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

Tabletop: The most common amateur failure mode is a magnet that works but leaves no port for the probe or pump; run this five-item checklist 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

Tabletop: 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

Tabletop: Make the source mount adjustable by a few mm in both directions and tune position for beam, not for geometric center.

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

Tabletop: Hood or collimate the reference machine's source so only ~1/3 of the dee aperture height of plasma column is exposed; more column means RF load, not more beam.

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

Tabletop: Direct rule for the reference machine's source-to-puller spacing and any dee-to-ground clearance: a few-kV dee needs sub-mm minimum, but leave margin because sputtered metal films spoil the 'clean surface' assumption fast.

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

Tabletop: Bring the reference machine's dee and extraction voltages up over tens of minutes on first pump-down, watching for micro-discharge pulses; a gap that arcs at 15 kV cold will often hold 20+ kV after patient conditioning.

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.

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

Tabletop: Sizes the reference machine's HV stalk directly: for a grounded 25-mm-bore chamber port, a ~9-mm center conductor minimizes field stress; 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.

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

Tabletop: In the reference machine's small chamber everything sees the source; a simple washer-stack or skirt shielding the feedthrough ceramic from the chimney slit will multiply time-between-cleanings.

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

Tabletop: An off-the-shelf, cheap, replaceable filament choice plus the RF-bypass detail that keeps the filament supply alive next to a live Dee.

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.

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

Tabletop: Graphite source parts keep metal sputter off insulators and chamber walls; a feeler (puller) on the dee edge is the single cheapest first-turn-capture upgrade.

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

Tabletop: Explains why source-to-dee geometry (chimney position, puller gap, aperture height) dominates beam capture on small machines: the magnet cannot help until several turns out.

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

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

Tabletop: Matches the reference machine's ~1.3 kV operating point today; at their planned 5-13 kV the same geometry needs proportionally more ceramic creepage distance.

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

Tabletop: Moot for pump choice today, but the underlying rule stands: condensable metal vapors on HV electrodes trigger field emission; keep electrode surfaces free of conductive films.

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

Tabletop: Sets the historical proton-conversion baseline: expect percent-level proton yield from a gas discharge and budget discharge power accordingly.

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.

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

Tabletop: The 'gap smaller than the dark space' principle is how the builder can force their source discharge to localize at the extraction aperture rather than wander.

At first this beam consists very largely of molecular ions, but after running for some time it changes over and becomes nearly all protons

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

Tabletop: Critical for p-B11: an unconditioned source delivers H2+ that behaves as half-energy protons, silently killing the expected alpha yield at fixed magnetic rigidity.

admitting hydrogen till it was possible to run a discharge at about 20-60 kilovolts... 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. 265

Tabletop: A concrete glow-discharge conditioning schedule the builder can scale for dee and extraction electrodes that must hold voltage without sparking.

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

Tabletop: A triage rule for the reference machine's low-current debugging: measure current at small radius first; if it's already low there, more RF power won't fix it - the source will.

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

Tabletop: These operating points scale down gracefully; the key architecture point - a differentially pumped cavity at ~1e-2 torr feeding a chamber at 1e-5 - applies at any size.

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.

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

Tabletop: A 60 Hz-heated filament in a 0.59 T field literally shakes itself apart; 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

Tabletop: The builder should expect an order-of-magnitude pressure rise when hydrogen flows; low-2e-5 territory while running is normal and workable, not a leak.

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

Tabletop: Concrete fix for a failure mode the builder will hit at 0.6-1.7 T with a hairpin/spiral filament: filament life is a chronic tabletop problem.

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.

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

Tabletop: The reference machine's MFC should be sized and calibrated around the 0.1-1 sccm range, and the arc supply must tolerate a several-kV open-circuit ignition transient before folding back to run voltage.

Stainless steel is an excellent material up to about 1000 C... It forms low-melting alloys with tantalum and molybdenum above 900 C... Tungsten... has the highest melting point of about 3400 C and is best suited for filaments.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 355

Tabletop: Do not clamp Ta filament legs directly in stainless fixtures near the hot zone; use Mo or graphite intermediate parts in the next machine's chimney.

Boron nitride is an excellent material for most applications for temperatures up to 1200 C... 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

Tabletop: 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

Tabletop: 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.

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

Tabletop: For the puller gap in a next machine: make the source-slit half-width about half the slit-to-puller distance, then tune arc density (not geometry) until the beam is parallel.

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

Tabletop: The reference machine's hydrogen filament source lives or dies on filament temperature stability; a constant-current supply with fine adjustment is worth more than raw power.

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

Tabletop: 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

Tabletop: For a next machine, a fatter filament run cooler at ~0.1-1 A/cm^2 buys weeks of run time instead of days; treat used Ta hairpins as brittle after hydrogen exposure.

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

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

Tabletop: At 0.2 sccm feed and 50% efficiency only ~0.1 sccm of H2 leaks into the chamber; doubling source gas efficiency is worth as much as doubling pump speed for keeping the beam path at low pressure.

The arc current is 1 to 3 A and the arc voltage just 40 to 70 V... The lifetime of the source is given by the lifetime of the filament, which is between 10 and 100 h... Changing the polarity of the filament... improves cathode lifetime.

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

Tabletop: For a next machine: a thick rod cathode instead of thin wire is the cheapest lifetime upgrade, plus a DPDT reversing switch on the heater and an arc-hours log.

The extraction slit is usually about 2 mm wide and about 40 mm long. Larger slits are possible, such as 90 mm, but... the current density is not uniform along the long slit.

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

Tabletop: For a cyclotron chimney only the few-mm of slit facing the dee gap matters; a ~1-2 mm wide slit is the proven starting width before puller optimization.

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. 81-82

Tabletop: The reference machine's cyclotron field (>0.1 T at the center) already satisfies the PIG minimum, so a next machine's internal PIG source can trade the fragile filament for a self-heated cathode running a sub-kV, multi-ampere arc.

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

Tabletop: With a ~1 mm^2 chimney slit, even a 1-A arc gives ~0.1-1 mA available at the slit, orders of magnitude above the reference machine's nA beams; source output will not be the bottleneck.

The arc power for cold cathode operation is limited to about 1 kW per cathode... The cold and hot cathodes are worn out when the erosion crater's depth reaches around the anode bore radius.

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

Tabletop: Gives a concrete inspection criterion: measure the cathode pit depth against the chimney bore 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

Tabletop: A next machine's source can keep a small filament hidden behind a Ta block cathode, out of the hydrogen plasma, converting filament sputtering into slow self-sputtering of a thick block.

at normal operating pressures of 10^-4 mm Hg, between 1/2 to 2 amps at 100 to 500 volts will be required

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 6, 10

Tabletop: Directly applicable operating envelope for a simple hot-filament source at the reference machine's scale.

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

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 6, 10

Tabletop: Directly applicable gas-flow set-point; the reference machine's parker metering valve fills the needle-valve role.

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

Tabletop: Directly applicable filament sizing; the modern equivalent of the battery filter is a well-filtered DC (not raw rectified) filament supply to stop magnetically driven filament vibration.

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

Tabletop: A proven upgrade from a bare filament for a next machine: better-defined source position, less RF loading of the plasma.

Higher frequency, lower H2 and base pressure, lower filament voltage

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

Tabletop: For the reference machine's current-hunting: before adding RF watts, cut chamber pressure and re-optimize filament bias - Houghton's 7x gain cost zero watts.

fusion efficiency is enhanced by transparency of at least 92 percent (Donovan). The inner grid is 99.18 percent transparent with three loops

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

Tabletop: The transparency bookkeeping (wire cross-section vs aperture area) is the same calculation the builder needs for any grid, mesh, or slit that their beam must pass repeatedly.

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

Tabletop: When the builder meters 'beam current' anywhere near a hot cathode, part of it is electrons; a high-work-function collector surface and magnetic electron suppression keep the nA readings honest.

Assuming that sagging occurs at ~1,500 K and equating the black body radiation rate to the input power... This gives 9.5 mA of ion current at 200 kV.

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

Tabletop: Same balance sizes any wire electrode, probe, or beam stop in the reference machine's chamber: compute AeσT^4 at the material's sag temperature and keep beam-power deposition below it.

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.

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

Tabletop: W-Re thermocouple wire is commercially available in small quantities and is the best upgrade for any sputtered electrode in the reference machine's source: W durability with Ta-like workability.

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

Tabletop: When the builder scales chamber geometry or pressure for the p-B11 test cell, keep pd constant to preserve the discharge; and remember all sputtering damage happens at the cathode sheath edge.

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

Tabletop: Explains why the reference machine's source may need a several-kV kick to strike but then runs at a few hundred volts, and why current-limited (ballasted) supplies are mandatory to stop glow-to-arc runaway.

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

Tabletop: For any glow-driven ion supply in the p-B11 experiment, pressure is the ignition control: strike at higher pressure, then throttle the MFC down to the running point.

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

Tabletop: If the builder builds an IEC-style p-B11 test stand, a few large openings aligned with the beam axis beat a fine mesh: fewer grid hits, higher effective transparency, longer grid life.

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

Tabletop: Matches the reference machine's hydrogen filament source philosophy: a modest positive bias (order 100-200 V) on/near an emitter sustains ionization at pressures where a self-sustained discharge dies.

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

Tabletop: Same rule protects the reference machine's Faraday cup stalk and source supports: unshielded biased metal collects spurious current and sputters.

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

Tabletop: Saves tuning time: spend effort on dee voltage and pressure, not filament bias, when hunting current.

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

Tabletop: Gives the builder a target pressure window and the expected non-monotonic current-vs-pressure curve to map on their own machine.

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

Tabletop: 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.

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.

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

Tabletop: Directly sets the gas-handling operating window for the reference machine and explains a common 'no beam' failure at too-good vacuum.

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

Tabletop: An amateur-grade insulated feedthrough scheme (alumina tube + Ceramabond) the builder can reuse for chimney anodes or filament leads inside the next machine.

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

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

Tabletop: A directly copyable permanent-magnet source recipe for the next machine's external or test-stand source at exactly hobby machining tolerances.

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

Tabletop: Directly applicable to the reference machine's filament/arc supply metering; logging supply volts instead of electrode volts corrupts any operating-point map.

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

Tabletop: The reference machine's MFC feed into the source chimney matters most when the main chamber is well-pumped; in a small chamber the distinction between injection and backfill largely disappears.

the plasma discharge ignites easily at 1 kV or less for all cases and produces a continuous positively charged ion beam.

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

Tabletop: Tens-of-uA proton output at under 1 kV anode drive is ample for the reference machine's nA-scale accelerated beam; a multi-kV arc supply is not required to start.

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

Tabletop: Gives the builder a sanity check: nA-to-uA beams need only uA-to-mA class discharges; if their beam/arc ratio is far below ~20% the extraction geometry is losing beam.

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

Tabletop: 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

Tabletop: Benchmarks source lifetime for a next machine; hot filaments burn out far faster than a cold-cathode PIG at this scale.

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

Tabletop: A direct benchmark for the reference machine's MFC-vs-chamber-pressure curve; large deviations from ~1.5e-5 Torr per sccm (at similar pumping speed) indicate leaks or conductance problems.

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. 19

Tabletop: Relaxes the reference machine's machining tolerances on the next machine's source gap and sizes the arc supply: a 3 kV current-limited unit suffices.

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

Tabletop: At the reference machine's much lower arc powers passive/conductive cooling may suffice, but the sanded-cathode arc-striking trick transfers directly.

Their cathode was a U-shaped tantalum filament, heated with about 400 amps... 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

Tabletop: Brackets the design space above the reference machine's filament source: proton output scales with arc current and slit area over 3+ orders of magnitude, so their nA needs are met with sub-ampere arcs.

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

Tabletop: Tells the builder exactly what to expect when they widen their next machine's chimney slit: current scales faster than linearly with width, emittance grows more slowly - widen until the machine acceptance is filled.

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

Tabletop: Sets the reference machine's dee-tip/puller gap voltage budget: with clean electrodes, plan on order 10 kV per mm of gap and generous edge radii.

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

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

Tabletop: Decides a next machine's chimney aperture style: cut a tall narrow slit, not a drilled hole, if beam brightness and predictable optics matter.

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

Tabletop: For the builder: cranking arc power buys current with diminishing returns but does not spoil beam quality below ~230 uA - space charge is negligible at their nA-uA scale.

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

Tabletop: Directly actionable on the reference machine's MFC: starving the source of gas silently changes beam species; their flow setpoint should stay above the arc-mode transition.

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

Tabletop: Gives the builder the initial-condition recipe for any first-turn orbit simulation of their next machine's central region.

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

Tabletop: The 3-degree-taper Series 20 spread over 9 turns gives the fine, repeatable hydrogen admission an ion source needs; log turns-open as the process setpoint.

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

Tabletop: Put an isolation valve between the gas bottle and the metering valve; forcing the tapered stem closed to seal will ruin the calibrated taper and still leak 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

Tabletop: Arc V-I and few-cc/min gas flow transfer almost unchanged to a small chimney source; graphite chimney/slit parts resist sputtering far better than copper or steel.

The alignment of the ion source with the magnetic field and with the accelerating slits is critical and is carefully adjusted to obtain best performance.

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

Tabletop: 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

Tabletop: Directly applicable control philosophy, trivially implemented today with two small feedback supplies; a constant-current arc is what makes beam current reproducible shot to shot.

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.

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

Tabletop: Cheap, high-leverage geometry rule for the reference machine's PIG-style source: chamfer the slit edges ~45 degrees and keep it tall-and-narrow before touching anything else.

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

Tabletop: If a next machine ever moves to an external source and axial injection, inject at a few kV below the dee amplitude rather than pushing injection energy up for easier transport.

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

Tabletop: Explains why only ~30% of source output ever accelerates in the reference machine; the builder tool should launch macroparticles over 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

Tabletop: The reference machine's source will sit at the bottom of the cold-cathode range (tens-hundreds of mA); crossing into the self-heated regime (AMIT saw it at ~250 mA) flips the V-I slope negative, so the arc supply must be a stiff current source in both regimes.

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

Tabletop: Means ion energy hitting the cathodes ~ full arc voltage (sputtering scales with it), and the chimney (anode) can be grounded to the chamber with the cathodes run negative — one floating supply only.

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

Tabletop: The reference machine's 0.59 T and a higher-field successor's ~0.9 T are both comfortably above threshold — the PIG will ignite and run without any special field tailoring, and cyclotron field tuning won't detune the arc.

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

Tabletop: 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

Tabletop: Run current-regulated and watch arc voltage as the health/flow indicator — creeping arc voltage at fixed current means gas starvation (or a worn cathode), long before the arc actually drops out.

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

Tabletop: The reference machine's 50-150 W arc is 10x below this ceiling — pure secondary-emission operation, cathodes stay "cold" (no filament economics), and dc operation is fine.

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

Tabletop: Cathode buttons are the only consumable: a 3 mm thick disc with a ~3 mm bore anode lasts until ~3 mm of crater. Make them screw-in Ta (hydrogen, low power, may run warm) and stock spares; lifetime is hours-to-hundreds-of-hours depending on arc power, not the tens of hours a bare filament source gives.

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

Tabletop: The headline for the reference machine is the gas line — full-size accelerator PIGs run on 0.2-0.6 sccm, a 3-10x reduction from its current 2 sccm open filament feed, because the chimney confines the neutral gas where the ionization is. Dimensions scale down for a 38 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

Tabletop: Plumb the MFC line into the chimney base near a cathode (AMIT feeds through the cathode cavity itself), not into the chamber — this is where the chamber-pressure win over the bare filament comes from.

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

Tabletop: For the symmetric cold-cathode chimney just strap both cathodes together on one HV feed; a floating anticathode also works if the second feedthrough is awkward, at some cost in control.

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

Tabletop: A 10-50 eV spread against a few-keV first gap is a phase-space nonissue for the reference machine; do not trade source simplicity for energy spread.

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

Tabletop: Corroborated by AMIT (up to -3 kV and 10 sccm, strikes in seconds, sustains <1 kV) and Forringer (3 kV/1 A Glassman in current limit). Spec the arc supply for 3 kV compliance even though running voltage is ~500-1500 V, and automate: gas up -> HV on -> detect V collapse -> gas down.

For internal sources, the anode is usually grounded and 30-100 kV of rf voltage is used for extraction with a feeler or puller extending from the dee.

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

Tabletop: The reference machine extracts with its few-kV dee — 10x less voltage than any literature machine. Compensate with a small source-puller gap (1.5-2.5 mm, cf. Siemens 2.3 mm, K100 2.9 mm) since extracted current scales ~V^1.5/d^2, and expect proportionally lower beam than published uA figures.

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

Tabletop: That figure is for 1-15 A heavy-ion arcs; sputter erosion scales down with arc power and hydrogen sputters far less than argon/xenon — the Siemens PET machine (0.27 A, H2) gets 120-300 h. At the reference machine's <=150 mA expect hundreds of hours per cathode set.

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

Tabletop: Existence proof that mA-class hydrogen PIG output needs only tens of watts and home-shop fabrication (spot-welded sheet anode, epoxied alumina tubes). The axial-extraction geometry differs from a cyclotron chimney but the discharge economics transfer directly.

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

Tabletop: The 25% utilization is for axial extraction of the whole column; radial slit extraction runs ~0.1-0.5% (Forringer) because the slit samples a sliver of the plasma. Use the right figure for the right geometry when predicting a next machine's beam.

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

Tabletop: Start a next machine with the 0.5 mm x 5 mm slit: at 50-150 mA arc it made 230-590 uA at 40 kV; even derated ~30x for a 4 kV dee (V^1.5 scaling at fixed gap) that is ~10-20 uA available — four orders of magnitude over the present 3 nA best.

The chamfer in both of the slit chimneys tested was 10 [deg] ... was 0.010" deep (out of a 0.020" thick chimney wall) leaving a 0.010" [land]

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 77, 84, 95-97

Tabletop: These are the actual machining callouts for a chimney a home shop can cut — thin land so the slit doesn't collimate away the beam, chamfer opening outward toward the puller.

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

Tabletop: Generous mechanical tolerance — the chimney stack-up doesn't need precision fitting. But take the cooling warning seriously even at 100 W-class 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

Tabletop: Species purity is a tuning knob the reference machine has never had: run the PIG current-regulated at healthy gas flow for a clean proton beam at f = qB/2*pi*m, or starve it deliberately to hunt H2+ on harmonics. Removes the H+/H2+ ambiguity that has dogged the reference machine's run interpretation.

have been used in magnetic fields as high as 4.5 Tesla in the Harper Medical Cyclotron (and as low as 0.5 Tesla during low magnetic field tests in the NSCL ion source test stand)

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. 27, 39

Tabletop: The reference machine's 0.59 T sits just inside the demonstrated envelope, and its existing turbo + 1e-6-ish base pressure meet the start requirement as-is.

The minimum gap between the chimney and the puller is 2.9 mm [K100 geometry]

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

Tabletop: Gap scales with voltage to hold gradient — at a few kV dee the builder can close the chimney-puller gap to ~1.5-2 mm to recover extraction field, still an easy gradient (<2 kV/mm) against vacuum breakdown limits.

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. 3

Tabletop: Drop-in starting condition for the reference machine's central-region orbit models — start protons at 4.5 eV from a flat sheet across the slit, not from rest at a point.

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

Tabletop: 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. Note it makes H-; a positive-ion version at the same point yields substantially more H+ since H- is the minority species.

anodes made from molybdenum with circumferential groove features lowered the arc power by 7% and increased the target beam current by 20%

Potkins et al., Improvements to Siemens Eclipse PET Cyclotron Penning Ion Source (2017) — p. 3-6

Tabletop: The cool-ring and Cs tricks are H--specific (volume/surface production of the minority ion); for the reference machine's positive-ion source the transferable lessons are the material one (Mo anode fine, fancy cathode materials not worth it) and that geometry near the slit dominates output.

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

Tabletop: For a machine starved of axial acceptance a hole source wastes less injected beam, but total current favors the tall slit. The weak-focusing reference machine with a 1.5" gap has generous axial acceptance — use the slit.

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

Tabletop: If the builder keeps the arc <=150-200 mA it stays in the well-behaved positive-impedance regime where a simple current-regulated supply plus modest ballast is unconditionally stable.

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

Tabletop: Scale to the reference machine's ~100 W arc — cathode heads still run incandescent (they are meant to), so mount them on refractory stems; the chimney body dissipates tens of watts, manageable by a copper stalk conduction path to a water-cooled or finned feedthrough flange.

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

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

Tabletop: Direct chimney-bore callout for a next machine — 7-8 mm ID copper or Mo tube, matching Ta cathode discs. At 0.59 T the electron column is fatter than at 2 T, so err toward 8 mm.

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

Tabletop: 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 of ~ +/-2 deg with sub-degree feel for slit-to-puller aiming — set-and-lock, in-vacuum.

Ion Source Power [kW] 1.5 (Table 1)

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

Tabletop: Sets the ceiling-class datum; the reference machine's design point (~0.1-0.2 kW) is a deliberate 10x derating of commercial practice, consistent with uA-class rather than 100-uA-class internal beam.

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

Tabletop: The half-step option — chimney-over-filament keeps the reference machine's existing filament supply and adds gas confinement + defined emission aperture. Worth knowing it exists, but a PIG chimney gets the same geometry benefits and deletes the filament.

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

Tabletop: Conditionally applicable - a bipolar, current-limited bias supply on the next machine's dee lets the builder try both polarities safely and keep whichever helps beam.

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

Tabletop: 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 even good 1950s machines lost most of the beam at extraction, 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

Tabletop: Strong population-level evidence for upgrading a next machine from cold-cathode PIG to a hooded filament arc; that single change is what separated 100 uA-class machines from starved ones.

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

Tabletop: The geometry lesson is scale-free even though these are milliamperes of internal beam - a doubled capture fraction and cooler dee tips from source position/orientation alone; for the reference machine's filament source, radial position and slot azimuth are cheap, high-leverage experiment variables (directly relevant to a planned source-species test).

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

Tabletop: A 26% energy gain from moving the source — on the reference machine, treat filament/chimney height relative to the median plane as a tuned parameter worth systematic scans, not a set-and- forget dimension. Symmetric placement about the magnetic (not mechanical) midplane is the target.

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.

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

Tabletop: 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

Tabletop: 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 dominate at weak arc — run the arc hard for protons. (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

Tabletop: On a tabletop machine where every watt of RF matters, an oversized source aperture wastes drive as ion loading; try a shorter emission slit on the reference machine's source and watch accepted beam per unit dee loading, not raw source output.

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

Tabletop: Worth a cheap experiment on the reference machine (a DC bias supply on the dee), but the ORNL conclusion is that geometric phase selection (a slit) beats electrostatic tricks — put the effort into the puller/slit geometry first.

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

Tabletop: Strong design input for a next machine: budget at least one live source degree of freedom (rotation or z) through the vacuum wall — both ORNL machines retrofitted it after finding the optimum could not be reached blind. On the reference machine, even a graduated feedthrough beats vent-adjust-pump iteration.

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

Tabletop: 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

Tabletop: Current bookkeeping is free diagnosis — on the reference machine, meter the puller and chimney drains separately from the Faraday cup; a weak beam with a hot puller is a geometry problem at the source exit, and no arc-power increase will fix it.

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

Tabletop: 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

Tabletop: The same arithmetic the builder runs with the MFC - P = Q/S plus pump ultimate. A 0.1-1 sccm hydrogen feed is 1.3e-3 to 1.3e-2 torr-l/s; divide by the honest effective speed at the chamber to predict running pressure before touching hardware.

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.

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

Tabletop: Direct lesson for the reference machine's central-region debugging — the source body's DC potential is a real optics knob (or a real gremlin). Verify the filament/chimney ground path is defined and logged; an intermittent source ground would masquerade as day-to-day beam irreproducibility of exactly the kind ORNL-1347 warns about.

It is now possible to accelerate the beam through the difference-coupling resonance vr - vz = 1 without attenuation, even without the horizontal magnetic field compensated.

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

Tabletop: Scale-free: central-region collimation and source definition (a planned source-species test on the reference machine) buy margin against every downstream loss mechanism; fix beam quality at birth, not at radius.

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

Tabletop: Any reference-machine or next-machine source-bias or puller experiment must respect the same ordering - source extraction potential is bounded by the rf accelerating potential actually available at the first gap, or the first gap runs backward.

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

Tabletop: For the reference machine's filament source (and a planned source-species test) the lesson is that arc electron energy is gas-pressure-coupled - lowering flow raises mean electron energy, which shifts the H+/H2+ balance; align source slits to B before blaming the arc supply.

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

Tabletop: The reference machine's chimney-slit geometry is a free knob - but ornl-1339 (same machine, five quarters earlier) showed arc-slit LENGTH also feeds z-wise beam loss, so pair any slit lengthening with the z-distribution probe check.

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

Tabletop: The reference machine's central tuning trap - a source tweak that fattens the inner-radius signal can starve the Faraday cup at full radius. Always score source changes at the outermost probe position.

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

Tabletop: A caution for any puller-electrode or biased-extraction scheme on the reference machine - after four quarters of trials (ornl-1269 through -1531) ORNL's dc injection still lost to the ordinary rf gap; 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

Tabletop: 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. It keeps a neutron survey requirement honest even though the expected yield at tabletop beam densities is tiny.

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

Tabletop: The staging discipline transfers to every machine even where activation does not — low-duty, small-radius-first commissioning is also how you protect septa, collectors, and instruments; at a few hundred keV and above the activation logic itself starts to matter.

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

Tabletop: For sliding/rotating shafts into the chamber, dual O-rings in polished glands (surface finish and land tolerance doing the real work) outlast fancier stack packings; seal geometry matters less than the finish it rides on.

the ion discharge aperture (0.09" x 0.50") 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

Tabletop: Source aperture height and tilt relative to the median plane set 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

Tabletop: The keV-yield plateau means any small ion gun in the 5-25 keV range is a usable deposition tool; choose Ar for economy, Kr/Xe when a 2-3x rate matters more than gas cost.

A typical deposition rate for substrates located 2.5 cm from the sputtering source is 20 ug/cm2/min. of titanium.

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. 114

Tabletop: Calibration point for sizing any home sputter-deposition scheme — mA and tens of keV, i.e. small-accelerator ion-source technology, not exotic hardware; a boron deposition run for a 100 ug/cm2 target is minutes, not days.

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

Tabletop: A documented small PIG design point (geometry, discharge mode, gas flow, stability) from outside the cyclotron literature — the filament-free argument is the same one that favors PIG sources inside a cyclotron.

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

Tabletop: The bench recipe for making Ti-H/Ti-D loaded pieces — hydride targets or gas reservoirs — with nothing but an RF or furnace heater, a differential gauge, and scrupulous gas drying.

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

Tabletop: The commercial gun class (Ion Tech FAB11NS type) is bench-scale and vacuum-modest — the natural route to boron and refractory films for targetry without an e-gun; neutral-beam operation also suits insulating targets that would charge under ion-only sputtering.

a magnetic mirror built into the upper end of the arc hood by the simple insertion of a steel bearing ball 1/8" in diameter.

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

Tabletop: DIRECT and nearly free for any filament hooded source running in the main field: a bearing ball is stock hardware and the hood already exists. This is the halfway house between a plain filament arc and a cold-cathode PIG — same electron-reuse physics, no second cathode, no separate supply.

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

Tabletop: A diagnostic that costs a glance: if the chimney/hood top of a small source runs orange-hot, the arc power is exiting axially instead of ionizing gas — evidence for adding reflection (mirror or repeller) and a before/after check that it worked.

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

Tabletop: The physics argument for reflex geometry at any scale — the same multiple-pass ionization a PIG buys with two cathodes, obtained here with one filament, its own space charge, and a ball. Severalfold less arc current means severalfold less filament drive, heat, and gas decomposition in a source the size of a thumb.

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

Tabletop: Directly answers the standing filament-source maintenance complaint: a 3-7x life extension from a passive part is worth more per run-hour than any filament-material change. Tungsten evaporation is brutally steep in temperature, so every ampere of arc current not needed pays back in hours.

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

Tabletop: An honest negative result from 1961 that still stands: the electron injection angle into the mirror (set by filament orientation relative to B) decides whether electrons are inside or outside the loss cone. Plan the mirror experiment as an A/B test with the glow diagnostic, and try filament orientation as a variable if the first try fails.

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

Tabletop: Two rules in one: (a) the chimney slit is the gas throttle — sizing it small is the cheapest pumping upgrade a small machine can get; (b) the asymmetric erosion (beam-side, along rotation) is both a wear mechanism and an inadvertent beam diagnostic showing where first-turn ions strike the hood.

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

Tabletop: Concrete supply-sizing anchors: ~100 W of arc fed a 27" machine's proton beam. The saturation observation is the operating doctrine — beyond the knee, extra arc current buys filament wear and gas load, not beam. Find the knee on your own source and park below it.

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

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

Tabletop: Mostly a scoping warning for any future gas change: a source tuned for hydrogen is not a universal source. The tantalum-button-on-quartz construction detail is also this collection's only sketch of a helium-specific hooded source, 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 (c. 1950) — p. 33

Tabletop: A central field bump gives axial focusing in the first turns, where small machines lose most of their beam. A machined center button is one of the cheapest beam-current experiments available to the reference machine or a next machine — the no-minimum constraint is the part that takes care.

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 (c. 1950) — p. 65

Tabletop: The reference machine's filament-change downtime is this exact problem, solved in 1951: a small gate-valved source lock plus an external sylphon/bellows positioner turns a half-day vent cycle into a minutes-long swap and adds live source alignment — high payoff on any filament-eating small machine. (The shuttered viewport is a free detail worth stealing.)