H2+ at half the charge-to-mass ratio accelerates at a different frequency and appears as a second resonance. The transferable method is the sweep — run the RF quickly across the band and see which resonances light up; no mass spectrometer needed for identification. The 5:1 proton-to-H2+ figure is this machine's result under its conditions, and resonance amplitudes fold in acceleration and detection efficiency, so treat ratios read this way as qualitative until independently analyzed. **dg-1818** · applicability level 3 · ion-source, detectors · https://cyclotroninfo.com/design-guide/ion-source/#dg-1818 - **Rule (this site's paraphrase of the source):** On the Rutgers 12-inch cyclotron, 5 mA arc current is enough for beam-physics demonstrations and higher currents quickly burn the phosphor screens; at 5 mA the Mark-III PIG runs more than 40 hours between servicing, and demanding greater arc current reduces source lifetime. - **Source quote (verbatim):** “At 5 mA, the Mark-III PIG sources operate for greater than 40 hours without requiring servicing. … Beam current from an arc current of 5 mA is sufficient for beam physics demonstrations, operating at greater currents quickly burns the phosphor screens. … Demanding greater arc currents reduces the source’s lifetime.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367. A working-point philosophy worth copying: run the source at a small fraction of its capability and collect the dividends — a 40-plus-hour service interval on this Mark-III, and diagnostic phosphors that survive. On a machine whose main instrument is a phosphor screen (the usual amateur situation), the screen-burn limit binds before the source does; find your own minimum useful arc current the same way. **dg-1819** · applicability level 3 · ion-source, materials, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-1819 - **Rule (this site's paraphrase of the source):** The most common failure of the Rutgers miniature PIG is a buildup of tantalum flakes shorting a cathode to its copper base; repair is simply disassembly and scouring with acetone and methanol. Separately, after several hundred hours of operation at 5 mA the tantalum cathodes must be replaced due to erosion, with visible erosion and Ta buildup in the BN cup and chimney base after as little as 10 hours. - **Source quote (verbatim):** “After several hundred hours of operation at 5 mA the Ta cathodes need to be replaced due to erosion. … The most common failure is a build up of Ta flakes shorting a cathode to the copper base. Repair simply requires the PIG to be disassembled and scoured with acetone and methanol. … Figure 4 displays an inspection after 10 hours of operation.” - **Source:** [Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-282) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.367; the 10-hour inspection is Fig. 4. The maintenance picture to plan for before committing to a miniature PIG: the routine fault is a conductive tantalum-flake short cleared by disassembly and solvent scouring, cathodes are consumables (several hundred hours at this source's 5 mA setting), and deposits are visible after as little as 10 hours. The design consequence stands regardless of whose numbers apply: build the source so it comes apart easily and the consumables are reachable. **dg-1836** · applicability level 3 · beam-dynamics, ion-source, pedagogy · https://cyclotroninfo.com/design-guide/ion-source/#dg-1836 - **Rule (this site's paraphrase of the source):** On the Rutgers 12-inch cyclotron, small axial (vertical) betatron motion is deliberately initiated by a vertical electric field that kicks the ions upward immediately as they leave the ion source chimney. - **Source quote (verbatim):** “Small axial motion is initiated by a vertical electric field that imparts an upward kick to the ions immediately upon their exit of the chimney.” - **Source:** [Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013)](https://cyclotroninfo.com/library/#lib-283) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** PDF p.2 = printed p.370. A controlled way to excite vertical motion for diagnosis rather than waiting for it to appear as a fault: an intentional electric kick at the chimney exit launches the oscillation, which a turn-resolving diagnostic (here, the radial-draw phosphor image) then converts into a tune number. The caution reads in reverse too: a stray vertical field near the source will do the same thing uninvited. **dg-1852** · applicability level 2 · dee, ion-source, chamber · https://cyclotroninfo.com/design-guide/ion-source/#dg-1852 - **Rule (this site's paraphrase of the source):** On the nine-inch cyclotron the second accelerating electrode is a "Dummy DEE" mounted diametrically in the chamber in direct electrical contact with it, which also serves as the central mounting surface for the ion source; the chamber median plane is adjusted to coincide with the magnetic median plane. - **Source quote (verbatim):** “The chamber's median plane is adjusted to be the same as the magnetic field's median plane. The Dummy DEE is mounted diametrically in the chamber making excellent electrical contact as it provides the aperture of the second accelerating electrode. The dummy DEE also provides a central mounting surface for the ion source.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A topology that simplifies a small build: one driven dee (one HV feed-through) against a grounded dummy dee that doubles as a rigid, on-axis, at-ground mounting surface for the source — exactly where the source must sit. Whether one dee or two suits a given machine is an RF and symmetry decision, and some sources need bias or insulation rather than grounded mounting. The alignment rule worth copying outright: set the chamber median plane to the MAGNETIC median plane, not to the pole faces. **dg-1864** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-1864 - **Rule (this site's paraphrase of the source):** Nine-inch cyclotron ion source - a W-Th-Ir (tungsten-thoriated-iridium) filament roughly 1 inch of exposed length, suspended between two electrical feed-throughs with spring loaded clamps at the tip, mounted on the face of the dummy dee near the top centre of the chamber; approximately 7 amps heats it white hot, and the optimum negative bias with respect to chamber ground was found to be -320 Volts D.C. - **Source quote (verbatim):** “A W-Th-Ir filament is suspended between two electrical feed-throughs with spring loaded clamps at the tip. When approximately 7 amps flow through the filament it is heated to glow white hot. ... The exposed filament is roughly 1 inch long, thereby producing a very thin sheet of electrons with a similar width of 1 inch. It was found that an optimum bias voltage of the filament was -320 Volts D.C.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** An extremely simple internal PIG-less source that works at tabletop scale. The spring loaded clamps address a real problem - the filament expands when hot and a rigid clamp will either bow it out of position or snap it. The -320 V optimum is an empirical optimum for this geometry, not a universal number; the reported run 91699C used the same -320 V but at 5.75 A filament current, less than the ~7 A quoted here for white heat. Ellipsis marks omitted intervening text. **dg-1865** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1865 - **Rule (this site's paraphrase of the source):** The nine-inch cyclotron's source relies on the cyclotron's own field to focus the ionizing electrons - electrons emitted from the filament near the top of the chamber travel downward along the strong parallel magnetic field in a tight helix rather than a straight line, forming a thin ionizing sheet through the median plane, while the electric fields of the source and the accelerating RF sweep the freed electrons away and leave the protons behind. - **Source quote (verbatim):** “Further more, because of the very strong magnetic field parallel to the desired electron path, strong focusing occurs. Any electron that attempts to stray off of a vertical ascent or decent is immediately steered back towards the central axis of motion. Due to this corrective focusing, the electrons tend to oscillate back and forth in both X and Y while traveling downward in Z. Instead of following a linear path, the traversal then becomes a helical path with a very tight radius. … The electric fields of the ion source and accelerating RF sweep away the freed hydrogen electrons, leaving the massive protons behind.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Why a crude filament-across-the-gap source works at all inside a cyclotron: the ~0.9 T field pins the ionizing electrons to tight helices about their field lines (the source describes this as steering back toward the central axis — strictly, gyration confines each electron about its own line rather than restoring it to a common axis), forming a thin ionizing sheet through the median plane right where ions must be born, with — the source's own statement — the ion-source and RF electric fields sweeping the freed electrons away. Corollary, scoped: emission, heating and vacuum behaviour bench-test fine outside the magnet; the magnetized TRANSPORT that makes the geometry work does not, so beam-relevant performance is a property of source plus field together. **dg-1866** · applicability level 3 · ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1866 - **Rule (this site's paraphrase of the source):** Filament emission in the nine-inch cyclotron ion source is exponential in filament current - at -300 VDC bias a test W-Th-Ir filament produced essentially zero emission below about 4.5 amps and about 3 mA at 5.0 amps (Fig.9) - so small filament current changes give large changes in thermionic electron supply and hence in proton beam current; the author states filament heating limitation was the factor limiting maximum achievable beam current at the periphery. - **Source quote (verbatim):** “Fig.9 shows the exponential emission of electrons in a test of the W-Th-Ir material. Hence slight changes in the filament current can produce great changes in thermionic emission. Ultimately changing the number of thermionic electrons available to ionize the hydrogen. In this way the cyclotron proton beam current can be controlled. As of yet the limiting factor in the maximum achievable beam current at the periphery is due to filament heating limitations.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The practical control law: filament current is the beam-current knob, and the response is STEEP — Fig. 9's test filament went from essentially nothing below 4.5 A to ~3 mA emission at 5.0 A (read from the rendered figure, bias −300 VDC; the operating optimum on p.5 is −320 V). The physics under it is Richardson-Dushman: emission exponential in inverse temperature, temperature a nonlinear function of current — hence fine adjustment and a stable, monitored supply (current regulation is the natural choice; what matters is stable emission, however achieved). The author names filament heating as the beam-current limiter of record. **dg-1867** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1867 - **Rule (this site's paraphrase of the source):** The nine-inch cyclotron's source shows a visible discharge failure mode - for pressures greater than 5E-5 Torr combined with filament emission currents greater than 1 mA, a dramatic cathode ray appears running from the filament down the field lines to the bottom of the chamber, photographed through a view-port looking down the accelerating gap. - **Source quote (verbatim):** “For pressures greater than 5E-5 Torr, and filament emission currents greater than 1 mA, a dramatic cathode ray appears. Plate 3 was taken through the view-port that looks down the accelerating gap. Electrons travel down from the filament along the magnetic field lines to the bottom of the chamber.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A free visual diagnostic worth a view-port: the glowing electron column (visible above ~5E-5 Torr and ~1 mA emission ON THIS MACHINE — thresholds that belong to its geometry, gas and gauge) confirms the source is emitting and shows roughly where the ionizing column runs. The source reports the phenomenon; it neither calls it a hazard nor a limit — find your own onset conditions and use the view as qualitative confirmation, not as a calibrated marker. **dg-1868** · applicability level 2 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1868 - **Rule (this site's paraphrase of the source):** Hydrogen feed on the nine-inch cyclotron was a calibrated leak backed by a high pressure regulator taking hydrogen from a lecture bottle at a few thousand PSI down to approximately 10 PSI; the optimum hydrogen pressure in the chamber was found to be 5.5E-5 Torr, with higher pressures cutting collected beam through reduced proton mean free path and lower pressures starving the source of hydrogen to ionize. - **Source quote (verbatim):** “It was found that the optimum hydrogen pressure was 5.5E-5 Torr. Pressures higher would decrease the collected beam due to the protons decreased mean free path, while pressures lower than optimum decreased the available hydrogen of which to create ions from.” - **Source:** [Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999)](https://cyclotroninfo.com/library/#lib-284) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The clearest statement of the pressure trade for a small internal-source machine, with both sides named: too high and the protons scatter (mean free path), too low and the source starves. This machine's optimum was 5.5E-5 Torr (5.1E-5 on the run of record), about an order of magnitude above its base pressure — gauge readings and geometry make the number machine-specific, so transfer the METHOD: establish a clean base, admit hydrogen controllably, sweep pressure against collected beam, and size pumping throughput to hold the optimum you find. **dg-1885** · applicability level 2 · extraction, vacuum, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1885 - **Rule (this site's paraphrase of the source):** The author states that H- acceleration with stripping-foil extraction gives about 100% extraction efficiency, and that the one disadvantage of low-energy H- is the high vacuum it requires (the paper gives no reason; the standard one is stripping of the loosely bound electron on residual gas). - **Source quote (verbatim):** “Extraction by stripping has about 100% efficiency, low energy H¯ ions has only one disadvantage, high vacuum is required.” - **Source:** [Karamyshev, A New Design of PET Cyclotron — IPAC2022, paper THPOMS016, JACoW (2022)](https://cyclotroninfo.com/library/#lib-285) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Relevant if a tabletop machine considers H- for easy extraction. Stripping extraction approaches unity in principle; the realised figure carries foil interception, scattering and foil-lifetime losses. High vacuum is one H- requirement among others — the loosely bound electron is lost in gas collisions along the whole path, and an H- source is more complex than a proton source. 'Only one disadvantage' is the author's framing for medical cyclotrons. **dg-1892** · applicability level 4 · rf, ion-source, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-1892 - **Rule (this site's paraphrase of the source):** High RF frequency can cause poor capture at the first accelerating gap because the transit takes a large RF phase; the author's remedy is to have particles arrive at the first gap already carrying some energy so they cross it quickly. - **Source quote (verbatim):** “high frequency of RF system can potentially lead to poor capture of particles in the first accelerating gap. But this problem can be solved if in the first accelerating gap particles will arrive with some energy” - **Source:** [Karamyshev, A New Design of PET Cyclotron — IPAC2022, paper THPOMS016, JACoW (2022)](https://cyclotroninfo.com/library/#lib-285) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Transit phase across a gap is roughly Δφ ≈ 2π·f·g/v, so the comparison depends on gap width and the ion's speed at the gap as well as on frequency: at ~9 MHz (protons, h = 1, ~0.6 T) the effect is weaker than at 145 MHz for the same gap and entry energy, and it grows with a higher harmonic, a wider first gap, or a lower injection velocity. **dg-1893** · applicability level 4 · ion-source, beam-dynamics, rf · https://cyclotroninfo.com/design-guide/ion-source/#dg-1893 - **Rule (this site's paraphrase of the source):** In the JINR RC3/6 central region a PIG source held at 7500 V pre-accelerates ions to a 'Cup' electrode, so they reach the first gap with 7.5 keV; the author notes that, owing to the symmetric centre, one source can deliver beam into each gap simultaneously. - **Formula:** `ΔT = |q·ΔV| between source and Cup; the paper reports 7.5 keV from a source at 7500 V, which reads as a Cup at or near ground, but the Cup's potential is not stated (Fig. 6 labels the source 7500 V, the dees 30 kV 145 MHz, and a separate 'Dummy, Grounded' electrode).` - **Source quote (verbatim):** “Particles start from the PIG source, which is placed under 7500 V and accelerate to the “Cup” (red part on Fig. 6) and arrive to the first gap with 7.5 keV energy. Also, the advantage of such central region is that one ion source placed in the middle can deliver beam in each gap simultaneously, due to the symmetry of such central region.” - **Source:** [Karamyshev, A New Design of PET Cyclotron — IPAC2022, paper THPOMS016, JACoW (2022)](https://cyclotroninfo.com/library/#lib-285) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A DC pre-acceleration stage between an internal source and the first RF gap is a transferable central-region idea: it raises the energy entering the first gap independently of the dee voltage, which can help a low-dee-voltage tabletop machine with first-turn clearance. **dg-1895** · applicability level 4 · physics-theory, extraction, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1895 - **Rule (this site's paraphrase of the source):** The author places the limit for H- acceleration at about 70 MeV: beyond it H- ions are stripped by the magnetic field (motional electric field), forcing a lower field and therefore a larger, more expensive cyclotron. [source prints 'magnetic dissipation'; the standard term is Lorentz/magnetic stripping (dissociation)] - **Source quote (verbatim):** “The limitation for H¯ acceleration is the energy of about 70 MeV, as further acceleration would result in magnetic dissipation of H¯ ions, and require reduction of magnetic field” - **Source:** [Karamyshev, A New Design of PET Cyclotron — IPAC2022, paper THPOMS016, JACoW (2022)](https://cyclotroninfo.com/library/#lib-285) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The 70 MeV figure is the author's limit for this magnet regime. Lorentz stripping depends on energy and field together through the rest-frame electric field E′ = γβcB, so a tabletop H- design compares a cited stripping lifetime at its own E′ with the transit time rather than assuming the loss negligible; residual-gas stripping is a separate loss mechanism. **dg-1914** · applicability level 4 · physics-theory, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1914 - **Rule (this site's paraphrase of the source):** The Red Book states that the H2+ electron-capture cross section depends on the vibrational level of the incident ion, with the effect growing as energy decreases; its v = 0-3 data (A-60, from Campbell et al., accuracy unknown) show v >= 1 about 1.4-1.6x v = 0 at 4 eV/amu, with the four levels still spread by about 25 % (5.97-7.43e-16 cm2) at 0.5 keV/amu, the top of the tabulated range. - **Formula:** `A-60 (PDF p. 76) sigma_c(H2+(v) + H2) at 4 eV/amu: v=0 7.65e-16, v=1 1.20e-15, v=2 1.22e-15, v=3 1.10e-15 cm2; at 500 eV/amu: 7.20e-16, 7.43e-16, 5.97e-16, 6.59e-16 cm2` - **Source quote (verbatim):** “It is well known that the H2+ electron capture cross sections are dependent on the vibrational levels of the incident H2+ ion. See the following set of data for the magnitude of this effect which increases as the energy decreases.” - **Source:** [Barnett et al., Atomic Data for Fusion, Volume 1: Collisions of H, H2, He and Li Atoms and Ions with Atoms and Molecules — ORNL-6086/V1, Oak Ridge National Laboratory (1990)](https://cyclotroninfo.com/library/#lib-287) — p. 74 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The vibrational-state data stop at 0.5 keV/amu, so for the accelerated beam the effect enters as an additional uncertainty on the H2+ loss rather than a correction; it matters most in the source and the first gap crossings, where H2+ energies per amu are lowest. **dg-1915** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-1915 - **Rule (this site's paraphrase of the source):** At thermal to few-eV energies H2+ in H2 converts to H3+ by H2+ + H2 -> H3+ + H with a very large cross section (Red Book H-10: 1.2e-14 cm2 at 0.01 eV/amu, 1.9e-15 at 1 eV/amu, 2.2e-17 at 7 eV/amu) and a thermal rate coefficient of (2.0 +/- 0.15)e-9 cm3/s; the compilation's accuracy for the cross section is +/- 45 %. - **Formula:** `k_thermal = 2.0e-9 cm3/s ; conversion rate per H2+ = k * n_H2 ; H-10 sigma: 1e-2 1.16e-14, 1e-1 6.23e-15, 1 1.87e-15, 2 8.51e-16, 4 2.09e-16, 7 2.22e-17 cm2 (eV/amu)` - **Source quote (verbatim):** “(6) Rate coefficient k at thermal energy for production of H3+ is: k = [2.0 ± .15]x10^-9 cm3/s” - **Source:** [Barnett et al., Atomic Data for Fusion, Volume 1: Collisions of H, H2, He and Li Atoms and Ions with Atoms and Molecules — ORNL-6086/V1, Oak Ridge National Laboratory (1990)](https://cyclotroninfo.com/library/#lib-287) — p. 656 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This reaction acts predominantly before acceleration — in the source plasma and extraction region, where H2 density is highest and H2+ is slow — shifting the extracted species mix toward H3+ as source pressure rises. The cross section falls steeply but the table ends at 7 eV/amu rather than at zero, so it is usually much less important after the first substantial acceleration; include it when estimating H2+ transmission through any dense, low-energy path. **dg-1920** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-1920 - **Rule (this site's paraphrase of the source):** For slow H2+ in H2 the dominant process is H3+ formation, not charge transfer: Phelps lists H3+ + H at 78e-20 m2 at 0.1 eV against 0.28e-20 for charge transfer (slow H2+), with the two crossing between 3.16 and 4.22 eV laboratory energy; above that charge transfer dominates, peaking at 11.0e-20 m2 near 7.5 eV, while H3+ formation falls to 0.42e-20 at 10 eV. - **Formula:** `Phelps Table 4 (PDF p. 11, 1e-20 m2) H3+ / slow H2+: 0.1 eV 78 / 0.28; 1 eV 22.7 / 1.53; 3.16 eV 8.4 / 5.9; 4.22 eV 5.4 / 8.5; 7.5 eV 1.3 / 11.0; 10 eV 0.42 / 10.8; 17.78 eV 0.015 / 10.2` - **Source quote (verbatim):** “The dominant cross section for low-energy H2+ in H2 is that for the formation of H3+ + H.” - **Source:** [Phelps, Cross Sections and Swarm Coefficients for H+, H2+, H3+, H, H2, and H− in H2 for Energies from 0.1 eV to 10 keV — J. Phys. Chem. Ref. Data 19, 653 (1990)](https://cyclotroninfo.com/library/#lib-288) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** H2+ ions below roughly 3–4 eV in the source or extraction gap convert mainly to H3+; above the crossover charge transfer dominates and H3+ formation falls to about 0.15 % of the charge-transfer value by 18 eV in the table (0.015e-20 vs 10.2e-20 m2). Its absolute probability after acceleration follows from that cross section times the gas column the ions traverse, and the loss physics of the preceding rules takes over. **dg-1922** · applicability level 4 · physics-theory, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1922 - **Rule (this site's paraphrase of the source):** Collisional dissociation of H2+ depends strongly on the ion's vibrational excitation (data of Guyon et al. at 8-32 eV and of Lindsay, Yousif and Latimer at 1 keV, as reviewed by Phelps); Guyon et al. suggest this explains why low-energy H+ formation cross sections measured with H2+ made by 80-eV electron impact are much larger than those from H2+ formed in known vibrational levels. - **Source quote (verbatim):** “Data showing a strong dependence of the cross section for collisional dissociation of H2+ on the degree of vibrational excitation have been obtained” - **Source:** [Phelps, Cross Sections and Swarm Coefficients for H+, H2+, H3+, H, H2, and H− in H2 for Energies from 0.1 eV to 10 keV — J. Phys. Chem. Ref. Data 19, 653 (1990)](https://cyclotroninfo.com/library/#lib-288) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A filament or discharge source produces H2+ in a spread of vibrational states, so the dissociation part of the H2+ loss in a working machine may differ from values measured with state-selected ions; carry this as an unquantified state-distribution uncertainty on H2+ survival — its direction depends on which states the source populates relative to the reference data. The Red Book's separate note that ion-source operating conditions shifted its measured H2+ totals by up to 10 % (G-46, p. 629, carried on dg-1912) is the only scale indication in these sources. **dg-1964** · applicability level 2 · beam-dynamics, space-charge, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-1964 - **Rule (this site's paraphrase of the source):** A low-voltage thermionic electron beam can be focused by a trace of gas instead of a magnetic lens: in Johnson's 1922 Western Electric oscillograph tube (300–400 V per the synopsis, p. 1; argon-filled, p. 8), gas at a few thousandths of a millimetre of mercury shrank a spot that would be 1 cm across in a high-vacuum tube to 1 mm diameter, with the focus controlled by beam current. - **Formula:** `spot 1 cm (high vacuum) -> 1 mm (few 1e-3 mm Hg gas); beam 300-400 V` - **Source quote (verbatim):** “The method of focusing that is used in the present tubes grew out of the suggestion by Dr. H. J. van der Bijl, that a small amount of gas be introduced into the tube. This gas, at a pressure of a few thousandths of a millimeter of mercury, serves to reduce to 1 mm. diameter a spot which would be 1 cm. across in a high vacuum tube. The sharpness of the spot depends also upon the current in the electron stream so that the focus may be controlled by the cathode temperature.” - **Source:** [Johnson, A Low Voltage Cathode Ray Oscillograph — Bell System Technical Journal 1(2), 142–153 (1922)](https://cyclotroninfo.com/library/#lib-295) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Gas focusing is a no-magnet way to keep a few-hundred-volt electron beam narrow in a fill gas. A visible-beam line run in argon at a similar pressure may show this ion-channel focusing whether or not it is wanted — the effect depends on beam current and energy, geometry, residence time and pressure, so its presence and useful range are measured for the actual geometry, with fill pressure one of the knobs. Johnson worked in argon; the source has no neon data. **dg-1970** · applicability level 2 · ion-source, safety, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1970 - **Rule (this site's paraphrase of the source):** To keep his gas-filled electron gun from arcing, Johnson made the volume shared by cathode and anode very small: both were sealed into a short narrow glass tube so that the common volume was under 1 cm^3, which in his account made every inter-electrode path too short for ionization to build an arc at the operating pressure. - **Formula:** `shared electrode volume < 1 cm^3` - **Source quote (verbatim):** “All paths between the electrodes are then so short that at this low pressure there is not sufficient ionization to build up an arc.” - **Source:** [Johnson, A Low Voltage Cathode Ray Oscillograph — Bell System Technical Journal 1(2), 142–153 (1922)](https://cyclotroninfo.com/library/#lib-295) — p. 3 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Johnson's arrangement — a shared cathode–anode volume under 1 cm^3 with short paths — is one observed way to keep a gas-filled gun from arcing at his pressure. It is not a guarantee for any gun: breakdown depends on gas species, pressure–gap product, voltage, field enhancement, electrode and insulator condition and the hot cathode's own electron supply. A tabletop design checks gas-specific breakdown at its actual voltage and geometry and uses current limiting, shielding, interlocks and testing. **dg-1975** · applicability level 3 · ion-source, vacuum, safety · https://cyclotroninfo.com/design-guide/ion-source/#dg-1975 - **Rule (this site's paraphrase of the source):** The Langley electron gun put the filament and cathode shield at -10 to -40 kV with the anode and drift tube at ground (a negative shield bias set the current, 0 to 1.5 mA), and a differential-pumping section of two 0.102 cm diameter x 2.54 cm long orifices with a mechanically pumped chamber between held the gun at 2 x 10^-5 to 2 x 10^-4 mm Hg while the region outside was as high as 10 mm Hg. - **Formula:** `gun 2e-5 - 2e-4 mm Hg (2.7-27 mN/m^2) vs outside up to 10 mm Hg (1.3 kN/m^2); orifices 0.102 cm x 2.54 cm` - **Source quote (verbatim):** “The beam of electrons (0 to 1.5 mA) leaves the filament and passes through the 0.318-cm-diameter orifice in the cathode shield” - **Source:** [Hillard, Ocheltree & Storey, Spectroscopic Analysis of Electron-Beam-Induced Fluorescence in Hypersonic Helium Flow — NASA TN D-6005, Langley Research Center (1970)](https://cyclotroninfo.com/library/#lib-296) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A template for running a keV gun next to a gas-filled volume: grounded anode and drift tube, current set by a shield bias, and a two-orifice differential-pumping section between the gun vacuum and the fill. The source's remark that the grounded anode eliminates the high-voltage hazard to operating personnel is the authors' for their installation; the filament, cathode shield, feedthroughs, cabling and supply remain at −10 to −40 kV, so enclosure, interlocks, current limiting, stored-energy control, bleeders and verified discharge before access are still required. The scanned beam current prints as '1-5 mA' in the text layer; the page image reads 1.5 mA. **dg-1993** · applicability level 3 · physics-theory, ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-1993 - **Rule (this site's paraphrase of the source):** Korolov & Donkó (2015) measured the DC Paschen curve of hydrogen between 7.5 cm stainless-steel electrodes 1 cm apart: minimum breakdown at (pL)\* = 1.2 Torr cm with V_BR,min = 290 V; deuterium matched at high pressure but its minimum was about 25 V higher and its low-pL breakdown voltage significantly higher. - **Formula:** `(pL)* = 1.2 Torr cm, V_min = 290 V (H2, stainless, L = 1 cm)` - **Source quote (verbatim):** “The present measurement gives a location of the Paschen minimum at (pL)\* = 1.2 Torr cm with VBR,min = 290 V” - **Source:** [Korolov & Donkó, Breakdown in hydrogen and deuterium gases in static and radio-frequency fields — Physics of Plasmas (2015), doi:10.1063/1.4929858; arXiv:1512.08726](https://cyclotroninfo.com/library/#lib-300) — p. 4 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Referee arithmetic: a 0.1–1 Pa hydrogen fill across a few-cm gap is pL ~ 0.002–0.02 Torr cm, two to three decades left of this minimum, where the source gives no breakdown data. The Paschen/Townsend curve describes gas breakdown only — field emission, surface flashover and particulates can break down an electrode assembly well below any extrapolated gas-breakdown voltage — so it is not a hold-off or electrical-safety guarantee; test the actual assembly conservatively. Electrode material and cleanliness move the minimum and especially the low-pressure branch. **dg-2058** · applicability level 2 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2058 - **Rule (this site's paraphrase of the source):** On the modified Ohio State University cyclotron (1954) the position of the U-shaped tungsten filament relative to the vertical opening in the discharge cone was found to be critical, so the filament assembly was made to slide inside the ion-source housing and be adjusted from outside the vacuum while the beam was watched. - **Source quote (verbatim):** “Positioning of the filament with respect to the vertical opening in the discharge cone is critical. Adjustment of this relative position may be accomplished from outside the vacuum system by sliding the filament assembly inside the ion source housing and the accelerated beam monitored at the target position.” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Similar hot-filament sources may be sensitive to filament position relative to the exit opening, since where electrons enter the ionizing volume sets where ions are born relative to the dee field. An externally adjustable filament stroke lets that coordinate be scanned while vacuum is maintained, with the beam monitored at the target as OSU did, instead of being fixed by a guess at assembly; the OSU report states that the position was critical but gives no tolerance figure. **dg-2059** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2059 - **Rule (this site's paraphrase of the source):** The OSU filament-position procedure: put the beam target close to the source (8 in.) so that electric and magnetic focusing of the resonant beam does not confound the reading (the report's stated reason), hold magnetic field and dee voltage fixed, and at each filament position re-maximize the beam by adjusting filament current and arc voltage before comparing positions. - **Source quote (verbatim):** “In order to eliminate other variables, such as electric and magnetic focussing of the resonant beam, which might affect beam intensity, the water-cooled target was placed at a distance of eight inahes [sic] from the ion source. At each filament position, for a fixed magnetic field and dee voltage, the beam current was maximized by adjusting filament current and arc voltage.” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The method transfers directly as a scan protocol: one geometric variable stepped, the two electrical source variables re-optimized at every step, the machine variables frozen, and the collector at small radius so that transport losses further out are reduced (not removed: capture, focusing and centering effects remain) and mask the source effect less. Comparing positions without re-tuning filament current and arc voltage would confound geometry with emission. **dg-2060** · applicability level 3 · ion-source, vacuum, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-2060 - **Rule (this site's paraphrase of the source):** The OSU source was a low-voltage gas discharge in a small Elkonite cavity (a trade name; the report does not give the composition) at the tank centre, fed by electrons from a heated U-shaped tungsten filament, inserted at the flange plate between the dee manifolds along the diametral line between the dees; a vacuum lock on the source housing allowed filament changes without losing tank vacuum. - **Source quote (verbatim):** “The ion source is essentially a low voltage gaseous discharge confined within a small Elkonite metal cavity at the center of the cyclotron tank. The discharge is maintained by electron emission from a heated "U" shaped tungsten filament. The ion source is inserted into the vacuum tank at the flange plate between the dee manifolds and extends along the diametral line between dees. A vacuum lock is provided on the ion source housing to allow changing filaments without loss of vacuum in the cyclotron system.” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a filament-driven internal source the filament is the consumable, so the access path for replacing it is a design requirement; a vacuum lock trades mechanical complexity against a full pump-down per filament change. Whether that trade pays depends on filament life and pump-down time on the machine in question. **dg-2061** · applicability level 4 · ion-source, fabrication, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2061 - **Rule (this site's paraphrase of the source):** OSU source assembly drawing (figure reading of the hand-lettered labels; the quoted cooling-tube note is the only label transcribed verbatim here): the filament is .080-in. diameter tungsten held in copper filament clamps with Mycalex insulation, the hood is G-17 Elkonite of 1/8-in. ID and 7/16-in. OD, four 3/16-in. OD copper filament cooling tubes are noted "Insulate separately (5 V.) Insulate together (500 V.)", and the case has its own 3/16-in. copper cooling line. - **Source quote (verbatim):** “3/16" O.D. Copper filament cooling tubes - 4 - Insulate separately (5 V.) Insulate together (500 V.)” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 14 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The drawing shows the construction pattern of a 1950s high-current internal source: a refractory hood with a small bore, a thick tungsten filament, and water cooling brought right up to the filament clamps. The insulation notes, read as 5 V between the tubes and 500 V for the group, are annotated isolation relationships, not withstand ratings or design margins (the drawing does not say 500 V to what). The filament here carried about 160 A, far more than a small tungsten hairpin; the conductor sizes and cooling do not scale down unchanged. **dg-2062** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2062 - **Rule (this site's paraphrase of the source):** The OSU cyclotron's satisfactory arc operating point was 160 A of filament heater current with 60-100 V of arc voltage; the filament was the .080-in. tungsten U-filament of the assembly drawing (p. 14, dg-2061; the quoted sentence does not itself give the diameter). - **Source quote (verbatim):** “A satisfactory arc has been observed using 160 amperes filament heater current and with an arc voltage of from 60 to 100 volts.” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This is one 1954 machine's operating point for a thick-filament arc source, not a requirement. It shows that a hooded filament arc in a cyclotron centre ran with tens of volts of arc voltage; the voltage is specific to this source and gas, and a thin-wire filament runs at a small fraction of this heater current and must be characterized on its own. **dg-2063** · applicability level 3 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-2063 - **Rule (this site's paraphrase of the source):** At OSU the gas lines carried over from the earlier system were long enough that the time lag in gas-input changes prevented valid measurements of beam intensity versus gas feed; the gas-input assembly was still being modified. - **Source quote (verbatim):** “Modifications of the gas input assembly are still under consideration. The length of the existing gas lines which were adapted without major modification from the previous system causes a sufficient time lag in the variations of gas input rate to prevent obtaining valid data on this at the present time.” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A gas-feed scan is only as good as the feed's response time: a long or large-volume line between the flow control and the source integrates changes, so beam current read soon after a setting change reflects an earlier setting. Keep the controlled volume small, and rather than assuming a single line time constant, measure the source-pressure or beam step response after a setting change and wait for demonstrated settling; conductance, adsorption and source volume can make the settling non-exponential. **dg-2064** · applicability level 3 · beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2064 - **Rule (this site's paraphrase of the source):** On the OSU cyclotron the beam current read directly on the insulated target was affected by a large secondary-emission current, so the meter reading was treated as a relative tuning indication rather than an absolute measurement. - **Source quote (verbatim):** “The large secondary emission current at the target makes these readings somewhat inaccurate. However, these readings serve as a relative beam indication” - **Source:** [Hausman, Development of the Modified Ohio State University Cyclotron — Final Report, Part II, Contract AT(11-1)-158, AECU-2907, Ohio State University Research Foundation (1954)](https://cyclotroninfo.com/library/#lib-310) — p. 8 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** An unsuppressed collector can be biased by secondary-electron emission (which raises the apparent positive-ion current) or by stray-electron collection (which lowers it); the size depends on ion energy, collector material, geometry and bias. Treat the reading as relative until checked with a suppressed cup or a second, independent method. **dg-2066** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2066 - **Rule (this site's paraphrase of the source):** The calutron cathode adopted at ORNL's stable-isotope programme was a four-inch U-shaped length of 170-mil or 145-mil tantalum heated by up to 500 A; its service life varied markedly with the element processed, from 200 h (mercury) to 15-20 h (iron, titanium), with most elements 30-50 h. - **Source quote (verbatim):** “consists of a four-inch length of 170-mil or 145-mil tantalum, bent into an approximately U-shape and heated by the passage of currents up to 500 amperes. The service life of this type filament was found to vary markedly, and often unpredictably with the element being processed. For mercury separations a filament life of 200 hours was obtained, but for iron and titanium the service life was only 15 to 20 hours. For most elements the service life fell between 30-50 hours.” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 7 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** These are calutron numbers for filaments carrying hundreds of amperes; the life figures do not transfer as hours. What transfers is that filament life in an arc source is not set by temperature alone: the discharge chemistry and ion bombardment can also affect it, so life on one gas does not predict life on another. **dg-2067** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2067 - **Rule (this site's paraphrase of the source):** Yonts lists three categories of filament failure in arc ion sources: growths on the filament, alloying or chemical reaction with the processed element, and erosion (sputtering) of the region exposed to positive-ion bombardment from the arc; he states that both singly and multiply charged ions arrive at the cathode with maximum energy approximately equal to the arc voltage — read as energy per unit charge: an ion of charge ze crossing the cathode-sheath drop ΔV gains up to about zeΔV, less collisional losses. - **Source quote (verbatim):** “The reasons for filament failure fall into three general categories (1) the formation of growths on the filament, (2) alloying or chemical reaction of the filament with the element being processed, and (3) erosion or sputtering of the filament, particularly in the region exposed to bombardment by positive ions from the arc. […] Both singly and multiply charged ions are formed in the arc and all arrive at the cathode with maximum energy approximately equal to the arc voltage” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 8 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In a hydrogen source the growth and alloying categories, which the report ties to the processed metals, are not expected to dominate (the report does not test hydrogen); the sputtering mechanism remains: ions fall through the cathode sheath and strike the filament with energy set by the arc voltage and their charge state (about eΔV for a singly charged ion). Lower arc voltage means lower bombardment energy per ion, which is the lever the rest of the report exploits. **dg-2068** · applicability level 4 · ion-source, magnet, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2068 - **Rule (this site's paraphrase of the source):** In the calutron, uranium alloyed with the tantalum filament formed a low-melting growth that migrated to one side under the electromagnetic force perpendicular to both the magnetic field and the filament current; heating with alternating rather than direct current prevented growth formation. - **Source quote (verbatim):** “Filament growths have been observed only in the processing of uranium. Uranium deposited on the surface of the filament alloys with tantalum forming a low melting point alloy which migrates to one side of the filament due to electromagnetic forces perpendicular to both the magnetic field and the filament current. […] the use of alternating rather than direct filament heating current effectively prevented growth formation” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 8 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The report states the force direction and that AC heating prevented the growths; reading this as the J×B force on the heating current, with DC giving it a fixed direction and AC reversing it each half-cycle, is an interpretation consistent with the report, not its words. For a filament in a cyclotron field the same force acts on the wire itself; the report documents its effect on a liquid alloy, not on solid-wire sag. **dg-2069** · applicability level 3 · ion-source, space-charge, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2069 - **Rule (this site's paraphrase of the source):** Yonts's Child's-law estimate for the calutron: with no gas the space-charge-limited emission at 150 V across 0.5 cm is about 19 mA/cm^2 (as printed; the printed inputs give ~17), i.e. of the order of 10 mA from the ~0.5 cm^2 of a 140-mil filament facing the slot, whereas the struck arc easily draws 5 A (~10 A/cm^2); the ion sheath at the filament is what makes arc currents of amperes possible, so ions must reach the filament. The report then solves for the sheath thickness and prints x = 6.7 x 10^-2 cm, "67 mm" and "about 7 mm" (decimal points lost in the typescript; evidently 0.67 mm and 0.7 mm) [referee: its x^2 step is ×10 high; the same inputs give x ≈ 2.1 x 10^-2 cm ≈ 0.2 mm]. - **Formula:** `j = 2.334e-6·V^1.5/d^2 [j in A/cm^2, V in volts, d in cm] (printed "2 334 x 10-6"; decimals lost in the typescript). Units pass: V = 150 V → V^1.5 = 1837 V^1.5; d^2 = 0.25 cm^2 → j = 2.334e-6 × 1837 / 0.25 = 0.0172 A/cm^2 = 17 mA/cm^2 (with the report's own V^1.5 ≈ 1.9e3 it is 17.7 mA/cm^2; the printed 19 mA/cm^2 is not reproduced from the printed inputs). × 0.5 cm^2 → ~9 mA, "of the order of 10 ma" as stated. Sheath: x^2 = 2.334e-6 × 1.9e3 / 10 = 4.4e-4 cm^2 → x = 2.1e-2 cm = 0.21 mm. The report prints x^2 = "2.334 x 10^-7 x 1.9 x 10^3 = 44 x 10^-4" (the product is 4.4 x 10^-4), then x = 6.7 x 10^-2 cm (= sqrt of 44e-4), "67 mm" (p.11) and "about 7 mm" (p.12): one ×10 slip in x^2 plus dropped decimal points. Corrected sheath ≈ 0.2 mm.` - **Source quote (verbatim):** “The calculations below show that it is necessary for these ions to pass to the filament if arc currents of several amperes are to be obtained […] For V = 150 volts and d = 0.5 cm (usual calutron conditions), the emission current density is approximately 19 ma per cm² of the filament. Since the total area of a 140-mil filament facing the collimating surface slot is just over 0.5 cm², space-charge-limited current is of the order of 10 ma. When charge gas is present and the arc is struck and an ion sheath is formed, arc currents of 5 amps are easily obtainable. This is a current of 10 amp/cm² of effective filament surface. [Decimal points and the cm² superscripts are lost in the typescript scan; restored here.]” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 11 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The same physics governs a small filament source: at the calutron's 150 V across 0.5 cm, space-charge-limited emission into vacuum is of the order of milliamperes, and a different gap and voltage must be put through Child's law on their own; drawing much more current than that needs ion neutralization near the filament. The ion flux that permits the high current is the flux that sputters the filament, so emission current and filament erosion are coupled. **dg-2070** · applicability level 3 · ion-source, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-2070 - **Rule (this site's paraphrase of the source):** Calutron sources were normally run with a filament-arc regulator: the filament is operated emission-limited, arc current is set by the filament current, and when arc voltage is changed the regulator automatically trims filament current to hold arc current constant. - **Source quote (verbatim):** “Control of the arc-type ion source used in the calutron is normally obtained by use of a "filament-arc regulator" designed to permit independent adjustment of arc current and arc voltage. The filament is operated emission-limited with the limiting emission and arc current being manually adjustable by variations of the filament current. The arc voltage is also manually adjustable, but changes in arc current that would normally accompany arc voltage changes are prevented by a filament-arc regulator which automatically introduces a compensating variation in the filament current.” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** ORNL-1525 (dg-2079) places 1950s cyclotron filament sources in this same emission-limited control family (arc current set by filament temperature). Yonts's iron-separation runs with the regulator bypassed (dg-2071) are his test of its cost: a regulator that answers every disturbance by changing filament temperature can drive the filament hotter than it needs to be. **dg-2071** · applicability level 3 · ion-source, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-2071 - **Rule (this site's paraphrase of the source):** When the filament-arc regulator was bypassed and the filament run manually at essentially constant current, calutron filament life in iron-isotope separation (notoriously short) almost doubled, to 25-30 h for 170-mil filaments; this led Yonts to drop the regulator, limit arc current with a series ballast resistor and set arc voltage through arc-chamber pressure. - **Source quote (verbatim):** “Filament life was almost doubled (to 25-30 hours for 170-mil filaments) by this mode of operation” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 15 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In Yonts's iron-calutron conditions, bypassing the regulator as part of this operating change (manual control at essentially constant filament current, a series ballast, arc voltage set by pressure) nearly doubled life. For a filament source on a feedback loop, check whether the loop is moving filament temperature to chase arc or beam current; fixed filament current — not fixed temperature, since resistance and heat loss change in service — may lengthen life at the cost of output steadiness, which is a test to run, not a guaranteed trade. The doubling is a calutron result on one charge material. **dg-2072** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2072 - **Rule (this site's paraphrase of the source):** In Yonts's preliminary 16-h runs (145-mil Ta, ferrous chloride, in a small 180° Dempster-type mass spectrograph of 3-in. radius per ORNL-1758), full diode-like operation (arc drop 20 V, 2.3 A per the run summary on p. 16, whose decimals the typescript scan loses) cut average arc power from 300 W to 46 W and halved average ion output (2.0 versus 4.0 mA) while reducing filament erosion; both filaments still lost heavily to evaporation, attributed to temperatures above 2200 °C needed in the open-construction arc chamber. [Source-internal: ORNL-1525 describes one preliminary experiment on the "vapor test magnet" with an arc drop of about 18 V against a normal 80–100 V for iron, and the same 46 W / 300 W and 2 / 4 mA figures.] - **Source quote (verbatim):** “Significant differences between the two runs are (1) reduction in average arc power (46 versus 300 watts), (2) loss in average ion output current (2.0 versus 4.0 ma), (3) reduction in filament erosion. Both filaments showed a high rate of loss due to evaporation, as evidenced by visual inspection and by measurements of filament diameters. This excessive evaporation loss is attributed to the fact that filament temperatures above 2200°C were required in both runs because of low vapor density in the arc region due to open construction of the arc chamber” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 16 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In these runs, obtaining low-voltage operation required a high filament temperature, which reduced bombardment erosion while increasing evaporation, and a poorly confined discharge volume pushed the filament hotter for the same arc. That coupling is not inherent to every source; above 2200 °C these tantalum filaments in that chamber lost heavily to evaporation, and a different filament metal and diameter must be checked against its own evaporation data. **dg-2073** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2073 - **Rule (this site's paraphrase of the source):** Diode-like operation lost output because the arc did not fill the arc chamber (bright at the filament end, weak at the far end); raising the arc voltage from 38 V to 80-100 V by slightly reducing filament temperature made the arc extend the full length and restored output to near that of normal 150-175 V operation, with substantially longer filament life ('modified diode' operation) [Source-internal: ORNL-1758 gives the SiCl4 diode voltage as 38 V, ORNL-1525 as 45 V; both give 80–100 V for modified diode.] - **Source quote (verbatim):** “In appearance, the arc was extremely bright at the filament end and very weak at the opposite end of the arc chamber. On increasing the arc voltage from 38 volts (the normal diode voltage for SiCl4 charge) to 80-100 volts the arc was observed to extend the full length of the arc chamber, and the ion output rose to about the value characteristic of normal operating voltage (150-175 volts). This increase of voltage across the arc was accomplished by reducing the filament temperature slightly. This type of operation, called modified diode operation, was used in runs 8, 9, 15, and 17, and resulted in a substantial increase in service life of the filament over that of normal operation with little, if any, loss of output.” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 21 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The arc must reach the region from which ions are drawn; the visible length of the discharge is a qualitative diagnostic, to be confirmed by extracted-current or plasma-density measurement. In a small source the ionizing volume is short, but the same balance applies: arc voltage high enough to sustain ionization where the ions are extracted, no higher than needed, since bombardment energy rises with it. **dg-2074** · applicability level 4 · ion-source, materials, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2074 - **Rule (this site's paraphrase of the source):** Yonts measured calutron filament temperature with an optical pyrometer through a quartz window, correcting brightness temperature to true temperature: normal operation 1950-2000 °C, modified diode 2000-2075 °C, full diode 2100-2150 °C; tantalum evaporation in this range was under 1 mg/h, and for the SiCl4 runs the report states (p. 18) that ion erosion was the predominant factor. - **Source quote (verbatim):** “The filament temperature was measured with a Leeds and Northrup optical pyrometer sighted on the filament through a quartz window. The observed "brightness temperatures" were corrected by use of the temperature correction curves given in Figure 9 […] For normal operation the filament temperature was in the range 1950°C to 2000°C. For modified diode type operation the temperature range was 2000°C to 2075°C and for diode type operation the temperature range was 2100 - 2150°C. It has been shown by Normand that evaporation loss from tantalum filaments in this operating range is less than 1 milligram per hour” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 24 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Optical pyrometry through a window, with the brightness-to-true correction for the filament metal (window transmission and spectral emissivity accounted for), gives the temperature from which the evaporation contribution to filament loss can be estimated; whether sputtering dominates needs separate operating or wear data, not pyrometry alone. The quoted temperatures belong to these thick tantalum filaments; the evaporation rate for a thin tungsten wire must be taken from tungsten data at its own diameter. **dg-2075** · applicability level 3 · ion-source, controls, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2075 - **Rule (this site's paraphrase of the source):** Track filament erosion on line from the decay of filament heating current: Yonts plotted filament-transformer primary current against time, its fall reflecting net erosion, and states that the time to fall through a fixed current range is inversely proportional to the average erosion rate, which he used to compare operating modes. - **Source quote (verbatim):** “These decay times are inversely proportional to the average filament erosion rates during the selected period of operation” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 29 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A logged filament current (or resistance, from current and voltage) is an inexpensive wear gauge for a characterized filament run from a stable, specified heater supply under otherwise constant conditions: with the heater at fixed voltage the current falls as the wire thins. A trend indicates wear; converting its slope to an erosion rate needs calibration (for instance against weighed filaments) and exclusion of thermal and electrical causes such as temperature, resistivity, supply regulation and contact resistance. The calutron figures (4.8 A to 3.0 A transformer-primary current) are specific to that supply. **dg-2076** · applicability level 3 · ion-source, space-charge, beam-dynamics · https://cyclotroninfo.com/design-guide/ion-source/#dg-2076 - **Rule (this site's paraphrase of the source):** At constant pressure and filament current, measured ion current at the receiver peaked and then fell as arc current rose, because rising ion density in the exit region produced strong defocusing; Yonts warns that the optimum arc condition is specific to the electrode configuration and the accelerating and focusing voltages. - **Source quote (verbatim):** “Total ion output probably does continue to increase with increasing arc current, but as ion density in the ion exit region increases, a strong defocusing action arises to reduce the ion current entering the receiver. […] The exact values of arc current and voltage at which strong defocusing sets in depends on both the configuration of the accelerating electrode system and on the accelerating and focusing voltages applied. Consequently, the optimum arc conditions found for a particular source unit may not apply to a unit having a different electrode configuration, nor to the same unit operated at different accelerating or focusing voltages” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 36 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The useful figure of merit is the beam that arrives where it is wanted, not arc current: pushing the arc harder can lower delivered beam. In a cyclotron the dee voltage affects first-gap extraction, acceleration and focusing in the way the calutron's accelerating and focusing voltages do, so a source optimum found at one dee voltage should be re-measured at another. **dg-2077** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2077 - **Rule (this site's paraphrase of the source):** With arc conditions set for maximum received ion current, 13-h optimized runs weighed before and after gave filament weight loss of 95.5 mg/h in normal operation and 49.4 mg/h in modified-diode operation, a reduction of almost 50 %; the report states elsewhere (p. 18) that ion erosion was the predominant loss factor in its calutron runs. - **Source quote (verbatim):** “Taking as optimum those values of arc current and voltage for which the maximum ion current at the receiver was obtained, (Figures 16 and 17) optimized runs were made with normal and with modified-diode operation. Each of these runs was of 13 hour duration, and the filaments used were weighed before and after running to provide a quantitative comparison of filament erosion under the two types of operation. In normal operation, filament weight loss occurred at the rate of 95[.]5 mg/hr, while with modified-diode operation the rate of weight loss was only 49[.]4 mg/hr, a reduction of almost 50 per cent” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 36 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Weighing the filament before and after a timed run is a net mass-loss measurement that can be repeated at small scale with a microbalance; deposits, oxidation or material transfer can confound it, so blanks, cleaning controls and inspection for deposition are needed before reading it as erosion. The rates are for 140–170-mil tantalum in a TiCl4 calutron arc and are not a prediction for a thin hydrogen-source filament. Table IV marks the 95.5 mg/h normal run "Receiver shorted on this run" (30 mA average output against 41.6 mA for the 49.4 mg/h modified-diode run), so the output comparison for that pair is not clean. **dg-2078** · applicability level 4 · ion-source, materials, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2078 - **Rule (this site's paraphrase of the source):** Yonts's empirical erosion fit for the calutron filament (TiCl4 charge): weight loss per ampere-hour of arc current scales as (arc power)^(3/5), J/I = A·P^(3/5) with A = 0.36, a form suggested by Townes's cold-cathode sputtering law; in conclusion, full diode operation minimized wear but reduced output 'to the point of uselessness', while modified diode gave about normal output with useful life increased by a factor of at least 2 (ORNL-1758 p.38 of the report) [ORNL-1525: a factor of 2 to 3]. - **Formula:** `J/I = A·P^(3/5) with A = 0.36 (printed "0 36"), J in mg/h, I in A, P in W → J/I in mg/(A·h), A in mg/(A·h·W^0.6). Units check vs Table IV run 1: P = 798.8 W → P^0.6 = 55.1 (table 55.2) → 0.36 × 55.1 = 19.9 mg/(A·h); measured 95.5 mg/h / 5.03 A = 19.0 mg/(A·h) (table "Actual J/I" 18.98). Consistent to ~5 %. [Source-internal: Table IV's computed J/I column (20.9, 19.6, 16.1 …) implies a coefficient ≈ 0.37, not 0.36; its run-9 P^3/5 entry 38.7 does not match 635.1^0.6 = 48.0.]` - **Source quote (verbatim):** “It has also been shown that operation of the full diode type reduces filament wear to a minimum but also reduces ion output to the point of uselessness” - **Source:** [Yonts, Filament Life in Low Pressure Arc Type Ion Source — ORNL-1758, Oak Ridge National Laboratory (1954)](https://cyclotroninfo.com/library/#lib-311) — p. 42 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The fitted coefficient and exponent belong to that calutron, charge material and operating range, and the fit is for the normalized loss J/I, so total erosion J has no simple sub-linear law in P unless arc current is held fixed. The transferable content is the method — plot weight loss per ampere-hour against arc power and fit — and the finding that the operating mode that minimizes wear is not the one that maximizes useful output, so the choice is a compromise set by measurement. **dg-2079** · applicability level 3 · ion-source, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-2079 - **Rule (this site's paraphrase of the source):** Yonts (ORNL-1525) states that the normal control mode of many arc-type ion sources, naming high-current calutron and cyclotron sources, is to control the arc by changing filament temperature, because this allows independent adjustment of arc voltage and arc current. - **Source quote (verbatim):** “The normal operation of many arc-type ion sources (in particular, various high-current calutron and cyclotron sources) involves control of the arc by changing filament temperature. This type of control is generally used because it permits independent adjustment of arc voltage and current (Fig. 1).” - **Source:** [Yonts, Filament Life Extension in High-Intensity Ion Sources — ORNL-1525, Oak Ridge National Laboratory (1953)](https://cyclotroninfo.com/library/#lib-312) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The statement places 1950s cyclotron filament sources in the same control family as calutron sources, which motivates checking a cyclotron filament source for an analogous erosion/output trade-off; the calutron's quantitative result need not carry over, since gas species, sheath voltage, cathode material and ion flux change it. It applies to emission-limited filament arcs; a source run without an arc (pure electron impact) has no arc voltage to trade. **dg-2080** · applicability level 4 · ion-source, materials, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2080 - **Rule (this site's paraphrase of the source):** Yonts contrasts arc-source practice with the gas-filled diode: there the tube runs on the nearly vertical part of the emission curve with an arc drop near the gas ionization potential, and filaments last a very long time provided the positive-ion energy stays below a critical value that depends on the gas (he cites 22 V for mercury-vapour diodes), which is why oxide-coated or thoriated-tungsten filaments are usable in diodes. - **Source quote (verbatim):** “The filaments give extremely long life, provided the velocity of the positive ions does not exceed some critical value (22 volts in mercury vapor diodes) which depends on the type of gas in the tube.” - **Source:** [Yonts, Filament Life Extension in High-Intensity Ion Sources — ORNL-1525, Oak Ridge National Laboratory (1953)](https://cyclotroninfo.com/library/#lib-312) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The physics behind low-voltage operation as Yonts presents it: below some ion energy, cathode sputtering is small enough that low-work-function cathodes survive. The 22 V is his reported operating limit for mercury-vapour diodes, not a universal threshold: sputtering depends on projectile and cathode material, incidence angle, charge state and surface condition, so any hydrogen-source limit must be established for the particular ion species, cathode material and sheath conditions; low ion energy only tends to reduce sputtering, and an oxide cathode can also fail by poisoning or chemical attack. **dg-2081** · applicability level 4 · ion-source, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-2081 - **Rule (this site's paraphrase of the source):** The ORNL circuit change for diode-like operation was simple: a ballast resistance — four 150 W incandescent bulbs in parallel — in series with the arc supply, arc current set with the supply voltage (through the induction regulator normally used to change arc voltage) and filament temperature with the maximum-filament-current control. - **Source quote (verbatim):** “of four 150-watt incandescent bulbs in parallel was inserted in series with the arc supply. Arc current was adjusted by changing the supply voltage by means of the induction regulator normally used to change arc voltage. Filament temperature was adjusted by means of the maximum-filament-current control mentioned previously.” - **Source:** [Yonts, Filament Life Extension in High-Intensity Ion Sources — ORNL-1525, Oak Ridge National Laboratory (1953)](https://cyclotroninfo.com/library/#lib-312) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A series ballast lets the arc find its own voltage at a current set jointly by the supply voltage and the ballast's nonlinear load line, which is one way to try low-voltage (diode-like) operation on a filament arc without a regulated supply. Lamps as ballast have a resistance that rises with current; that behaviour, and the bulb rating needed, depend on the arc current of the source in question. **dg-2082** · applicability level 3 · ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2082 - **Rule (this site's paraphrase of the source):** ORNL-1525's conclusions: true diode operation greatly increased filament life with about 50 % loss of ion output, while modified diode operation increased filament life by a factor of 2 to 3 with no significant output loss; the author listed cyclotron sources with hydrogen or deuterium, and thoriated-tungsten or coated filaments, as untested next steps. - **Source quote (verbatim):** “It has been shown that true diode operation greatly increases filament life and results in an ion output loss of about 50%, but that modified diode operation increases filament life by a factor of 2 to 3 and causes no significant loss in output. Further experimentation is desirable along the following lines: (1) to investigate applications to other ion sources such as those used in cyclotrons, […] (3) to study charge materials other than silicon and iron, (4) to investigate thoriated tungsten or coated filaments, particularly in a cyclotron type of source with deuterium or hydrogen charges” - **Source:** [Yonts, Filament Life Extension in High-Intensity Ion Sources — ORNL-1525, Oak Ridge National Laboratory (1953)](https://cyclotroninfo.com/library/#lib-312) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The factor 2-3 is a calutron result on silicon and iron charges; Yonts explicitly left the cyclotron hydrogen case uninvestigated. The testable idea for a hydrogen filament source is the same: hold arc current by ballast, raise filament temperature modestly to lower the arc voltage, and measure beam and filament wear against the normal mode. **dg-2083** · applicability level 4 · ion-source, vacuum · https://cyclotroninfo.com/design-guide/ion-source/#dg-2083 - **Rule (this site's paraphrase of the source):** In ORNL-1525 the arc-power-versus-filament-life correlation shifted with the gas-baffle geometry across the arc chamber behind the collimating slot (Figs. 6 and 8, whose captions name the quantity "arc power"; the horizontal axis is the time for filament primary current to decay to 3.0 A, the report's life measure; figure reading: the 3/16-in. baffle curve runs at roughly 550–700 W for 20–70 h, the 1/4-in. curve at roughly 300–380 W for 10–35 h), and Yonts recommended further study of the baffle's effect. - **Source quote (verbatim):** “The curve showing power dissipation vs. filament life is apparently affected by the gas-baffle geometry in the arc chamber (Figs. 6 and 8). Further investigations of the effect of this baffle on filament life should be performed. […] Fig. 8. Influence of Arc Power on Useful Filament Life.” - **Source:** [Yonts, Filament Life Extension in High-Intensity Ion Sources — ORNL-1525, Oak Ridge National Laboratory (1953)](https://cyclotroninfo.com/library/#lib-312) — p. 9 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The source gives no mechanism; it records that the baffle geometry moved the measured arc-power-versus-life curve. In a small source the hood or chimney bore plays the baffle's role, so a change in that geometry should be expected to move the life-versus-power relation and needs re-measuring. **dg-2084** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2084 - **Rule (this site's paraphrase of the source):** Smyth (Princeton, 1925) concluded from magnetic-deflection ion analysis that the only primary product of electron-impact ionization in hydrogen is H2+, with H+ arising by secondary dissociation of H2+ even when the electron energy is just above 16 V and H3+ appearing in large numbers as a secondary product at any voltage above 16 V — a 1925 interpretation under his apparatus conditions (see the note). - **Source quote (verbatim):** “However, atomic ions H+ are readily produced by secondary dissociation of molecular ions H2+ even when the maximum electron energy is just above 16 volts.” - **Source:** [Smyth, Primary and Secondary Products of Ionization in Hydrogen — Physical Review 25, 452 (1925)](https://cyclotroninfo.com/library/#lib-313) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Smyth's conclusion is a 1925 reading of one apparatus. Modern data separate the channels: H2+ formation opens at the H2 ionization energy, 15.426 eV, and direct dissociative ionization H2 + e → H+ + H + 2e opens at an appearance energy of 18.078 eV (NIST Chemistry WebBook, hydrogen ion-energetics page, retrieved 2026-10-25), so H+ is not only a secondary product; H3+ is chiefly made by the ion–molecule reaction H2+ + H2 → H3+ + H. For a filament source in hydrogen the species mix is therefore set by electron energy (which primary channels are open) together with gas density, the field and the ions' path and residence time (how much secondary chemistry occurs). **dg-2085** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2085 - **Rule (this site's paraphrase of the source):** In Smyth's apparatus (electron energy V1 = 25 V, ion-drift voltage V2 = 9 V) H2+ dominated at low pressure — at 0.0007 mm Hg the spectrum was essentially H2+ — while at 0.053 mm the H2+ peak was almost suppressed and H3+ and H+ were strong. Figure reading of Fig. 4: H2+ peaks near 0.002 mm and falls steeply; H3+ overtakes it near 0.012–0.015 mm and peaks near 0.03 mm; H+ (plotted ×10) keeps rising to 0.07 mm. - **Source quote (verbatim):** “Curve B in Fig. 3 taken at p=.053 mm shows the H2+ peak almost suppressed but H3+ and H+ strong.” - **Source:** [Smyth, Primary and Secondary Products of Ionization in Hydrogen — Physical Review 25, 452 (1925)](https://cyclotroninfo.com/library/#lib-313) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The pressures are those of Smyth's ionization region with fixed fields, electron energy and path length: there, raising pressure suppressed H2+ and strengthened H3+ and H+. What transfers to another source is the collision-depth comparison (gas density times path length, or residence time), not the direction of the H+ change, which depends on the electron-energy distribution, ion collision energy and competing reactions and must be measured or modelled for the source in hand. **dg-2086** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2086 - **Rule (this site's paraphrase of the source):** From fitting H2+ intensity against pressure, Smyth concluded that the H2+ ion is dissociated about 15 times more readily than a kinetic-theory collision rate would give — it travels on average only about 1/15 of the ordinary molecular free path before being destroyed. - **Formula:** `λ_destroy = 1/(n2·p) with n2 ≈ 1100 per cm of path at 1 mm Hg (Smyth's fit in his apparatus, drift field V2/d2 = 9 V/0.8 cm). Units: n in collisions per cm at 1 mm Hg. Smyth takes 1/n0 ≈ 4√2 × molecular free path with n0 = 12.7 /cm, so his molecular rate ≈ 4√2 × 12.7 ≈ 72 /cm (free path ≈ 0.014 cm at 1 mm); 1100/72 ≈ 15. Example: p = 1e-3 mm Hg (0.13 Pa) → λ ≈ 1/1.1 cm ≈ 0.9 cm; p = 1e-4 mm Hg (0.013 Pa) → λ ≈ 9 cm.` - **Source quote (verbatim):** “the distance an H2+ ion travels on an average before being dissociated by the proximity of another molecule is about 1/15 the ordinary molecular free path.” - **Source:** [Smyth, Primary and Secondary Products of Ionization in Hydrogen — Physical Review 25, 452 (1925)](https://cyclotroninfo.com/library/#lib-313) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The short destruction length means H2+ survives only where gas density times path length is small: on Smyth's fitted value, about 0.9 cm of path at 1e-3 mm Hg and about 9 cm at 1e-4 mm Hg (formula). Where a source's pressure and ion path put the product near or above one destruction length, the molecular-ion fraction will track pressure strongly; the fitted rate belongs to Smyth's fields and ion energies and must be re-measured for another geometry. **dg-2087** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2087 - **Rule (this site's paraphrase of the source):** Smyth found H+ always relatively much stronger than H3+ at higher values of V2, the field through which ions drift after formation; he explains that faster ions associate with neutral molecules less readily while dissociation continues. Figure reading of Fig. 5 (V2 = 25 V, p ≈ 0.045 mm): H+ peak tallest, H3+ next, H2+ smallest. [Notation: Smyth's V1 is the electron energy, V2 the field across the ionization region and V3 the analyser accelerating voltage; Hogness and Lunn use (V1+V2) for electron energy, V3 for the ion draw-out (electron-retarding) field and V4 for acceleration, so Smyth's V2 corresponds to their V3 (they call it V3 when citing Smyth's Fig. 6, p.9 of their paper). The subscript on p.12 is hard to read in the scan; the "only condition varied" sentence fixes it as V2.] - **Source quote (verbatim):** “It was found that H+ was always relatively much stronger at higher values of V2” - **Source:** [Smyth, Primary and Secondary Products of Ionization in Hydrogen — Physical Review 25, 452 (1925)](https://cyclotroninfo.com/library/#lib-313) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The transfer is a testable hypothesis, not a prediction: in a cyclotron source the local extraction or bias field at the source exit — distinct from the dee voltage itself, which is RF, phase-dependent and may be screened inside the source — changes ion residence time and so may alter the species mix. Faster removal can also preserve H2+ rather than shift H3+ toward H+. This is a 1925 tube result; the direction and size of any shift in a particular source must be measured. **dg-2088** · applicability level 4 · ion-source, physics-theory, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2088 - **Rule (this site's paraphrase of the source):** Smyth reports that the apparent appearance potential of H+ or H3+ can be observed anywhere between 16 and 21 V depending on pressure and fields, and concludes that H3+ and H+ may appear as secondary products as soon as H2+ is formed; on his reading, measured 'critical potentials' for the secondary species reflect the tube conditions rather than separate primary processes. - **Source quote (verbatim):** “an apparent critical potential for H+ or H3+ may be observed anywhere between 16 and 21 volts if conditions are properly chosen and not varied.” - **Source:** [Smyth, Primary and Secondary Products of Ionization in Hydrogen — Physical Review 25, 452 (1925)](https://cyclotroninfo.com/library/#lib-313) — p. 15 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A species threshold measured on one source by sweeping electron energy says as much about that source's pressure and geometry as about hydrogen; the 16–21 V range is Smyth's observed apparent-onset range. Modern thresholds separate the channels: H2+ opens at 15.426 eV and direct dissociative production of H+ at 18.078 eV (NIST Chemistry WebBook, hydrogen ion-energetics page, retrieved 2026-10-25), so electron energy does change which primary channels are open, while pressure and residence time set the secondary chemistry. Just above threshold the H2 ionization cross section rises with electron energy; it peaks and then falls, so more energy is not simply more yield. **dg-2089** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2089 - **Rule (this site's paraphrase of the source):** Hogness and Lunn (California, 1925) measured the H+/H2+/H3+ mix from below 1e-5 mm to 0.006 mm Hg and electron energies to 60 V: at low pressure only H2+ forms, H3+ rises in proportion to pressure up to 60 %, and in their apparatus H+ did not exceed 4 % (abstract). [Source-internal: Table I lists H+ up to 4.6 % (at 39 × 1e-4 mm) and H3+ up to 57.8 %, against the abstract's "did not exceed 4 percent" and "reached 60".] - **Source quote (verbatim):** “At low pressures only H2+ ions are formed; as the pressure is increased the percentage of H3+ increases in proportion to the pressure. In the apparatus used, the percentage of H+ increased with pressure but did not exceed 4 percent” - **Source:** [Hogness & Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis — Physical Review 26, 44 (1925)](https://cyclotroninfo.com/library/#lib-314) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This is the second independent 1925 measurement agreeing with Smyth that H2+ dominated the low-pressure spectrum and that H3+ was secondary. The low H+ fraction is specific to their tube, drawing-out field and sensitivity: H+ also has a direct dissociative-ionization channel from H2 (appearance energy 18.078 eV, NIST Chemistry WebBook, hydrogen ion-energetics page, retrieved 2026-10-25), open at their electron energies, and both papers show more H+ with stronger fields along the ion path. **dg-2090** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2090 - **Rule (this site's paraphrase of the source):** Hogness and Lunn's Table I (pressure in units of 1e-4 mm Hg, electron energy 48 V): 2.0 → ~97 % H2+, 2 % H3+, ~1 % H+; 11-12 → ~80-87 % H2+, 12-18 % H3+; 28 → ~67 % H2+, ~30 % H3+; 56 (0.0056 mm) → 39 % H2+, ~58 % H3+, ~3 % H+. Figure reading of Fig. 2: H2+ and H3+ cross near 0.0045 mm (interpolating Table I gives ~0.0047 mm). - **Formula:** `Units: 56 × 1e-4 mm Hg = 5.6e-3 Torr = 0.75 Pa; 2.0 × 1e-4 mm Hg = 2e-4 Torr = 0.027 Pa (1 Torr = 133.3 Pa)` - **Source quote (verbatim):** “Electrometer readings for H+, H2+ and H3+ peaks, at various pressures.” - **Source:** [Hogness & Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis — Physical Review 26, 44 (1925)](https://cyclotroninfo.com/library/#lib-314) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The table gives the measured shape of the species-versus-pressure curve for one positive-ray tube. The crossover sits at a lower pressure than the figure reading of Smyth's Fig. 4 recorded under dg-2085 (H3+ overtaking H2+ near 0.012–0.015 mm); different ion path lengths are one plausible apparatus-dependent cause, not an established explanation, and a source's own crossover depends on its geometry and other parameters and must be measured. **dg-2091** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2091 - **Rule (this site's paraphrase of the source):** When Hogness and Lunn raised the field drawing ions out (their V3, which corresponds to Smyth's V2) of the ionization chamber, so that ionization occurred only in its upper part and ions had a longer path, (H+ + H3+) rose relative to H2+ and the H+/H3+ ratio rose considerably; their 1925 interpretation is that H2+ ions gaining energy before collision break up more often, the H+ formed escaping instead of being captured into H3+. - **Source quote (verbatim):** “When the field V3 for drawing the positive ions from the ionization chamber was increased to such an extent that only those electrons in the upper portion of that chamber had ionizing energy, then the intensity of (H+ + H3+) increased with respect to that of H2+ as might have been expected since the H2+ ions formed had greater chance of collision having had a longer average path to traverse. Moreover the ratio of the intensity of H+ to that of H3+ increased considerably. This can be explained by assuming that under these conditions H2+ breaks up more often in accordance with reaction (4). This would happen if when the H2+ ion acquires sufficient energy before colliding, the H+ formed by disruption were not trapped by the H2 molecule to form H3+ but passed on into the resolving chamber.” - **Source:** [Hogness & Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis — Physical Review 26, 44 (1925)](https://cyclotroninfo.com/library/#lib-314) — p. 5 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Ion path length through gas and the energy ions gain along it both move the species mix; in a cyclotron source these are set by where the filament's electrons ionize relative to the exit and by the field at the exit. The mechanism is the authors' historical reading (the fast H3+ channel in modern terms is H2+ + H2 → H3+ + H, not capture of H+); the effect is described qualitatively, and its size in a given source must be measured. **dg-2092** · applicability level 3 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2092 - **Rule (this site's paraphrase of the source):** Hogness and Lunn's summary recipe for which hydrogen ion predominates in a discharge tube: H+ with a large potential difference plus some inert gas such as helium; H2+ at low pressure; H3+ at higher pressure and small potential difference. With helium and a little hydrogen the last line of their Table I reads 68.6 % H+, 31.4 % H2+ and no H3+ (table reading). - **Source quote (verbatim):** “It was found that the percentage of H+ was much greater than in pure hydrogen at any pressure employed (see the last line of Table 1). […] For H+, large potential difference and the addition of some inert gas such as helium; for H2+, low pressures; for H3+, higher pressure and small potential difference.” - **Source:** [Hogness & Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis — Physical Review 26, 44 (1925)](https://cyclotroninfo.com/library/#lib-314) — p. 9 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This gives the direction of each knob for a hydrogen filament source: pressure, and the applied potential in their tube (the draw-out field V3), which is not interchangeable with a generic source field without identifying which electrodes and ion energies are affected. The helium-admixture result shows that collision partners matter as well as density; using it on a cyclotron would change gas load and discharge behaviour, and the paper does not test that. **dg-2093** · applicability level 4 · ion-source, physics-theory · https://cyclotroninfo.com/design-guide/ion-source/#dg-2093 - **Rule (this site's paraphrase of the source):** Hogness and Lunn found that lowering electron energy from 48 V toward 18 V at fixed pressure raised the H3+ percentage, and suggest ("may be explained") that in their tube the stronger retarding field moved ionization farther from the exit gauze, lengthening the ion path, rather than the impact energy being responsible. - **Source quote (verbatim):** “The increase in the percentage of H3+ as (V1+V2) was decreased may be explained as due to the characteristics of the discharge tube. The now greater retarding potential V3 decreased the velocity of those electrons that had penetrated into the lower part of the ionization chamber to such an extent that they could not ionize the gas. The H2+ ions were then formed at a greater average distance from the gauze J, and having had a longer average path to traverse had greater chance to collide.” - **Source:** [Hogness & Lunn, The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis — Physical Review 26, 44 (1925)](https://cyclotroninfo.com/library/#lib-314) — p. 6 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In a filament source, changing electron energy can also change where ionization happens, so an apparent energy dependence of the species mix may be a geometry effect; whether an arc or bias scan moves the place of ion birth depends on the electrode geometry and must be checked rather than assumed. **dg-2094** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2094 - **Rule (this site's paraphrase of the source):** On the SC200 hot-cathode PIG test bench (1 T, arc 170 V, 2 sccm H2) arc current was a steep function of filament heating current: by figure reading the thin filament went from ~3 mA at ~177 A to ~18 mA at ~190 A, and the thick filament from ~0 at ~192 A to ~40 mA at ~220 A — a few-percent change in heater current moved arc current several-fold, so on this bench filament heating current was a highly sensitive source knob. - **Formula:** `Fig. 4 readings (labelled, ±1 mA / ±1 A): thin 177 A→3 mA, 186 A→10 mA, 190 A→18 mA; thick 192 A→0, 196 A→4 mA, 200 A→20 mA, 210 A→35 mA, 220 A→40 mA. Thin: ×6 arc current for +7% heater current (190/177 = 1.073, dimensionless).` - **Source quote (verbatim):** “With the increase of filament current, arc current rises rapidly in both thick filament and thin filament.” - **Source:** [Zhao, Xu, Chen et al. (ASIPP / USTC), Recent Progress on Ion Source of SC200 Cyclotron — Cyclotrons 2019, paper MOP002, JACoW (2019)](https://cyclotroninfo.com/library/#lib-315) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Interpretation (not stated by the authors): the steepness reflects the strong (Richardson) temperature dependence of thermionic emission, which is not specific to a PIG, so a small filament source may also respond strongly to small heater-current changes, though other discharge limits can dominate. The SC200 currents (175–220 A) and arc currents belong to that source and do not scale to a fine-wire filament. Measure the local heater-current-to-arc-current transfer curve on the source in hand, then choose the heater supply's resolution and stability from the arc-current repeatability wanted. **dg-2095** · applicability level 3 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2095 - **Rule (this site's paraphrase of the source):** SC200 compared a thin bent-plate filament (run at 175 A) with a variant thickened at the base for mechanical strength (run at 215 A, same 1 T / 170 V / 2 sccm conditions) and adopted the thin one, which met the >100 µA target at the lower heater current — even though, by figure reading, the thick filament gave more beam at equal extraction voltage (~72 vs ~46 µA at 6 kV; ~104 vs ~80 µA at 7.5 kV). The trade is beam margin versus heater current. - **Formula:** `Fig. 5 readings (labelled; the caption says "thin filament" but the legend plots both): thin 6 kV→~46 µA, 7 kV→~70, 7.5 kV→~80, 8 kV→~94, 9 kV→~100, 9.5 kV→~110 µA; thick 6 kV→~72, 7 kV→~96, 7.5 kV→~104 µA. Conditions 1 T, 170 V arc, 2 sccm; extraction gap ~2 mm, slit 4.3 × 1 mm (p. 1).` - **Source quote (verbatim):** “The thin filament current is set to 175 A, while the thick filament current is set to 215 A. With a current of more than 100 µA, we chose the thin filament as the final filament” - **Source:** [Zhao, Xu, Chen et al. (ASIPP / USTC), Recent Progress on Ion Source of SC200 Cyclotron — Cyclotrons 2019, paper MOP002, JACoW (2019)](https://cyclotroninfo.com/library/#lib-315) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The transferable point is the trade: on this bench the thickened variant required more heater current under its tested operating points, while the thin one met the beam target. Heater demand, J×B load in the field, supply size and lifetime are quantities to re-evaluate for each filament redesign; added metal does not by itself predict any of them. The SC200 numbers are that source's and set expectations for nothing smaller. **dg-2096** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2096 - **Rule (this site's paraphrase of the source):** Thickening a filament for strength can defeat itself: on the SC200 bench the authors report that high filament current causes permanent damage and makes breakage more likely, and their Fig. 6 shows the base-thickened ("thick") filament fractured at high current. - **Formula:** `thick filament needed 215 A vs 175 A for the thin one (215/175 = 1.23, i.e. +23%); Fig. 6 caption: "Fracture of thick filament at high current" (p. 3); image reading: the break is at the foot of one leg, near the mounting tab. Mechanism of the fracture is not analysed in the paper.` - **Source quote (verbatim):** “In addition, high current will cause permanent damage to the filament and more easily cause the filament to break, as shown in Fig. 6.” - **Source:** [Zhao, Xu, Chen et al. (ASIPP / USTC), Recent Progress on Ion Source of SC200 Cyclotron — Cyclotrons 2019, paper MOP002, JACoW (2019)](https://cyclotroninfo.com/library/#lib-315) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This is the SC200 authors' observation on one filament design, not a general strength law. It is a reason to qualify any filament redesign by running it at its real heating current (and in the real field) before trusting it, rather than assuming extra metal means extra life. **dg-2097** · applicability level 3 · ion-source, beam-measurement, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-2097 - **Rule (this site's paraphrase of the source):** The SC200 group, whose bench magnet reached 1 T, took the source to an external high-field laboratory for repeated runs at 3 T — a test of the source at a field representative of the cyclotron centre region, although the cited text reports no 3 T result. The abstract reports a filament lifetime above 100 h and >100 µA extracted, while the body shows only a 1 h discharge and 0.5 h extraction stability record. - **Formula:** `bench field ≤1 T (p. 1); stability test 1 h discharge / 0.5 h extraction (p. 2, Fig. 7); lifetime >100 h (abstract, p. 1, conditions not stated). Derived J×B load per unit length (units: A × T = N/m), hypothetical local maxima assuming the bench currents of 175–215 A at 3 T and a conductor perpendicular to B: 525–645 N/m; at 1 T, 175–215 N/m — a factor 3 between bench and 3 T.` - **Source quote (verbatim):** “we went to the high magnetic field laboratory of the Chinese Academy of Science and carried out repeated experiments under the 3T magnetic field generated by their equipment.” - **Source:** [Zhao, Xu, Chen et al. (ASIPP / USTC), Recent Progress on Ion Source of SC200 Cyclotron — Cyclotrons 2019, paper MOP002, JACoW (2019)](https://cyclotroninfo.com/library/#lib-315) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A filament tested on the bench with the magnet off has not been tested against its in-field load; the J×B force exists only with the field on. A small machine can run the same check in its own magnet before a beam campaign. The >100 h figure is the authors' claim for their source with unstated conditions. **dg-2098** · applicability level 3 · beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2098 - **Rule (this site's paraphrase of the source):** A source test bench can measure total extracted ion current with a simple collector: space-limited, SC200 used a bent copper block in place of a Faraday cup behind a 4.3 × 1 mm extraction slit ~2 mm from the source — which measures the total of all extracted current, with no species separation or secondary-electron suppression reported. - **Formula:** `extraction electrode ~2 mm from source, slit 4.3 mm × 1 mm × 1 mm thick, negative DC extraction 6–9.5 kV (p. 1–2)` - **Source quote (verbatim):** “Because of space limitation, a bent copper block replaces the Faraday cup to collect the extracted ion beam. Such a system enables us to measure total amount of ion current extracted from the plasma chamber of the ion source.” - **Source:** [Zhao, Xu, Chen et al. (ASIPP / USTC), Recent Progress on Ion Source of SC200 Cyclotron — Cyclotrons 2019, paper MOP002, JACoW (2019)](https://cyclotroninfo.com/library/#lib-315) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A collector of this kind reads the sum of H+, H2+, H3+ plus whatever secondary-electron current leaves or reaches it (which can bias the reading either way), so a "total extracted current" from a bench is not a proton current. Reporting which collector was used beside any source-current number keeps comparisons honest. **dg-2099** · applicability level 4 · ion-source, materials, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-2099 - **Rule (this site's paraphrase of the source):** In the 3.0 T Sumitomo superconducting AVF cyclotron the hot-cathode PIG filament was judged at risk of deformation by the Lorentz force from its own heating current, and the source was switched to AC heating; the authors credit this with making a hot-cathode PIG usable in that field (their judgment; no deformation data, AC frequency or comparison with DC are given). - **Formula:** `Derived J×B load per unit length (units A × T = N/m) at the bench conditions of Fig. 3: 178 A × 3.2 T = 570 N/m, 180 A × 3.2 T = 576 N/m, taking the stated filament currents as RMS (the paper does not say RMS or peak, nor whether the Fig. 3 bench run was AC-heated; a sinusoid peaks at √2 × RMS, i.e. ≈810 N/m peak).` - **Source quote (verbatim):** “the filament heated by current receives the Lorentz force strongly. It may be a problem that this force deforms the filament. To avoid the deformation, AC current heating is newly introduced into this ion source.” - **Source:** [Kamiguchi, Oda, Kanakura, Kumata et al. (Sumitomo Heavy Industries), Development of a Center Region for New Sumitomo Cyclotron — Cyclotrons 2019, paper TUP035, JACoW (2019)](https://cyclotroninfo.com/library/#lib-316) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** With symmetric zero-mean AC the force reverses every half cycle, so its mean is zero, which removes a steady one-way load; the alternating stress remains, so the heating frequency and the filament's mechanical response need a test in the field. Livingston & Blewett advise DC or ~100 kHz AC because low-frequency AC vibrates the filament in the field (dg-369), and Iowa State's 1.5 MeV cyclotron used high-frequency AC on its spiral filament for the same reason (dg-371). IB is the load on the segment perpendicular to B (a factor sin θ otherwise). At a lower field and current the force is smaller but not zero. **dg-2100** · applicability level 3 · ion-source, beam-measurement · https://cyclotroninfo.com/design-guide/ion-source/#dg-2100 - **Rule (this site's paraphrase of the source):** Bench-measure the source in its operating field before the cyclotron: Sumitomo's hot-cathode PIG, tested in a superconducting test magnet at 3.2 T with static (DC) extraction, gave up to ~300 µA H+, and by figure reading a filament-current change of only 178 → 180 A raised the extracted current at 100 V arc from ~200 to ~305 µA. - **Formula:** `Fig. 3 readings (labelled, from a 500-dpi crop, ±5 µA): V_arc 30 V: 178 A ~13, 180 A ~20 µA; 60 V: ~105 / ~138 µA; 80 V: ~166 / ~232 µA; 100 V: ~199 / ~307 µA. Derived: 180/178 = 1.011 (+1.1% heater current) → 307/199 = 1.54 (~+50% beam) at 100 V arc; dimensionless ratios.` - **Source quote (verbatim):** “The performance test was conducted under the condition that 3.2 T magnet field and static extraction. The H+ beam current was measured about 300 μA at most (Fig. 3) [2].” - **Source:** [Kamiguchi, Oda, Kanakura, Kumata et al. (Sumitomo Heavy Industries), Development of a Center Region for New Sumitomo Cyclotron — Cyclotrons 2019, paper TUP035, JACoW (2019)](https://cyclotroninfo.com/library/#lib-316) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** In this source a ~1.1 % filament-current step coincided with ~54 % more extracted current at 100 V arc; that motivates fine heater-current scans on other thermionic sources (stepping heater current at fixed arc voltage and gas flow) but does not predict their sensitivity, which depends on geometry, plasma regime and emission saturation. The absolute currents and field belong to the Sumitomo source. **dg-2101** · applicability level 3 · ion-source, vacuum, fabrication · https://cyclotroninfo.com/design-guide/ion-source/#dg-2101 - **Rule (this site's paraphrase of the source):** Treat filaments as consumables and design the exchange without venting the machine: the Sumitomo cyclotron carries a mechanical drive under the cyclotron that withdraws the internal ion source without breaking vacuum, so the authors report that source maintenance can be done easily and rapidly. - **Source quote (verbatim):** “In case of hot cathode type PIG ion sources, filaments are supplies and must be exchanged periodically. As the mechanical driving system which evacuate the ion source from the cyclotron without broking vacuum is equipped under the cyclotron,” - **Source:** [Kamiguchi, Oda, Kanakura, Kumata et al. (Sumitomo Heavy Industries), Development of a Center Region for New Sumitomo Cyclotron — Cyclotrons 2019, paper TUP035, JACoW (2019)](https://cyclotroninfo.com/library/#lib-316) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** For a machine whose filament change requires venting the whole chamber, every change also costs a vent, pump-down and outgassing cycle; a valved withdrawal port is one way to remove that, at the cost of a seal and a bellows or sliding feedthrough in the centre region. **dg-2102** · applicability level 2 · beam-measurement, ion-source · https://cyclotroninfo.com/design-guide/ion-source/#dg-2102 - **Rule (this site's paraphrase of the source):** Put a beam probe at small radius as a standing source diagnostic: in the Sumitomo centre region a probe at 42 mm radius measures beam current in the centre region both for the Smith–Garren (phase) measurement and to confirm the status of the ion source. - **Formula:** `probe radius 42 mm (p. 2); first orbits ~15 mm radius (p. 1); centre region fits within ~0.2 m diameter (p. 1).` - **Source quote (verbatim):** “The beam measurement probe is located at 42 mm radius and can measures the beam current at the center region to perform the Smith – Garren measurement and to confirm the status of the ion source.” - **Source:** [Kamiguchi, Oda, Kanakura, Kumata et al. (Sumitomo Heavy Industries), Development of a Center Region for New Sumitomo Cyclotron — Cyclotrons 2019, paper TUP035, JACoW (2019)](https://cyclotroninfo.com/library/#lib-316) — p. 2 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** A probe a few turns out localizes a fault to the source, extraction and early-capture region versus losses beyond the probe — the first split to make when the final collector reads low — but it does not by itself say the source stopped producing, since extraction failure, poor RF capture, phase error or first-turn loss also read low there. Its useful radius on a smaller machine follows that machine's first-turn radius, not Sumitomo's 42 mm. **dg-2103** · applicability level 2 · beam-dynamics, ion-source, dee · https://cyclotroninfo.com/design-guide/ion-source/#dg-2103 - **Rule (this site's paraphrase of the source):** In the Sumitomo centre region (3.0 T), 50 kV between puller and ion source extracts the beam onto accelerated orbits that turn at around 15 mm radius, all within a centre region of ~0.2 m diameter. First-orbit radius scales as sqrt(V)/B (derived), which is what sets how far the source hardware must sit from the first turns. - **Formula:** `ρ = sqrt(2 m V / q) / B (units: sqrt(kg·V/C) = kg·m/(s·C) = T·m; ÷ T → m) is the local curvature radius. Derived: protons after one 50 kV crossing at 3 T → sqrt(2×1.6726e-27×5e4/1.602e-19) = 0.0323 T·m; /3 T ≈ 10.8 mm; after two crossings (100 keV) → 0.0457/3 ≈ 15.2 mm, which coincides with the paper's "around 15 mm" — the paper does not define which turn or energy it means, so this reading is unverified. Illustrative low-field case: 1 kV at 0.6 T → 0.00457 T·m / 0.6 T ≈ 7.6 mm curvature radius; an ion launched from the source into the field alone reaches about 2ρ ≈ 15 mm from its start before the half-turn closes, so the hardware clearance is of order 2ρ, modified by the electric fields and orbit centring.` - **Source quote (verbatim):** “The voltage of 50 kV is loaded between the puller and the ion source and the beam is extracted to accelerated orbits. Extracted beams turn around 15 mm radius” - **Source:** [Kamiguchi, Oda, Kanakura, Kumata et al. (Sumitomo Heavy Industries), Development of a Center Region for New Sumitomo Cyclotron — Cyclotrons 2019, paper TUP035, JACoW (2019)](https://cyclotroninfo.com/library/#lib-316) — p. 1 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Radius scales as sqrt(V)/B, so a low-voltage, low-field machine has first-half-turn curvature radii of millimetres (≈7.6 mm for a proton after 1 kV at 0.6 T, derived) and the first half-turn reaches about twice that, ≈15 mm, from the launch point in the field alone — the clearance the filament mount, hood and leads must respect, to be confirmed by tracing the centre-region orbit through the extraction and RF fields rather than taken from ρ. **dg-2104** · applicability level 3 · ion-source, materials, magnet · https://cyclotroninfo.com/design-guide/ion-source/#dg-2104 - **Rule (this site's paraphrase of the source):** The patent's inventors trace filament performance loss in a 1–3 T internal source to deformation by the Lorentz force on the heating current, made possible, in their account, because the hot filament loses strength and is progressively thinned by what they call sputtering by electron, so a filament strong enough when new deforms later. - **Formula:** `F/L = I × B for current ⊥ B (units: A × T = A × N/(A·m) = N/m). Derived: patent example 200 A × 1.75 T = 350 N/m (0.35 N per mm of conductor ⊥ B). Illustrative small case: 10 A × 0.6 T = 6 N/m (350/6 ≈ 58× less). Self-weight per length = ρ·A·g (kg/m³ × m² × m/s² = N/m): W wire 0.25 mm dia, ρ 19,300 kg/m³, A = π(1.25e-4 m)² = 4.91e-8 m² → 9.3e-3 N/m; Ta plate 5 × 0.5 mm, ρ 16,600 kg/m³, A = 2.5e-6 m² → 0.41 N/m.` - **Source quote (verbatim):** “the strength of the filament in use decreases gradually since the filament is in a high temperature state and the filament is thinning due to sputtering by electron.” - **Source:** [Miyashita & Matsumura (Sumitomo Heavy Industries), Cyclotron — US Patent 9,041,318 B2 (2015)](https://cyclotroninfo.com/library/#lib-317) — p. 10 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** This is the patent's explanation. Its "electron sputtering" term is physically questionable: at ~185 V an electron transfers of order 10^-3 eV to a tantalum atom, far below a displacement energy, so thinning is more plausibly thermal evaporation and positive-ion bombardment. The force-per-length arithmetic shows the in-field load dominating gravity at both scales (6 N/m is ≈650× a 0.25 mm W wire's weight; the patent plate's 350 N/m is ≈860× its weight; derived, with 0.6 T and 10 A an illustrative pairing), but similar force-to-weight ratios do not mean similar deformation: whether a given hot wire bends depends on support length, section orientation, hot strength and creep, and is found by a bending-stress or deflection calculation and test. **dg-2105** · applicability level 4 · ion-source, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2105 - **Rule (this site's paraphrase of the source):** Measured remedy: reversing the DC filament current periodically reverses the J×B force. In Sumitomo's one four-hour test (Ta Ω-bent plate 25 mm high × 5 mm wide × 0.5 mm thick, 200 A DC, 1.75 T, 185 V arc, cyclotron operating) hourly polarity reversal was associated with about 0.2 mm of bending versus about 1 mm under fixed polarity — about one fifth; sample size not stated. - **Formula:** `text: ~0.2 mm vs ~1 mm, "about 1/5" (p. 12). Fig. 7 box-plot readings (p. 9, labelled, from pixel calibration 0–1.2 mm axis): no switching box ~0.95–1.13 mm, median ~1.07, mean ~1.05; switching box ~0.14–0.31 mm, median/mean ~0.23 → ratio 0.23/1.05 ≈ 0.22. 4 h at 1 h intervals = 3 reversals; sample size not stated.` - **Source quote (verbatim):** “A test was performed for four hours while changing the direction of the current supplied to the filament every hour in a state in which the cyclotron was operating. Then, the amount of bending (displacement of the apex of the filament) of the filament was measured. […] the amount of bending of the filament was about 0.2 mm. […] In a comparative example, for the same filament as in the example, a test was performed for four hours without changing the direction of the current, and the amount of bending was measured. […] the amount of bending of the filament was about 1 mm. The amount of bending in the example was about 1/5 of that in the comparative example.” - **Source:** [Miyashita & Matsumura (Sumitomo Heavy Industries), Cyclotron — US Patent 9,041,318 B2 (2015)](https://cyclotroninfo.com/library/#lib-317) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Reversal does not remove the force; it makes the creep alternate in direction, so the net bend stayed smaller over this test (residual ~0.2 mm here). The Handbook of Ion Sources gives a second reason for the same switch: arc-source filament erosion is stronger at the positive end and periodic polarity change improves cathode lifetime (dg-381). For a DC-heated filament in any field, a reversing switch on the heater supply is a cheap experiment; the 1 h interval and the ~5× reduction are this filament's results from one short test. **dg-2106** · applicability level 3 · ion-source, fabrication, materials · https://cyclotroninfo.com/design-guide/ion-source/#dg-2106 - **Rule (this site's paraphrase of the source):** Only the part of the filament whose current crosses the field is loaded: in Sumitomo's hot-cathode PIG the filament legs run along B and the force acts on the curved tip where current is perpendicular to B, which falls over with operating time; orienting the bent plate so its WIDTH lies along the force direction gives the stiff section against the load. - **Formula:** `F = I L × B (zero for current ∥ B). Derived section stiffness: I_width / I_thick = (t·w³/12)/(w·t³/12) = (w/t)² = (5 mm/0.5 mm)² = 100 (units m⁴/m⁴, dimensionless).` - **Source quote (verbatim):** “In addition, in the cyclotron 1, the filament 11 is formed by bending one metal plate, and the width direction of the metal plate is made to match a direction in which the Lorentz force is applied.” - **Source:** [Miyashita & Matsumura (Sumitomo Heavy Industries), Cyclotron — US Patent 9,041,318 B2 (2015)](https://cyclotroninfo.com/library/#lib-317) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** Derived for the other common layout: a hairpin lying in the midplane, perpendicular to a vertical field, has its whole length loaded, and its two legs carry opposite currents, so the forces push the legs apart or together (sense set by polarity) in the plane. A ribbon or strip turned edge-on to the force, or legs run parallel to B, reduces the bending for the same current. **dg-2107** · applicability level 4 · ion-source, controls · https://cyclotroninfo.com/design-guide/ion-source/#dg-2107 - **Rule (this site's paraphrase of the source):** The patent discloses controlled DC filament-current reversal: a controller can reverse on a schedule, change the interval with operating conditions, or reverse on the basis of the detected extracted-ion signal, which the inventors say allows current control "considering the state of the filament"; AC heating is also allowed as a variant, and the patent does not demonstrate superiority over AC. - **Source quote (verbatim):** “For example, the control unit 8 may change the direction of the current on the basis of the detection state of ions extracted from the chimney 10.” - **Source:** [Miyashita & Matsumura (Sumitomo Heavy Industries), Cyclotron — US Patent 9,041,318 B2 (2015)](https://cyclotroninfo.com/library/#lib-317) — p. 12 - **Editorial note, tabletop extrapolation (written by this site, not taken from the source):** The patent tests DC reversal against fixed DC only, and Sumitomo's own 2019 centre-region paper (Kamiguchi et al., dg-2099) reports AC heating adopted on its newer source, also without a comparison. The Handbook of Ion Sources notes that AC heating increases plasma instabilities and the energy spread of the extracted ions (dg-381), a source-specific observation rather than a universal one. A logged reversal schedule lets beam-current changes at each reversal be checked as part of the source record. > **Page provenance.** Last reviewed: 23 August 2026 · 291 source-extract rules from 77 cited documents · [Methodology](https://cyclotroninfo.com/about/methodology/) · [Report a correction](mailto:info@cyclotroninfo.com?subject=Correction%3A%20Cyclotron%20Ion%20source%20Design%3A%20291%20Sourced%20Rules) · [Changelog](https://cyclotroninfo.com/changelog/)