Vacuum 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.

The total required aperture size is the sum of the good field region, the vacuum chamber thickness (0.3-2 mm) and a margin for installation and alignment (0-5 mm).

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 14

Tabletop: Explains why the pole gap must exceed the chamber's internal height by a centimetre or so; useful when trading gap (and hence amp-turns) against chamber wall thickness.

Polepieces of meehanite steel facemilled to a profile that gave appropriate field index... 1.6kVpp on Ds, 400Wpk. Base pressure 0.01mTorr

Niell, Effective Scientific Equipment Procurement Strategies: Building on a Budget (2010) — p. 11-17

Tabletop: An existence proof at exactly the reference machine's energy: modest dee voltage (1-2 kVpp), 1e-5 torr, and a machined pole profile suffice below ~300 keV; heroic RF and UHV are not prerequisites.

12 inch diameter poles pieces forming a 4-inch gap to which upper and lower pole tips up to 1-inch thick can be easily attached and removed.

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

Tabletop: A complete cross-check machine for a next machine's sizing; note the removable-pole-tip trick that lets one magnet host many field profiles.

small gap: reduced number of At of coils, pole radius reduced, orbits close to outer edge, no space, very sensitive to errors : vertical losses. large gap: large space: injection, extraction, probes, easier vacuum pumping, lower field

Beeckman, Cyclotron Magnets — ECPM37 lecture, Groningen (2009) — p. 65

Tabletop: Frames the central decision for a next machine (the reference machine's chamber must fit in the gap) with the actual list of consequences on both sides.

This loading of the D circuit by discharge currents holds the D potentials down to a few hundred volts ... Unless the loading is removed, the chamber will continue to operate in the low-voltage, blue-glow discharge condition indefinitely.

Livingston & Blewett, Particle Accelerators (1962) — p. 188

Tabletop: The reference machine's ~1.3 kV dee sits right in classic multipactor territory; surface conditioning, low pressure, and the ability to snap the drive up fast are the standard escapes.

about 50 per cent thicker than the depth of the groove to allow for compression ... 1/4-in. gaskets have proved adequate for even the largest seals ... Conductivity for rf currents through such a seal can be assured by half-covering the gasket with a thin copper-foil strip.

Livingston & Blewett, Particle Accelerators (1962) — p. 199-201

Tabletop: Directly usable rules for the reference machine's lid and port seals; the copper-foil RF bridge over elastomer joints prevents mysterious Q loss and local heating.

For typical cases of interest, 'vacuum' pressure is lower than 10-5 torr, and 'gas' pressure higher than 10-4 torr.

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 23

Tabletop: Cyclotrons run 1e-5 to 1e-4 torr with gas feed - squarely in the gray zone - so the reference machine's spark limit will move with operating pressure, and tests at base pressure overstate what they can hold with gas flowing.

r.f. power should never be left on for prolonged periods under these circumstances, else the risk is run of cracking the glass dee insulators. The power and length of application should be gradually increased

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

Tabletop: Directly applicable startup ritual at the reference machine's 1.3 kV dee level; persistent glow during conditioning signals organic contamination (grease, oil, rubber) in the tank.

40 of 52 contaminated sites broke down, while only 1 of 16 uncontaminated sites broke down at or below the maximum field

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 78

Tabletop: The single biggest lever on the reference machine's dee-voltage ceiling: gloves, solvent cleaning, and dust-free assembly of dee and stem buy more holdoff than any material upgrade.

breakdown occurs between 5 and 200 MV/m ... In general, smaller gaps can withstand higher fields.

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 78, 95

Tabletop: At 13 kV across the reference machine's ~6 mm gap the mean field is only ~2 MV/m - if it sparks there, the cause is edges, insulators, particles or gas pressure, never the vacuum gap itself.

In the 'early processing' regime, breakdown is overwhelmingly likely to increase the breakdown field of a cathode site.

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 91-92

Tabletop: After assembling the next machine, the builder should ramp dee voltage slowly and let a limited number of current-limited sparks condition the surfaces before declaring a voltage ceiling.

The screw holes need to be vented so that they do not trap air or water and slowly outgas when the dee is placed in the vacuum chamber.

Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009) — p. 52

Tabletop: Directly applicable to any screwed-together dee on a next machine: unvented blind holes are virtual leaks that cap the achievable base pressure.

The peripheral walls of the dees are perforated to permit high pumping speed. Graphite plates are attached to the inside of the dees ... to protect the copper from the stray proton beam.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 50, 7

Tabletop: Perforation transfers directly (pressure inside an unvented dee can be much worse than gauge pressure); graphite armor matters only if a next machine reaches activation-capable energies.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

201 through 284 / 1/8 / .139 +/-.004 / .101 to .107 / .028 to .042 / 20 to 30 / .177 to .187 / .158 to .164 / .010 to .025

Parker Hannifin, O-Ring Handbook — Design Chart 4-3: O-Ring Face Seal Glands — p. 1

Tabletop: Directly hands the mill the numbers for every lid and port groove on the next machine's chamber; note the vacuum groove width is narrower than the liquid-service column.

Surface finish X: 32 for liquids, 16 for vacuum and gases. Finishes are RMS values.

Parker Hannifin, O-Ring Handbook — Design Chart 4-3: O-Ring Face Seal Glands — p. 1

Tabletop: A fly-cut or turned finish on the chamber lid seat should be specified/checked to 16 RMS; a rougher face is a common reason a 1e-6 Torr system stalls in the 1e-5s.

For External Pressure (inward pressure direction) dimension the groove by its inside diameter (Hi) and width: (H)i = Mean I.D. of O-ring

Parker Hannifin, O-Ring Handbook — Design Chart 4-3: O-Ring Face Seal Glands — p. 1

Tabletop: For an evacuated chamber atmospheric pressure pushes the ring inward, so the groove ID (not OD) is the controlled dimension when laying out the lid groove.

A good rule of thumb is to provide a pumping speed of at least 1 liter/sec at 10-5 mm Hg per liter of volume ... 15 to 20 min is considered a good design figure.

Livingston & Blewett, Particle Accelerators (1962) — p. 197-198

Tabletop: For a ~30-50 liter tabletop chamber the SI100 (~100+ l/s class) comfortably beats the 1 l/s-per-liter rule - margin that matters because source gas load dominates.

A double-gasket seal is frequently used with a pump-out connection to the space between gaskets. This arrangement makes it possible to test the seal for vacuum-tightness quickly and with certainty.

Livingston & Blewett, Particle Accelerators (1962) — p. 200

Tabletop: Worth adopting on a next machine's main lid: a guard-vacuum groove turns the worst leak hunt into a valve twist.

increasing the squeeze reduced the leak rate dramatically... at 50% squeeze the beneficial effect of the grease was not detectable.

Parker Hannifin, O-Ring Vacuum Sealing, Catalog 5705B (1998) — p. 3-4

Tabletop: Justifies cutting a next machine's grooves at the deep end of the squeeze range (25-30%) rather than greasing the rings harder; grease is a crutch for light squeeze.

L = .7FDPQ(1-S)2 where: L = Approximate leak rate of the seal, std. cc/sec.

Parker Hannifin, O-Ring Vacuum Sealing, Catalog 5705B (1998) — p. 5

Tabletop: Lets the builder compute the permeation floor of their 10-inch Viton lid seal and check whether O-ring permeation, not leaks, sets their ultimate pressure.

care being taken to insure that there are no machine or tool marks perpendicular to the seal... The ideal surface finish for any vacuum seal flange has a circular lay

Parker Hannifin, O-Ring Vacuum Sealing, Catalog 5705B (1998) — p. 5

Tabletop: Face the lid seat on a lathe (concentric lay) rather than fly-cutting or hand-sanding radially; never sand a groove crosswise to remove a blemish.

Vacuum Level: Approximately 1 x 10-6 torr ... Butyl .18 ... Nitrile 1.06 ... Nitrile 3.45 ... Fluorocarbon .07

Parker Hannifin, O-Ring Vacuum Sealing, Catalog 5705B (1998) — p. 6

Tabletop: At exactly the reference machine's operating pressure: cheap Buna-N rings will slowly deposit oily film on feedthrough insulators and dee stems; Viton's 0.1%-class loss is why it is worth the money.

Butyl 6.5 @ 77F ... Fluorocarbon 12.7 @ 77F ... Silicone 238.0 @ 77F

Parker Hannifin, O-Ring Vacuum Sealing, Catalog 5705B (1998) — p. 7

Tabletop: Confirms Viton is a sound choice at 1e-6 Torr; if helium leak checking becomes routine, remember He walks through silicone and fluorosilicone.

Alpha resolution measurements should be made with a detector source spacing equal to 1.5 to 2 times the detector diameter and under good vacuum (< 100 microns HG or 10 Pa).

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1

Tabletop: For his ~8 mm active-diameter PIPS, that is 12-16 mm standoff; closer spacing degrades resolution through wide-angle entrance-window losses.

This maximum value called the 'critical forepressure,' ranges from 25-75 Pa (0.2-0.6 Torr)... The critical forepressure should never be exceeded.

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 232-233

Tabletop: Size and maintain the SI100's backing pump so the foreline stays well under ~0.2 Torr even during beam-gas loads; a tired rotary pump silently pushes the foreline over the cliff and dumps oil vapor into the chamber.

The outgassing rate of unbaked, uncleaned stainless steel is of order 10-5 Pa-m/s after 10 h of pumping... reduced by a factor of 10-100... to be suitable for high vacuum

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 308

Tabletop: Multiply the next machine's internal area by 1e-5 Pa-m/s and divide by delivered pumping speed to predict the 10-hour base pressure before drilling a single hole.

O-rings are typically compressed 15-20% of their diameter... the general criterion for high vacuum sealing to be a minimum initial contact pressure of 13 kg/cm2

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 337-338

Tabletop: The 2.7 kg/cm figure sizes the lid bolting: a 10-inch-circumference seal needs on the order of 200+ kg of clamping just for the ring, before atmospheric load helps.

An unbaked Viton O-ring will have an initial outgassing rate of 10-3 Pa-m/s... After a 4-h bake at 150C and 12 h of pumping, this value is reduced to 4x10-7 Pa-m/s.

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 340

Tabletop: Pre-baking the Viton rings in a small vacuum oven before assembly is one of the cheapest order-of-magnitude improvements available to a diffusion-pumped 1e-6 Torr system.

Grease is not needed to make a static seal between an elastomer and a metal surface. It will cause pressure bursts as trapped gas pockets are released.

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 340

Tabletop: Counters the amateur habit of greasing everything; on a clean 16 RMS seat with proper squeeze, dry Viton seals better and cleaner.

one should not rough a chamber with an oil-sealed mechanical pump below a pressure of circa 10-15 Pa (100-150 mTorr), otherwise oil backstreaming would contaminate the chamber... the '100-mTorr rule' is valid [for small systems]

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 379-381

Tabletop: The reference machine's chamber is exactly the 'prototypical small system': valve over to the SI100 at ~100 mTorr, don't let the rotary pump grind down to 10 mTorr first.

External leak checking with helium should begin at the top of the chamber; only a small helium flow rate is necessary... Welds and seals are the most common leak sites

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 467-470

Tabletop: Helium rises - spraying from the bottom up floods every joint at once and destroys localization on a chamber with many ports.

A molecular leak causes a linear increase in pressure with time. Outgassing causes the pressure to rise to a steady-state value

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 468-469

Tabletop: First diagnostic to run whenever a next machine won't reach base pressure - it needs only the existing gauge and a stopwatch, and decides whether to reach for the helium bottle or the bakeout tape.

The permeation time is about 20 min for a typical Viton O-ring... First, do not attempt to leak check the system during baking.

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 469-470

Tabletop: On an all-Viton chamber, spray briefly and wait; a slowly rising He signal minutes after spraying is gasket permeation, not a leak at the last joint sprayed.

Air leaks are discerned by the presence of oxygen at m/z = 32... Outgassing and water line leaks each can produce a large peak at m/z = 18, but they can be distinguished by the rate of rise.

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 471

Tabletop: A used RGA head is arguably the single best diagnostic upgrade for a next machine - one spectrum replaces a day of guessing.

the molecular conductance per unit area of any structure in molecular flow has a maximum value [11.6 L/(s-cm2) for air at 22C]

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 48-50

Tabletop: Sets the ceiling on what the SI100 can actually pump through the chamber port: a 4-inch (81 cm2) opening passes at most ~940 L/s, and a baffled elbow far less - size the pump port as large and short as possible.

Room temperature outgassing data for most gases sorbed on metals, including water vapor, show the outgassing rate to vary inversely with time, at least for the first 10 h

O'Hanlon, A User's Guide to Vacuum Technology, 3rd ed. (2003) — p. 80-81

Tabletop: Explains why the chamber keeps improving overnight without any leak being fixed, and why comparing pump-down curves is only fair at equal elapsed times.

Rule of thumb - one monolayer consists of ~1e15 molecules (atoms) per cm2

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 42-43

Tabletop: Explains why pump-down history and surface cleanliness dominate over chamber volume: the reference machine's chamber volume empties in seconds, the walls take days.

Real Leaks: external, constant flow, constant pressure rise. Virtual Leaks: internal, decreasing flow, decreasing pressure rise.

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 429-433

Tabletop: The decreasing-vs-constant slope distinction also flags virtual leaks from unvented hardware, which a helium sprayer can never find from outside.

Vacuum rated to 1 x 10-8 Torr (better suited to 1 x 10-6 Torr). Temperature rating is dependent on which elastomer o-ring is used (usually 150C)

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 443-446

Tabletop: Matches the reference machine's observed 1e-6 range with Viton - it is the natural floor of an all-elastomer system; a CF port or two on a next machine (gauge, RGA) buys headroom cheaply.

Avoid phrases like; leak tight, vacuum tight, good to 10-8 Torr, good for ultrahigh vacuum, etc.

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 456-464

Tabletop: When farming out a next machine's welds or buying used hardware, write the acceptance spec as a number (e.g. no single leak >1e-9 atm-cc/s He) - 'vacuum tight' is unenforceable.

Stainless Steel (unpolished) 266 [1 hr] 20 [4 hrs]... Mild Steel, slightly rusty 58,520 199 (mBar-l/sec-cm2 x 10-10)

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 49

Tabletop: The 200x penalty for rusty mild steel is the argument for keeping any exposed magnet pole faces inside the chamber plated, painted with vacuum-compatible coating, or clad in stainless.

Mechanical Cleaning; Degreasing or Solvent Cleaning; Detergent Cleaning; Chemical Etch; Electrolytic Polishing; High Pressure Spray; Bake-out

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 497-513

Tabletop: Scaled down: acetone wipe, hot detergent wash, DI rinse, N2 or oven dry, gloves-only handling afterward gets most of the professional benefit for chamber internals.

A virtual leak is a volume of trapped atmospheric gas that leaks into the vacuum vessel through holes or cracks that do not go all the way through the vessel wall. [Examples:] Unvented Screw, Two Welds in Series, Unvented Double O-rings

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 59-63

Tabletop: Every internal socket-head screw in the next machine (dee supports, ion source mounts) needs a vent hole, a slotted thread, or a vented washer; a slot machined in the O-ring groove floor serves the same purpose.

Face-type o-ring seals are recommended. Use as heavy a squeeze as possible... Two o-rings in series can drastically reduce permeation.

Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 71-74

Tabletop: If a next machine targets below ~5e-7 Torr with elastomers, a double O-ring lid groove pumped by the existing roughing pump (guard at ~15 mTorr) removes the permeation floor for the cost of one extra groove and a hose barb.

An acceptable vacuum would allow for a mean free path an order of magnitude larger than the expected flight distance.

Dewan, Design and Construction of a Cyclotron Capable of Accelerating Protons to 2 MeV — MIT thesis (2007) — p. 9-11

Tabletop: The quantitative vacuum spec for a next machine: total path length ~ (final energy)/(energy per turn) x orbit circumference; halving dee voltage doubles path length and tightens the pressure requirement proportionally.

Seam welds are continuous, with welding only on the atmosphere side. The internal braces are stagger welded to keep virtual leaks at a minimum.

Ramler & Parker, The Argonne 60-Inch Cyclotron — ANL-5907 (1959) — p. 7

Tabletop: Standard practice worth enforcing on any welded chamber or fitting on a next machine: no vacuum-side seal welds, no closed pockets.

the frequency with which starbursts appeared at particle sites, I have concluded that particles cause breakdown

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 46, 78

Tabletop: When a next machine sparks, a loupe inspection for starbursts/craters tells the builder exactly where the field problem is instead of guessing from outside the chamber.

if there are contaminant particles, then they, and not the substrate material, determine the breakdown voltage.

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 84

Tabletop: The builder can keep aluminum dees rather than exotic electrodes: cleaning and conditioning matter, native oxide does not.

Both sites reached 95 MV/m at 100 C with no evidence of field emission ... At room temperature (22 C), field emission began near 40 MV/m, and breakdown occurred around 90 MV/m

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 96

Tabletop: A gentle heat-lamp or heater-tape bake of the dee assembly before HV runs should measurably raise the reference machine's sparking threshold.

a preliminary vacuum of about 10^-5 mm hg should be attained; during 'bakeout' pressure should not exceed ~10^-3 mm. Operation as a cyclotron can be attempted with a pressure of 10^-4 mm or less

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

Tabletop: Directly applicable pressure targets; matches the regime the builder already operates in and sets the next machine's spec.

preliminary washing of the parts in CCl4 is recommended to remove organic matter

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 9

Tabletop: Directly applicable (use modern solvents, not CCl4); degrease every part of a next machine that sees vacuum.

a 3 inch diameter tube in the corner can extend directly downwards to a vacuum pump underneath. This design choice maximizes vacuum conductance.

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

Tabletop: Pumping a gas-fed cyclotron is conductance-limited; a next machine should place the pump under the chamber with the largest, straightest duct possible.

Steel supporting rods allow thin top and bottom plates to minimize thickness

Baumgartner & Heuer, The Cyclotron Kids 14-Inch Accelerator (2010) — p. 6-7

Tabletop: Every millimeter of lid steel is a millimeter of magnet gap; internal posts (placed outside the beam plane) let the builder close the next machine's gap without a lid that dishes under vacuum.

You can hasten the process by running the fusor to degas the inner surfaces. This sends the pressure upward, but after a few minutes it starts to drop

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 5-6

Tabletop: Same conditioning applies to the reference machine's chimney and dee surfaces: schedule a beam-on bake-in run and expect pressure excursions before stable operation.

To fully clean the system of residual gases, an initial base pressure of around 1e-6 Torr is necessary. A leak valve is then used to backfill the chamber with deuterium to a pressure in the range of 1 to 10 microns.

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

Tabletop: The base-pressure-then-backfill discipline is exactly the reference machine's MFC workflow; a 100:1 ratio of operating to base pressure keeps beam-gas composition dominated by the feed gas.

an Innovac R220 diffusion pump and Kurt J Lesker TNR6XA150QF cold trap are used, which can lower the pressure to about 1e-4 Pa (1e-6 torr)

Loucks, Initial Results from the Houghton College Cyclotron — Houghton College thesis (2007) — p. 41-43

Tabletop: Matches the reference machine's scale exactly: 1e-6 torr base bled up with hydrogen for the source is the working point of every successful machine in this peer group.

A 2.54 cm thick ring with an outer radius of 9.9 cm and an inner radius of 8.5 cm was milled from 6061 T6 aluminium ... Ports were made in the chamber wall using ten KF-16 flanges, which were secured using Hysol Loctite 1C vacuum epoxy

Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013) — p. 2

Tabletop: A complete, copyable chamber spec for an 8-inch-pole machine, including the epoxy-in-flange trick that avoids welding.

continuous square rubber gaskets located in grooves in the faceplates of sufficient cross section to accommodate the entire gasket under pressure. The resulting metal-to-metal contact ... has proved very satisfactory.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 41

Tabletop: Directly applicable to a next machine's chamber lids and faceplates; grooved captive gaskets beat flat sheet gaskets for repeatable sealing and alignment.

a steady stream of dry air injected into the outlet side of the pump cylinder could eliminate the need for a refrigerated vapor trap ... dry air is used in the tank in order to minimize the amount of moisture

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 44

Tabletop: Directly applicable: vent the next machine's chamber with dry nitrogen or desiccated air, never room air, and water-vapor pumpdown time drops dramatically.

the ion gauge is not turned on until the tank pressure is less than 0.5 microns ... the wall of the manifold provides the tube filament with some protection from the magnetic field

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 45

Tabletop: Directly applicable gauge practice near a stray-field-rich H-frame magnet.

far more rugged than the triode ion gauge and sensitive to small changes in pressure; but it is probably not as accurate in reading absolute pressure.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 46

Tabletop: Directly applicable: a cheap Penning head is the right always-on interlock and gas-flow monitor for a next machine, with the ion gauge kept for absolute readings.

Rate of rise on tank assembly 0.00015 microns/sec

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 46

Tabletop: Scale by volume: an equally tight ~30 L chamber on a next machine would show ~4e-5 torr/s; measure rate-of-rise after every re-seal as the standard leak health metric.

Employing a seal squeeze of up to 40% inhibits media flow through the seal... because of the decreased groove depth, increased groove width is essential.

Apple Rubber Products, Seal Design Guide — p. 84

Tabletop: Endorses going beyond Parker's 30% on critical static vacuum joints if the groove is widened to take the displaced volume; 'postcuring' is the vendor name for the pre-bake O'Hanlon recommends.

the common boundary of the maximum voltage in the accelerating gaps in the central region of the accelerator is traced, which is 1.3-1.4 times higher than the Kilpatrick criterion

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 57-58

Tabletop: At the reference machine's few-MHz, few-kV/cm gap fields this gives huge margin, but it is the correct sizing formula if a next machine pushes dee voltage up to tens of kV across small central-region gaps.

Its second purpose is to ensure the stability of operation of electrical components of the accelerator... by increasing the breakdown voltage. In modern cyclotron facilities, a pressure of ~1e-7 Torr is practically possible.

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 14

Tabletop: The reference machine does not need 1e-7, but the dual criterion matters: if the dee sparks before the beam is lost to gas, vacuum improvement should be judged on breakdown margin, not just stripping loss.

The number of lost particles dN at each time step dt can be estimated by the formula dN = sigma nN v dt

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 70

Tabletop: Lets the builder tool convert the reference machine's gauge reading and total path length (hundreds of turns) into a survival fraction, quantifying how much beam a ~1e-5 Torr vacuum costs versus 1e-6.

the negative hydrogen ion beam simply passes a thin carbon foil (e.g. pyrolytic graphite, typically 50 to 200 ug/cm2), which strips off the electrons.

Botman & Hagedoorn, Extraction from Cyclotrons — CAS, CERN 96-02 (1996) — p. 3-4

Tabletop: At sub-MeV a 50 ug/cm2 foil costs ~10 keV of energy and some scattering; every other extraction problem (septum, HV, turn separation) vanishes if an internal-source H- beam and <=1e-6 Torr can be achieved.

the cross section of H- interactions with the gas molecules is maximal for the energy range (0.1 - 300) keV of the beam in the central region.

Calvo et al., Beam Stripping Interactions in Compact Cyclotrons — PRAB 24, 090101 (2021) — p. 14

Tabletop: A next machine's H- variant spends its whole life at the cross-section peak: ~25 m of path at 1e-6 Torr loses of order 5-10%, at 1e-5 Torr most of the beam - vacuum, not physics, decides this option. (70 MeV data: cyclotron_vacuum_model p.3.)

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.

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.

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.

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 chamber parts into two halves in a vertical plane through the center of the magnet, permitting the removal of the chamber without disturbing the magnet pole tips.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 15

Tabletop: Directly applicable packaging rule - make the next machine's chamber removable (or serviceable in place) without unbolting pole tips or shims.

Numerous holes are drilled in them to facilitate vacuum pumping.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 19

Tabletop: Directly applicable - virtual leaks behind liners and skins are a classic small-chamber trap; drill the next machine's liners generously.

Each assembly was leak-tested with a helium mass spectrograph after manufacture.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 20

Tabletop: Directly applicable - bench-test each next-machine spool, duct, and feedthrough with a helium sniffer (or pressure/soap plus rate-of-rise) before it disappears into the stack.

Only two leaks were detected, and these were in the gasket seals. They were believed to be due to non-uniform thickness of gasket material.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 24

Tabletop: Directly applicable leak-hunting prior - on a next machine's chamber, check O-ring/gasket joints first and control gasket thickness uniformity.

The vacuum reached was 3 x 10-6 mm of mercury. Starting with cool pumps and the system at atmospheric pressure ... 1 hour, 45 minutes to reach 10-5 mm mercury.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 24

Tabletop: Transferable practice - a recorded reference pump-down curve for the next machine's chamber is the cheapest early-warning leak/contamination diagnostic.

The valves are automatically operated by compressed air cylinders and are controlled by vacuum gauges so that they will close when a leak occurs which the pump is not able to handle.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 58

Tabletop: Directly applicable - an interlocked isolation valve (even a spring-loaded solenoid gate) protects a next machine's diff/turbo pump from a chamber let-up.

a .080" gap between copper or copper-plated surfaces having a reasonable polish would hold a maximum of 50 kilovolts at 13 mc at a pressure of about 5 x 10-6 mm.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 13

Tabletop: Directly applicable breakdown data for setting a next machine's dee-to-liner and puller gaps at 5-13 kV - and a warning that discharge-roughened surfaces lose ~40% of bench hold-off.

All discharges were eliminated by cutting down the available volume by means of perforated shields around the sides of the dee, by adding a grounded dummy dee and by applying a negative bias to the dee.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 23

Tabletop: Directly applicable - the complete 1948 recipe for the RF discharges that plague small chambers at kV-level dee voltages; perforated shields keep pumping speed.

There is sufficient magnetic field at the rotary condenser to allow a Philips gauge discharge when positive bias is applied; a negative bias is therefore imperative.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 23

Tabletop: Directly applicable - the entire next machine's dee sits in 0.59 T, so if bias is used to kill discharges, start negative; positive bias risks a permanent Penning discharge.

the discharge is usually intense enough, even at 10-5 mm of Hg to prevent the voltage from building up to this extinction value. Such a discharge can be eliminated by a sweeping field obtained in any manner.

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

Tabletop: The single most relevant discharge fact for the reference machine: its 1.3 kV dee lives just above this regime, and the 5-13 kV upgrade must punch through it - plan a DC bias supply on the dee from day one.

At 20 megacycles the space between electrodes which will allow an electron to reach an energy around 30 volts in 5 cm. There are very few paths, along the magnetic field, in the neighborhood of the dee that are greater than this.

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

Tabletop: Directly applicable geometry rule - at 9 MHz electron oscillation amplitudes are larger still, so keep open RF-exposed volumes and along-field gaps in the next machine's chamber small or shielded.

An auxiliary copper probe, shielded for RF pickup, was introduced into the main vacuum tank through a Wilson seal on the port near the ion source ... made adjustable as to its radial depth

Yeater, 184″ Cyclotron: Synchroscope Beam Pictures on Two Probes — MDDC-987 (1947) — p. 3

Tabletop: Exactly the right probe pattern for the reference machine's chamber: an O-ring/Wilson-sealed sliding shaft with grounded shield tube; unshielded probes near a 9 MHz dee read RF pickup, not beam.

a Phillips-Ion-Gauge-type discharge can start in the magnetic field inside the vacuum tank near the positive transmission line

Osterlund & Smythe, A Cyclotron Power-Amplifier RF System Using a 4CW50,000C/8350 Tetrode — COO-535-543 (1963) — p. 5

Tabletop: Very relevant at higher dee voltage on the reference machine or a next machine - crossed E and B in vacuum is exactly a PIG geometry (it is how the ion gauge and PIG source work), so any DC-carrying feedline, bias lead, or probe wire inside the field must be RF/DC separated; they melted an electron trap and a ceramic window learning this.

It was necessary to do this while the machine was down to air, in order to avoid multipactoring.

Smith, A Three-Phase Radiofrequency System for Cloverleaf Cyclotrons — UCRL-3153 (1955) — p. 18

Tabletop: Two transferable habits - quantify RF isolation as a measured coefficient with a pass number, and remember that low-level RF tests in vacuum sit exactly in multipactor territory (the reference machine has seen multipactor-like loading); atmospheric-pressure RF checks avoid it.

It takes about 30 sparks per cm2 to bake in high-voltage-electrode surfaces. Since it takes about a second for the vacuum to recover following a spark, the bake-in time of an electrode is about 30 sec/cm2.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 13

Tabletop: A palm-sized tabletop electrode (~100 cm2) conditions in under an hour - or ~10 h if 316SS. Write conditioning into the next machine's ops checklist as a scheduled activity, not a nuisance.

Hydrogen is let into the vacuum tank until the pressure becomes 200 to 300 u. ... A discharge current of about 100 mA is maintained for about an hour.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 32

Tabletop: The reference machine and a next machine use oil diffusion pumping, so expect the dirty-system dark-current regime; the ion-scrub recipe needs only a variac, a 480-V transformer, a limiting resistor, and the existing H2 feed - a directly copyable conditioning procedure.

the pressure was reduced to 10^-5 mm Hg. A rate of rise of 0.00025 microns/sec indicates that the system is vacuum tight.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 March 1952 — ORNL-1339 (1952) — p. 12

Tabletop: The practice and even the number are usable — rate-of-rise normalizes out pump speed, so it is the honest leak metric for the reference machine's chamber; log it after every reassembly as a regression test. (Big-chamber outgassing makes their absolute number lenient; a small clean chamber should beat it.)

S = 400 A^2/OL liters/sec ... For convenience of calculation the value 400 is used rather than 403; the results are hardly affected since the formula is only an approximation.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 144-145

Tabletop: The workhorse formula for every odd-shaped passage in a cyclotron - dee interiors, annular gaps around the dee, slots - where handbook circular-tube formulas do not apply. Directly usable for auditing the reference machine's pump path and sizing a next machine's ducts.

when applied to ducts of other than circular cross section, sizable errors may be introduced ... the correction factor K, by which the right side of Eq. 41 must be multiplied to give a more accurate value.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 145

Tabletop: The non-circular correction handbooks skip - and a ready-made margin policy; computing wide flat gaps (a/b 5-10, K~1.3-1.44) without K builds in ~30-45% pumping headroom automatically.

For an orifice small relative to the area surrounding it, S = 75A. For an orifice large relative to the area surrounding it, S = 75A Abar/(Abar - A).

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 145

Tabletop: With the duct rule, this is the complete kit for a chamber conductance budget - every baffle hole, dee mouth and internal constriction on the reference machine or a next machine reduces to a 75A element in the network.

the term "resistance" is used there to indicate the reciprocal of the conductance. The use of resistance presents perhaps a clearer picture through the use of an electrical analog.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 132

Tabletop: The report's method in one sentence - their 32-in pumps' 13,700 l/s collapsed to 8,300 l/s effective inside the dee (air). Amateur systems routinely lose the same 40-60% to geometry; budget from the source outward, not the pump inward.

This additional pumping speed then can be considered as being in parallel with that through the opening at the mouth of the dee.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 129

Tabletop: Dees are pumping dead-ends by construction - drilling the dee back and any stem shrouds (small holes, below RF-significant size) is free conductance exactly where the ion source dumps its gas.

Thus the 32-in. pumps will handle almost twice as much gas as the 20-in. pumps, and the decision to use 32-in. pumps is an obvious one.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 135-137

Tabletop: The right way to evaluate a diff-pump upgrade for a next machine - work in throughput (torr-l/s) at the pressure the source needs, with the MFC's known gas feed as the load, instead of comparing nameplate l/s.

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.

The fact that the conductances are considerably greater for hydrogen, therefore will have very little effect toward increasing the net speed in this region.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 138-139

Tabletop: Kills a tempting error for hydrogen-fed machines - do not credit the 3.8x conductance factor to the whole system; check which element (duct or pump) is the bottleneck for H2 specifically.

Neglecting outgassing and assuming a perfectly tight system, the pump-down times are as follow.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 139

Tabletop: The calculation pattern transfers at 1/1000 the volume - compute the ideal V/S time for the next machine's chamber; if observed pump-down is many times the ideal, the excess IS the outgassing/leak signature, a diagnostic the reference machine's logs can use today.

opened automatically when the mechanical pump is shut down so as to break the vacuum in the line and prevent the pump oil from backing up the line.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 140

Tabletop: Both bites transfer verbatim to a garage system - an automatic vent on the roughing pump (or a check valve) prevents the classic oil-suckback chamber contamination, and bellows belong in vertical runs.

They permit, however, the backing of all three diffusion pumps by a combination of any two of the booster pumps, should any one of the booster or mechanical backing pumps become inoperative.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 140-142

Tabletop: Scales down to one gauge and two relays - a foreline-pressure interlock that kills the diff-pump heater and an over-temperature switch on its casing are the two automatics that save an unattended amateur system.

welding neck flanges with double O-ring gasket grooves machined in a standard flat face flange and provided with a pump-out connection between the two gaskets.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 141

Tabletop: The double-O-ring-with-interspace-pumpout trick is worth stealing for any large troublesome amateur flange (chamber lids especially) - the interspace can be sniffed for leak location or held at rough vacuum to null permeation across the inner ring.

by passing a current of about 280 amp at 8 volts through the boat, a sufficiently high temperature was reached (white heat) to vaporize the boron.

Hoke & Newman, Self-Supported Cyclotron Targets of Boron and Magnesium — ORNL-3021 (1961) — p. 6

Tabletop: Numbers verified on the page image. Scope honestly: this is EVAPORATION producing research-grade ug/cm2 self-supported films — exactly right for a p+B11 cross-section or resonance-yield measurement, and NOT the route to a thick sputtered/pressed target for a maximum-alpha-yield demo. 2.2 kW low-voltage supply and a 1e-5 torr bell jar are amateur-reachable.

increasing the current slowly over a period of 10 to 20 minutes so that the outgassing can occur quietly.

Hoke & Newman, Self-Supported Cyclotron Targets of Boron and Magnesium — ORNL-3021 (1961) — p. 9

Tabletop: Three generalizable tricks for any future target work — sacrificial carbon parting layers under fragile or reactive films, slow-ramp outgassing before full evaporation power, and a cheap glass hood (lantern-slide covers) so expensive enriched material can be scraped back and reused.

The net speed of these pumps was assumed to be 25% of the speed at the mouth of the pump, because of the usual losses in baffles and valves.

Oak Ridge National Laboratory, A Proposal for the Mc² Isochronous Cyclotron — ORNL-3540 (1963) — p. 158

Tabletop: Scale-free sizing doctrine (their 2.6e6-liter tank is not): the 25% derate and outgassing-dominates logic apply verbatim to any diff-pumped chamber, including the reference machine's SI100 system.

elastomer seals are used only where the predicted 10-yr radiation dose is less than 10^8 rad and where the seal is easily changed.

Oak Ridge National Laboratory, A Proposal for the Mc² Isochronous Cyclotron — ORNL-3540 (1963) — p. 157

Tabletop: The 1e8-rad number is their 810-MeV flux environment; the decision matrix (dose x replaceability -> seal type) is scale-free and becomes relevant the moment a next machine makes real beam current near median-plane seals.

The liner, dees, and dee-stem housing are being fabricated by an outside contractor. The faceplates, dee stems, ion source, target probe, and vacuum system were fabricated locally

Howard (ed.), Electronuclear Research Division Semiannual, period ending 20 March 1954 — ORNL-1670 (1954) — p. 20

Tabletop: The three-report arc (1670 -> 1795 -> 1884) is this collection's cleanest outsourcing lesson - brazed/water-cooled vacuum parts are where contractors fail, and each failure costs a reporting period. For a next machine, buy simple machining, but keep brazing, leak-checking, and anything water-to-vacuum under your own torch, or specify inspection windows up front.

several leaks in very inaccessible locations have delayed final assembly. In order to repair the leaks in the internal water-cooling tubes it was necessary to cut windows through the sides of the dees.

Howard (ed.), Electronuclear Research Division Semiannual, period ending 20 September 1954 — ORNL-1795 (1954) — p. 19

Tabletop: If a next machine's dees carry water, route tubing so every brazed or welded joint can be reached, pressure-test the dee as a unit BEFORE it meets the liner, and treat a cut-window-and-reweld as a planned repair mode (it worked) - the recovery technique is as instructive as the failure.

The tips formed the top and bottom of the vacuum chamber of the magnet, while the side walls of the chamber were strips of non-magnetic stainless steel welded to the tips.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 9

Tabletop: DIRECT construction pattern for any next-machine analyzer or spectrograph - poles-as-chamber eliminates the gap-wasting separate tank (the alternative Bromley rejected for his condenser on machining/gasketing grounds, nyo-3823 p.6). The anti-scattering baffles and the tenth-mil spacer discipline are the details that make emulsion-grade spectra possible.

One of the other ports is located opposite the entrance slit to facilitate alignment of the magnet and the fourth one houses the nuclear magnetic resonance probe.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 9

Tabletop: DIRECT and free at design time - a straight-through optical path (laser today) plus a permanent probe port turn alignment and field checks from teardown jobs into ten-minute jobs. A next machine's chamber/beamline port lists should include both.

Three emulsions each 80 x 200 mm can be mounted in a special camera ... which allows six different exposures to be made without breaking the spectrograph vacuum.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 10

Tabletop: DIRECT principle (vacuum cycles are the tax on focal-plane work; amortize them) with a modern translation: a movable frame of CR-39/film chips, or a silicon-strip array, behind the next machine's analyzer. Their two-detector split - survey in emulsion, precision groups in counters - maps to CR-39-survey vs SiPM/diode-array.

The oxygen from the air condensed in the liquid nitrogen, radiolyzed to ozone and left in concentrated form after the evaporation of the nitrogen presents a significant explosion hazard.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 19

Tabletop: Directly applicable to any LN2 cold trap on the diff-pump line if machine energies ever rise, and worth a line in ops procedures now — never let a trap that has sat in a radiation + discharge environment boil dry unattended (ozone also forms from HV corona, no radiation needed).

Serious changes in the pressure differential on the up and down stream sides indicate that the filter has either clogged or ruptured.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 176

Tabletop: The delta-P-as-health-monitor pattern transfers to every filtered exhaust in the lab (pump exhaust filters, fume paths for boron sputtering later) — instrument the pressure drop, not the filter's appearance.

a "Ferrofluidic" vacuum seal having ~ 0.005 in. radial gaps in which a ferrite loaded low vapor pressure liquid is held by magnetic fields

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 10

Tabletop: Transferable component class, already commercial in 1971 and cheap today — the clean answer any time an accelerator mechanism (chopper, rotating target, variable capacitor) needs rotary motion through the chamber wall.

The capacitor housings have separate vacuum systems using turbomolecular pumps. RF feed through insulators separate them from the main cyclotron vacuum system.

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 10

Tabletop: Scales down well — a differentially pumped appendage for any mechanism (the reference machine already does this in spirit with the diff-pumped source region) keeps ion-gauge-clean chamber pressure honest.

The dee resonator will be dc floating so a negative bias of amount sufficient to control multipacting can be applied.

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 10

Tabletop: Directly relevant at a next machine's planned 5-13 kV dees where multipactor bands are widest; corroborates the glow corner's multipactor-mechanism rules with a 1971 operating-lab remedy and a concrete bias magnitude to scale from.

Vacuum 128.6 ... 9.3 ... R. F. 22.1 ... 1.6 ... Power Supply 140.4 ... 10.2

Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970) — p. 33

Tabletop: Matches the failure record of small machines - the exotic subsystems (RF, source) are not the availability drivers; unglamorous supply and pump maintenance is where uptime is bought.

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.

Three days were lost due to failure of the refrigerator for the cold-trap above the diffusion pumps.

Harvard University Cyclotron Laboratory, Quarterly Progress Report, 1 June – 31 August 1964 — p. 1

Tabletop: Chillers, trap refrigeration, and compressed-air auxiliaries deserve the same spares-and-monitoring attention as the pumps they serve; when a trap warms, the machine is down just as surely as if the diffusion pump died.

Another day was lost because of inadequate oil levels in the diffusion pumps.

Harvard University Cyclotron Laboratory, Quarterly Progress Report, 1 June – 31 August 1964 — p. 1

Tabletop: Oil charge in a diffusion pump depletes slowly by backstreaming and accident; a sight-glass check (or scheduled measurement) before each running block is the cheapest downtime insurance a diffusion-pumped machine can buy.

the pressure gauge gives an indication of the rate of reduction

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. 58

Tabletop: Lets a target come straight from a stable oxide powder with no separate metallurgy step, and the vacuum gauge doubles as the process monitor — no optical pyrometry needed.

the valve opened with a POOMPF and all the carbon substrates disappeared.

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. 274

Tabletop: Short-throw closed-boat geometry is how milligram quantities become usable targets (efficiency scales as 1/d^2); and every pump-down/vent of a chamber holding fragile foils needs a throttled soft-start path — the foils die from the pressure transient, not the vacuum.

At 1e-3 torr, the mean free path in the vacuum chamber is about 1 cm

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. 103

Tabletop: If building a small sputter rig, separate the ion source (differentially pumped duoplasmatron-class gun) from a high-vacuum deposition region rather than lighting a glow discharge in the whole chamber — the film quality difference is structural, not cosmetic.

Some targets may be hydroscopic, while others may oxidize rapidly.

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. 84

Tabletop: A miniature version — one valved transfer pot pumped by the machine's own roughing line — lets an air-sensitive target (Li, Ca, some borides) move between evaporator and chamber intact; the load-lock principle scales down to one target.

The increase in observed lifetime was about a factor of 40.

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. 206

Tabletop: Radiation-damage annealing is concurrent, not a pre-treatment — a small radiant heater keeping a carbon foil dull-red-adjacent (~500 C) during operation is the cheapest 40x in stripper/target life on record; keep hydrocarbons out of the vacuum or the beam writes a thickening carbon spot on every foil.

the only way to avoid destruction of the targets is to cool the substrate or to periodically interupt the evaporation process

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. 236

Tabletop: Substrate meltdown during deposition is the same radiation/conduction bookkeeping as beam heating (Corwin, this volume) with condensation enthalpy as the source term; refractory evaporants punish the substrate through radiation long before the film is thick.

The problem was a poor vacuum of 10-5 Torr in the scattering chamber which allowed oxidation (Kellner & Maier-Komor, "Rolling Thin Uranium Foils")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 38

Tabletop: A 1e-5-torr-class chamber actively burns reactive targets under beam — the beam spot acts like a getter pump. Budget target life against chamber pressure, and expect oxide growth in the spectrum before mechanical failure.

Hydrocarbons crack during the sputtering process and deposit car[b]on or form carbides with the refactory [sic] metals used (Stinson, "Nitrogen Targets Produced by Reactive Sputtering")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 62

Tabletop: The same cracking chemistry that contaminates sputtered films coats everything in any glow discharge backed by an untrapped oil diffusion pump — condition the discharge on a shutter before exposing the workpiece.

Tank pressure above 4 x 10-6 torr made the targets more brittle and shortened their shelf life (Ellsworth, "Preparation of 3/4-in Dia. Self Supporting 182W and 184W Targets for Cyclotron Bombardment")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 81

Tabletop: A cyclotron-target paper end to end; the quantified links rate-to-stress and pressure-to-brittleness carry to every evaporated self-supporting film, not just tungsten.

in cases of poor heat conduction temperatures up to 3000 C occur and exceed therefore the melting points of most of the usual target materials (Tietsch, Feist, Bethge & Schopper, "A High Density Windowless Gas Jet Target")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 82

Tabletop: The checklist of what actually kills targets as current rises — conduction, charge relief, and structure all have to be engineered, and a gas target is the limit case when none of them suffice.

The Balsam remains tacky and retains foils indefinitely. It also has a low vapor pressure (Riel, "Gallium Rich Ga2O Targets for Use at Room Temperature")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 105

Tabletop: A vacuum-compatible tacky mounting adhesive solves the foil-jumps-off-the-frame failure of float-mounting; pairs with the ORNL-3021 float-off recipes.

This prevents target damage by gas out-rush.

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 159

Tabletop: Even a desiccator-scale target store benefits from the two habits — throttled first venting/roughing near fragile foils, and treating cooling-water plugging as an expected failure mode with a flow alarm rather than a surprise.

The ringing frequency of the current in the sparker loop was found to be about 12 mc, independent of the oscillator conditions. The amplitude of ringing is found to decay 50% in about 3 cycles.

Fulbright, The Sparker, a Device to Overcome the Multipactor Difficulty in Starting the Oscillator of a Cyclotron — NYO-9359, University of Rochester (1961) — p. 4

Tabletop: Sets expectations honestly: the shock cures the multipactor stall, not bad vacuum or a detuned feedback network. If a spark does not start the machine, the fault list is pressure, tune, or outgassing state — a diagnostic branch in itself. The low-Q broadband ring means one fixed sparker covers a whole tuning range (trivially true at fixed frequency).

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.

Aluminum was chosen over stainless steel because of its short half-life property.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 46

Tabletop: DIRECT for any machine that will make neutrons: aluminum's activation products die in hours-days while stainless (Co-60 from cobalt traces) lives for years. Choose the beam-facing metal for the machine you hope it becomes, and TIG aluminum is proven UHV-adequate practice from 1951.

Double gaskets with a pump-out space between the two gaskets are used wherever possible for making seals at the joints in the system.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 51

Tabletop: Same guard-vacuum doctrine as ornl-1196/anl-5907 — on a tabletop machine the pumped interspace is most worth its complexity on the largest lid and on any joint that gets opened often; the 1951 materials list maps to modern Buna-N/Viton.

Initial testing of the system disclosed two leaks in welds, both of which were in stainless to mild steel joints.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 53

Tabletop: DIRECT — stainless-to-mild transitions (and any dissimilar pair) crack and porosity-leak preferentially; put them where they can be reached for repair, or design them out with transition flanges and gaskets.

Installation of the copper tank liners, R. F. loops and loop insulators approximately tripled the interior surface area

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 53

Tabletop: DIRECT: every liner, loop and insulator added to a chamber is outgassing area — expect the base pressure to track it. And a $20 variac experiment (heater power vs measured speed) is how to find a surplus diffusion pump's real optimum, exactly as done here.

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.)

It usually involves permitting the dee to spark several hundred thousand times. Afterwards, it will usually hold many times the voltage that it would initially.

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. 4

Tabletop: DIRECT for the 5-13 kV dee upgrade: plan a conditioning campaign (auto-recycle protection makes it unattended) rather than interpreting early sparking as failure. A tabletop resonator stores millijoules, so conditioning is gentle — the count, not the violence, does the work. Corroborates the ornl-2648/nyo-9683 conditioning rules and quantifies them.

The rf-dc interlock compares the dee voltage with the amount of oscillator anode dc. If the ratio is too low, indicating the presence of an arc, the fault detector opens the anode circuit and recycles

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. 7

Tabletop: DIRECT and cheap: a comparator on (dee pickup voltage vs forward power) with a ~1 s drop-and-retry turns dee sparks from session-enders into log entries, and is precisely the automation a conditioning campaign needs. The ratio form matters — absolute thresholds miss arcs that still draw full power.