Design Guide › Vacuum chamber
Cyclotron vacuum chamber design rules
55 of the guide’s 1878 rules carry the chamber tag.
Rules for the vacuum chamber in the pole gap: gap and aperture budgets, lid and wall thickness, port layout, and the ways the chamber walls become part of the magnetic circuit.
Each rule keeps its formula where the source gives one, a verbatim quote, a page-level
citation, and a stable identifier (dg-NNNN) that resolves here and on the
all-in-one guide. Where an editorial note says
“the reference machine”, its parameters are on the
guide’s front page.
By applicability level: level 1 (1) · level 2 (32) · level 3 (15) · level 4 (7) — levels rank breadth, never license to skip (method). Related domains, by shared rules: Fabrication (24), Vacuum (16), Magnet (12), RF (10), Dee (8). To combine tags or levels, open this domain in the filterable view.
Verify before use. Every rule here is a source extract in the vocabulary of the editorial methodology — faithful to its cited page, not an independently validated engineering requirement. Re-read any rule that drives a real design decision at the cited page before committing metal, money, or high voltage to it. The editorial note under each quote is this site’s extrapolation to a tabletop machine, not something the source said: an editor’s judgement, audited for overreach, never a citation.
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Choose the pole gap as a compromise: a small gap cuts the ampere-turns and lets orbits run close to the pole edge, while a large gap buys space for ion source, probes, and easier vacuum pumping at the price of field and power.
Source quote & editorial note
small gap: reduced number of At of coils, pole radius reduced, orbits close to outer edge; large gap: large space: injection, extraction, probes, easier vacuum pumping
Zaremba, Magnets for Cyclotrons (2005) — p. 22
Editorial note, tabletop extrapolation: Frames the central tradeoff for a next machine: shrinking the gap raises B at fixed ampere-turns while the iron stays unsaturated (dg-021's measured case shows the ideal 1/g is an upper bound) - and everything (dee aperture, ion source, probes) must still fit and pump through the smaller gap.
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Build the aperture budget as: good field region + vacuum chamber wall (0.3-2 mm) + installation/alignment margin (0-5 mm), with the paper allowing a further 5-10 mm within the good field region for closed-orbit distortion.
aperture = GFR + chamber wall (0.3-2 mm) + margin (0-5 mm); GFR includes 5-10 mm closed-orbit allowanceSource quote & editorial note
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).
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.
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Make vacuum-chamber top and bottom thin, circular steel plates - the quoted design, chosen to decrease the magnetic gap as much as possible - and make the side wall non-magnetic (brass, per the source) so field is not bypassed around the gap.
Source quote & editorial note
top and bottom of the vacuum chamber should be thin, circular steel plates ... to decrease the magnetic gap as much as possible. To prevent field bypassing, the tank wall must be non-magnetic, preferably brass
Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 5
Editorial note, tabletop extrapolation: Directly applicable chamber architecture for a small machine; every millimeter of chamber wall inside the gap costs ampere-turns.
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The gap drives the field: for a gap-dominated, unsaturated magnet B ~ mu0*NI/g, so keep the pole gap as small as the vacuum chamber, dee clearance and beam aperture allow, even at the cost of a harder chamber design - the source calls its tight spacing 'essential' despite the chamber difficulty it caused. [Corrected 2026-08-23: earlier text also asserted the magnet is 'the single most expensive subsystem', which the quote does not say.]
B ~ mu0*NI/g for a gap-dominated, unsaturated circuit; real magnets add fringe, yoke reluctance and saturationSource quote & editorial note
it is advantageous to keep the gap between the magnet poles small. This tight spacing made the design of the vacuum chamber more difficult, but it was essential.
Baumgartner, The Cyclotron Kids' 2 MeV Proton Cyclotron — Cyclotrons 2013, WE1PB05 (2013) — p. 1-2
Editorial note, tabletop extrapolation: The central trade for a next machine: each millimetre of gap saved is field (at fixed ampere-turns), and energy scales as B^2 (at fixed radius and species) - but only within the unsaturated, gap-dominated regime, and only after dee-voltage clearance, pumping and field quality have had their say. Verify the saturation and fringe terms in FEMM before banking the gain. [Note revised 2026-08-23: an earlier text called the gain 'for free'; the chamber redesign it costs is the quote's own point.]
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A modeled upgrade with real leverage: replacing the Houghton chamber's aluminium lids with magnetic stainless-steel lids reaching 2.2 cm beyond the poles makes them act as wide pole faces drawing field outward - in the thesis's PSF model this pushed n = 0.2 from r = 5.9 cm out to r = 8.3 cm, cut the effective pole gap from 3.9 cm to 2.54 cm, and raised B from 1.27 T to 1.77 T (27.0 MHz, 0.91 MeV computed, vs 0.47 MeV for the unmodified design).
modeled: lid radius = pole radius + 2.2 cm; gap 3.9 -> 2.54 cm; B 1.27 -> 1.77 T; f = 27.0 MHz; Tmax 0.47 -> 0.91 MeVSource quote & editorial note
The maximum magnetic field of the unmodified design is B = 1.27 T and is B = 1.77 T for the lid design. ... B = 1.77 T corresponds to a Dee frequency of 27.0 MHz
Morrow, Focusing in the Houghton College Cyclotron — Houghton College thesis (2015) — p. PDF 54 (printed 49) and PDF 55 (printed 50)
Editorial note, tabletop extrapolation: Cheap in materials and potentially the highest-leverage change of this class, but the numbers are one thesis's model of one geometry: model your own lid as part of the magnetic circuit, verify the full B(r) and n(r), confirm the chosen stainless grade is actually ferromagnetic and vacuum/structurally suitable, and recompute energy from the usable orbit radius.
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Trade pole gap deliberately: a small gap needs fewer ampere-turns and allows a smaller pole radius - which pushes the orbits close to the outer edge, leaves no room for probes, injection and pumping, and is very sensitive to errors (vertical losses); a large gap eases vacuum, injection, extraction and diagnostics at the cost of field.
Source quote & editorial note
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.
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Choose dee-to-lid clearance for the working dee voltage: MIT's 1.25-in clearance (5-in lid gap) capped dee voltage at ~70 kV by breakdown, and the source's remedies are greater clearance plus round, smooth contours and clean, polished surfaces.
MIT: 5-in gap between lids, 2.5-in dee height, 1.25-in clearance -> ~70 kV limit (~56 kV/in working gradient)Source quote & editorial note
The gap between chamber lids was chosen to be 5 in., leaving 1 1/4-in. clearance between D's and lids ... resulting in a D-voltage limit of about 70 kv due to breakdown. ... The limit can be raised by designing for greater clearance between D's and chamber lids and by providing round, smooth contours and clean, polished surfaces.
Livingston & Blewett, Particle Accelerators (1962) — p. 175, 189
Editorial note, tabletop extrapolation: At 1.3 kV the reference machine has large margin against this failure mode. For a next machine at several kV, treat MIT's ~56 kV/in at breakdown as one calibration point, not an allowable: analyze peak surface fields, round and polish, assemble clean, and expect to condition (see dg-253) - no universal safe kV/in exists for vacuum gaps.
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Expect high-voltage conditioning of a freshly opened chamber: assemble clean (no dust, grease, or fingerprints; never steel wool or coarse abrasives), round and polish the high-field contours - and still expect conditioning, which no amount of smoothing or polishing eliminates; the oscillator must be able to ride through the sparking without manual resets.
Source quote & editorial note
It is common experience, however, that no amount of smoothing or polishing will eliminate the necessity of some high-voltage conditioning under vacuum. Clean laboratory techniques in preparing a chamber for reassembly after opening are essential; dust should be controlled and all grease removed (even fingerprints), and under no circumstances should steel wool or coarse abrasives be used in cleaning. The oscillator circuit must be capable of driving the cyclotron through these varied conditions of sparking and discharge, without the necessity of tuning or of manual resetting of overload relays.
Livingston & Blewett, Particle Accelerators (1962) — p. 189
Editorial note, tabletop extrapolation: After every chamber opening, ramp dee voltage gradually with vacuum and arc-rate monitoring until sparking subsides before expecting stable beam; how long that takes is the machine's answer, not a fixed budget.
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Iowa State's dee geometry: thin sheet-copper dees 22.5 cm in diameter and 2.4 cm high, separated by a 1.5 cm gap and water-cooled through the supporting stems - about 0.89 of their pole diameter.
dee dia 22.5 cm vs 25.4 cm pole face (0.886); dee height 2.4 cm; dee-dee gap 1.5 cmSource quote & editorial note
The dees, made of thin sheet copper, arc 22.5 cm in diameter, 2.4 cm high, and they are separated by a gap of 1.5 cm.
McGuire, The Iowa State University 1.5 MeV Undergraduate Cyclotron (1961) — p. 7
Editorial note, tabletop extrapolation: A documented dee geometry near the reference machine's scale - note it exceeds an 8-inch pole, so it fits 10-inch-class machines as-is: scale the proportions, not the dimensions. Dee cooling need tracks the dissipated RF power and construction, not a fixed kilowatt line: compute it from the RF budget (dg-313) and watch dee temperature during commissioning.
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Thin chamber lids over a wide flat span bow inward under vacuum, changing dee capacitance (detuning the RF) and reducing flashover voltage - the source machine tack-welded internal support posts under its lids to stop it.
the source machine's case: 3/16-in lids over a ~2 ft span bowed enough to need postsSource quote & editorial note
the top and bottom of the chamber to bow in, which affected the capacitance of the dee and reduced the maximum voltage that the dee could withstand before flashing over.
Baumgartner, The Cyclotron Kids' 2 MeV Proton Cyclotron — Cyclotrons 2013, WE1PB05 (2013) — p. 2
Editorial note, tabletop extrapolation: Directly relevant to any thin-lid chamber on a next machine squeezed into a small magnet gap: design the lids to a calculated stiffness (the lid-deflection calculator) from the start. Internal posts clear of the beam spiral and the RF high-field region are one remedy; thicker or dished lids and external ribs are others, and each needs its own deflection, buckling, venting and weld checks. [Note revised 2026-08-23: earlier note planned posts as the remedy.]
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One machine's design point for dee-to-liner spacing: its selected 100 kV peak required about 1.5 in of vacuum clearance (~26 kV/cm), taken at the minimum because magnetic gap is precious.
cited design point: ~1.5 in clearance at 100 kV peak (~26 kV/cm); not a linear scaling lawSource quote & editorial note
The selected value of 100 kv peak voltage requires about 1.5-in. clearance from dee-to-liner ... Since the magnetic gap is so precious ... this minimum value is taken for design.
Editorial note, tabletop extrapolation: The reference machine's 1.3 kV is electrically trivial by this calibration - its clearances are set by beam aperture and mechanical tolerance. For a 20-50 kV dee on a next machine, set clearance from electrostatic analysis of the actual geometry (edges, finish, conditioning, pressure regime), not by scaling kV/cm linearly.
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Design the chamber, dee, dummy dee and filament to disassemble with screws rather than glue or solder - the 2006 Houghton chamber's glued glass insulation could not be repaired after a dee-to-wall spark, forcing a complete rebuild.
Source quote & editorial note
This design strategy made it impossible to fix a single component of the apparatus, such as the insulation, without replacing the entire piece.
Editorial note, tabletop extrapolation: A next machine should assume sparks and insulator damage happen across a machine's life: modular fastening where practical turns rebuilds into part swaps - the source's glued chamber is the cautionary case. Where glue or solder is structurally necessary, design the bonded assembly itself as the replaceable unit.
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Build the Dee/dummy-Dee pair from one 1.27 cm thick, 0.6 cm wide aluminium ring of 15.6 cm OD, cut into a 7.8 cm Dee and a 3.2 cm dummy Dee separated by 0.635 cm ceramic spacers, skinned with 0.13 cm sheet and supported on three KF-16 feedthroughs at 120 degrees.
ring 15.6 cm OD, 1.27 cm thick; Dee 7.8 cm wide, dummy 3.2 cm; accelerating gap 0.635 cm; skins 0.13 cm; 3 supports at 120 degSource quote & editorial note
Ceramic spacers hold the Dee and Dummy Dee apart with a gap of 0.635 cm. The entire Dee electrode assembly is supported by three KF-16 electrical feedthroughs through ports at 120 degrees from each other. ... A circular ring of 6061 T6 aluminium, 1.27 cm thick, 0.6 cm wide, and 15.6 cm outside diameter, formed the walls for both the Dee and Dummy Dee. Two 5052 aluminium sheets, 0.13 cm thick, were fastened to the top and bottom of the ring with vented screws.
Editorial note, tabletop extrapolation: Direct fabrication prior art at exactly tabletop scale; the single-Dee-plus-dummy topology needs live RF on only one electrode - the design rationale for fewer HV feedthroughs - and the vented screws are the kind of vacuum detail worth copying wholesale.
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Add deliberate clearance between the filament and the chamber lid - Houghton milled a 0.3 cm deep circular depression into the lid specifically to prevent a repeat filament-to-lid discharge.
0.3 cm milled recessSource quote & editorial note
To make room for a filament and to avoid another electrical discharge from the filament to the lid, a 0.3 cm deep circular depression was milled out of the bottom of the upper lid.
Editorial note, tabletop extrapolation: In the reference machine's tight pole-gap geometry, check every HV-to-ground clearance near the median plane; milling relief pockets is cheaper than chasing sparks later.
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Budget unbaked, uncleaned stainless steel at ~1e-5 Pa-m/s (~7.5e-9 Torr-L/s-cm2) after 10 h of pumping, reduced 10-100x for high-vacuum suitability - the quoted figures; the book's bake schedules (mild vs 150 C) and UHV reduction factors are its adjacent material (scan re-read queued).
q(304 SS, unbaked, 10 h) ~ 1e-5 Pa-m/s; HV needs 10-100x reduction; UHV needs 1e4-1e5x; unbaked systems ~1e-6 Pa base, UHV bake ~150 CSource quote & editorial note
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
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No structure can beat the aperture limit: molecular-flow conductance of any opening is at most 11.6 L/s per cm2 for room-temperature air, and any real tube delivers only a fraction a (transmission probability) of that.
C(L/s) = 11.6*A(cm2) for a thin aperture; C = 11.6*a*A for a real duct; long round tube a ~ 4d/(3l)Source quote & editorial note
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
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A virtual leak is trapped atmospheric gas bleeding out through a blind path; its gas load is bounded by Santeler's envelope Q <= Pa*V/(e*t), and the classic culprits are unvented screws in blind tapped holes, double welds enclosing a void, and unvented double O-rings - vent (drill or slot) every trapped volume.
Q_max(t) = Pa*V/(e*t) - the worst case at time t over all connecting conductances; a specific path with conductance C gives Q(t) = C*Pa*exp(-C*t/V) (Santeler, NASA SP-105)Source quote & editorial note
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
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Make thin vacuum-chamber lids workable inside a tight magnet gap by supporting them with internal steel rods/posts that carry the atmospheric load, instead of thickening the plates - as the cited machine did.
Source quote & editorial note
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.
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Match the chamber to the magnet - the paper's build: a 2.54 cm thick aluminium ring of 9.9 cm outer / 8.5 cm inner radius, ten KF-16 ports secured with vacuum epoxy, with 0.65 cm lids carrying a Viton O-ring groove, reaching 2e-6 Torr.
wall ring 2.54 cm thick, r_out 9.9 cm, r_in 8.5 cm; lids 0.65 cm; 10 x KF-16; Viton O-ring; base 2e-6 TorrSource quote & editorial note
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.
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Avoid welding lids onto a thin flat vacuum chamber: weld shrinkage warped the whole frame; grinding off the weld and sealing with a flat Viton gasket fixed it - prefer demountable elastomer seals for flat chambers.
Source quote & editorial note
after the welding, the bottom plate contracted so much that it bent the whole frame out of shape... seal the bottom plate against the frame using a flat Viton ring.
Baumgartner, The Cyclotron Kids' 2 MeV Proton Cyclotron — Cyclotrons 2013, WE1PB05 (2013) — p. 2-3
Editorial note, tabletop extrapolation: A fabrication trap the builder can sidestep: demountable elastomer seals on both lids avoid weld distortion entirely on a thin flat chamber - the route the source machine retreated to after its frame warped. Where welding is preferred, controlled sequence and post-weld machining are the professional counters; for a garage build, not welding thin flat plates is the cheap answer.
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Size the deflector with septum radius increment dR ~ 0.15R - MIT's typical figure, with the formula showing voltage cost growing with dR - and taper the channel gap, the quoted 1/8 in at entry opening to 1/2 in or greater at exit, to accommodate divergence.
V_d ~ (2T/e)*d*(1/R - 1/(R+dR)); MIT 16 MeV, d=0.3 in: dR=0.1R -> 47 kV, dR=0.2R -> 87 kV; typical dR=0.15RSource quote & editorial note
A typical figure, used in the MIT cyclotron, is a dR of 0.15R. The deflector gap is usually tapered ... Spacings as small as 1/8 in. can be used at the entry slit, opening to 1/2 in. or greater at the exit.
Livingston & Blewett, Particle Accelerators (1962) — p. 180-181
Editorial note, tabletop extrapolation: Scaled to ~150 keV the same normalized geometry needs only ~500-900 V on the deflector - an easy supply. Entry-slit width is set against the local turn separation and beam width together (dg-495), not by a fixed prescription.
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Choose 304L (not 304) stainless for welded vacuum chambers - the low-carbon grade is the standard vacuum choice for weld integrity - and remember TIG/MIG joint design, cleanliness, and (for aluminum) high weld speed control distortion and leaks.
Source quote & editorial note
304L SS, most commonly used in vacuum, a little more expensive... Joint design is critical from vacuum, metallurgical and distortion standpoints. Cleanliness is essential.
Bertolini, Accelerator Vacuum and Mechanical Engineering — USPAS course, UCRL-MI-201847 (2004) — p. 355-360
Editorial note, tabletop extrapolation: For a next machine's chamber welds, specify 304L filler and stock where practical: the low-carbon grade resists weld sensitization (carbide precipitation and intergranular attack near welds). Plain 304, welded cleanly, also serves - the lecture's 'most commonly used' is a preference with reasons, not an exclusion - and leak-tightness comes from joint design and cleanliness either way.
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Verify chamber lid thickness with the fixed-edge circular-plate deflection formula (Roark): the thesis's example - a 10 cm radius aluminum lid only 3.5 mm thick deflects under 1 mm at full vacuum. Deflection is set by elastic modulus and thickness (D ~ E*t^3), which alloy choice barely moves; a higher-yield alloy like 7075-T6 raises the stress margin, not the stiffness.
delta_center = -q*a^4/(2D)*(L14-L11), D = E*t^3/(12(1-v^2)); alloy trades yield margin (7075-T6 505 MPa vs 6061-T6 275 MPa), not deflection - E is nearly identicalSource quote & editorial note
a lid with radius 10 centimeters and thickness of 3.5 millimeters would undergo less than 1 mm of deflection when covering a chamber with internal pressure of 1e-3 Torr
Editorial note, tabletop extrapolation: The actual formula for trading a next machine's lid thickness against magnet gap: a few mm of plate suffices at 8-12 inch chamber diameter IF the edge support is real (the lid-deflection calculator covers both edge conditions). Alloy choice buys yield margin at the price of 7075's poorer weldability and corrosion behavior - it stiffens nothing.
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Everything inside a strong cyclotron field must be magnetically transparent - aluminum, copper, brass - since ferromagnetic parts distort the field and disrupt measurements.
Source quote & editorial note
all cyclotron components must be made of magnetically transparent materials such as aluminum, copper, or brass
Editorial note, tabletop extrapolation: Standard but easily violated rule: screws, feedthrough bodies, and detector hardware inside the reference machine's gap should be checked with a hand magnet before installation.
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Design for maintenance access from day one: ANL mounted the dee assembly on a motor-driven rail carriage so the entire dee system rolls out of the chamber for service - the quote; the mobile diffusion-pump provision is the report's neighboring detail (scan re-read queued).
Source quote & editorial note
the VTO box and obround are mounted on a motor-driven carriage which operates on a rail system. This permits the removal of the dee heads... to facilitate maintenance.
Ramler & Parker, The Argonne 60-Inch Cyclotron — ANL-5907 (1959) — p. 6-7
Editorial note, tabletop extrapolation: At tabletop scale this means: chamber slides out of the gap, dee removable through a lid, pump cart disconnectable - the difference between a research tool and a sealed monument.
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Place phase slits where the beam's radial size is largest, as close to the center as possible, on different turns azimuthally separated by half a magnet period, and away from accelerating gaps (along the centerlines between dees).
Source quote & editorial note
The slit is most functional if it is installed in the place of the largest radial size of the beam... The closer to the center the device is installed, the more efficient it is, and the less radiation losses thereon. ... If there are several slits, then it is advisable to place them at different revolutions and azimuthally with a difference of half the period of the system, e.g., in a hill and a valley. ... Elements should be installed away from accelerating gaps, e.g., along the center lines of the space between the dees
Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 56
Editorial note, tabletop extrapolation: Practical placement rules if the builder adds a beam-defining post or slit to clean up phase spread and improve turn separation at extraction radius.
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Design the vacuum chamber to split and withdraw without disturbing the shimmed magnet pole tips, so chamber service never invalidates the field map.
Source quote & editorial note
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.
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Drill numerous holes in pole-tip liners so the volume behind them is pumped instead of trapping gas, as the CIT chamber did.
Source quote & editorial note
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
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Check for a re-entrant cavity resonator mode between the two magnet pole pieces with the vacuum tank walls as the return circuit; the 184-inch found one near its lower frequency limit and suppressed it easily by strapping the pole pieces together.
Source quote & editorial note
disclosed a re-entrant cavity resonator mode between the two pole pieces of the magnet with the vacuum tank walls as the return circuit resonant near the lower frequency limit. This was easily suppressed by strapping the pole pieces together.
MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 22
Editorial note, tabletop extrapolation: The pole-chamber geometry of an 8-inch machine forms the same class of parasitic cavity - sweep or model the assembled structure, and add a verified pole-to-pole RF bond if a mode lands near the operating band; don't strap preemptively, since added straps can perturb the intended RF structure or form current loops.
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Keep RF-exposed electrode spacings along the magnetic field short: at 20 Mc an electron gains ~30 eV over a 5 cm path, so paths of ~20 cm sustain ionizing oscillation discharges while the short dee-region paths gave no trouble.
at 20 Mc, ~30 eV in 5 cm; danger paths ~20 cm; safe paths < ~5 cm (worse at lower f)Source quote & editorial note
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.
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Do not build a deflector septum from 0.002-inch copper foil supported as the 184-inch first tried: sparking between the HV electrode and the foil locally heated and badly warped it in one run - size and support the septum to survive spark heating, not just beam heating.
Source quote & editorial note
There was considerable sparking between the HV electrode and the .002 inch copper foil. The copper foil was warped badly ... The 0.002 inch copper foil supported in this manner is not suitable for this job.
Sewell, 184″ Cyclotron: Vertical D.C. Electrostatic Deflector — MDDC-1051 (1947) — p. 2
Editorial note, tabletop extrapolation: A next machine's septum should be sized against the deflector's stored spark energy and thermal impulse, then tensioned or heat-sunk accordingly - conditioning sparks are part of deflector life, and the septum edge is where they concentrate. Thickness follows from that calculation, not from a fixed minimum.
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An in-tank DC electrostatic deflector electrode held about 60 kV in the operating 184-inch cyclotron - amid magnetic field, RF, and beam - a demonstrated 1947 operating value (fed, per the report, through a current-limiting series resistor; scan re-read queued for its value).
Source quote & editorial note
Approximately 60 kv could be held on the high voltage electrode of this deflector.
Sewell, 184″ Cyclotron: Vertical D.C. Electrostatic Deflector — MDDC-1051 (1947) — p. 2
Editorial note, tabletop extrapolation: Compute the next machine's required deflector field from beam rigidity, channel length and allowed interception - then design insulation, clearances and stored-energy limiting for that voltage in its own right. The series spark-limiting resistor is worth copying; the assumption that deflector HV is low-risk is not.
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One machine, two energies by mechanical reconfiguration: on the ORNL 44-inch, shifting the position of the dees and target selects a working radius of 11 in. or 20 in., while the ion source position remains unchanged and the beam orbits remain centered; the spacer dimension (14.5 in.) and the 1.5/4.9-MeV proton energies are reported in the companion specifications (ORNL-1670 and the ORNL-1663 spec table, dg-947).
fixed B and f; target radius 11 or 20 in. -> 1.5 or 4.9 MeV (E ~ r^2)Source quote & editorial note
a choice of radius, 11 in. or 20 in., is thus obtained by shifting the position of the dees and target. In either case the ion source position remains unchanged and the beam orbits remain centered
Editorial note, tabletop extrapolation: Variable energy WITHOUT retuning B or rf - E ~ r^2 at fixed field and frequency - by repositioning the dee assembly AND target together as ORNL did; a target-only intercept at reduced radius is a simpler tabletop variant (an extrapolation, not ORNL's method), and either way the delivered energy is verified from the mapped field and measured target radius, not assumed calibrated.
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Magnetic force on ferromagnetic chamber covers inside the gap can exceed the atmospheric load - size the structure for both: UW's model study found the pull on the mild-steel vacuum-tank cover plates exceeded 35 tons against 24 tons of atmospheric force - half again the vacuum load, on that machine.
UW 60-inch: magnetic pull on covers > 35 tons vs atmospheric 24 tonsSource quote & editorial note
the results indicated a force greater than 35 tons for the cyclotron magnet. For comparison the force of atmospheric pressure is 24 tons.
Editorial note, tabletop extrapolation: A ferromagnetic chamber lid or pole-integrated cover sees magnetic clamping of the same ORDER as the vacuum load at tabletop fields (B^2/(2*mu0) vs one atmosphere - dg-177's arithmetic): check deflection in both states (energized and not) and expect assembly/disassembly forces. A non-magnetic lid opts out of the magnetic term entirely.
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Choose chamber material for activation, not just vacuum: the UW tank is 2.5-in 61S-T4 aluminum, heliarc (argon TIG) welded, machined in an outside shop — "Aluminum was chosen over stainless steel because of its short half-life property" — and held 2e-6 mm Hg. The steel cover plates were poured from the same heat as the magnet forgings (they are part of the magnetic circuit): 4.5-in plate plus 1-in plate attached by screws.
Source quote & editorial note
Aluminum was chosen over stainless steel because of its short half-life property.
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.
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The pole gap equals the chamber height plus the walls, so let the lid do double duty: COLUMBUS mills a 150 mm diameter, 12 mm deep recess into the chamber lid, lowers the upper pole into it - giving the chamber a fixed seat in the magnet - and houses the Hall probe in the recess; the chamber height dropped to ~72 mm and the minimum pole spacing to ~75 mm.
delta_z = h_chamber_internal + t_base + t_lid_remainingSource quote & editorial note
In den Deckel ist eine Vertiefung mit einem Durchmesser von 150 mm und einer Tiefe von 12 mm eingefräst. Dort befindet sich eine Hallsonde für die Messung der magn. Flussdichte. In diese Vertiefung wird der obere Pol des Magneten abgesenkt; so erhält die Kammer im Magneten einen festen Sitz. Außerdem konnte dadurch die Kammerhöhe auf ca. 72 mm verringert werden. Unter Berücksichtigung der Materialstärke beträgt der minimale Polabstand des Magneten schließlich ca. 75 mm. [tr.: a 150 mm diameter, 12 mm deep recess is milled into the lid. A Hall probe for measuring the flux density sits there. The upper pole of the magnet is lowered into this recess, giving the chamber a fixed seat in the magnet; the chamber height could thereby be reduced to ~72 mm, and allowing for material thickness the minimum pole spacing is finally ~75 mm]
Editorial note, tabletop extrapolation: Every millimetre of gap costs ampere-turns; the recessed-lid trick keeps the poles within a few mm of the dee envelope while fixing the chamber and giving the field probe a home. Size the recess floor (and any thin base) by an actual vacuum-vessel calculation - plate deflection and buckling for the real material and span - not by copying this machine's dimensions; and note the probe reads the field at the recess, not the median plane, so calibrate the offset.
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COLUMBUS's chamber as built: 200 mm diameter, ~100 mm tall, rolled from 2 mm wall stainless tube with a 5 mm stainless base carrying a 150 mm centring ring seating on the lower pole; ISO200 flange lid on four claw clamps; ten radial ports.
Source quote & editorial note
ist aus einem Edelstahlrohr mit Wandstärke 2 mm gefertigt. Der Boden, ebenfalls aus Edelstahl, hat eine Dicke von 5 mm [tr.: made from 2 mm wall stainless tube with a 5 mm base]
Editorial note, tabletop extrapolation: Historical construction data, not a thickness table: a chamber's wall, lid, base, clamp and port loads get an external-pressure buckling and plate calculation (or validated FEA) for the actual geometry and alloy - a 300 mm evacuated lid alone carries ~7 kN of atmosphere. The transferable advice that survives: port count is the main regret driver on small chambers, so allocate spares.
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El Cerrito's chamber history: the first chamber - curved copper sheets clamped and gasketed around the magnet poles - made 1.5 uA but could not maintain vacuum; the replacement was a rigid ring, 16.5 cm brass tubing with two 0.3 cm steel plates, bottom soldered, top screwed down onto a rubber gasket - and with it the beam reached 7 uA.
Source quote & editorial note
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.)
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Chamber lids of annealed glass plates held on by external air pressure alone, sealed with vacuum grease against a stainless-steel ring, worked on Niell's high-school cyclotron (1994-95); Knox likewise used external air pressure to seal its top plate.
Source quote & editorial note
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.
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Build the prototype's vacuum chamber to the final machine's requirements where the roadmap is firm: Rutgers' 22.9 cm prototype (0.889 T) deliberately used a stainless chamber - ports and flanges included - sized for the ultimate 30.5 cm machine (finished 2001, operated in excess of 1.0 T), which then reused the same chamber with only a different ion source.
Source quote & editorial note
one a 22.9 cm diameter prototype and the other was the final 30.5 cm diameter machine, finished in 2001. The prototype operated at 0.889 T, using a dee and dummy dee design. The prototype chamber was constructed for use in the 30.5 cm cyclotron that was the ultimate goal of this project, and so was much larger than required. It was stainless steel, as were the ports and flanges. ... The larger machine used a 30.5 cm pole face electromagnet that operated in excess of 1.0 T, with the same chamber as the 22.9 cm cyclotron but with a different ion source.
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 17
Editorial note, tabletop extrapolation: Oversizing the first chamber lets the highest-labor component survive the upgrade - a trade, not a law: a larger chamber costs pumping speed, gap (if it sits in the magnet) and money now against rework later; the same survey documents the opposite staging too, so decide from where the rework hurts most on YOUR roadmap.
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Eight-port ring chamber construction, a 0.9 mm thick by 2.5 cm wide brass strip soldered inside two 0.6 x 0.6 cm brass rings (inner diameter 15.2 cm, rings spaced 1.3 cm apart), with eight 1.3 cm holes drilled through the strip at 45-degree intervals and brass quick-flanges soldered into each; lids are 0.64 cm thick 6061-T6 aluminum discs, 17.1 cm diameter, clamped by eight 8-32 brass screws passing through clearance holes in the top plate into tapped holes in the bottom plate.
Source quote & editorial note
a .9 mm thick by 2.5 cm wide strip of brass soldered to the inside of two 0.6 cm by 0.6 cm rings of brass
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 38
Editorial note, tabletop extrapolation: Putting every service penetration on the cylinder wall leaves the removable lids free of vacuum-service ports - apart from seal grooves, fastener holes and any needed clearance reliefs - which is what makes them simple to re-machine or replace; the build is lathe-mill-drill-and-solder work, all within a hobby shop.
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Chamber lid sealing details, each aluminum lid carries a milled O-ring groove of 0.25 cm depth (inner diameter 15.24 cm) for a 0.32 cm thick Viton O-ring, giving roughly 22 percent cord compression; the top plate is additionally relieved with a shallower milled section in the center to clear the filament, the tallest element in the chamber, and prevent shorting against the plate.
Source quote & editorial note
by 0.25 cm deep groove with an inner diameter of 15.24 cm to accommodate a 0.32 cm thick Viton O-ring
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 39
Editorial note, tabletop extrapolation: The ~22% nominal squeeze is this design's number and in the normal static-seal band - but size a new gland from a current O-ring manufacturer's vacuum face-seal table (depth AND width, gland fill, tolerances, stretch), not from one thesis dimension. The printed 3.28 cm groove width is image-verified as printed and geometrically impossible on the 17.1 cm plate - an unresolved source misprint, flagged do-not-copy; the plausible 0.328 cm reading is a guess, not a correction.
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Eight-port budget for a minimal gas-fed machine with internal target diagnostics, two glass viewports (QF16-075-VP), one power feedthrough for the dee (Lesker EFT1213258), one multi-conductor feedthrough shared by the filament and the dummy-dee ground (Lesker EFT0082038), one Faraday collector port, one gas-inlet port with needle valve, one ion-gauge port, and one pumping port.
Source quote & editorial note
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.
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Staged chamber sizing in the other direction, the as-built chamber and electrodes do not use the magnet's full pole diameter, and the stated longer-range plan is to build a larger vacuum chamber and electrodes later to take full advantage of the field diameter, along with ferromagnetic shimming of the field.
Source quote & editorial note
Longer range plans include building a larger vacuum chamber and electrodes
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 48
Editorial note, tabletop extrapolation: Starting with an undersized chamber inside a full-size magnet is the documented counter-strategy to Rutgers' build-the-final-chamber-first (dg-1451) - the stated plan here being a larger chamber and electrodes later. Faster first beam and deferred precision work are the plausible payoffs to EVALUATE, not documented outcomes; either staging is defensible depending on where rework hurts.
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The two hardest procurement items for a school-built cyclotron, a homogeneous-field magnet and a custom vacuum chamber, were both solved by donation, per the 2013 account: a research institute (Juelich, IKP) donated a Bruker BE-15 laboratory magnet, and a vacuum-component company (VACOM) fabricated the ten-port chamber free of charge, with further support from regional companies, foundations and a youth-science sponsor pool.
Source quote & editorial note
At the very beginning there were two big problems: How to get a magnet for the homogenous field and How to get a suitable vacuum-chamber. The first problem was solved by the Research Institute of Jülich. Prof. Dr. Maier and his team donated a Bruker BE-15. … The second problem was solved by VACOM, a company specialized in vacuum-components. VACOM built the vacuum-chamber, i.e. Fig. 1, for us free of charge.
Editorial note, tabletop extrapolation: For an educational build, soliciting institutional donations for the few components a home or school shop cannot make is a documented alternative to surplus-market hunting.
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Exploit additive manufacturing's function integration for vacuum vessels by printing a network of flow channels directly into the chamber wall, shaped with a CFD program for good flow; the same channels heat the vessel during evacuation (bake) and cool it during later operation.
Source quote & editorial note
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.
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.
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A complete working vacuum chamber can be built as a printed complex base body with integrated channels, finished by welding on standard commercial components; the approach avoids unnecessary rework, and its geometry can be re-adapted per build since no tooling or molds are involved.
Source quote & editorial note
Since no moldings and other tools are necessary for the production of 3D printed components, there are no further costs. … The basic body of the vacuum chamber was supplemented with a complex geometry and integrated flow channels and completed by welding standard components. In addition to a cost-effective production by avoiding unnecessary rework, this method also has the advantage of a flexible adaptation to different customer requirements.
Editorial note, tabletop extrapolation: For a multi-port chamber whose port pattern is unique to one machine, a printed body with welded catalog flanges is a demonstrated alternative to welded-plate fabrication and machining from solid, and the port layout can be revised in CAD between builds without molds or dedicated tooling - the build itself still costs supports, fixtures, inspection and sealing-surface machining, so the comparison is build-specific.
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Fabrication status of the IUAC table-top cyclotron chambers (no beam) — two chambers for the project are listed among the institutional mechanical workshop's completed in-house jobs for the programme year, alongside chambers and RF components for other facilities; the report states the entire requirement of machining, welding and assembly is carried out by the workshop without any outsourcing.
Source quote & editorial note
Some of the major in-house jobs that were successfully completed are; the low energy nuclear physics chamber for the High Current Injector, SS jacketing work of the spare Niobium Resonators for linac, two chambers for the Table Top Cyclotron project and several RF components like a prototype high power directional coupler, heat sinks for RF power amplifiers etc ... As of today, the entire requirement of machining, welding and assembly is fully carried out by the IUAC workshop without any outsourcing which is one of its mandates.
IUAC, Annual Report 2024–25, Chapter 3 — Research Support Facilities (table-top cyclotron RF system) — p. 36, 37
Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: chamber fabrication at this machine scale is workshop-grade machining and welding, done entirely in-house by a national lab as routine job-shop work — not exotic vessel-making. Why the project consumed two chambers the report does not say (iterations, or distinct functions), so read the count as a capacity observation, not a revision history.
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In the Rutgers deflection channel a 0.005 inch thick curved grounded stainless steel sheet forms the septum separating the main accelerating volume from the deflection channel, with a slightly larger-radius HV electrode arranged concentrically at an average 0.31 inch gap; the whole channel is a modular assembly that can be removed and replaced.
Source quote & editorial note
A 0.005 inch thick, curved, grounded stainless steel sheet forms the septum and separates the main accelerating volume and the deflection channel.
Editorial note, tabletop extrapolation: PDF p.3 = printed p.368. A buildable worked example at tabletop scale: 5-thou stainless shim, curved and grounded, forms the septum, with the concentric HV electrode at an average 0.31 inch gap — formable without a machine shop. Choose your own thickness from stiffness, supports and intercepted beam power rather than copying the number. The design choice worth copying outright is modularity: the whole channel removes as a unit, which is what keeps a crowded small chamber serviceable. (The 0.31 inch average gap figure is on p.3.)
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The Rutgers 12-inch cyclotron's chamber can be moved horizontally with respect to the magnet's center, which is how deliberate initial radial-position errors (and hence radial betatron motion) are introduced.
Source quote & editorial note
The cyclotron chamber’s position can be moved horizontally with respect to the magnet’s center. … Initial ion radial-position errors can be introduced by a horizontal offset of the chamber, and hence ion source, with respect to the magnet center.
Editorial note, tabletop extrapolation: PDF p.1 = printed p.369 (purpose stated on PDF p.2-3 / printed p.370-371). An unusual design freedom: the chamber (and hence source) translates horizontally with respect to the magnet center, and the same adjustment that centers the source doubles as the deliberate-error knob for radial betatron studies. Copy it as a constrained, lockable, measurable translation — an unlocated chamber is not the feature; a controlled offset is — and remember one move shifts source, dees and probes together.
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Nine-inch cyclotron vacuum chamber as-built - stainless steel circular wall of 11.00 inch inside diameter and 0.750 inch wall thickness, top and bottom lids of 0.25 inch aluminum sealed to the wall with 451 Viton O-rings, outside height 2.00 inches and inside height 1.50 inches, accessory ports TIG welded and terminated in CF2.75 or CF1.33 metal gasket flanges, with the main vacuum port a standard KF25 Viton O-ring seal.
Source quote & editorial note
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.
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).
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Dee mounting and high-voltage feed on the nine-inch cyclotron - the dee is carried on a 0.500 inch copper rod mounted to a CF2.75 flange, the whole assembly suspended from the chamber by a ceramic break terminated with CF2.75 flanges at either end, forming a vacuum-tight high-voltage feed-through whose copper stem protrudes several inches outside the flange for direct connection to the RF matching cabinet mounted just outside the magnet coils.
Source quote & editorial note
The DEE is supported by a 0.500 inch copper rod that is mounted to a CF2.75 flange. This whole assembly is then suspended from the chamber by a ceramic brake terminated with CF2.75 flanges at either end. This provides a substantial vacuum tight high voltage feed-though. The copper stem protrudes the vacuum flange by several inches allowing direct connection to the high voltage terminal in the RF matching cabinet, which is mounted just outside of the magnet coils.
Editorial note, tabletop extrapolation: The mechanically simplest dee feed-through arrangement in the amateur literature - the same copper rod is structural support, RF conductor and vacuum feed-through, with a commercially available ceramic break doing the insulating. Keeping the matching cabinet immediately outside the coils keeps the high-impedance high-voltage run short. Note the appendix drawing (PDF p.16) dimensions this copper stem as 0.375 inch with a 0.75 inch brass collar, which disagrees with the 0.500 inch in the text. The source spells "break" as "brake" and "feed-through" as "feed-though".
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On the nine-inch cyclotron the second accelerating electrode is a "Dummy DEE" mounted diametrically in the chamber in direct electrical contact with it, which also serves as the central mounting surface for the ion source; the chamber median plane is adjusted to coincide with the magnetic median plane.
Source quote & editorial note
The chamber's median plane is adjusted to be the same as the magnetic field's median plane. The Dummy DEE is mounted diametrically in the chamber making excellent electrical contact as it provides the aperture of the second accelerating electrode. The dummy DEE also provides a central mounting surface for the ion source.
Editorial note, tabletop extrapolation: A topology that simplifies a small build: one driven dee (one HV feed-through) against a grounded dummy dee that doubles as a rigid, on-axis, at-ground mounting surface for the source — exactly where the source must sit. Whether one dee or two suits a given machine is an RF and symmetry decision, and some sources need bias or insulation rather than grounded mounting. The alignment rule worth copying outright: set the chamber median plane to the MAGNETIC median plane, not to the pole faces.
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On the nine-inch cyclotron the magnet's own attractive force squeezed the vacuum chamber lids inward at high field and detuned the RF: from the frequency change, a parallel-plate-capacitor approximation gave a gap decrease on the order of 7 nanometers; the inter-pole attractive force at 1 Tesla was separately estimated at approximately 16,000 N (equivalent to a 3,500 pound mass on the top yoke), under which the author adds that deflection on the order of 70 Angstroms — the same 7 nm — is reasonable to imagine.
Source quote & editorial note
the magnet poles must be attracting one another under the tremendous force, thereby squeezing the lids on the vacuum chamber. The inward movement of the lids would decrease the distance between the DEE and the lids creating an increase in chamber capacitance, thereby bringing down fr. The distance of movement was calculated from the change in frequency. Just using the approximation for a parallel plate capacitor the distance the gap decreased was on the order of 7 nanometers. The attractive force between the two poles was also estimated, at 1 Tesla the attractive force is approximately 16,000 N which the equivalent of placing a 3,500 pound mass on the top yoke. … Under such forces it is reasonable to imagine deflection on the order of 70 Angstroms.
Editorial note, tabletop extrapolation: The most surprising transferable failure mode in the document, appearing when the chamber is shimmed snugly between the poles: Fig. 8 shows the tank fr flat at ~13.559 MHz from 0.17-0.67 T then falling to ~13.551 MHz near 1.0-1.07 T — an ~8 kHz walk, comparable to this RF source's 10 kHz tuning step. Expect the tank to move during a magnet ramp and either retune per field point or decouple the lids from the pole faces. The 16,000 N checks against B²A/2μ₀ for a 9-inch pole at 1 T (computed, ≈16,300 N); the attribution of the shift to lid motion is the author's interpretation, consistent between his frequency-derived 7 nm and force-based plausibility argument.
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The nine-inch cyclotron's appendix drawings are half-scale (Scale 1/2) top and side views dimensioned entirely in inches, laying out the chamber accessory ports at 0, 45, 90, 180, 225 and 270 degrees around a wall of 5.5 inch inside radius (11.0 inch inside diameter), with the dee shown as a 10.0 inch diameter D inside it; the side view carries the same 11.0 inch inside span with a 13.0 inch flange-to-flange overall, 2.0 inch chamber outside height and 0.25 inch lids.
Source quote & editorial note
All dimentions are in inches Scale: 1/2 TOP VIEW
Editorial note, tabletop extrapolation: A dimensioned drawing set — rare in the amateur literature — for one 11-inch-bore chamber: ports at 0/45/90/180/225/270 degrees, a 10.0-inch dee in the 11.0-inch bore (about 0.5 inch radial dee-to-wall clearance, computed), 13.0 inch flange-to-flange, 2.0 inch outside height, 0.25 inch lids. Use the angular map as a planning EXAMPLE — whether six azimuths serve a collector, flag, viewports and gauge without crowding depends on port diameters and the dee-stem geometry — and re-check mechanics, seals and RF clearances before cutting. (Dimensions read from the rendered sheets: top view PDF p.12, side view p.13, both printed rotated 90 degrees; "dimentions" as printed.)