Cyclotron ion source design rules

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.

Zaremba, Magnets for Cyclotrons (2005) — p. 3, 45

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 164

Editorial note, tabletop extrapolation: 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

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 178

Editorial note, tabletop extrapolation: 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.

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).

Wolf (ed.), Handbook of Ion Sources (1995) — p. 379

Editorial note, tabletop extrapolation: 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).

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 111-113

Editorial note, tabletop extrapolation: 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.

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 117, 122-124

Editorial note, tabletop extrapolation: 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.

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 87, 105, 109

Editorial note, tabletop extrapolation: 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.

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.

Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 166-178

Editorial note, tabletop extrapolation: 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.

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.

Humphries, Principles of Charged Particle Acceleration (1986) — p. 524, 526

Editorial note, tabletop extrapolation: 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.

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

Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009) — p. 54

Editorial note, tabletop extrapolation: 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.

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.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 259-260

Editorial note, tabletop extrapolation: 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).

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.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 260-261

Editorial note, tabletop extrapolation: 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.

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

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 260-261

Editorial note, tabletop extrapolation: 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.

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.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 261-262, 269

Editorial note, tabletop extrapolation: 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.

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.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 7 (printed page 265; offset = printed minus 258)

Editorial note, tabletop extrapolation: 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.

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

Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 175-178

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 177-178

Editorial note, tabletop extrapolation: A mains-frequency-heated filament in a 0.59 T field risks vibrating itself to death; DC heating and clean hydrogen are cheap reliability.

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.

Livingston & Blewett, Particle Accelerators (1962) — p. 198

Editorial note, tabletop extrapolation: 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

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.

McGuire, The Iowa State University 1.5 MeV Undergraduate Cyclotron (1961) — p. 7

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. PDF p.101 (printed p.90), TABLE 5.5 in section 5.3.7 Operating Data

Editorial note, tabletop extrapolation: 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

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. PDF p.355 (printed p.344), section 2.1 High-Temperature Metals

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 356

Editorial note, tabletop extrapolation: 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.

In more practical units, this equation can be rewritten: j[mA/cm2] = 1.72 * sqrt(q*/u) * phi[kV]^(3/2) / d[mm]^2.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 376-377

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 379

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 38-39

Editorial note, tabletop extrapolation: 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.

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).

Wolf (ed.), Handbook of Ion Sources (1995) — p. 39

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 41-42

Editorial note, tabletop extrapolation: 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.

Gas efficiency: >50% for hydrogen and higher for other gases.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 57, 69, 110

Editorial note, tabletop extrapolation: 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

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

Wolf (ed.), Handbook of Ion Sources (1995) — p. 73

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 74, 76

Editorial note, tabletop extrapolation: 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.]

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. PDF p.82 (printed p.71), section 5.2.2 Characterization of the PIG Discharge

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 82

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 84-85

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 86, 101

Editorial note, tabletop extrapolation: 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.

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.

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — 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: 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.

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

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — 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: 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.

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.

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 6-7

Editorial note, tabletop extrapolation: 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.

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.

Baumgartner, The Cyclotron Kids' 2 MeV Proton Cyclotron — Cyclotrons 2013, WE1PB05 (2013) — p. 3

Editorial note, tabletop extrapolation: 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.

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

Yuly et al., Modifications on the Houghton College Cyclotron (2010) — p. 17-18

Editorial note, tabletop extrapolation: 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.

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.

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 19-20

Editorial note, tabletop extrapolation: 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.

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).

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 135, 144

Editorial note, tabletop extrapolation: 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.

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 145

Editorial note, tabletop extrapolation: 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.

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

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 145-146

Editorial note, tabletop extrapolation: 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.

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 86-88

Editorial note, tabletop extrapolation: 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

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 89-91

Editorial note, tabletop extrapolation: 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.

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 92, 94

Editorial note, tabletop extrapolation: 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

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.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 94-96

Editorial note, tabletop extrapolation: 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.

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)

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 7

Editorial note, tabletop extrapolation: 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.

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.

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 7

Editorial note, tabletop extrapolation: 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.

It appears that filament bias has no effect on the beam current.

Fuller, Exploring the Capabilities of the Houghton College Cyclotron — Houghton College thesis (2013) — p. 48-49

Editorial note, tabletop extrapolation: 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.

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.

Fuller, Exploring the Capabilities of the Houghton College Cyclotron — Houghton College thesis (2013) — p. 51-52

Editorial note, tabletop extrapolation: 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

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.

Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009) — p. 50

Editorial note, tabletop extrapolation: 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

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

Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013) — p. 5

Editorial note, tabletop extrapolation: 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

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 1-2

Editorial note, tabletop extrapolation: 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.]

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — 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: 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).

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 2

Editorial note, tabletop extrapolation: 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

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 2-3

Editorial note, tabletop extrapolation: 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.

the source has a current utilization efficiency (ratio of target to discharge current) of 25% and requires 32.4 W of power.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 3

Editorial note, tabletop extrapolation: Template for a bench extraction test stand to characterize the next machine's source before it goes into the magnet.

The ion source is an internal cold cathode Penning Ion Gauge (PIG) source that operates in excess of 40 hours before requiring service.

Koeth, Undergraduate Education with the Rutgers 12-Inch Cyclotron (2015) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 17-29

Editorial note, tabletop extrapolation: 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

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)

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. PDF p. 29 (printed p. 19)

Editorial note, tabletop extrapolation: 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.

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).

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 19-20

Editorial note, tabletop extrapolation: 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.

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).

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 3-4

Editorial note, tabletop extrapolation: 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.

The chimney with the larger slit produces a beam with a larger emittance. However, the beam is also of higher intensity.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 66-69

Editorial note, tabletop extrapolation: 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.

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).

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 68, 75

Editorial note, tabletop extrapolation: 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.

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)).

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 73-76, 91-107

Editorial note, tabletop extrapolation: 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.

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

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 77-78, 81

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 79-80

Editorial note, tabletop extrapolation: 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.

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).

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 91-107

Editorial note, tabletop extrapolation: 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.

Vernier knob for repeatable flow settings ... Flow Coefficient (Cv): 0.029 (Series 20) ... Stem Taper: 3 deg ... Turns to Open: 9 (+/-1)

Parker Hannifin, Series 20 & 30 Metering Valves (datasheet) — p. 1-2

Editorial note, tabletop extrapolation: 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.

Not recommended for positive shut-off. If bubble-tight shut-off required, the use of a Series HR Metering Valve is suggested.

Parker Hannifin, Series 20 & 30 Metering Valves (datasheet) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 62, 64

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. PDF p. 64 = printed p. 64 (section 'The Ion Source')

Editorial note, tabletop extrapolation: 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.

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.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 66

Editorial note, tabletop extrapolation: 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.

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).

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 52-53

Editorial note, tabletop extrapolation: 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.

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

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 55-56

Editorial note, tabletop extrapolation: 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.

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)

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 56

Editorial note, tabletop extrapolation: 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.

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

Wolf (ed.), Handbook of Ion Sources (1995) — p. 82

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 82

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 82

Editorial note, tabletop extrapolation: 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.

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

Wolf (ed.), Handbook of Ion Sources (1995) — p. 82-83

Editorial note, tabletop extrapolation: 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.

the arc voltage increases with decreasing gas flow or particle density in the discharge chamber until the discharge becomes unstable

Wolf (ed.), Handbook of Ion Sources (1995) — p. 83

Editorial note, tabletop extrapolation: 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

The arc power for cold cathode operation is limited to about 1 kW per cathode, because of the start of thermal electron emission

Wolf (ed.), Handbook of Ion Sources (1995) — p. 84

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 84-85

Editorial note, tabletop extrapolation: 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.

Gas consumption (sccm) 0.2 [hot cath.] / 0.2 [cold cath.] / 0.2-0.6 [heated cath.] (Table 5.5; verified against page image)

Wolf (ed.), Handbook of Ion Sources (1995) — p. 101

Editorial note, tabletop extrapolation: 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).

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

Wolf (ed.), Handbook of Ion Sources (1995) — p. 81

Editorial note, tabletop extrapolation: 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.

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.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 86

Editorial note, tabletop extrapolation: 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.

PIG ion source 10-50 [energy spread, V] 5-500 [typical ion current, mA] (Table 2.1)

Wolf (ed.), Handbook of Ion Sources (1995) — p. 51

Editorial note, tabletop extrapolation: 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.

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.

Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981) — p. 3

Editorial note, tabletop extrapolation: 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.

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

Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981) — p. PDF p.3 (printed p.233 of the 9th Int. Conf. on Cyclotrons proceedings)

Editorial note, tabletop extrapolation: 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.

A disadvantage is the need for cathode replacement and anode cleaning at intervals of a few hours to a day.

Clark, Ion Sources for Cyclotrons — Cyclotrons '81, Caen (1981) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 1-3

Editorial note, tabletop extrapolation: 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+.

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%

Rovey, Ruzic & Houlahan, Simple Penning Ion Source for Laboratory Research and Development Applications (2007) — p. 2-3

Editorial note, tabletop extrapolation: 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.

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

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 88-91

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — 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: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 29

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 89

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — 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: 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.

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]

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 78, 85

Editorial note, tabletop extrapolation: 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.

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.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 3

Editorial note, tabletop extrapolation: 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.

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)

Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017) — p. 2-3

Editorial note, tabletop extrapolation: 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.

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.

Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017) — 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: 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.

Post-to-foil transmission increased dramatically (from 19% to 30%) but the total target current decreased from 120 uA to 40 uA

Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017) — p. 3-4

Editorial note, tabletop extrapolation: 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.

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

Obradors et al., Characterization of the AMIT Internal Ion Source with a Devoted DC Extraction Test Bench — IPAC 2017 (2017) — p. 3

Editorial note, tabletop extrapolation: 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.

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

Zakerhosseini et al., Heat Transfer Study of PIG Ion Source for 10 MeV Cyclotron — IPAC 2016 (2016) — p. 1-3

Editorial note, tabletop extrapolation: 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.

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.

Mu et al., Simulation of Electron Behavior in PIG Ion Source for 9 MeV Cyclotron (2015) — p. 3, 5

Editorial note, tabletop extrapolation: 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.

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

Mu et al., Simulation of Electron Behavior in PIG Ion Source for 9 MeV Cyclotron (2015) — p. 4-6

Editorial note, tabletop extrapolation: 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.

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

Lee et al., Investigation of Minimized Consumption Power about 10 MeV Cyclotron — Cyclotrons 2016 (2016) — p. 2-3

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rutgers 12 Inch Cyclotron Ion Source Studies: Part I (2006) — p. 2-3

Editorial note, tabletop extrapolation: 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).

For reasons which are not clearly understood this bias usually increases the size of the beam by a factor of two or more.

MacKenzie & Waithman, R.F. System for Frequency Modulated Cyclotron — MDDC-1045 (1946) — p. 12

Editorial note, tabletop extrapolation: 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.

Internal Beam, Stable, ua 1000-2000 ... External Beam, Stable, 800 ua; 100 ua focused on target 15 ft from machine

Howard, Cyclotrons and High-Energy Accelerators, 1958 — ORNL-2644 (1958) — p. 107

Editorial note, tabletop extrapolation: 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.

Ion source, type hooded arc, tungsten filament

Howard, Cyclotrons and High-Energy Accelerators, 1958 — ORNL-2644 (1958) — p. 26

Editorial note, tabletop extrapolation: 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.

A major improvement was effected when an off-center source was installed which injected azimuthally into one of the dees.

Heusinkveld et al., Studies with a Three-Dee Three-Phase Proton Cyclotron — UCRL-3187 (1955) — p. 12

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 8

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 10

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 16

Editorial note, tabletop extrapolation: 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.)

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 16

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 16

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 10

Editorial note, tabletop extrapolation: 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.

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+++.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 24

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 24

Editorial note, tabletop extrapolation: 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.

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.

Jungerman, Kibbe & Peek, Central Region Studies for Incorporating an Axial Ion Source in the Davis 76-in. Cyclotron — UCD-CNL-49 (1966) — p. 5

Editorial note, tabletop extrapolation: 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.

If 200 ml/hr is considered as a maximum rate of gas injection, this results in ... 0.042 liter-mm/sec.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 136

Editorial note, tabletop extrapolation: 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

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.

Cohen, Spatial Distribution of Current on an Internal Cyclotron Target — ORNL-1348 (1952) — p. 9

Editorial note, tabletop extrapolation: 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.

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

Oak Ridge National Laboratory, A Proposal for the Mc² Isochronous Cyclotron — ORNL-3540 (1963) — p. PDF p.285 (printed p.271)

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 December 1951 — ORNL-1269 (1952) — p. 47

Editorial note, tabletop extrapolation: 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.

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

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 December 1951 — ORNL-1269 (1952) — p. 49

Editorial note, tabletop extrapolation: 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.

The output of the ion source was found to be approximately proportional to the effective length

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 September 1952 — ORNL-1383 (1953) — p. 21

Editorial note, tabletop extrapolation: 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.

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

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 September 1952 — ORNL-1383 (1953) — p. 22

Editorial note, tabletop extrapolation: 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.

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.

Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953) — p. 20

Editorial note, tabletop extrapolation: 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.

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.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 78

Editorial note, tabletop extrapolation: 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.

stopping the beam at r < 10 in. radius in graphite targets. This avoids neutron production and induced cyclotron radioactivity

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970) — p. 26

Editorial note, tabletop extrapolation: 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

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.

Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970) — p. 26

Editorial note, tabletop extrapolation: 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.

At focused ion beam energies, sputter yields between 2 and 10 atoms per argon ion are typical.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. 94

Editorial note, tabletop extrapolation: 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.

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.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — 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: 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.

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")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 125

Editorial note, tabletop extrapolation: 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.

The trap is essential; the gas is not absorbed otherwise (Gursky & Sherwood, "Hydriding of Titanium Cones for a Sputter-Ion Source")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 57

Editorial note, tabletop extrapolation: 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.

a cold filament which produces a temperature rise of the evaporant of only ~ 10 C

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 249

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 2

Editorial note, tabletop extrapolation: 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.

the top of the graphite hood glowed a bright orange color when the arc was operating, because of the intense electron bombardment.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 3

Editorial note, tabletop extrapolation: 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

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Fulbright, A Hooded Arc Ion Source with a Magnetic Mirror Feature — NYO-9358, University of Rochester (1962) — p. 4

Editorial note, tabletop extrapolation: 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.

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.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 33

Editorial note, tabletop extrapolation: 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.

the filament may be replaced without breaking the vacuum of the tank proper.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 65

Editorial note, tabletop extrapolation: 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

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 42-43

Editorial note, tabletop extrapolation: 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.

Über sie kann eine zusätzliche „Saugspannung“ an das Dee angeschlossen werden [tr.: through it an additional extraction voltage can be applied to the dee]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 46

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 46

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 51-53

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 58

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 30

Editorial note, tabletop extrapolation: 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.

Dieser Druck wird durch einen Druckminderer auf pH2 = 300 mbar reduziert [tr.: the pressure is reduced by a regulator to 300 mbar]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 61

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 62, 64

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 62, 70

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 63-64

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 64, 66

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 64

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 64-65

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 65-66

Editorial note, tabletop extrapolation: 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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 66, 70

Editorial note, tabletop extrapolation: 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.

either a filament was created from that metal, or a nichrome wire was coated with the metal, and raised to a negative potential

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 16

Editorial note, tabletop extrapolation: 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.

The filament was kept isolated from ground so it could be negatively biased to increase the energy of the emitted electrons.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 17

Editorial note, tabletop extrapolation: 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).

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

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 17

Editorial note, tabletop extrapolation: 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.

As the ion source was considered experimental and a weak design aspect, it was made to be completely removable.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 18

Editorial note, tabletop extrapolation: 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.

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.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 18

Editorial note, tabletop extrapolation: 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.

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.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 12

Editorial note, tabletop extrapolation: 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.

At this level at least 90% of the gas in the chamber has been purposefully introduced

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 30

Editorial note, tabletop extrapolation: 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.

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]

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 42

Editorial note, tabletop extrapolation: 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.

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.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 43

Editorial note, tabletop extrapolation: 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.

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]

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 17

Editorial note, tabletop extrapolation: 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).

Vaccum in the chamber 10-6 mbar dto with H2 10-5 mbar

Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022) — p. 2

Editorial note, tabletop extrapolation: 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.)

or investigate a Penning ion source with the aim of using it for the installation in the accelerator.

Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022) — p. 2

Editorial note, tabletop extrapolation: 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).

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

Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: 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.

the angle of emission shall be adjustable for a better acceleration and to prevent that the protons remain in the gap between the dees

Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: 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.

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"

Frank, Wolf & Held, COLUMBUS — A Simple Ion Source — WEPPT021, Proceedings of Cyclotrons2013 (2013) — p. 1, 2

Editorial note, tabletop extrapolation: 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.

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

Clark, Halbach, Kunkel, Leung, Li & Young, A Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of Cyclotrons'95, Cape Town (1995) — p. 1, 2

Editorial note, tabletop extrapolation: 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.

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

Clark, Halbach, Kunkel, Leung, Li & Young, A Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of Cyclotrons'95, Cape Town (1995) — p. 2

Editorial note, tabletop extrapolation: 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.

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

Young, Bertsche, Clark, Halbach, Kunkel, Leung et al., Development of a Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of PAC1993 (1993) — p. 2

Editorial note, tabletop extrapolation: 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.

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

Young, Bertsche, Clark, Halbach, Kunkel, Leung et al., Development of a Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of PAC1993 (1993) — p. 1, 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 2

Editorial note, tabletop extrapolation: 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.

[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]

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 2

Editorial note, tabletop extrapolation: 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".)

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 3

Editorial note, tabletop extrapolation: 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.

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).

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 4

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 4

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 5

Editorial note, tabletop extrapolation: 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.)

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 6

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 6

Editorial note, tabletop extrapolation: 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.

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]

Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011) — p. 3

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011) — p. 9

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011) — p. 11

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 4

Editorial note, tabletop extrapolation: 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).

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 4

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 7

Editorial note, tabletop extrapolation: 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.

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.

Hernalsteens, Ponter, Beaudoin, Koeth, Ruisard & Miller, Betatron Tune Characterization of the Rutgers 12-Inch Cyclotron for Different Magnetic Poles Configurations (2016) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 1

Editorial note, tabletop extrapolation: 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.

Early filament based designs generated mere nanoamps of protons and would only operate a few hours.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: 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.

The best arc stability was found for the smallest (0.031 inch) circular aperture.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

As expected, the collected ion current follows the arc current and extraction voltage.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

Rapid sweeping operation of the cyclotron has shown simultaneous generation of protons and +H2 ions in a 5:1 ratio.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 2

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 5

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 6

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 6

Editorial note, tabletop extrapolation: 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.

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.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 6

Editorial note, tabletop extrapolation: 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.