Cyclotron 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

Editorial note, tabletop extrapolation: A magnet that works but leaves no port for the probe or the pump is a classic amateur trap - exactly what this five-item checklist exists to prevent; run it on every layout iteration for a next machine.

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

Editorial note, tabletop extrapolation: Explains why the pole gap exceeds the chamber's internal height by several millimetres once walls and margins stack - sum the budget's terms in a consistent full-gap or half-gap convention rather than quoting a round figure, since mixing conventions double-counts the allowances.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: the engineering menu at the reference machine's energy class — modest dee voltage (1-2 kVpp), 1e-5 torr, a machined pole profile, not heroic RF or UHV — is what the deck describes pursuing below ~300 keV. It documents the approach, not a completed machine: the existence-proof framing is withdrawn, and the census carries the documented Niell beam record separately.

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. ... all capable of producing a maximum central axial field, Bz(r=0), of 1.2 Tesla ... a single 5-inch radius DEE with a 0.9 inch vertical aperture and a matching dummy DEE. The Radio Frequency (RF) supply is tunable from 2 to 30 MHz with adjustable power up to 1.5 kW ... capable of achieving a peak DEE voltages on the order of 10 kV ... the 2-inch tall, 13-inch diameter cyclotron vacuum chamber's operating pressure of 1E-5 Torr.

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

Editorial note, tabletop extrapolation: 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

Editorial note, tabletop extrapolation: 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.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: The reference machine's dee operates in the range where these discharge phenomena live: the ~100 V-class multipactor band is crossed at every start, and blue-glow gas discharge appears when pressure and surfaces allow. Surface conditioning, low pressure, and drive that can snap up fast are the standard escapes - and whether a given stall is multipactor or gas discharge is diagnosed, not assumed (dg-1273).

Cited in: The Vacuum Budget of a Cyclotron

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. ... Most natural or artificial rubbers have unacceptable vapor pressures and also deteriorate when used with lubricating greases. Neoprene is free of these faults and is widely used in cyclotrons.

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

Editorial note, tabletop extrapolation: The copper-foil RF bridge over elastomer joints prevents mysterious Q loss and local heating and transfers directly. For the gasket itself, a modern machine should size grooves from the O-ring manufacturer's vacuum-service squeeze and gland-fill tables - the historical 1.5x ratio is the era's flat-gasket practice, not an O-ring spec.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: A gas-fed cyclotron chamber often sits in exactly this transition decade, so the spark limit can move with operating pressure: measure holdoff with the actual gas flowing at operating pressure as well as at base vacuum, and interlock conservatively - which direction the limit moves depends on where the geometry sits relative to the Paschen minimum.

Cited in: The Vacuum Budget of a Cyclotron

The power and length of application should be gradually increased until the vacuum remains less than 10^-4 mm with r.f. on steadily at, perhaps 2 kv. ... it may mean the presence of organic matter in the tank

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. PDF p.10 (printed -11-)

Editorial note, tabletop extrapolation: Directly applicable startup ritual at the reference machine's 1.3 kV dee level - ramp in short bursts with current-limited RF, arc detection and pressure monitoring. The report reads failure to reach its endpoint as organic contamination (grease, oil, rubber) in the tank; leaks and ordinary outgassing can mimic it, so inspect or run an RGA before blaming contamination.

Cited in: The Vacuum Budget of a Cyclotron

most uncontaminated cathode sites did not break down at 95MV/m (figure 4.8). Excluding the two sites for which tests were halted prematurely (as explained in the caption of figure 4.8), 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

Editorial note, tabletop extrapolation: A big lever on the reference machine's dee-voltage ceiling: gloves, solvent cleaning, and dust-free assembly of dee and stem are cheap holdoff - one major control among several, not a guarantee.

breakdown occurs between 5 and 200 MV/m ... In general, smaller gaps can withstand higher fields. ... Note that cathodes can reach fields higher than 100 MV/m, but, observing the maximum voltage, only with a gap smaller than 150 microns

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

Editorial note, tabletop extrapolation: At 13 kV across the reference machine's ~6 mm gap the mean field is ~2 MV/m, comfortably low - but mean field is only the first check. Local enhancement at edges and asperities, particles, insulator surfaces and gas pressure can still start an arc, so treat sparking there as a diagnostic checklist, not an impossibility.

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

Editorial note, tabletop extrapolation: Ramp the next machine's dee voltage slowly and accept the limited, current-limited micro-discharges that come with first processing - that conditioning is what raises the ceiling. Deliberately provoking arcs as 'cleaning' is a different matter: arcs can damage electrodes and insulators, and current limiting does not control the stored-energy delivery into the fault (dg-285). Let conditioning happen; do not manufacture it.

To vent the screw holes, a small hole was drilled in the side of each screw hole using a No. 55 drill bit. 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

Editorial note, tabletop extrapolation: Directly applicable to any screwed-together dee: unvented blind holes are virtual leaks that slow pumpdown and add residual gas load - size and place vents for conductance and cleaning access.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Perforation transfers directly - pressure inside an unvented dee can sit far above gauge pressure (the dee interior is a conductance-choked volume). Graphite armor earns its place wherever stray beam dwells, at ANY energy: heating, sputtering and erosion first (dg-426's material lesson), with activation reduction joining the list at higher energies.

Cited in: The Vacuum Budget of a Cyclotron

Fast pumping is required and it is desirable to use oil rather than mercury diffusion pumps as mercury seems to promote autoelectronic discharges from the electrodes.

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

Editorial note, tabletop extrapolation: Moot for pump choice today; the observation transfers cautiously: the source found mercury vapor SEEMED to promote field emission from HV electrodes, and condensable conductive films on electrodes are a recognized breakdown risk generally - keep electrode surfaces free of deposition, sputtered films included (dg-261's clean-surface caveat).

This is continued at as high a current density as possible for about half an hour and on pumping out the hydrogen it is usually found that the tube is quite hard and stable up to 200,000 volts.

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

Editorial note, tabletop extrapolation: A historical conditioning observation for electrode structures that must hold voltage - adapt, don't copy: ramp with current and stored-energy limits, remote operation, interlocks, and a measured breakdown-rate criterion, and remember DC column conditioning does not transfer one-to-one to RF dees.

With no gas flow, chamber pressures of better than 1 x 10-6 mm Hg are obtained. With the deuterium gas flow from the ion source, the operating pressure is about 2 x 10-5 mm Hg.

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

Editorial note, tabletop extrapolation: Expect a large pressure rise when source gas flows: on a tight system the flow-on/flow-off ratio identifies the source as the load, while a rise WITHOUT flow is the leak-or-outgassing signature. What operating pressure a machine can afford is the beam-survival calculation's answer (the vacuum calculator's orbit mode), not MIT's 2e-5.

Cited in: The Vacuum Budget of a Cyclotron

Operating Data of Penning Ion Sources: Arc voltage 0.3-1.3 / 1-5 kV; Ignition volt. 3 / 5 kV; Gas pressure 1-10 Pa; Gas consumption 0.2 sccm; Extraction voltage 5-25 / 5-35 kV; Anode aperture 1 x 25 / 1.5 x 25 mm; Cathode distance 10 / 6.5 cm.

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

Editorial note, tabletop extrapolation: The reference machine's MFC should be sized and calibrated around the table's ~0.2 sccm scale, and the arc supply must tolerate a several-kV open-circuit ignition transient before folding back to run voltage - the table's ignition/run split is the reason.

Cited in: The Vacuum Budget of a Cyclotron

Macor or glass ceramic can be easily machined, but is very brittle. It has good vacuum behavior and can be used up to about 1000 C. ... Boron nitride is an excellent material for most applications for temperatures up to 1200 C. It can be used up to 1500 C but starts to decompose and releases large quantities of nitrogen. It outgasses badly and tends to absorb water, which can destroy the parts when heated too fast.

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

Editorial note, tabletop extrapolation: BN filament insulators in a home source must be pre-baked and brought up to arc power slowly the first time after air exposure, or they crack and gas up the chamber.

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

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

Editorial note, tabletop extrapolation: At 0.2 sccm feed and 50% efficiency only ~0.1 sccm leaves the chimney as neutrals - but the extracted ions end their lives in the same vacuum envelope (implanted, neutralized, desorbed later), so higher gas efficiency shifts where and when the load appears more than it deletes it. It still pays: neutral leakage at the source is continuous and concentrated in the beam region, so better confinement is worth real pumping speed there even though total throughput is conserved.

Cited in: The Vacuum Budget of a Cyclotron

hydrogen may be admitted to the tank, "opening" the valve until the tank pressure rises by another 10^-4 mm, meanwhile watching the arc current ... a needle valve ... a loose fitting thread ... a palladium metal valve

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. PDF p.10 (printed -11-) for the admission step; PDF p.7 (printed -8-) for the valve-type list - NOT PDF p.6

Editorial note, tabletop extrapolation: Transfer the method, not the number: admit gas gradually while watching pressure and arc behavior, and find the reference machine's own setpoint with its calibrated gauge and pumping stack (its parker metering valve fills the needle-valve role). The 1e-4 mm rise is the source machine's figure - gauge species, gauge location and pumping speed make it non-portable.

3.55 MHz 1700 Vpp (26 W) H2 1.5 10-5 torr Total 4.0 10-5 torr -100 V filament ... 6.04 MHz 1700V (26 W) H2 2.2 10-6 torr Total 1.3 10-5 torr -6 V filament ... Higher frequency, lower H2 and base pressure, lower filament voltage

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

Editorial note, tabletop extrapolation: For the reference machine's current-hunting: before adding RF watts, cut chamber pressure and re-optimize filament bias - Houghton's gain cost zero watts - but change one variable at a time so you learn which knob actually paid.

The product of pressure and distance between the electrodes (pd) is a better parameter to characterize the discharge... The voltage is mostly in the range between 300 and 1500 V, but... the current is generally in the mA range.

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

Editorial note, tabletop extrapolation: When scaling chamber geometry or pressure for the p-B11 test cell, pd similarity is the right first knob - it organizes breakdown - but sustained-glow behavior also moves with gas, electrode material and area, and current density, so expect to re-tune rather than translate. Either way, sputter damage concentrates at the cathode sheath edge.

Cited in: The Vacuum Budget of a Cyclotron

The ion mean free path at 2 mTorr is ~7 cm, while at 20 mTorr it is around 0.7 cm... The striking voltage increases with decreasing pressure.

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

Editorial note, tabletop extrapolation: For any glow-driven ion supply in the p-B11 experiment, pressure is the ignition control: strike at higher pressure, then throttle the MFC to the running point - a device-specific procedure to commission, with the actual striking curve measured (Paschen-type behavior depends on pd, gas, geometry and surfaces, not the ion mfp alone).

Cited in: The Vacuum Budget of a Cyclotron

If there is too little gas, less ionization will occur... Too high a pressure and the ionized particles will likely interact with gas inside the dee and fall out of resonance.

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

Editorial note, tabletop extrapolation: Map current vs pressure on your own machine, recording resonance width and source stability along with current - expect an apparatus-dependent optimum and a non-monotonic curve, and use Houghton's window as calibration context, not a target.

Cited in: The Vacuum Budget of a Cyclotron

The pressure in the chamber has a large effect on the beam current obtained, and typically needs to be in the range from 1e-6 to 1e-4 Torr for the cyclotron to operate. ... [higher pressures] reduce the mean free path of the ions, and cause the resonance peaks to become broad and shift. The largest beam current recorded, shown in Figure 6, was about 0.1 uA

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

Editorial note, tabletop extrapolation: Directly sets the gas-handling operating window for the reference machine and explains a common 'no beam' failure at too-good vacuum - throttle up before concluding the source is dead.

Cited in: The Vacuum Budget of a Cyclotron

the pressure internal to the ion source is only approximately a factor of 2 larger than the chamber pressure... source operation has also been achieved by simply backfilling the chamber.

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

Editorial note, tabletop extrapolation: Worth testing on the reference machine: in a small chamber the injection-vs-backfill distinction may shrink - but the source-to-chamber pressure ratio is set by aperture conductance, flow and pump placement, so measure it (or model the conductances) rather than assuming 2x transfers.

Cited in: The Vacuum Budget of a Cyclotron

The boron-nitride insulator, which is a tight fit, separates the high vacuum region behind the insulator (on the order of 10-5 Torr), from the lower vacuum region in the chimney and between the anodes and cathodes. ... The best vacuum achieved in the ion source test stand (with source gas supply turned off) was 8 x 10-7 Torr. With a gas flow rate of 2.5 cc/min of hydrogen, the pressure in the main vacuum chamber is around 4e-5 Torr.

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

Editorial note, tabletop extrapolation: A single calibration point (about 1.6e-5 Torr per cc/min at that stand's pumping speed), not a slope: characterize the reference machine's own MFC-vs-chamber-pressure curve with its calibrated flow and gauges before reading deviations as leaks or conductance faults.

Cited in: The Vacuum Budget of a Cyclotron

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

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

Editorial note, tabletop extrapolation: The 3-degree taper spread over 9 turns gives the fine, repeatable hydrogen admission an ion source needs. Log turns-open as the VALVE-POSITION setpoint - repeatable flow additionally needs regulated upstream pressure and a calibration of flow (or chamber pressure) against turns under operating conditions; the vernier repeats position, not sccm.

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

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

Editorial note, tabletop extrapolation: Practical form for the gas panel: give the metering valve an isolation valve between it and the bottle - or specify a metering valve designed for shut-off duty, the HR-class option the sheet names. Forcing a plain tapered stem closed to seal ruins the calibrated taper and still leaks into the vacuum system.

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

Editorial note, tabletop extrapolation: Hands the mill the numbers for the chamber's lids and ports - per ring size and per geometry: these are STATIC AXIAL FACE seals; a port using a different cross-section or seal configuration gets its own chart row or chart. Note the vacuum groove width column is narrower than liquid service.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Specify and check the chamber lid seat to 16 RMS (fly-cut or turned); a rough or cross-scratched sealing face can contribute to leakage and belongs on the leak-diagnosis checklist - as one suspect among several, not a signature of any particular pressure plateau.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

For Internal Pressure (outward pressure direction) dimension the groove by its outside diameter (HO) and width: (HO) = Mean O.D. of O-ring ... Tolerance = Minus 1% of Mean O.D., but not more than -.060 ... For External Pressure (inward pressure direction) dimension the groove by its inside diameter (Hi) and width: (H)i = Mean I.D. of O-ring ... Tolerance = Plus 1% of Mean I.D., but not more than +.060

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

Editorial note, tabletop extrapolation: 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.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: For a ~30-50 liter tabletop chamber the rule asks for 30-50 l/s DELIVERED at the chamber; the SI100's 100+ l/s class inlet rating leaves margin that the plumbing then spends - baffle, elbows and port conductance cut delivered speed (1/S_eff = 1/S + 1/C, dg-906) - so compute the delivered figure before crediting the margin. On a gas-fed machine the source load dominates either way.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Worth adopting on a next machine's main lid: a guard-vacuum groove turns the worst leak hunt into a valve twist for TESTING; riding out a leak in service additionally needs the interspace continuously pumped with adequate speed, and only helps for leaks through the outer seal.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

One butyl compound has been tested in face-type O-ring seals, using grooves that provide 15%, 30%, and 50% squeeze. It will be seen from the results plotted in Figure I that increasing the squeeze reduced the leak rate dramatically... at 50% squeeze the beneficial effect of the grease was not detectable. ... It is therefore recommended that dovetail or face type O-ring grooves be used whenever possible for static vacuum seals, employing a suitable vacuum grease as a sealing lubricant and surface coating in addition to a heavy squeeze on the O-ring.

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

Editorial note, tabletop extrapolation: Cut a next machine's grooves toward the heavy end per the source's recommendation, but set the nominal from the ring manufacturer's static-vacuum gland tables under worst-case tolerances - 50% was a test point, not a design target; gland fill, compression set and assembly damage cap real designs. Grease is a crutch for light squeeze.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

L = .7FDPQ(1-S)2 where: L = Approximate leak rate of the seal, std. cc/sec. F = Permeability rate of the gas through the elastomer at the anticipated operating temperature. Std cc cm/cm2 sec bar ... D = Inside diameter of the O-ring, inches. P = Pressure differential across the seal, lb/in2. Q = Factor depending on the percent squeeze and whether the O-ring is lubricated or dry. (From Figure II) S = Percent squeeze on the O-ring cross section expressed as a decimal. ... This formula provides only a rough order of magnitude approximation ... For convenience, the formula contains mixed units. ... The .7 factor provides dimensional homogeneity.

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

Editorial note, tabletop extrapolation: Computes the permeation floor of the 10-inch Viton lid seal - then convert to pressure via P = Q_gas/S_eff with the actual effective pumping speed, and remember outgassing and real leaks usually dominate above the permeation floor.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: 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.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: At exactly the reference machine's operating pressure, nitrile's high weight loss marks it a potential outgassing concern near feedthrough insulators, optics and RF surfaces - where the lost mass actually lands was not measured, so treat the ranking as a screening result and prefer the low-loss compounds (Viton's 0.1%-class loss is the cheap insurance) rather than claiming proven film deposition.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

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

Editorial note, tabletop extrapolation: Viton's placement plus its other properties is why it is the default; silicone's high permeability matters most when helium leak checking (He walks through silicone and fluorosilicone seals, confusing the sniffer) and in permeation-limited systems - compute the actual permeation gas load for the seal geometry before ruling a compound in or out, since at 1e-6 Torr with decent pumping the load is often ignorable either way.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

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

Cited in: Experiments by Energy Band

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

Editorial note, tabletop extrapolation: Size and maintain the backing pump so the foreline stays well under the pump's critical forepressure during beam-gas loads - for the SI100, take the manufacturer's figure; the quoted 0.2-0.6 Torr is the generic design range. A tired rotary pump silently pushes the foreline over the cliff and dumps oil vapor into the chamber.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: The 2.7 kg/cm figure sizes the lid bolting: a 10-inch-circumference seal (25.4 cm) needs about 69 kg of clamping just for the ring - a 10-inch-diameter ring (79.8 cm around) needs about 216 kg - before atmospheric load helps. Size bolts and flange stiffness from the complete load and allowable-stress calculation.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Argues for baking the assembled system under vacuum where the components allow it. An ex-situ pre-bake in a small vacuum oven helps only to the extent air exposure before assembly is minimized, and the payoff in chamber pressure depends on whether the rings dominate the gas load - budget the gas loads before promising an order of magnitude.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Counters the amateur habit of greasing everything: on a clean, undamaged seat with proper squeeze, a dry Viton ring seals without grease's gas burden. A scratched flange is a repair item first; grease is the temporary expedient, not the standard practice.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: For the reference machine: valve over to the SI100 around 100 mTorr rather than letting the rotary pump grind into the 1e-2 Torr range - after checking the SI100's own maximum inlet/crossover and foreline specs, which are the binding numbers for the diffusion-pump side.

Cited in: The Vacuum Budget of a Cyclotron

the mechanical pump should be disconnected and connected to a blank flange containing only a thermocouple gauge. ... If the pump is operating properly, sections of the foreline and roughing line can be pumped sequentially and systematically until the leaky section is isolated. ... External leak checking with helium should begin at the top of the chamber; only a small helium flow rate is necessary. ... Alcohol freezes in a small leak and allows adjacent areas to be checked without confusion. The alcohol can be removed with a heat gun. ... Welds and seals are the most common leak sites

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

Editorial note, tabletop extrapolation: Helium rises and migrates: working top-down with small flow keeps the migrated-helium background from swamping localization on a chamber with many ports (the source suggests nitrogen-flushed plastic wrap where sites crowd together). Alcohol near energized equipment is a flammability point - sensible precautions.

A molecular leak causes a linear increase in pressure with time. Outgassing causes the pressure to rise to a steady-state value that is determined by the vapor pressures of the desorbing species.

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

Editorial note, tabletop extrapolation: First diagnostic whenever a next machine won't reach base pressure - existing gauge plus stopwatch. A constant slope points toward the helium bottle, a rolling-over curve toward bakeout - as the leading hypothesis, not a verdict: virtual leaks also roll over, water outgassing can mimic a leak on an RGA, and a real leak departs from linearity once the pressure rises far enough.

Cited in: The Vacuum Budget of a Cyclotron

This pressure rise is due to helium permeation. The permeation time is about 20 min for a typical Viton O-ring. ... First, do not attempt to leak check the system during baking. Second, helium background from a loaded O-ring will not decrease until it has been pumped from the gaskets. A coffee break may be required before proceeding.

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

Editorial note, tabletop extrapolation: On an all-Viton chamber, spray briefly and wait: a slowly rising, broad He signal minutes after spraying is CONSISTENT WITH gasket permeation rather than a leak at the last joint - confirm by letting the baseline recover and re-testing for a prompt, reproducible local response before moving on.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: A used RGA head is arguably the single best diagnostic upgrade for a next machine - one spectrum plus a short rate-of-rise watch 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

Editorial note, tabletop extrapolation: 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.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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

Editorial note, tabletop extrapolation: Explains why pump-down history and surface cleanliness dominate at high vacuum: the wall inventory dwarfs the volume inventory for ordinary chamber geometries - by a factor you compute from the actual area, volume and outgassing rate, which is also what sets whether the walls take hours or days to give up their load.

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

Editorial note, tabletop extrapolation: 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

Editorial note, tabletop extrapolation: Matches the reference machine's observed 1e-6-range vacuum with Viton seals - typical of all-elastomer systems, where permeation and outgassing usually hold operation near the recommended regime, though well-designed elastomer systems can run lower. A CF port or two on a next machine (gauge, RGA) buys bake and UHV headroom cheaply.

Cited in: Cyclotron Glossary · Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: When farming out welds or buying used hardware, write the acceptance spec as a number DERIVED from the machine's gas-load budget: Q_leak,max = S_eff x (allowable pressure contribution), split between total and single-leak allocations, with tracer gas, test pressure and calibrated detection limit stated - detector sensitivity is what the instrument can see, never itself the acceptance criterion.

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

Editorial note, tabletop extrapolation: The ~200x one-hour penalty (dropping to ~10x by four hours) for rusty mild steel is the argument for keeping exposed in-chamber pole faces from corroding at all - and for qualifying any specific remedy (plating, vacuum-rated coating, stainless cladding) on its own outgassing, adhesion and magnetic-gap costs rather than prescribing one.

Cited in: The Vacuum Budget of a Cyclotron

Mechanical Cleaning; Degreasing or Solvent Cleaning; Detergent Cleaning; Chemical Etch; Electrolytic Polishing; High Pressure Spray; Bake-out ... Remove all tape, ink, & other residues with Acetone & a clean cotton rag ... DI rinse (2 x 10^6 Ohm min. resist. @ 65oC) Air dry or dry with filtered compressed nitrogen ... Protect with lint free paper, foil, or plastic bags ... Acid pickle (50% by vol. HNO3 ... @ 25oC) 10 minutes if removing mill scale, 30 seconds to remove trace alkaline ... A 200oC bakeout is still required after glow discharge cleaning.

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

Editorial note, tabletop extrapolation: 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. The acid pickle stays professional - HF work needs formal controls and alloy-specific procedure, and is not part of the amateur-safe subset.

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

Editorial note, tabletop extrapolation: 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.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: To push an elastomer-sealed system's floor lower on a next machine, a double O-ring lid groove with a guard vacuum from the existing roughing pump attacks the permeation term specifically - the dominant elastomer floor once outgassing is conditioned down - for the cost of one groove and a hose barb. The guard reduces pressure-driven permeation through the inner seal (DARHT's numbers are that installation's); the inner ring's own outgassing remains, so the floor drops rather than disappears.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

An acceptable vacuum would allow for a mean free path an order of magnitude larger than the expected flight distance. For protons accelerated by a 2.7 T magnetic field and a voltage difference of 1000 V between the electrodes, the expected flight distance is approximately 300 meters.

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

Editorial note, tabletop extrapolation: The quantitative vacuum spec for a next machine: turns = final energy / energy-per-turn, and total path is turns times the average orbit circumference (about two-thirds of the final one for r proportional to sqrt(E)); halving dee voltage doubles the path and tightens the pressure requirement proportionally. Evaluate lambda with sigma(E) from ORNL-6086 along the orbit (the vacuum calculator's orbit mode does this); a 150 keV, 1 kV-per-dee proton machine needs ~1e-5 torr for 10% loss, not 1e-3.

Cited in: Beam Quality: What It Is and What Degrades It · The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: On any welded chamber or fitting for a next machine the question to ask of every joint is: is there a pocket sealed on both sides, or a crevice open to vacuum? Vent it, or weld it through. Argonne's atmosphere-side seams are one way to satisfy that, not the rule itself.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: When a next machine sparks, a loupe inspection for starbursts and craters gives the builder candidate locations for the field problem instead of guessing from outside the chamber - corroborate with particle, geometry and field checks before machining anything.

if there are contaminant particles, then they, and not the substrate material, determine the breakdown voltage. ... The Cu and Au films were about 1000 A thick; the oxide films were hundreds of angstroms thick. ... there seems to be no significant difference in breakdown voltages on niobium and copper cathodes.

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

Editorial note, tabletop extrapolation: The builder can reasonably keep aluminum dees and spend the effort on cleaning and conditioning instead of exotic electrodes - with the caveat that the tests covered Nb, Cu, Au and their oxides, not aluminum's native oxide; let the machine's own conditioning behavior confirm it.

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

Editorial note, tabletop extrapolation: Motivates a controlled experiment on the reference machine, not a guaranteed fix: try a gentle bake of the dee assembly before HV runs and measure field-emission onset and holdoff after cooldown - the cited data compare performance AT temperature and don't establish that the improvement survives cooling, or the mechanism.

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

Editorial note, tabletop extrapolation: Historically grounded milestones, and the regime the reference machine operates in. What pressure a given machine NEEDS is the charge-exchange survival calculation (dg-460; the vacuum calculator's orbit mode) - at 1e-4 torr a proton spiral loses heavily, which is why this collection's operating rules sit in 1e-5-class territory.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Degrease everything on a next machine that sees vacuum - machining oil, fingerprints, rubber residues - with a solvent chosen per material (elastomers, coatings and trapped volumes need their own compatible process); CCl4 itself is excluded on toxicity grounds.

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

Editorial note, tabletop extrapolation: Pumping a gas-fed cyclotron is conductance-limited, so place the pump under the chamber with the largest, straightest duct possible - the term you control at layout time. What pressure results is the whole budget's answer: throughput, pump speed and conductance together (the vacuum calculator).

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

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

Editorial note, tabletop extrapolation: Every millimeter of lid steel is a millimeter of magnet gap - but posts are not free: ferromagnetic posts in or near the gap distort or shunt the field, so place them outside the useful-field region (or use nonmagnetic posts) and verify by model or map; and do the plate-stress and buckling arithmetic for full atmospheric load before trusting a thin lid.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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 ... Turning the fusor power down or off after a few minutes of on time will have the pressure plunge to new lower levels.

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

Editorial note, tabletop extrapolation: The same logic applies to the reference machine's chimney and dee surfaces - but translate it as controlled RF or discharge conditioning with pressure and arc interlocks, not an open-ended beam-on bake-in: beam operation adds sputtering, beam loss, and (at higher energies) activation questions a conditioning plan should assess first.

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

Editorial note, tabletop extrapolation: The base-pressure-then-backfill discipline is exactly the reference machine's MFC workflow; at the quoted fusor numbers the operating-to-base ratio is 1,000-10,000:1, which is what keeps the feed gas dominant - but composition is earned by measurement (RGA or gas-load accounting), not by a pressure ratio alone.

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

Editorial note, tabletop extrapolation: Matches the reference machine's scale exactly: 1e-6 torr base, bled up with source hydrogen, is the working point of the documented machines in this peer group (Houghton, the Rutgers 12-inch, the reference machine - the census's compare rows carry the values). The recipe is the proven one at 15 cm scale; the pressure a machine actually needs remains the survival calculation's answer (dg-460).

Cited in: The Vacuum Budget of a Cyclotron

Two 0.65 cm thick circular lids ... included a gland for a Viton O-ring for the vacuum seal. ... The chamber can be evacuated down to a final pressure of approximately 2 × 10−6 Torr

Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013) — p. PDF p. 2 for the lids and Viton seal; PDF p. 3 for the 2 × 10−6 Torr

Editorial note, tabletop extrapolation: A complete documented chamber design for an 8-inch-pole machine, including the epoxied-flange trick that avoids welding. Copy from the paper - then qualify your own copy: epoxy joints and lid stiffness are workmanship-dependent, so leak-check the flanges and run the lids through the lid-deflection calculator rather than inheriting the paper's result.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: A strong pattern for a next machine's chamber lids: the metal stop limits further squeeze after closure and makes reassembly repeatable - still check gland fill and squeeze for the actual compound (groove depth sets the squeeze; a too-shallow groove over-crushes even with a metal stop), including tolerance, swell and thermal growth.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Two separable methods: vent the next machine's chamber with dry nitrogen or desiccated air rather than room air (admitted water vapor drops and pumpdown shortens), and treat exhaust-side purging as pump-specific - follow the pump manual, keep any inlet trap the pump needs for vapor handling or oil backstreaming, and mind oxygen deficiency when nitrogen-venting in a small space.

Cited in: The Vacuum Budget of a Cyclotron

the ion gauge is not turned on until the tank pressure is less than 0.5 microns ... In this position the conductance from the diffusion pumps around the gate valves to the ion gauge has been estimated to be approximately the same as the conductance from the diffusion pumps to the tank proper. ... 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

Editorial note, tabletop extrapolation: Directly applicable gauge practice near a stray-field-rich H-frame magnet: place the gauge to read the pressure you care about (conductance gradients bias a badly placed gauge under gas flow), and verify the shielding by comparing readings with the field on and off.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: A cheap Penning head earns its keep as a trend and gas-flow indicator, with the ion gauge kept for absolute readings. For protection interlocks use fail-safe, manufacturer-approved instrumentation - Penning cells can ignite late and drift with contamination - and commercial heads carry their own magnet: mount and shield per the head's specification rather than borrowing the cyclotron's field.

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

Editorial note, tabletop extrapolation: Measure rate-of-rise after every re-seal as the standard leak-health metric, and state the benchmark as a gas load, not a pressure rate: the ORNL figure corresponds to Q = V*dP/dt ~ 1.2e-3 torr-L/s. A ~30 L chamber would rise at ~4e-5 torr/s only if it carried that same total load - rate-of-rise includes real leaks, virtual leaks and outgassing, so 'equally tight' means equal Q, not equal construction scaled by volume. [Note revised 2026-08-23: earlier note scaled the expectation by volume alone.]

For vacuum seals, O-rings must be comprised of elastomeric materials featuring low gas permeability, low weight loss under vacuum, and good compression set characteristics. ... With outstanding low permeability to gases, Butyl is especially effective in vacuum sealing applications. ... 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

Editorial note, tabletop extrapolation: Endorses heavier-than-usual squeeze on critical static vacuum joints when the groove is widened to take the displaced volume - within the compound's own application limits. A pre-bake ('post cure' in vendor language) to drive off volatiles before service is cheap insurance on silicone and fluorocarbon compounds.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: The right sizing framework if a next machine pushes dee voltage to tens of kV across small central-region gaps: compute the LOCAL peak surface field from the electrode geometry (not the average gap field), compare against Kilpatrick as a benchmark, and plan on conditioning and breakdown testing - margin is demonstrated, not assumed.

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

Editorial note, tabletop extrapolation: The dual criterion is the transferable part: if the dee sparks before the beam is lost to gas, vacuum improvement should be judged on breakdown margin, not just stripping loss. What pressure the reference machine actually needs comes from its own gas-loss arithmetic and holdoff behavior - not from this figure in either direction.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Lets the builder tool convert a gauge reading and total path length (hundreds of turns) into a survival fraction - with the composition stated, the gauge's gas-sensitivity factor applied, and the cross sections taken at the right energies. An assumed oxygen-like composition is a labeled assumption, not a guaranteed worst case: water and hydrocarbons can exceed it for the processes that matter.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: At sub-MeV a 50 ug/cm2 foil costs ~10 keV of energy and some scattering. The septum, HV and turn-separation problems genuinely disappear - replaced by the H- problems: an internal H- source, and the 1e-6 Torr-class vacuum that gas stripping of the fragile H- demands (dg-599).

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

Editorial note, tabletop extrapolation: A next machine's H- variant spends its whole life at the cross-section peak. Run the loss arithmetic explicitly through T = exp(-n*sigma*L) with measured H- detachment cross-sections - the 1e-15 cm2 class near the peak; fetch sigma(E) for the actual gas mix when designing. At that scale ~25 m of spiral at 1e-6 Torr loses of order 5-10%, and 1e-5 Torr costs most of the beam: vacuum, not physics, decides this option. (70 MeV data: cyclotron_vacuum_model p.3.)

Cited in: The Vacuum Budget of a Cyclotron

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

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

Editorial note, tabletop extrapolation: Run current-regulated and watch arc voltage as a flow/health indicator: creeping arc voltage at fixed current is evidence of falling gas density and approaching instability - cross-check against gas supply and cathode condition before acting, since a worn cathode and other drifts move arc voltage too.

Cited in: The Vacuum Budget of a Cyclotron

Gas is fed to the discharge usually through the anode close to the cathode(s) to ease ignition of the arc and to keep the neutral gas flow through the extraction slit in the anode low

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

Editorial note, tabletop extrapolation: Plumb the MFC line to feed near the cathode end of the chimney where the geometry allows (AMIT feeds through the cathode cavity - a variant of, not identical to, the quoted through-anode arrangement): it eases ignition and keeps neutral flow out the slit low. Chamber backfill still works (dg-409) - the injection win is lower chamber pressure for the same source density, to be verified by measurement on the actual machine.

the plasma discharge ignites easily at 1 kV or less for all cases ... a current utilization efficiency (ratio of target to discharge current) of 25%

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

Editorial note, tabletop extrapolation: Use the right utilization figure for the right geometry when predicting a next machine's beam: Rovey's ~25% is axial extraction; Forringer's radial-slit configurations measured I_beam/I_arc of about 0.0005 to 0.0046 - nearly two orders lower, because the slit samples a small part of the plasma - and neither number transfers to a new source without measurement.

there needs to be a base vacuum (with the ion source gas supply turned off) in the 10−6 Torr range ... Various turbo pumps ranging from 600 to 800 liters/second were used ... With a gas flow rate of 2.5 cc/min of hydrogen, the pressure in the main vacuum chamber is around 4 × 10−5 Torr.

Forringer, Phase Space Characterization of an Internal Ion Source for Cyclotrons — MSU dissertation (2004) — p. PDF p. 39 (printed p. 29) for the vacuum/flow practice; PDF p. 27 (printed p. 17) for the 4.5 T / 0.5 T endpoints

Editorial note, tabletop extrapolation: The reference machine's 0.59 T sits just inside the demonstrated field range - demonstrated at the endpoints, not characterized as uniform performance across it - and its existing turbo and 1e-6-class base pressure match the thesis's start conditions as-is.

The 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

Editorial note, tabletop extrapolation: Directly applicable packaging rule: make the next machine's chamber removable or serviceable in place without unbolting pole tips or shims - and still re-verify the field after any reassembly that could have moved iron. Undisturbed tips make the recheck quick, not unnecessary.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

Numerous holes are drilled in them to facilitate vacuum pumping.

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

Editorial note, tabletop extrapolation: Virtual leaks behind liners and skins are a classic small-chamber trap: vent every otherwise-trapped volume on the next machine with holes or slots sized for pumping conductance - checked against RF current paths, structure and field quality - and deburr and clean the openings.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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

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

Editorial note, tabletop extrapolation: Bench-test each next-machine spool, duct, and feedthrough before it disappears into the stack - vacuum-mode helium mass-spectrometer testing is the acceptance method the source used. Rate-of-rise and sniffing are preliminary screens only; keep soap solutions off vacuum-wetted surfaces, and pressurize a vacuum-only part for testing only if it has a documented pressure rating.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: A useful prior for a next machine's leak hunt: check O-ring/gasket joints first - while still testing welds and feedthroughs, since one chamber's tally doesn't make welds innocent; compression, gland condition and damage are additional gasket failure modes beyond thickness.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

The vacuum reached was 3 x 10-6 mm of mercury. Starting with cool pumps and the system at atmospheric pressure, the pump-down times were as follows: 1 hour, 45 minutes to reach 10-5 mm mercury; 2 hours, 30 minutes, to reach 3 x 10-6 mm mercury.

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

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

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Directly applicable: an interlocked isolation valve (even a spring-loaded solenoid gate) protects a next machine's diff or turbo pump from a chamber let-up - with closure speed and actuation chosen for the pump being protected.

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

Editorial note, tabletop extrapolation: Directly applicable breakdown data for setting a next machine's dee-to-liner and puller gaps at 5-13 kV - with the derate compared in FIELD, not voltage (the two units had different gaps), and remembering vacuum RF hold-off does not scale as fixed kV-per-gap: bench-verify the actual geometry (dg-419).

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

Editorial note, tabletop extrapolation: Directly applicable - the 1948 combination that cleared THAT machine's discharges: reduced free volume (perforated shields preserve pumping speed), a grounded dummy dee, and negative dee bias. On a new machine, apply the elements as diagnosis suggests (dg-1273's discrimination between multipactor and gas discharge) rather than as one obligatory bundle - though all three are cheap to design in from the start.

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

Editorial note, tabletop extrapolation: The next machine's dee sits in 0.59 T, so if a DC bias is used to kill discharges, start negative on the strength of this precedent - then verify empirically: whether a Penning discharge ignites depends on the E/B geometry and pressure, not the field alone.

Above this voltage, which is in the neighborhood of 500 volts, the discharge is rapidly extinguished as electrons can no longer oscillate. However, 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. The sweeping field was obtained on the 37-inch cyclotron by biasing the dee, transmission line, and condenser stator parts a few hundred volts positive.

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

Editorial note, tabletop extrapolation: 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 during every start - plan for a bias supply on the dee from day one, and note the source's polarity (positive on the 37-inch; dg-320's machine used negative - both worked, because any sweeping field defeats the resonance).

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, so no trouble has occurred in this region. In the rotary condenser however, most of the paths are of the order of 20 cm. Electrons oscillating in this space can reach efficient ionizing energies long before their amplitude becomes equal to the distance between electrodes.

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

Editorial note, tabletop extrapolation: 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.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Exactly the right probe pattern for the reference machine's chamber: an O-ring/Wilson-sealed sliding shaft with grounded coaxial shield tube and a defined exposed collector. Near a 9 MHz dee an unshielded probe's reading is dominated by RF pickup superposed on any beam signal - shield, then verify with beam-off RF-only background runs and filtering before crediting the remainder as beam.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: 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 gauge and the source work - so route DC-carrying feedlines, bias leads and probe wires out of the field region or shield them. This failure mode is designed out at layout time.

It was necessary to do this while the machine was down to air, in order to avoid multipactoring. ... The coefficients for the 20-inch cyclotron were below 3%. In order to adjust the coupling loops of the neutralizing lines the dee stems were excited one at a time

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

Editorial note, tabletop extrapolation: Two transferable habits: quantify RF isolation as a measured coefficient (set the pass number from your own loop-stability analysis), and remember low-level RF in vacuum can sit in a multipactor window - the reference machine has seen multipactor-like loading. Venting for the test sidesteps multipactor but is not blanket safety: corona, heating and hazardous RF voltage remain, so keep monitoring and interlocks in place.

all of them baked in in a similar fashion except 316 stainless steel, which required about ten times as many sparks to reach the ultimate breakdown voltage. 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

Editorial note, tabletop extrapolation: Applying the source's scaling to a palm-sized ~100 cm^2 electrode gives about 50 minutes of spark time - or roughly 8.3 hours for 316 stainless - excluding setup, failed ramps and downtime. 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

Editorial note, tabletop extrapolation: The reference machine and a next machine use oil diffusion pumping, so the dirty-system dark-current regime is the thing to MEASURE, not assume. The hydrogen ion-scrub is a historical conditioning procedure to adapt, not a weekend recipe: it needs an isolated, current-limited supply (a variac is not isolation and 480 V is lethal), controlled H2 admission with pressure regulation, a safe purge/exhaust path, and interlocks - reviewed against the actual apparatus before first use.

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

Editorial note, tabletop extrapolation: Log an isolated rate-of-rise after every reassembly as a regression test against the machine's OWN baseline - the number folds together leaks, outgassing and permeation scaled by volume, so it does not transfer between chambers in either direction; where true leak-tightness must be established, helium leak testing is the tool.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: The workhorse formula for long, odd-shaped passages in a cyclotron - annular gaps around the dee, slots, duct runs - where circular-tube handbook formulas fail. Its own conditions ride along: LONG ducts in molecular flow, and 'only an approximation' by the source's own words; short apertures, bends and abrupt area changes take end corrections or the orifice forms (dg-839), and a complex dee cavity is a network of elements, not one duct.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: The correction handbooks skip - and a margin policy worth copying with its limits understood: omitting K is a duct-conductance allowance, not a system margin. Effective speed obeys 1/S_eff = 1/S_pump + 1/C, so when the pump dominates, the extra conductance buys little; run the series combination before crediting headroom.

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

Editorial note, tabletop extrapolation: With the duct rule this covers most of a chamber conductance budget: baffle holes, dee mouths and constrictions become orifice or short-duct elements in a network. Finite-thickness holes transmit less than the zero-thickness 75A form - they are short ducts; interpolate or use transmission-probability tables - and series elements combine only approximately, so the budget is an estimate the pumpdown curve then checks.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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; the report's own worked numbers). The size of that collapse is the reason to budget from the source outward, not the pump inward - compute the conductance chain for the actual geometry rather than assuming any fixed fraction survives.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Dees are pumping dead-ends by construction, and the ion source dumps its gas inside one: added holes in the dee back or stem shrouds are valuable conductance exactly there - size and place each pattern with an RF-current and field review, a structural check, and a molecular-flow conductance estimate; below-RF-significant hole size is the starting constraint, not the whole analysis.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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.

Cited in: The Vacuum Budget of a Cyclotron

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

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

Editorial note, tabletop extrapolation: The same arithmetic the builder runs with the MFC: a 0.1-1 sccm hydrogen feed is 1.3e-3 to 1.3e-2 torr-l/s; divide by the honest effective speed FOR HYDROGEN at the chamber, then add the pump ultimate and the outgassing floor, to predict running pressure before touching hardware. The formula assumes the source feed dominates the incremental load - the flow-on/off test verifies that (dg-370).

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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) limits for H2 specifically, using the selected pump's own hydrogen speed and compression data - pumps differ.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: The calculation pattern transfers to any chamber: compute t = (V/S)*ln(P1/P2) per stage with the pressure-appropriate effective speed (roughing pumps slow markedly with falling pressure, and series conductance caps S). When the observed pump-down runs many times the ideal, treat the excess as a prompt to check - outgassing, leaks, conductance restrictions, pump condition, gauge error - rather than as proof of any one of them.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Transfers directly to a garage system: an automatic vent interlocked with the roughing pump - or a vacuum-rated anti-suckback valve, which is not the same thing as a generic check valve - prevents the classic oil-suckback chamber contamination. The source's practice of putting flexible connections in vertical runs (so oil cannot pool in them) is worth copying too - reported practice, scan re-read queued.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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 protect an unattended amateur system's pump and oil - necessary automatics, not a complete unattended-operation case. Setpoints come from the pump's own tolerable forepressure, not the source's 50/160 microns.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: The double-O-ring-with-interspace-pumpout trick is worth stealing for any large troublesome amateur flange (chamber lids especially): sniff the interspace for leak location, or hold it at rough vacuum to intercept most of the atmospheric load across the inner ring - it reduces, not nulls, permeation, since the elastomer still outgasses and a gradient to the chamber remains.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

Pressure was maintained below 1 x 10-5 mm of Hg while the boat was being brought to temperature. Then, 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. The progress of the evaporation was followed by observing the material as it heated in the boat. The boron remained darker than the boat until just before vaporization, then it became bright and quickly disappeared. The boron was evaporated onto 3 1/4 x 4-in. glass plates.

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

Editorial note, tabletop extrapolation: Scope honestly: this is EVAPORATION producing ug/cm2-class self-supported films - potentially suitable for a p+B11 cross-section or resonance-yield measurement once areal density, uniformity and purity are characterized - and NOT the route to a thick target for a maximum-alpha-yield demo. The hardware (2.2 kW low-voltage supply, 1e-5 torr bell jar) is within amateur reach ONLY with the engineering done: rated water-cooled feedthroughs for 280 A, fault protection, implosion screening, and hot-material handling.

For the evaporation of magnesium, boats of 3-mil tantalum about 3/4-in. wide were used. The pressure was maintained below 2 x 10-5 mm of Hg, and the current was increased to about 100 amperes. The scattering of the MgO by violent outgassing can be minimized by increasing the current slowly over a period of 10 to 20 minutes so that the outgassing can occur quietly. ... the glass was coated with a weak soap solution (Calgonite) and allowed to dry before it was coated with about 5 to 10 ug/cm2 of carbon from an arc ... One function of the carbon layer is to help keep the magnesium from making contact with the water; magnesium is slightly soluble in water and decomposes to form Mg(OH)2. The carbon also helps hold the magnesium film together both while it is being removed from the glass and afterwards. ... a glass hood was constructed from lantern slide covers so that all of the collected material could be recovered.

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

Editorial note, tabletop extrapolation: Three tricks generalizable WITH per-material validation: sacrificial arc-carbon parting layers under fragile or water-reactive films (validate compatibility - carbon can add reaction background or stick badly to another material), slow-ramp outgassing before full evaporation power, and a cheap glass recovery hood (lantern-slide covers) so enriched material can be recovered - recovered stock needs a purity check before reuse.

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

Editorial note, tabletop extrapolation: Scale-free in structure, not numbers: size from the outgassing load, compute the actual duct and baffle conductances (1/S_eff = 1/S_mouth + 1/C - the vacuum deep dive's budget method), and treat handbook outgassing rates as early-time bounds. The 25% is what THEIR plumbing cost them; the reference machine's SI100 stack has its own conductance chain to compute.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: 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 1e8-rad line is that design's criterion for its compounds and lifetime - qualify the actual elastomer against predicted dose, temperature, compression set and access before borrowing the number.

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

Editorial note, tabletop extrapolation: The three-report arc remains this collection's cleanest outsourcing story: the contracted brazed, water-cooled vacuum parts were where the delays landed - one program's experience, and a fair prior. For a next machine: buy simple machining, keep leak-integrity parts in-house or design them repairable.

Cited in: The Vacuum Budget of a Cyclotron

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. The windows were then closed by Heliarc welding.

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

Editorial note, tabletop extrapolation: If a next machine's dees carry water: treat internal cooling leakage as a credible failure and route tubing so joints and runs can be reached (or provide removable covers) where RF and vacuum allow; pressure-test the dee as a unit BEFORE it meets the liner; and note the historical recovery mode - cut a window, fix, reweld - is documented practice worth keeping in the back pocket.

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

Editorial note, tabletop extrapolation: The poles-as-chamber pattern eliminates the gap-wasting separate tank (the alternative Bromley rejected on machining/gasketing grounds, nyo-3823 p.6) - carry the METHOD and derive the gap tolerance from the analyzer's own field-error and resolution budget, minding weld distortion across the span.

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

Editorial note, tabletop extrapolation: Cheap at design time and expensive to retrofit: a straight-through optical path (laser today) opposite the entrance slit plus a permanent probe port turn alignment and field checks from teardown jobs into routine ones - each port still buys its window, its leak path and its magnetic clearance, so put both on the port list and budget them honestly.

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

Editorial note, tabletop extrapolation: The principle is vacuum cycles are the tax on focal-plane work - amortize them: a movable frame of film/CR-39 chips (integrating, etched after removal - a survey detector, not prompt readout) or a silicon strip/PIN-diode array (direct charged-particle detection; a bare SiPM is a photon detector and needs a scintillator) behind the next machine's analyzer. Their split - survey in emulsion, precision groups in counters - still maps cleanly.

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

Editorial note, tabletop extrapolation: Directly applicable to any LN2 cold trap on the diff-pump line if machine energies ever rise - and worth a procedures line now: a trap that has sat in a radiation-plus-discharge environment gets attended warm-up and venting, because the quoted mechanism concentrates oxidizer exactly at boil-dry. (An editorial precaution drawn from the quoted physics.)

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

Editorial note, tabletop extrapolation: 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. Delta-P sees gross changes - clog rising, rupture falling - while pinholes and seal bypasses can pass it silently, so where a release would actually matter, periodic sampling still closes the loop.

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

Editorial note, tabletop extrapolation: A candidate commercial component - available since 1971 - whenever an accelerator mechanism (chopper, rotating target, variable capacitor) needs rotary motion through the chamber wall; prices vary widely, so treat cost like any other spec. Verify the specific seal's pressure rating (one-atmosphere capability included), leak rate, vapour and backstreaming cleanliness, bakeout limit, speed and torque, and its behaviour in a nearby magnetic field before designing it in. [Note revised 2026-08-23: earlier note called it 'the clean answer any time'.]

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Scales down as a case-by-case method: a sealed partition (like Nevis's insulator barrier) actually isolates the gas load; an OPEN differentially pumped appendage - the reference machine's diff-pumped source region - only reduces transfer through its conductance. Pick per mechanism from a conductance and gas-load estimate, and remember debris control is geometry, not pumping.

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

Editorial note, tabletop extrapolation: Directly relevant at a next machine's planned 5-13 kV dees, where multipactor bands are widest: a 1971 operating-lab remedy with a concrete magnitude to scale from. Bias works by breaking the multipactor resonance condition; what trajectories do in detail depends on the local fields, so 'sufficient to control' is found empirically - exactly as Nevis wrote it.

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

Editorial note, tabletop extrapolation: The transferable content is the Pareto METHOD on your own log, not NRL's ranking: on that machine in that period, unglamorous supply and pump maintenance was where uptime was bought - a small machine's ranking may differ, so measure before allocating effort.

Cited in: The Vacuum Budget of a Cyclotron

The Buna N, chevron shaped vacuum seals between the cyclotron accelerator tank and the radial and azimuthal drive mechanisms ... were unreliable and displayed a short life expectancy.

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

Editorial note, tabletop extrapolation: For sliding or rotating shafts into the chamber, write a real dynamic-seal specification: compound, gland dimensions and squeeze, surface finish and land tolerance, lubrication, the motion profile, and an interseal vent or differential-pumping stage where leak-tightness matters - geometry, finish and compound all do real work, and a second O-ring buys redundancy at the cost of friction and a possible trapped-volume virtual leak.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

Editorial note, tabletop extrapolation: Chillers, trap refrigeration, and compressed-air auxiliaries deserve the same spares-and-monitoring attention as the pumps they serve - on any system whose operation actually depends on them: where a warm trap means contamination or lost vacuum margin, the machine is down as surely as if the pump died.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Diffusion-pump fluid level and condition belong on the maintenance checklist: check per the manufacturer's procedure at an interval set by operating history, plus after any abnormal heating, air inrush, or suspected loss - Harvard's lost day shows the failure mode is real and mundane. Some pumps need cooldown to check; plan for it.

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: Lets a target come straight from a stable oxide powder with no separate metallurgy step. The total-pressure gauge is a qualitative process indicator only - it cannot identify the gas or prove completion; use temperature measurement, and an RGA or a validated endpoint where gas identity matters.

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

Editorial note, tabletop extrapolation: Every pump-down and vent of a chamber holding fragile foils needs a throttled soft-start path - the foils die from the pressure transient and gas-flow forces, not the vacuum. Short-throw closed-boat geometry remains the milligram-economy move, with collection efficiency verified for the actual source and collimator rather than assumed pure 1/d^2.

At 10-3 torr, the mean free path in the vacuum chamber is about 1 cm ... At 10-6 torr, the mean free path is of the order of meters

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. PDF p.103 (printed p.87) for the 1e-3 torr sentence; it completes on PDF p.104 (printed p.88), which also carries the 1e-6 torr / meters sentence and the Xe figure

Editorial note, tabletop extrapolation: For a small sputter rig the choice is real but not one-sided: a differentially pumped gun with a high-vacuum deposition region preserves arrival energy and directionality; glow-discharge and magnetron processes at millitorr nonetheless make dense, adherent films through substrate heating and plasma bombardment. Choose by what the film needs and measure adhesion, structure and gas incorporation on the result rather than assuming pressure decides quality.

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

Editorial note, tabletop extrapolation: The load-lock principle scales down to one target: a valved transfer pot REDUCES atmospheric exposure for Li, Ca or boride targets - how much depends on its achievable pressure, residual water and oxygen, pump backstreaming and valve sequencing, so qualify the pot against a sacrificial target before trusting it with the real one.

radiative heating of the foil to a temperature of approximately 500 C. The increase in observed lifetime was about a factor of 40. ... There was no substantial difference between annealed and non-annealed foils.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. PDF p.206 (printed p.190)

Editorial note, tabletop extrapolation: Concurrent annealing is the transferable idea: a small radiant heater on a carbon stripper/target holder is a cheap experiment with a large historical payoff - run it as an experiment, monitoring actual foil temperature, outgassing and vacuum cleanliness, rather than booking the 40x (which belongs to the cited foil, beam and conditions). Keep hydrocarbons out of the vacuum or the beam writes a thickening carbon spot on every foil.

the energy impinging on the substrate is ten times as large for Mo than for Au. Here 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. PDF p.236 (printed p.219)

Editorial note, tabletop extrapolation: 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.

In the first experiments the Uranium foils were destroyed by a heavy ion beam during the first 1 or 2 hours. The monitor spectrum showed almost pure Uranium oxide. ... The problem was a poor vacuum of 10-5 Torr in the scattering chamber which allowed oxidation similar to the effect in an ion getter pump. In the next experiment the vacuum was in the 10-6 Torr range due to an additional cryo-pump and the targets lived much longer, but one could see still in the monitor spectrum, that oxidation took place.

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

Editorial note, tabletop extrapolation: A 1e-5-torr-class chamber actively burned this reactive uranium target under beam - the beam spot acting like a getter pump. For any reactive target, budget life against chamber pressure (and specifically oxygen/water partials), expect oxide growth in the monitoring spectrum as the early warning, and treat the uranium numbers as that experiment's calibration, not thresholds.

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

Editorial note, tabletop extrapolation: The same cracking chemistry threatens any glow discharge backed by an untrapped oil diffusion pump - hydrocarbon backstreaming can contaminate whatever the discharge sees. Condition the discharge on a closed shutter before exposing the workpiece (removes initial cathode contamination), and control CONTINUING contamination with a working cold trap/baffle or oil-free pumping - the shutter trick does not cure ongoing backstreaming.

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

Editorial note, tabletop extrapolation: Transfer the method - control pressure, rate and substrate temperature, then calibrate stress, adhesion and shelf life on the actual material - not the tungsten numbers: the 4e-6 torr boundary and the rate-stress trend are that process's results, and residual stress can move the other way in another material/substrate system.

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

Editorial note, tabletop extrapolation: The checklist stands: conduction, charge relief and structure all have to be engineered as current rises, and a gas target is the limiting alternative when no solid survives - trading foil failure for nozzle, flow-stability and differential-pumping engineering rather than achieving unbreakability.

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

Editorial note, tabletop extrapolation: A tacky mounting adhesive solves the foil-jumps-off-the-frame failure of float-mounting; pairs with the ORNL-3021 float-off recipes. 'Low vapor pressure' is the source's claim for their chamber - run an outgassing/base-pressure test (and consider beam-induced decomposition near the spot) before trusting balsam in a tighter vacuum budget.

This prevents target damage by gas out-rush.

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

Editorial note, tabletop extrapolation: Even a desiccator-scale target store benefits from the transferable habit: throttled first venting/roughing near fragile foils (the source's restrictor-valve recovery). The legacy failure list is instructive where the corresponding hardware exists - IF the store or target uses water cooling, monitor flow and let a hazard assessment decide whether the monitor must interlock beam or heating rather than just alarm.

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

Editorial note, tabletop extrapolation: Sets expectations honestly: the shock cures the multipactor stall, not bad vacuum or a detuned feedback network - if a spark fails to start the machine, work the fault list (pressure, tune, outgassing state). Whether one fixed sparker covers a whole tuning range is a startup test at the band edges, not an assumption (trivially satisfied at fixed frequency).

The gas pressure in the cyclotron tank is lower. This came about partly because the opening in the hood (through which the ions to be accelerated are [extracted]) ... reduced in size to about 1/32 in ... after a few days of operation, it was found to have become somewhat enlarged in the direction of ion rotation.

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

Editorial note, tabletop extrapolation: Two lessons: (a) the chimney slit is the gas throttle, and sizing it down is a cheap pumping win - balanced against plasma and beam extraction, so optimize rather than minimize; (b) the asymmetric erosion (along rotation) is a clue about where early-turn ions strike the hood - corroborate with tracking or witness marks before reading it as a diagnostic.

Cited in: The Vacuum Budget of a Cyclotron

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 (1951) — p. 46

Editorial note, tabletop extrapolation: DIRECT for any machine that will make neutrons: aluminum's dominant activation products are short-lived compared with stainless steel's cobalt-trace Co-60 (years) - the report's reasoning - though aluminum is not activation-proof: fast neutrons make 24Na (15 h) and alloying elements add their own products, so 'short half-life' is comparative, never absolute. Choose the beam-facing metal for the machine you hope it becomes; TIG-welded aluminum is proven UHV-adequate practice from 1951.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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 (1951) — p. 51

Editorial note, tabletop extrapolation: 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 any joint opened often. Material translation: the 1951 Hycar parts are the nitrile (Buna-N/NBR) family; Viton/FKM is a DIFFERENT modern option chosen on temperature, chemistry, permeation and compression-set grounds, not a synonym. UW's leak record (two stuffing-box seals, one flat gasket, zero double-gasket joints) is favorable single-system experience for the ranking, not proof.

Cited in: Cyclotron Vacuum Chamber Design and Sealing · The Vacuum Budget of a Cyclotron

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 (1951) — p. 53

Editorial note, tabletop extrapolation: Treat dissimilar-metal welds (stainless-to-mild first among them) as leak-hunt and inspection PRIORITIES - their risk depends on filler choice, joint design and thermal cycling, so this is a where-to-look-first rule, not a they-always-leak rule. Keep such transitions accessible for repair, or design them out with transition flanges and gaskets.

Cited in: The Vacuum Budget of a Cyclotron

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 (1951) — p. 53

Editorial note, tabletop extrapolation: DIRECT: every liner, loop and insulator added to a chamber is outgassing area, and UW's base pressure roughly doubled when their additions tripled the surface. Base pressure follows total outgassing over delivered speed (P ~ sum(q_i*A_i)/S_eff), so area is the usual driver - materials and cleaning move the q's. The variac experiment (heater power vs measured speed) remains the way to find a surplus diffusion pump's real optimum.

Cited in: The Vacuum Budget of a Cyclotron

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

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

Editorial note, tabletop extrapolation: The reference machine's filament-change downtime is this exact problem, solved in 1951: a small gate-valved source lock plus an external bellows positioner removes the main-tank vent from the service cycle - how much time that saves depends on the lock's own pump-down and the machine's recovery habits, so measure it rather than promise minutes. Positioning through the bellows under vacuum is the designed use; adjusting with arc, RF or HV energized is a separate safety analysis with its own interlocks, not an included feature. (The shuttered viewport is a free detail worth stealing.)

Cited in: The Vacuum Budget of a Cyclotron

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

Editorial note, tabletop extrapolation: For the 5-13 kV dee upgrade, plan a conditioning campaign rather than reading early sparking as failure - a supervised one: compute the actual stored and delivered fault energy first, current-limit and arc-detect, set the auto-recycle behavior from that arithmetic, monitor temperatures, and inspect between sessions. Corroborates the ornl-2648/nyo-9683 conditioning rules and quantifies the count.

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

Editorial note, tabletop extrapolation: DIRECT and cheap: a comparator on the dee-voltage-to-drive ratio with a drop-and-retry turns dee sparks from session-enders into log entries - the ratio form matters, because absolute thresholds miss arcs that still draw full power. Two amendments for a tabletop copy: cap the retry count and latch out on repeated faults, since an endless auto-recycle would keep re-feeding a failed feedthrough or persistent arc; and if forward power stands in for anode dc, validate the arc signature on the actual amplifier - it is not the same quantity Smith's ratio used.

Bei einem Druck von p = 10−6 mbar [...] würden die H2+-Ionen (im Mittel) also erst nach mehr als 123 m auf ein Stickstoff-Molekül treffen [tr.: at 1e-6 mbar H2+ travels more than 123 m between collisions]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 50

Editorial note, tabletop extrapolation: The table is a historical order-of-magnitude estimate with two labeled limitations: a hydrogen-FED machine's residual gas is mostly H2 (measure it - an RGA settles it), and the loss process that matters for beam survival is charge exchange, whose energy-dependent cross-section must come from evaluated data (dg-460), not hard spheres. Use lambda_loss(E) = 1/sum_j n_j*sigma_loss,j(E) over the actual partial pressures.

muss die mittlere freie Weglänge für die betreffenden Ionen größer oder gleich der gesamten Bahnlänge sein [tr.: the mean free path must be >= the total path length]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 54

Editorial note, tabletop extrapolation: The qualitative lever is real - raising dee voltage shortens the spiral and relaxes the pump requirement - but pressure thresholds don't follow from radius and voltage alone: compute survival as exp(-integral n*sigma_loss(E) ds) with the charge-exchange cross-section for the actual species, gas and energies (dg-460's lesson), and pick pressure from an explicit acceptable loss fraction.

Für 16 Beschleunigungen wären 2,76 m Weglänge erforderlich, die mit 3 m knapp erreicht werden [tr.: 16 accelerations need 2.76 m of path, barely reached with 3 m]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 54-55

Editorial note, tabletop extrapolation: Recomputed: r1 = 17.5 mm, sum sqrt(i) for i=1..16 = 44.47, giving 2.45 m of arcs plus 16*0.02 = 0.32 m of gap = 2.76 m. Caution: the bitmap Table 6.2 lists 2.44 m and 1.27 m, i.e. arcs only without the k*gap term; use the text figure.

für einen Volumenstrom von ca. 0,14 ml/min sich ein Enddruck pE = 4,0 · 10−5 mbar einstellt [tr.: at about 0.14 ml/min a final pressure of 4.0e-5 mbar establishes itself]

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

Editorial note, tabletop extrapolation: The one-line balance is the first thing to validate against the gauge on a new machine - at several MFC settings, with the background term measured separately (feed off) and the flow convention of the actual controller pinned down before trusting any prediction.

Allerdings darf für S nicht das Nennsaugvermögen SN = 28 l/s der Turbomolekularpumpe für Wasserstoff angesetzt werden [tr.: the nominal 28 l/s hydrogen speed of the turbo must not be used for S]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 52, 82-83

Editorial note, tabletop extrapolation: The lesson is the calculation, not a flange size: compute each line's conductance for each gas that matters and pick the port from the required chamber speed - short and fat wins, and mounting the pump directly on the chamber removes the term entirely. The 39/75% figures are this installation's; other lines and gases differ.

Damit erhält man letztlich als Berechnungsformel für den Rohr-Strömungsleitwert: GL = π/12 v̄ D³/L [tr.: the working formula for tube conductance]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 82-83

Editorial note, tabletop extrapolation: The D^3 dependence means a DN63 line has ~4x the conductance of DN40 at the same length (compute from actual bores - DN designations don't fix the ID). For short stubs (L/D < 10) the long-tube limit OVER-predicts - it diverges as L -> 0 - so cap it with the aperture term via the series combination.

Dabei ist noch zu berücksichtigen, dass jetzt nicht mehr Luft, sondern im wesentlichen nur noch Wasserstoff H2 abgepumpt wird [tr.: it is now essentially only hydrogen that is pumped]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 52, 83

Editorial note, tabletop extrapolation: Take the H2 column from the pump datasheet and compute conductances with hydrogen's v_bar (1.75 km/s at 293 K vs 0.469 for N2). Terminology discipline: BASE pressure is the no-feed number; during source operation the relevant quantities are OPERATING pressure and residual composition - hydrogen-dominated when the feed throughput exceeds the measured background load.

Für V̇G = 0,10 ml/min ergeben sich mittlere freie Weglängen von 12,6 m bzw. 4,2 m [tr.: at 0.10 ml/min the mean free paths are 12.6 m and 4.2 m]

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

Editorial note, tabletop extrapolation: Specify the feed instrument from the measured requirement: the flow range and step stability the source actually needs (state the reference conditions of the flow unit - sccm vs actual ml/min matters here), then choose a calibrated MFC or a precision metering valve with regulated upstream pressure accordingly. Table 7.2 is a bitmap in the scan; the pressure row recomputes exactly from p_E = 300 mbar * V_G / 17.2 l/s.

Nun lässt sich mit der Vorpumpe der Druck nicht weiter erniedrigen. Die weitere Druckreduzierung erfolgt jetzt durch die Turbomolekularpumpe [tr.: the backing pump can go no lower; the turbo takes over]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 55-56

Editorial note, tabletop extrapolation: The two-stage division of labor is standard but its numbers are technology-specific: take the crossover pressure and backing requirement from the high-vacuum pump's own specification (turbo, diffusion, cryo all differ - a diffusion stage wants a rotary-vane backer and a trap or baffle). An oil-free diaphragm backer keeps hydrocarbons out and is classroom-quiet - this machine's genuine transferables.

gibt es auch bei der Druckmessung kein Messgerät, das über den gesamten Druckbereich von neun Zehnerpotenzen messen kann [tr.: no single gauge covers the nine-decade range]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 56-57

Editorial note, tabletop extrapolation: Both gauge types are gas-species dependent: a Pirani reads hydrogen differently from nitrogen and a cold cathode needs a hydrogen correction factor, so the pressure that enters the mean-free-path budget should always carry its gas correction; and keep magnetically sensitive heads out of the stray field or shield them per their spec.

Nach einem Ansatz von Maxwell wird dies durch einen Faktor √2 im Nenner berücksichtigt [tr.: following Maxwell this is accounted for by a factor sqrt(2) in the denominator]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 80-81

Editorial note, tabletop extrapolation: For a beam ion crossing slow gas the stationary form is the better physical model (relative speed ~ ion speed) - but only with the right sigma: gas-kinetic hard-sphere values are not loss cross-sections, so a beam-loss budget needs sigma_loss(E) from evaluated data (dg-460), whatever the sqrt(2) bookkeeping.

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

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

Editorial note, tabletop extrapolation: Fix the reducer pressure and log it - it is a term in the balance. Whatever meters the flow, state its reference conditions and take accuracy and repeatability from its specification rather than assuming a resolution.

Außerdem steigt durch die größere Heizleistung die Temperatur in der Vakuumkammer, was zu einer Verschlechterung des Vakuums führt [tr.: higher heater power raises chamber temperature and worsens the vacuum]

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

Editorial note, tabletop extrapolation: Log heater current against the vacuum gauge to find the knee for the actual source - the transferable procedure. Filament-life sensitivity to temperature is steep (evaporation-limited life, dg-379's tables) but the '10% hotter halves life' shorthand has no source here and current is not temperature; work from the W evaporation tables at the actual filament temperature if a lifetime estimate matters.

ein Wert der in guter Übereinstimmung mit dem gemessenen Druck steht [tr.: a value in good agreement with the measured pressure]

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

Editorial note, tabletop extrapolation: One-point agreement checks consistency; to actually MEASURE the pump stand's hydrogen speed at the chamber, do the differential version (baseline, step the flow, gauge-corrected delta-p) and repeat after every plumbing change or pump swap, logging the result.

The first attempted vacuum chamber was made of curved sheets of copper that clamped around the magnet's poles. Using gaskets to seal the chamber, the machine produced a beam current of 1.5 microamperes. However, the system could not maintain vacuum and a new design was sought. The modified chamber consisted of a section of 16.5 cm brass tubing used as the wall of the chamber, and two 0.3 cm thick circular steel plates as the top and bottom. The bottom plate was soldered to the brass, the top plate was screwed to the bottom plate with a rubber gasket between the brass and steel to form a seal.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 15

Editorial note, tabletop extrapolation: A rigid soldered ring with one permanently sealed plate and one demountable gasketed plate is a simple chamber architecture with this documented precedent; the conformal clamp-around-sheet chamber has a documented vacuum-failure precedent. (The survey doesn't cost either build - 'low-cost' is our reading of brass tube and hand tools.)

Cited in: Cyclotron Vacuum Chamber Design and Sealing

The faces of the chamber were annealed glass plates, with the external air pressure used to clamp them to the stainless steel ring, with vacuum grease to ensure a seal. ... [Knox:] like Niell, the external air pressure was used to seal the top plate to the rest of the chamber.

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

Editorial note, tabletop extrapolation: Atmosphere supplies ~10 N/cm2 of clamping - and the same pressure is an implosion load (~1.5 kN on a 15 cm glass lid). Historical construction, not a qualified design: before copying it, check plate stress and deflection for the actual glass and span, support the edges, retain the lid positively against venting transients, and put an implosion shield between glass and students. The visual access is real; so is the failure mode.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

A mechanical roughing pump with a cold trap were used to evacuate the chamber

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

Editorial note, tabletop extrapolation: Read as recorded history, not a pumping recipe: a cold trap captures condensables, not hydrogen or air, so rough-pump-plus-trap has no general sufficiency - what made this credible is the solid coated-filament source (no continuous gas load). For any repeat: measure base and operating pressure under load and check mean free path against the spiral; the same survey's gas-fed machines carry diffusion pumps.

The negatively biased filament was mounted in a block of ceramic material to which hydrogen gas was supplied through a small hole. The ion source was then covered with a ceramic plate with an aperture ... [allowing] a cone of protons to stream out in the center of the evacuated cyclotron chamber, while maintaining a higher pressure of hydrogen around the filament

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

Editorial note, tabletop extrapolation: A drilled ceramic block with an aperture is a buildable chimney-style source. The pressure decoupling it delivers is set by the aperture conductance against the gas throughput and chamber pumping - match those (the dg-409/dg-1400 balances) rather than expecting the geometry alone to do it.

The electrical feed-throughs were made from nylon plugs, o-rings, and brass screws and were held in place with Plumber's Goop

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

Editorial note, tabletop extrapolation: Historical construction with NO implied qualification - the machine never ran to publication. For anything carrying voltage, RF or bias, use vacuum-rated feedthroughs selected for creepage, clearance, outgassing and the actual electrical ratings; improvised polymer-and-sealant penetrations are leak, tracking and outgassing liabilities that a leak-checked commercial part retires for tens of dollars.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

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

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

Editorial note, tabletop extrapolation: The ten-to-one operating/base ratio estimates the intended-gas fraction ONLY if the background stays at its base value - hot filaments, desorption and species-dependent pumping can break that, so verify with an RGA where purity matters. And lambda exceeding the orbit length is survival-of-order-e^-1, not adequacy: use the loss-fraction calculation (dg-1398) for the actual criterion.

act both as a baffle to contamination from backstreaming diffusion pump oils

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 31

Editorial note, tabletop extrapolation: Stacking trap over pump buys line-of-sight oil baffling with minimal conductance loss - the real benefits. Gravity is not one of them: at apparatus scale, gravitational energy is utterly negligible against thermal molecular energy, so molecules do not 'fall' into the pump. Compare side-mounting by conductance and line-of-sight geometry.

air is allowed into the system through the dessicant to reduce water vapor levels in the system

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

Editorial note, tabletop extrapolation: Adsorbed water is OFTEN the dominant gas load of an unbaked, frequently opened system - when it is, a desiccant vent or dry-nitrogen backfill is near-zero-cost mitigation; where pumpdown is limited by conductance, permeation or trapped volumes instead, drying the vent air buys little. A rate-of-rise curve says which regime you're in (dg-447).

thermocouples are only reliable at pressures above about 10-3 torr

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 32

Editorial note, tabletop extrapolation: The allocation pattern transfers; the thresholds don't - take each gauge's usable range from its own manual. The placement lesson is real at small-machine conductances: measuring at the pump and inferring at the chamber can misstate the pressure the beam sees, so put the high-vacuum gauge where the answer matters (dg-475).

The first peak is due to molecules of hydrogen, which is outgassed by the stainless steel components of the vacuum system.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 34

Editorial note, tabletop extrapolation: An RGA gives INDICATORS, not verdicts: paired N2/O2 (with Ar) in air ratios is consistent with an air leak (or residual air), and a dominant mass-2 peak in a stainless system is commonly outgassing - but mass 2 has multiple origins, so confirm attributions with isolation tests and rate-of-rise (dg-449's discipline) before acting on a single scan.

silicon oil is heated by an electrical heating element at 120 VAC, drawing about .5 A

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 31

Editorial note, tabletop extrapolation: The external wrapped-coil water jacket and DC-704 fill are transferable STARTING points for a self-built vapor pump (validate boiler power and temperature for the actual geometry - the diff_pump project's own design work governs there). The printed '.5 A' at 120 VAC implies ~60 W, low for this pump class: REPORTED BUT UNVERIFIED - check the R220 manual or a nameplate before treating it as datum or misprint.

two QF16-075-VP Kurt J. Lesker glass viewports, one Kurt J. Lesker EFT1213258 power feed-through for the dee

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 39

Editorial note, tabletop extrapolation: The cited machine's eight-port budget with named catalog parts is a concrete STARTING template - port count and ratings are functions of your source biasing, RF monitoring, cooling and diagnostics, so derive your own list and check current catalog substitutes' voltage/current/vacuum ratings. One specific: a dummy dee wanting RF ground usually needs a short low-inductance chamber bond, not a shared multi-pin conductor - verify which this machine's sharing actually implies before copying it.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

the Edwards LV10K needle valve attached directly to the vacuum chamber with a quick flange. The system can be flushed with the gas from the cylinder by closing the needle valve and opening the helium flush valve. The higher pressure helium will force the air in the line into the atmosphere, so that it does not contaminate the gas. By using the needle valve and the regulator control, the pressure of helium in the vacuum chamber can be controlled in the 10-6 to 10-5 torr range.

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

Editorial note, tabletop extrapolation: A tee with a flush valve upstream of the metering valve is the core of the purge system - dead legs and line volume set how long a real purge takes, so verify with the RGA or gauge rather than assuming any fixed duration; without a purge path, line air feeds the chamber at every startup for as long as the line holds.

A small brass screw was bored through its axis to allow air to escape the screwhole

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

Editorial note, tabletop extrapolation: Blind tapped holes under screws are classic virtual leaks that masquerade as outgassing for hours. The cure is venting wherever a fastener seals a blind volume - a bored screw (as here), a vented screw, a groove, or a through-hole - chosen per joint; drilling every in-vacuum fastener indiscriminately weakens screws that never needed it.

The vacuum was produced by a vacuum reservoir with a cryopump system.

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

Editorial note, tabletop extrapolation: Read carefully: a cryopump IS a pump (it keeps pumping while cold), so this is oil-free, low-vibration pumping plus buffer capacity - not a pumpless machine. The architecture suits a source with little gas load (Cyclotrino's cesium-sputter source); the reservoir buys hold time against transients, not indefinite operation. Get the actual cryogenic arrangement before copying claims about power or vibration at the machine.

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

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

Editorial note, tabletop extrapolation: Plan pumping capacity for the gas-on state, not the base pressure; a decade of pressure rise under source gas load is the demonstrated working regime for a keV-class internal-source machine at this scale. (Quote reproduces the table verbatim including its spelling; exponents are superscripts in the original.)

This work is limited to the area of high vacuum. The limitation is due to the simple handling of the components and the existing pumping station, with which a minimum of 10-5 mbar is not undercut. … The present work shows that metal-based 3D printing can meet the requirements of vacuum technology in the area of high vacuum.

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 1, 4

Editorial note, tabletop extrapolation: Printed 316L-class components are demonstrated at high vacuum down to the study's achieved 1.5·10-5 mbar; the 10-6 decade was not reached by its pump station and UHV is explicitly untested, so claims below the tested pressure are extrapolation, not evidence.

Due to an elaborate post-processing, it is clear that the 3D printing of standard components will hardly be worthwhile. Consequently, in order to achieve an economic use of this technology, it is necessary to retrofit the printed components with standard parts from conventional manufacturing.

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 2

Editorial note, tabletop extrapolation: For a low-budget build the demonstrated pattern is catalog KF/CF hardware joined to a printed complex body; a plain straight connector is exactly the case the source found uneconomic to print. Compare current quotations - the economics move with the market.

With both parts a high vacuum of 1.5·10-5 mbar was reached without problems.

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 2

Editorial note, tabletop extrapolation: Mid-10^-5 mbar is already the working range of many small accelerator chambers, so this is a meaningful screening result - and only that: a reached pressure folds together pumping speed, outgassing and any leaks, so it proves the assembly pumpable on that stand, not leak-free. Cleaning and an acceptance test still precede installation.

Before the actual examination a background measurement of the chamber without specimen was performed. Here, as with the test objects, the pressure increase Δp was recorded over a period of Δt = 24 h

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 2

Editorial note, tabletop extrapolation: An amateur-affordable gas-load screening test: it bounds total leak-plus-outgassing without a helium leak detector, but it cannot distinguish real leaks from outgassing or localize anything, so helium detection keeps its place where a leak must be found or a specified limit certified. The background run is essential because chamber outgassing (reported background 1.00*10^-7 mbar*l/s) is the same order as the specimen signal being measured.

the 3D-welded KF-SC DN-40 in the uncleaned state behaves slightly worse than a conventionally manufactured component KF-SC DN40 made of stainless steel. … Table 2: Leakage Rates … 3D Welded KF-SC DN40 uncleaned … 7.39·10-7 … Edelstahl KF-SC DN40 … 5.25·10-7 [Leakage Rate column, mbar·l/s]

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 2, 3

Editorial note, tabletop extrapolation: The penalty for a printed part fresh from post-processing is a factor of about 1.4 against wrought stainless in this 24 h test; whether that matters in a given system is a gas-load-budget question, not a constant.

the influence of a pretreatment can be checked by cleaning the 3D-welded KFSC DN-40 with isopropanol in an ultrasonic bath and rerun the pressure increase measurement. … When cleaned, the 3D printed part is even better than the conventional one. … Table 2: Leakage Rates … 3D Welded KF-SC DN40 cleaned … 2.15·10-7 [Leakage Rate column, mbar·l/s]

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 2, 3

Editorial note, tabletop extrapolation: A 3.4x improvement from one solvent ultrasonic cleaning makes validated cleaning one of the cheapest vacuum upgrades going; transferring it to other parts means checking solvent compatibility, trapped volumes, rinsing and complete drying rather than assuming the same factor.

Through the flow channels, the recipient can be heated during evacuation and alternatively cooled when needed in operation. The exact shape of the channels was determined by a CFD-program to ensure optimal flow conditions.

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 3

Editorial note, tabletop extrapolation: Integrated wall channels give a small chamber bakeout and cooling with no external jacket or brazed lines - a capability that is expensive to add to a one-off machined chamber - at the price of fluid connections and a leak qualification of the channel walls against the vacuum volume.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

the leakage rate is essentially attributable to the Viton flange gaskets and the material properties, for example the roughness of the surface, are not yet effective, they will have a decisive influence when the pressure falls below 10-7 mbar. How big this influence ultimately is, must result in appropriate tests, which require a much greater effort.

Wolf, Beck, Franz & Neumaier, 3D Printing for High Vacuum Applications — THC04, Proceedings of Cyclotrons2019 (2019) — p. 4

Editorial note, tabletop extrapolation: On an elastomer-sealed machine, gasket permeation can dominate the gas load, as it did in this test - but the crossover is system-specific, so build the gas-load budget (seals, wall outgassing, leaks, trapped volumes, pump speed) before deciding which term to chase; no universal pressure divides gasket-dominated from wall-dominated systems.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

Running the cyclotron with supplemental pumping, the hydrogen gas flow was increased to the point where the primary beam can be visibly seen via recombination. […] Figure 12 shows an intense beam spiraling to the left and downward while operating at 600 Watts. The beam is terminating at the leftmost portion of the chimney base. Secondary electron emission can be noted by vertical striations observed emanating from the ion beam's impact location.

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

Editorial note, tabletop extrapolation: A deliberately dirty operating mode used as a diagnostic: with supplemental pumping in place, over-gas the chamber until the beam glows by recombination — this machine photographed an intense spiral (600 W) terminating on the chimney base, with secondary-electron striations marking the impact point. On a machine with a diffusion pump and an MFC the trick is free to try; whether YOUR beam becomes visible depends on gas excitation, optical access and background light, and the glowing trace is the beam path, not necessarily a single identified turn.

The ion source chimney allows thermionic electrons to freely leave the biased filament following the vertical magnetic field lines to the median plane all the while ionizing hydrogen. Admission of hydrogen gas to the enclosed volume of the filament and chimney improved vacuum performance. A 1/16-inch aperture in the chimney wall located at the height of the median plane launches the protons directly into the DEE as pictured in figure 6.

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

Editorial note, tabletop extrapolation: Two benefits from one part: local gas confinement (less load on a small pump) and a defined emission aperture at the median plane. The 1/16-inch aperture is this machine's as-built dimension — a reference point, with the right size for another source set by its extraction optics and gas-conductance budget (the same program's later aperture sweep, dg-1814, is the method).

The operational sequence was as follows: pump the cyclotron chamber below 1E-5 Torr, shut off ion gauge, turn on the magnet with approximately 20 amps of excitation current, turn on filament bias supply (-200V), then slowly ramp filament heater supply until thermionic emission on order of 10mA is reached, slowly admit hydrogen gas until an increase in emission current was noted. Final optimal filament heater current is noted at 20.6 Amps (for 0.015 inch diameter 1% Th-W wire) and final optimal leak dial setting of 104 was recored. RF was turned on at a low level and tuned to resonance (found to be 14.8640 MHz), the RF drive was increase to 300 watts – corresponding to 7,500 Vp-p on the DEE. … To satisfy the “cyclotron resonance condition” the magnet current was slowly swept up while monitoring the electrometer needle for deflection.

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

Editorial note, tabletop extrapolation: A complete, numbered startup sequence at exactly the target machine class, including the filament wire spec (0.015 inch 1% thoriated tungsten) and its 20.6 A heating current, and the order of operations: vacuum, gauge off, magnet, bias, heater, gas, RF to resonance, then sweep the magnet current up while watching the electrometer. The numbers are this machine's optimum, not universal setpoints; the ORDER is the transferable part.

The cold cathode PIG ion source can provide beam currents as high as 1 µa, but a mixture of operational constraints limited the beam current on target to about 100nA or less.[5] Ion production linearly follows the PIG discharge up to 60 mA. However, a sustained discharge current greater than 30 mA leads to the negative impedance regime and an associated thermal runaway. In that regime, without water-cooling, the ion source would quickly suffer failure. Thus the ion source operation was limited to 20 mA discharge current. The gas flow had to be severely throttled because of the vacuum systems inadequate pumping speed; the chamber's operating pressure was maintained at 4E-6 Torr or less. … The beam current on target quickly diminished at higher pressure.

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

Editorial note, tabletop extrapolation: The real limiter chain on this machine, as the source tells it: the source could give 1 µA, but a MIXTURE of constraints left ~100 nA or less on target — pumping speed forced hard gas throttling (4E-6 Torr or less, with target current quickly diminishing at higher pressure), and the uncooled PIG's negative-impedance runaway above 30 mA capped discharge at 20 mA. The thresholds are this source's; the chain — pumping limits gas, gas limits source output, thermal runaway limits it again — is the pattern to budget against on any small machine.

The operating pressure of 1E-5 Torr is provided by a standard 4-inch diffusion pump stack.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: PDF p.1 = printed p.369. Calibration context for the tabletop class: this 12-inch chamber with an internal PIG source holds 1E-5 Torr on a standard 4-inch diffusion stack — no turbo or cryo claimed. Size another machine from its own gas throughput: P = Q/S with the EFFECTIVE speed after conductance and baffle losses, with the source's hydrogen feed as the dominant Q. The Rutgers datum says the answer can come out '4-inch diff pump'; it does not say it will.

The chamber’s construction is of a stainless steel wall, accessory ports, and flanges. The top and bottom lids of the chamber are of 0.25 inch aluminum. The lids make a vacuum tight seal to the circular stainless steel wall with the use of 451 Viton O-rings. The accessory ports were TIG welded and are terminated in either CF2.75 or CF1.33 metal gasket seal flanges. The vacuum port on the chamber is a standard KF25 Viton 0-ring seal. … The chamber has an inside diameter of 11.00 inches and a wall thickness of 0.750 inches. The outside height of the chamber measures 2.00 inches and the inside height measures 1.50 inches. The DEE is 1.00 inch thick allowing for 0.25 inches of clearance between the top and bottom of the lid. The DEE wall is 1/16 inch thick brass. The DEE and chamber are symmetrical about the chamber's median plane.

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

Editorial note, tabletop extrapolation: A fully specified chamber at exactly this scale, whose internal consistency checks out: 2.00 in outside minus two 0.25 in lids = the stated 1.50 in inside; the 1.00 in dee leaves the stated 0.25 in per side. The elastomer-for-big-seals, metal-gasket-for-instrument-ports split is a pragmatic cost/performance pattern worth copying. Copy the PATTERN and re-derive the numbers: lid deflection under atmosphere, seal compression, and HV clearances are per-design calculations (the magnet gap this chamber fits — 2.1875 in — is on the magnet card, dg-1846-class).

The Precision mechanical pump has an absolute pressure of 1E-4 Torr, and a pumping speed of 195 liters/minute. The diffusion pump is a Veeco 4 inch water cooled pump that uses Dow Corning 704 oil, with water cooled baffles, and a liquid nitrogen trap. … The ultimate pressure of this four inch pump is 1E-8 Torr and has a pumping speed of 425 liters/minute. Directly after the LN2 trap the plumbing steps down from a four inch flange to a two-inch KF40 Viton flange. A valve manifold and 18 inches of two-inch metal bellows connect the LN2 trap to the chamber. Only at the chamber does the vacuum line reduce to one-inch. After great care in assembling a clean and tight vacuum system the chamber can routinely be evacuated to 1E-5 Torr in approximately 30 minutes, and < 5E-6 Torr in less than 2 hours.

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

Editorial note, tabletop extrapolation: An achieved pumpdown benchmark for one clean, tight chamber of this size — 30 minutes to 1E-5 Torr, under 2 hours below 5E-6 — a realistic anchor, not a guarantee, since gas load and conductance own the result. The conductance practice embedded here is the copyable part: hold the largest line diameter from the trap and neck down only at the chamber itself (4 in → 2 in → 1 in at the last joint). Pump ultimates are manufacturer specifications, not measured chamber pressures. (The quote begins at the foot of p.2 and concludes on p.3.)

Because it is mounted directly on a chamber accessory port, the gauge is in a significant magnetic field while the magnet is energized. Since the operation of the ion gauge utilizes low energy ion currents, even the slightest magnetic field will alter the ion current incident on the collector. This ion current change thereby guarantees erroneous pressure readings.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 3

Editorial note, tabletop extrapolation: A failure mode that bites anyone who mounts an ion gauge on the chamber inside the yoke — and is easy to misread as a real pressure excursion when the magnet ramps. The physics: fringe field bends the gauge's electron and ion trajectories, shifting its calibration by amounts that depend on field, orientation and gauge geometry (the source's "guarantees erroneous readings" is its emphatic version). Remedies in preference order: mount the gauge on a stub outside the fringe field; characterize the gauge at operating current; or, as this machine did, set the leak with the magnet off and hold the mechanical setting — accepting blindness to gas-load changes mid-run, which argues for interlocks on what you CAN see.

For pressures greater than 5E-5 Torr, and filament emission currents greater than 1 mA, a dramatic cathode ray appears. Plate 3 was taken through the view-port that looks down the accelerating gap. Electrons travel down from the filament along the magnetic field lines to the bottom of the chamber.

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

Editorial note, tabletop extrapolation: A free visual diagnostic worth a view-port: the glowing electron column (visible above ~5E-5 Torr and ~1 mA emission ON THIS MACHINE — thresholds that belong to its geometry, gas and gauge) confirms the source is emitting and shows roughly where the ionizing column runs. The source reports the phenomenon; it neither calls it a hazard nor a limit — find your own onset conditions and use the view as qualitative confirmation, not as a calibrated marker.

It was found that the optimum hydrogen pressure was 5.5E-5 Torr. Pressures higher would decrease the collected beam due to the protons decreased mean free path, while pressures lower than optimum decreased the available hydrogen of which to create ions from.

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

Editorial note, tabletop extrapolation: The clearest statement of the pressure trade for a small internal-source machine, with both sides named: too high and the protons scatter (mean free path), too low and the source starves. This machine's optimum was 5.5E-5 Torr (5.1E-5 on the run of record), about an order of magnitude above its base pressure — gauge readings and geometry make the number machine-specific, so transfer the METHOD: establish a clean base, admit hydrogen controllably, sweep pressure against collected beam, and size pumping throughput to hold the optimum you find.