Materials design rules

The magnet yoke, poles and tips, acceleration chamber lids, and shims are of soft iron forgings with the impurity analysis as follows: Carbon 0.12%...

Ramler & Parker, The Argonne 60-Inch Cyclotron — ANL-5907 (1959) — p. 11

Tabletop: A concrete steel spec to hand a supplier for a next machine's yoke stock: 1010/1018-class low-carbon steel is fine; avoid high-carbon or unknown scrap for pole tips.

Our magnet is constructed out of 1060 steel, which saturates at around 1.7 T; above this magnetic flux density the yoke is unaffected by further excitation.

Heuer & Baumgartner, Design of a 2 MeV Cyclotron (2009) — p. 6, 29

Tabletop: Directly applicable: at 0.59 T the builder is far from saturation, but a next machine pushing past ~1.5 T must budget yoke cross-sections against the 1.7 T ceiling.

When passive materials such as iron are operated close to or above saturation the approximation mu_p = infinity does not hold and the method of permeance estimation is not readily practicable.

Leupold & Potenziani, A Permanent Magnet Circuit Design Primer — ARL-TR-946 (1996) — p. 6

Tabletop: Same lesson as Tanabe from the PM side: all quick hand methods assume unsaturated iron, another reason to keep a next machine's yoke flux under ~1.5 T.

no unique mmf can be assigned to a conventional permanent magnet... the magnet mmf will always be that corresponding to the lowest point on the demagnetization curve reached

Leupold & Potenziani, A Permanent Magnet Circuit Design Primer — ARL-TR-946 (1996) — p. 8-10

Tabletop: Practical warning: alnico horseshoe magnets salvaged for a PM gap lose field every time the circuit is opened for chamber access; NdFeB tolerates gap changes reversibly.

required volume of PM material depends only on particle energy, magnet gap and PM working point and doesn't depend on pole radius or average magnetic field value.

Antokhin et al., Magnet System for PET Cyclotron Based on Permanent Magnets (2006) — p. 1

Tabletop: Scaling law that makes a permanent-magnet follow-on build thinkable: at ~1 MeV and a 2 cm gap the required NdFeB volume is a few percent of the 1 ton needed for 10 MeV.

The temperature coefficient of gap magnetic field was measured as about -0.07%/0C. Such coefficient is acceptable for normal work of cyclotron.

Antokhin et al., Magnet System for PET Cyclotron Based on Permanent Magnets (2006) — p. 2

Tabletop: A PM cyclotron in an unheated garage will drift off resonance with the seasons: 10 degC swing = 0.7% field change, far more than the few-parts-in-10^4 the resonance wants.

The iron yoke area uses mat=2, which uses the BH curve for a 'generic' iron whose magnetic properties approximate the behavior of 1010 steel.

Tanabe, Iron Dominated Electromagnets, Lecture 4: POISSON — A Two-Dimensional Magnetostatic Solver (2005) — p. 9

Tabletop: Removes the main excuse for not simulating: home-built yokes are usually A36/1018 mild steel and the default curve is close enough for first-pass design.

The BH characteristics of iron are variable and depend on the chemistry of the iron (dominated by the Carbon content, which is highly variable from heat to heat).

Tanabe, Iron Dominated Electromagnets, Lecture 8: Core Fabrication, Assembly, Installation and Alignment (2005) — p. 7, 9

Tabletop: Practical purchasing rule: buy a next machine's pole and yoke stock as one lot from one heat, and expect top/bottom asymmetry if pieces come from different sources.

It is good practice to keep the iron yoke reluctance smaller than a few per cent of air reluctance ... such that the magnetic flux in the iron remains smaller than 1.5 T ... the efficiency is better than 99%.

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 15

Tabletop: The single most useful yoke-sizing rule for an H-frame homebuilt magnet: pick return-leg area = flux/1.5 T and the magnet behaves predictably.

Sheet thickness 0.3 <= t <= 1.5 mm ... Coercivity Hc < 65 A/m ... Coercivity spread dHc < +/- 10 A/m

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 23

Tabletop: For a DC cyclotron magnet solid mild steel is fine, but this gives the numeric target for 'good' steel and explains why scrap-plate yokes vary.

The BH relationship becomes highly nonlinear at B >= 1.5 Tesla and the material exhibits fully saturated behavior at B >= 2.0 Tesla.

Tanabe, Iron Dominated Electromagnets: Design, Fabrication, Assembly and Measurements — SLAC-R-754 (2005) — p. 249-251

Tabletop: Sets the iron budget for the next machine: yoke and pole cross-sections should be sized so flux density stays under ~1.5 T anywhere on the return path, and pole-tip fields much above 1.8 T are not worth chasing with iron.

ferromagnetic materials lose their advantages above their saturation field (typically 2 T).

Humphries, Principles of Charged Particle Acceleration (1986) — p. 104, 108

Tabletop: Defines the absolute ceiling of the iron-magnet approach for a next machine (~1.6-1.8 T practical); beyond that only superconductors or air-core help.

once the iron magnet poles become saturated (at about 2 T) the maximum energy is determined by R

Loucks, Initial Results from the Houghton College Cyclotron — Houghton College thesis (2007) — p. 18

Tabletop: Frames the next machine's tradeoff space: pushing the reference machine's 0.59 T toward 1.2-1.5 T is cheap energy gain (E ~ B^2), but above ~1.8 T iron stops helping and only pole diameter buys more.

Laminated: Limited thickness : 300 mm max, usual 200 mm. Good magnetic and mechanical properties. Slight anisotropy.

Beeckman, Cyclotron Magnets — ECPM37 lecture, Groningen (2009) — p. 57

Tabletop: For an amateur the practical read is: mild-steel plate stock is fine for a DC magnet; note the anisotropy if you stack plate for pole tips.

Steel (0.9% C) 50 / 1000; Iron (99.8%) 150 / 5000; Iron (99.95%) 10,000 / 200,000

Beeckman, Cyclotron Magnets — ECPM37 lecture, Groningen (2009) — p. 72-73

Tabletop: Concrete reason to buy A36/1018 low-carbon plate rather than whatever scrap steel is on hand for an H-frame yoke.

The magnet is of a conventional closed-yoke design with a 1/1 ratio of pole base cross section to yoke cross section.

Livingston & Howard (eds.), The Oak Ridge Relativistic Isochronous Cyclotron — ORNL-2648, OSTI 4275955 (1958) — p. 118-119

Tabletop: Directly applicable: 1018/1010-class steel is the right iron for a next machine, and yoke area comparable to (Wouters says 25% above) pole area is the design corridor.

The voltage breakdown strength of a resin-impregnated layer of glass cloth or cotton mesh is usually over 100 volts/mil ... necessary to utilize mica-sheet or mica-flake insulation to obtain the higher voltage-to-ground insulation.

Livingston & Blewett, Particle Accelerators (1962) — p. 278

Tabletop: Potting the reference machine's coils stops the slow insulation abrasion that coil hum causes; their low coil voltage means the resin-glass numbers alone give ample margin.

Our magnet can achieve a maximum temperature of 173 oF and will normally operate at no more than 142 oF.

Heuer & Baumgartner, Design of a 2 MeV Cyclotron (2009) — p. 33

Tabletop: Sets the thermal design point for any potted coil in a next machine; consistent with Tanabe's <30 C rise rule for long potted-coil life.

For water velocities > 15 fps, flow vibration will be present resulting in long term erosion of water cooling passage.

Tanabe, Iron Dominated Electromagnets, Lecture 6: Excitation, Coil Design, System Design and Water Flow (2005) — p. 42

Tabletop: Hard upper bound when the builder sizes pump and passage diameter for a next machine's hollow-conductor coil.

Inter-turn insulation thickness is normally between 0.3 mm and 1.0 mm, the ground insulation thickness should be between 0.5 mm and 3.0 mm depending on the applied voltage.

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 28-29

Tabletop: Sets realistic packing-factor expectations for a hand-wound 538-turn coil and how much window the insulation eats.

Water resistivity higher than 0.1x10^6 Ohm m; pH-value between 6 and 6.5; dissolved oxygen below 0.1 ppm

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 34

Tabletop: If a next machine uses water-cooled coils at high voltage, tap water will leak current and corrode; a small DI cartridge loop is the fix.

Flow velocity v <= 4 m/sec to avoid flow vibration and erosion... An acceptable coil temperature rise which protects the coil epoxy encapsulation from damage is dT <= 30 C.

Tanabe, Iron Dominated Electromagnets: Design, Fabrication, Assembly and Measurements — SLAC-R-754 (2005) — p. 134-135

Tabletop: Direct water-cooling design window for a next machine's hollow-conductor coil; also warns that a lazy laminar-flow circuit cools far worse than the handbook film coefficient suggests.

This operated normally at 65 C but when an identical coil, which had been nickel plated, was substituted, the operating temperature rose to 350 C.

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 4

Tabletop: Reject nickel-plated hardware (and nickel underlays beneath chrome or silver) anywhere RF current flows in the resonator, coil, or ground-return path.

Most commercially available copper tube contains 0.015% to 0.08% phosphorus as a de-oxidising agent, so that its conductivity may range from 60% to 90% I.A.C.S.

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 6

Tabletop: Buy the tank-coil tubing as electrolytic/electrical-grade (C10100/C11000) copper, not generic plumbing tube, for up to ~20% lower RF resistance.

as if Rs had the value of 800mOhm - sixteen times that of the expected coil Rs ... take into account the stainless steel vacuum chamber return, the stainless steel Conflat DEE stem support and RF feed throughs.

Koeth, Theoretical Calculations and Measurements of the DEE Voltage in the Rutgers 12 Inch Cyclotron (2005) — p. 2-3

Tabletop: When predicting a next machine's dee voltage, don't use the coil resistance alone; the stainless chamber and stem return path dominates losses, so use copper return paths where possible and expect ~1 ohm scale Rs.

Dielectric strength / Thickness: 240 kV/mm at 0.025 mm; 70 kV/mm at 5 mm.

Wolf (ed.), Handbook of Ion Sources (1995) — p. 523

Tabletop: When insulating the reference machine's extraction or dee leads with PTFE sheet or heat-shrink, use the bulk (70 kV/mm-class) figure with a 5-10x safety factor, not the datasheet film value.

They found that at a critical angle of 31.5 deg, the surface charge was zero... by screening the section of the insulation surface near the cathode... the breakdown voltage was raised by a factor of approximately 2.5.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 113-114

Tabletop: Free flashover margin for the next machine's source stalk and dee-stem insulators: cone the insulator ends at ~30 degrees toward the negative electrode and recess the triple junction behind a metal skirt.

Gleichauf also found that the breakdown voltage was strongly dependent on the material of the insulator but independent of the material of the electrodes.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 113-114

Tabletop: Budget ~2 kV per mm of insulator surface path in vacuum (before sputter contamination); a 20-kV extraction stalk wants >=10 mm of clean creepage plus corrugations.

Air spaces exist in solid and liquid dielectrics... the air will have the higher stress, possibly causing sparkover through the air space... The stress in the air gap can thus be k times that in the solid.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 116, 119

Tabletop: The classic failure of home-built HV feedthroughs: a loose PTFE sleeve over a rod arcs in the annular air film; pot it, oil-fill it, or evacuate the annulus so Paschen cannot be satisfied.

two 12 in. split silver-plated, water-cooled copper rings which can be clamped securely around the stems; the dee stems are also silver plated over the adjustment range

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 53

Tabletop: Scaled down: any sliding or bolted joint in the reference machine's dee-stem/coil path should be a broad, clean, plated, firmly clamped contact - RF joints, not wires, set small-resonator Q.

The ceramic 'Lapp' coils originally used for introducing cooling water to the tube and the plate line failed whenever the oscillator voltage was increased to give 200 kv. They have since been replaced with choke coils wound from copper tubing.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 59

Tabletop: The principle (a conductive-liquid line into an RF-hot electrode must itself be an insulator or a choke) applies whenever a next machine adds cooling or bias plumbing to the dee.

No solder to hold the board to the spreader, the screws are enough. Heat sink compound between copper spreader and aluminum heat sink.

Buckler, Solid-State, 2-Decade, 1.25 kW Linear Amplifier — Development Notebook (2015) — p. 10

Tabletop: Standard practice for any kW-class dee driver a home builder assembles from LDMOS boards.

a plating having about half the conductivity of the copper base will cause the greatest increase in overall resistance ... the conductivity of much of the commercial silver plating is about half of that of pure copper

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 1

Tabletop: Skip decorative silver plating on the dee and coil; a jobbing-shop bright-silver finish would raise, not lower, resonator loss at 9 MHz.

a layer of high conductivity copper plating at least two skin depths in thickness, at the operating frequency, then protecting this against corrosion by a very thin layer of low conductivity plating or a layer of low-loss lacquer

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 10

Tabletop: For dees, stems, and tank coils at 9 MHz: bare electrical-grade copper plus thin lacquer beats commercial silver or nickel plate.

The resistance of the composite conductor reaches a maximum value when the thickness of the plating is approximately one and one half times the skin depth for the plated metal.

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 3

Tabletop: A sub-micron corrosion-protection flash on copper is harmless at 9 MHz; a mid-thickness medium-conductivity coating is the worst case to avoid.

A gold flash (10 micro-inches) is often used although many workers have shown that the deposits are not pore-free and that at least 200 micro-inches of gold are necessary to provide adequate protection.

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 7

Tabletop: For RF contact fingers and connectors on the resonator, distrust thin gold flash; specify thick gold or use bare copper with lacquer instead.

the contact resistance of two silver-plated wires rose from 6 milliohms to 200 milliohms after two hours' exposure to hydrogen sulphide.

Fowler, Radio Frequency Performance of Electroplated Finishes — Proc. IREE Australia (1970) — p. 7

Tabletop: Any silver-plated RF joints in the shop atmosphere (or near vacuum-pump exhaust) need protection or periodic cleaning, or kV-level circulating currents will heat them.

Graphite is coming into wide use for cones, arc bodies, and also for D feelers or accelerating electrodes; it operates at high temperatures with a minimum of sputtering or evaporation.

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

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

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

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

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

Aluminum=290 kV/inch ... We settled on a minimum radius of R=.1875 inches ... Emax=170 kV/inch

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 8

Tabletop: The edge-radius rule the builder needs when pushing dee voltage to 5-13 kV: radius all dee and stem edges so the enhanced edge field stays under ~half the material's breakdown value.

Four machinable ceramic strips, each roughly 2.53 cm long, 0.77 cm wide and 0.18 cm thick, hold the two dees together at the appropriate separation gap of 0.635 cm.

Haas, Characterizing the Performance of the Houghton College Cyclotron — Houghton College thesis (2009) — p. 2, 52

Tabletop: Machinable ceramic (Macor-class) spacers are the spark-tolerant choice for holding the reference machine's dee-to-dummy-dee gap, replacing glass or plastic.

the RF voltage on the dee is typically between 1 and 2 kV, far greater than the 1-3 V DC placed across the filament. Thus, the filament and wires must be adequately insulated from the dee

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

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

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

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

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

The heating power is either dc or high-frequency ac (~100 kc) to avoid damage from vibration in the magnetic field at low frequencies. Cathode life is ... materially shortened by traces of oxygen.

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

Tabletop: A 60 Hz-heated filament in a 0.59 T field literally shakes itself apart; DC heating and clean hydrogen are cheap reliability.

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

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

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

Boron nitride is an excellent material for most applications for temperatures up to 1200 C... It outgasses badly and tends to absorb water, which can destroy the parts when heated too fast.

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

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

The increase of temperature for higher electron output is limited by the increasing evaporation of cathode material, which decreases the cathode lifetime. Tables 1.2 and 1.3 give the respective data for W and Ta.

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

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

A power supply cannot differentiate between an ion reaching the cathode grid and an electron leaving it (they both appear as positive current on the ammeter).

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

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

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

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

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

The stainless steel wires previously used by Murali lasted for under a week depending on the power load. In contrast, with the W-25%Re alloy, the grid lasted for over 2 years.

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

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

The rate of flow required during operation is from 2 to 3 cc/min ... Electrons are accelerated from the filament into the arc chamber by a 100 to 300 volt potential, the normal arc current being 0.5 to 1.5 amperes.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Apple Rubber Products, Seal Design Guide — p. 84

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

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

Tabletop: For a next machine's chamber welds specify 304L filler and pipe where possible; carbide precipitation in plain 304 welds is a known source of micro-leak porosity.

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

Dewan, Design and Construction of a Cyclotron Capable of Accelerating Protons to 2 MeV — MIT thesis (2007) — p. 12

Tabletop: Gives the builder the actual formula for trading a next machine's lid thickness against magnet gap - a few mm of 7075 plate suffices at 8-12 inch chamber diameter if the edge is well supported.

all cyclotron components must be made of magnetically transparent materials such as aluminum, copper, or brass

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

Tabletop: 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.

the septum is formed of two strips of tungsten, 0.020 in. thick and 12 in. long and with the edges spaced 1/8 in. apart. Each strip is silver-soldered to a copper bar bent to the correct curvature.

Livingston & Blewett, Particle Accelerators (1962) — p. 184

Tabletop: At the reference machine's microamp/keV beam power the thermal problem vanishes, but the slotted-septum geometry still maximizes transmitted current into the channel.

operating steadily for some time with 500 ua of 23 Mev protons on a 6 by 10 inch water-cooled aluminum target of the grazing-incidence type

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 24

Tabletop: Overkill at the reference machine's ~mW beam power, but the geometry trick transfers if a next machine ever puts tens of watts on a probe tip: tilt the target.

the target, which was composed of 56 +/- 2 ug/cm2 of isotopically pure 11B deposited on a 9 ug/cm2 carbon backing

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 360

Tabletop: Defines 'thin' for the reference machine's boron target (tens of ug/cm2) and gives two independent thickness checks they can perform with their own detectors.

Thread lubrication is one of the most effective measures to lessen the potential for galling... Heat contributes significantly to thread galling.

Fastenal, Technical Reference Guide, Rev. 9 (2005) — p. 8

Tabletop: Every stainless bolt into the stainless chamber flange gets anti-seize (outside the vacuum) or silver/moly plating (inside); one galled lid bolt can strand the whole chamber.

Pitting primarily in the outline of the electrode - not directly underneath or on top.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 45-47

Tabletop: When the builder opens the chamber after sparking, the pit geography tells them whether to fix edge radii (perimeter pits) or surface contamination (random pits).

We coated the HV electrode with Aerodag G dry lubricant, which is also conductive and has low secondary electron emission coefficient.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 53

Tabletop: A cheap surface treatment the builder can apply to deflector or dee edges if they hit breakdown limits near the top of their voltage range.

The grid should be made from tantalum or tungsten wire and be fusion or resistance welded.

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 5-8

Tabletop: Applies to the reference machine's chimney slits, puller edges, and beam stops: anything the beam or arc touches for long runs should be refractory metal with welded, not soldered, joints.

The cold and hot cathodes are worn out when the erosion crater's depth reaches around the anode bore radius. The discharge becomes unstable under these conditions ... Titanium has been selected as the best compromise ... If the cathodes are allowed to run hot, tantalum has been shown to be a good choice.

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

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

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

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

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

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

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

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

the maximum temperature of the cathodes are 1992 K, which is far away from the cathode melting point ... an electron current of 0.00706 A at 500 V which is negligible in comparison to the discharge current of 1.10352 A

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

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

The Hiperco tests were repeated but dropped when this material was found to be dimensionally unstable.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 9

Tabletop: Cautionary and transferable - exotic Co-Fe edge rings for the next machine's pole edge need a stability check; plain steel shims are the safe default.

A final pair of model poles was machined out of the steel forgings actually used for the full-scale magnet poles. The results were satisfactory, and the design was frozen.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 10

Tabletop: Transferable principle - steel-to-steel permeability variation is real; test a next machine's shim stock from the same material lot as the poles.

All removable shielding blocks were stacked in two vertical layers so that no straight-through cracks remained.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 43

Tabletop: Transferable - stagger any shielding blocks on a next machine (concrete, water, borated PE) so seams never line up with the beam plane.

requires the addition of an inhibitor to reduce attack on the aluminum and steel provoked by the presence of minute quantities of copper in the water.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 53

Tabletop: Directly applicable chemistry for any next machine's water loop touching Cu plus Al; use a modern inhibitor (chromate is toxic/regulated today).

To minimize rf power losses, all steel surfaces exposed to rf fields are copper-plated.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 10

Tabletop: Directly applicable - on a next machine keep steel (chamber walls, bolts, pole faces) out of RF current paths or plate/line it with copper; Q and dee voltage per watt are at stake.

The water circuit is completed to ground potential by means of sets of flexible polyethylene tubing, each several feet long. Treated water of low conductivity is used.

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

Tabletop: Directly applicable if the next machine's dee or stem is water-cooled while DC-biased - length of insulating hose plus DI water sets the leakage current.

The care taken in insuring that only pure tension and compression forces would be applied was thus well justified.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 24

Tabletop: Directly applicable to a next machine's dee-stem standoffs and feedthroughs - arrange the support geometry (threaded rods, spherical seats) so ceramics never see bending or shear.

It was tried this way at 20 megacycles, but it soon became necessary to copper plate most of the surfaces.

MacKenzie & Waithman, R.F. System for Frequency Modulated Cyclotron — MDDC-1045 (1946) — p. 6

Tabletop: Directly applicable at 9 MHz - bare steel may survive, but plating (or copper construction) is cheap insurance for Q and hot spots.

Polystyrene of this thickness used in this manner will stand over 15,000 volts DC and approximately 1500 volts r.f. provided the metal parts remain cool.

MacKenzie & Waithman, R.F. System for Frequency Modulated Cyclotron — MDDC-1045 (1946) — p. 8

Tabletop: Transferable construction recipe for homemade HV bypass/blocking capacitors in a next machine's RF chain (modern Kapton/PTFE substitutes upgrade the polystyrene).

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

Tabletop: A next machine's septum should be thicker (>= 0.010 in), tensioned, or heat-sunk at both edges; conditioning sparks are inevitable and each one dumps its energy into the nearest thin edge.

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

Tabletop: A next machine needs only a few kV/cm over a few cm of channel - an order of magnitude below what 1947 in-tank hardware sustained, so deflector voltage should not be the limiting risk; the series resistor for spark current limiting is worth copying.

no discoloration or other indication of heating of the contacts, despite routine operation to 110 A/in and occasional operation to higher current densities

Osterlund & Smythe, A Cyclotron Power-Amplifier RF System Using a 4CW50,000C/8350 Tetrode — COO-535-543 (1963) — p. 8

Tabletop: A tabletop coaxial resonator tuning short carries far less current, so 110 A/in is a generous ceiling - but the recipe (thick fingers, positive clamping, plated surfaces, cooling on both sides of the joint) is the proven pattern for any movable-short tuner.

for equal probability of sparking with given materials, the product of gap voltage and cathode gradient is a constant.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 8

Tabletop: Directly. For a next machine's deflector, pick a VE number and the gap/voltage trade falls out; a 3-mm gap at VE=1.5e4 (kV)^2/cm predicts ~67 kV and ~220 kV/cm.

stainless steel, inconel, molybdenum, K-monel, titanium, and nickel seem to be comparable and were the best materials. Copper, tantalum, and aluminum were intermediate. Silver showed the most severe spark damage.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 8

Tabletop: Make the next machine's deflector electrode 316 stainless (cheap, machinable, on the best-tier list); avoid copper or aluminum HV surfaces even though they are handy shop stock.

There seemed to be a critical magnetic field for each material beyond which the spark damage was severe and below which the spark damage was negligible. The critical fields ranged from 4 to 15 kG.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 7

Tabletop: The reference machine's field (~6 kG) sits at the low edge of the 4-15 kG damage band, a real advantage. Conditioning the deflector at reduced field, then raising B, is nearly free insurance.

when a 0.0125-uF capacitor was added across the gap, the electrodes baked-in to 60 kV, a six-fold increase. Adding a 0.5-uF capacitor across the gap reduced the breakdown voltage to 5 kV.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 8

Tabletop: Directly sets deflector-supply philosophy - provide an adjustable, limited energy per spark (see UCRL-10655 crowbar) rather than either a stiff low-impedance supply or one that quenches sparks entirely.

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

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

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

With the tungsten anodes, the VE number increased to 2.25 X 10^4 (kV)^2/cm, an increase of 17% in VE number. In addition, we found that the tungsten anodes resisted spark damage better.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 24

Tabletop: Cheap upgrade that scales down perfectly - line the grounded surfaces opposite the next machine's HV bar with thin tungsten (or at minimum molybdenum) sheet, edges overlapped.

When we increased the beam current, the carbon evaporated from the septum, contaminated the high-voltage electrode, and very little voltage could be held.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 28

Tabletop: A next machine's beam power is watts, not kilowatts, so a carbon septum's activation advantage may yet win at sub-MeV - but the contamination mechanism is temperature-driven, so thin-foil hot spots still apply. Default to tungsten/molybdenum septum, revisit carbon only with septum-temperature data.

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

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

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

the capacitor must withstand a complete reversal of charge in 0.3 us 100 times a second without failure.

Kerns et al., High Voltage Pulser for 184-inch Cyclotron Electric Deflector — UCRL-95 (1948) — p. 14

Tabletop: The two lessons that outlive the hardware - charge-reversal duty is what kills capacitors (modern pulse caps are still specced by % reversal), and ESL budgets, not just C and V, set rise time. Cable-as-capacitor remains a legitimate cheap trick for one-off pulse work.

grazing-incidence type aluminum targets were used because of the high beam intensities they withstand.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 6

Tabletop: Scale-honest — the reference machine's nA beams cannot melt anything, but the geometry trick matters for beam VIEWING (a grazing phosphor or foil intercepts more turns and lights up at lower current) and becomes thermally real on any 5-13 kV / uA-class upgrade path.

Carbon lips of a new design were installed on the edges of the dees to reduce sparking at the increased dee-to-dee voltage, 400-500 kv, required for operation at the high energy level.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 7

Tabletop: The 400-500 kV is MW-era and does not transfer; the material practice does — if the reference machine's 5-13 kV upgrade sparks at the dee gap, graphite edge pieces are the period-proven remedy and are trivially machinable.

no evidence of the mass transfer type of corrosion due solely to a thermal gradient is found. The enhanced corrosion observed in Figure 2a seems to be quite definitely associated with the proton irradiation.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 19

Tabletop: The control-experiment discipline transfers whole to any reference-machine or bench-scale target or activation claim — for every "the beam did X", run the identical setup minus beam; the 1339 quarter also flags their power-measurement accuracy as only +/-30%, a humbling uncertainty note worth copying into lab-book practice.

it should be made of magnetically good steel, and the optimum size is rather critical ... the quality of steel used in this part of the magnet [the yoke] is less important.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 33-36

Tabletop: For a next machine's steel shopping - spend on clean low-carbon (1006/1008) pole and pole-base stock, accept structural mystery steel in the return yoke, and size the pole base to run near but not into the knee (~1.8-2.1 T).

a careful choice of materials of construction, for example, using as much aluminum as possible and very little stainless steel, should reduce the radiation problem significantly.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 18

Tabletop: ENERGY SCOPE: this is a 730-MeV 1-uA machine; at <1 MeV protons the spallation and (p,xn) channels behind it are closed and material activation is a non-issue. The principle activates only if the reference machine ever makes neutrons (d-D, p-Li) or exceeds a few MeV — then bake material choice in early, because it cannot be shielded in later.

Aluminum yields no long-lived activities, while Co58 is produced from copper ... Stainless steel produces two long-lived isotopes, Co58 and Mn54, while only Mn54 is induced in iron.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 18

Tabletop: ENERGY SCOPE: nuclide-by-material bookkeeping from 730-MeV spallation; every one of these production channels is closed at sub-MeV proton energy. Value to the builder is the pattern — inventory follows alloy content (Ni -> Co58, Cr -> Cr51) — worth knowing when reading other labs' activation numbers or planning any future >MeV or neutron-producing work.

It was found necessary, however, to use a covered carbon boat both to reduce the radiation cooling of the boron and to prevent scattering of the material during the heating.

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

Tabletop: Boron is among the worst common elements to evaporate (needs ~2000 C+, attacks refractory-metal boats); carbon-rod stock is cheap and machinable with ordinary tooling. This is the boat design to copy for making B-11 films for the next machine's B11(p,alpha) experiment — the recipe is isotope-blind.

The boats are useful for only two evaporations at most since the slot rapidly becomes clogged with boron carbide.

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

Tabletop: Hot boron converts the carbon boat itself to B4C — no boat material choice fixes this, it is stoichiometry. Plan the enriched-B11 evaporation campaign around several pre-machined boats and one plate per boat-load rather than debugging mid-run.

The extreme radioactivity induced in type 304 stainless steel makes its use undesirable, the use of an aluminum alloy is now being investigated.

Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953) — p. 18

Tabletop: At reference-machine and next-machine energies activation is negligible, but the selection logic transfers to the planned higher-power machines and to the business plan's licensing story - prefer aluminum/graphite for probes, septa, and slits anywhere protons above a few MeV are contemplated.

The method of brazing is considered unsatisfactory because of the extreme probability of leaving large flux inclusions between the beryllium metal and the aluminum base, which would seriously impair heat transfer.

Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953) — p. 17

Tabletop: The corpus's targetry shelf is thin - this is a concrete bonded-target recipe. For a next machine's boron/beryllium targets on copper or aluminum backing, flux-free vacuum (or controlled-atmosphere) brazing with a thin Al-Si interlayer is the proven route to full-area thermal contact.

at an r-f load of 100 amp per lineal inch, the temperature rise could be held to less than 10 C by a water flow of only 0.5 gpm.

Howard (ed.), Electronuclear Research Division Semiannual, period ending 20 September 1954 — ORNL-1795 (1954) — p. 23

Tabletop: 100 A/in. is a design allowable for any sliding or clamped rf contact (shorting planes, tuning bars) in a next machine's resonator - and the material lesson (plate the stainless with copper; bare SS is an rf resistor) applies at any scale.

Teflon 5 x 104 ... Phenolic, Glass laminate >1 x 1010 ... Aluminum Oxide 1 x 1012

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 151

Tabletop: Counterintuitive and worth flagging in the next machine's design notes: PTFE, the amateur's default HV insulator, is the most radiation-fragile material on the list. Fine at the reference machine's dose rates, but in-chamber insulators near a future target station are better as ceramic or glass-filled phenolic.

We expect to use marble pole liners where possible, as in the past, to reduce sector iron, etc., activation

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 6

Tabletop: Below ~few-MeV protons activation is negligible, so this is a higher-energy note — but the general idea (choose what lost beam hits) already applies to sputter contamination and outgassing on any machine.

one should seek substances which combine high density with low atomic number. Among convenient and practical materials none would seem better than concrete.

Moyer, Hildebrand, Knable, Parmley & York, Character of the Radiation Field and Shielding at the 184-Inch Cyclotron — AECD-2149, UC Radiation Laboratory (1947) — p. 5

Tabletop: The shadow-effect argument is a >100 MeV argument, but the conclusion strengthens at low energy where hydrogen elastic scattering dominates moderation - concrete, water, and polyethylene beat any metal for neutron shielding per dollar and per pound.

so a metal target could conduct the heat away with a 12 C rise in temperature.

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. 238

Tabletop: The 100x conductivity gap between salts/insulating compounds and metals is the single biggest lever on target survival; a boron film on a thick copper or silver backing is conduction-cooled through the backing, while the same film self-supported is radiation-only. Thickness enters linearly — ultrathin films conduct almost nothing sideways.

evaporation efficiencies of only 1% are obtained.

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. 23

Tabletop: Budget isotope/material mass assuming ~1% of the charge lands on the substrate unless the geometry is engineered (tubular crucible, substrate close and directly above); crucible-evaporant chemistry (carbide formation, alloying) is chosen per material, not per convenience.

Zinc and cadmium condensed uniformly and with very high sticking coefficients.

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. 56

Tabletop: The crystal-structure-matching trick generalizes — when a film refuses to stick or beads up, a nanometer-scale nucleation layer of a structurally compatible metal fixes it; good sticking also raises tolerance to substrate heating during deposition.

the evaporation rates for these two metals differ by nine orders of magnitude, whereas their sputter yields differ by only a factor of two.

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. 100

Tabletop: When the target material is refractory (B, C, W, Ta) or reacts with every crucible, sputtering is the escape hatch; a graphite source holder adds only carbon, the lowest-yield contaminant.

Self-supported films usually display the same strength, toughness, and ductility as their bulk parent material.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. 103

Tabletop: For a target that must survive beam, handling, and mounting stress, sputter-deposited beats evaporated at equal thickness; and pick the release agent for the process — salt layers for sputtering, organics only where nothing scrubs them.

The targets are sent to the users in containers filled also with dessicated argon.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. 118

Tabletop: An argon-purged jar (or wide-mouth desiccator backfilled from a weld-gas cylinder) preserves oxidizable targets for months; assume any electroplated deposit is factor-of-2 nonuniform unless mapped.

two of the targets did not break (Ramsay, "Alternatives to Thin Film Carbon Foils")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 80

Tabletop: When a self-supporting film keeps failing, evaporating a few ug/cm2 of a conductive metal onto it is a cheap fix — it adds conduction paths and mechanical tempering for negligible energy loss.

too high a temperature can cause nitrogen diffusion into the tantalum substrate resulting in a target with a poorly defined thickness (Stinson, "The Preparation of Nitrogen-15 Targets")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 96

Tabletop: Any reacted-layer target (nitride, oxide, deuteride) on a metal backing has such a window; a smeared depth profile shows up as degraded resonance width or energy resolution.

Iron forms a carbide if a graphite boat is used (Heagney & Heagney, "Reduction Techniques for Isotopic Materials")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 98

Tabletop: The route from purchased oxide powder to rollable or evaporable target metal; the two-page table is the reference to consult before buying any element as oxide.

Usually better than 90% of the metal can be deposited on the cathode (Heagney & Heagney, "Reduction Techniques for Isotopic Materials")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 100

Tabletop: For milligram-scale enriched material the deciding metric is recovery fraction, not speed — electrolysis beats furnace reduction whenever the metal plates well.

Deuterated polyethylene could not be used because of its rapid deterioration under bombardment (Meens, "Deuterated Titanium Targets on Thin Backings")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 106

Tabletop: The standard durable D-target chemistry for a d-beam or D(p,..) work at any current; plastic CD2 targets are for lowest-current work only.

The maximum allowed beam current is about 20 particle nA for the HgS-ta[rget] and about 1 particle nA for the amalgam target (Friebel et al., "Preparation of Isotopically Enriched Mercury Targets")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 121

Tabletop: Compound-vs-element is a factor-of-20 beam-current decision, not a chemistry nicety; and the elastic-peak tail is the free in-beam diagnostic of target quality.

They are cooled from the edges by connecting to a copper block with silver paint (Maier, discussion of "Preparation of Isotopically Enriched Mercury Targets")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 200

Tabletop: The simplest conductive-cooling geometry for a target that cannot be water-backed — a cold finger to the frame plus a conductive-paint joint; budget tens of kelvin of drop across the joint.

the reaction with mercury oxide runs into an explosion (Friebel et al., "Preparation of Isotopically Enriched Mercury Targets")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 127

Tabletop: Strongest is not best in metallothermic reduction; a controllable reaction that completes in minutes beats a violent one that contaminates the product.

the crossover point is about 210 C for nickel, 100 C for copper, and about 300 C for iron (Gursky, discussion "Prevention of Stress in Foils by Substrate Heating")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 204

Tabletop: The missing variable when evaporated foils curl, buckle or shatter on float-off; set substrate temperature at deposition time — post-baking will not save a stressed film. Complements the ORNL-3021 evaporation recipes.

Rolled target foils withstand due to their crystalline structure longer a heavy ion beam than evaporated targets (Kellner & Maier-Komor, "Rolling Thin Uranium Foils and Other Exotic Isotopic Metals")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 32

Tabletop: When a target must survive sustained current, prefer rolled (or electrodeposited/annealed) material over as-evaporated film — durability is set by crystalline order, not thickness.

The defects at the grain bounderies [sic] set an early limit during the rolling process (Kellner & Maier-Komor, "Rolling Thin Uranium Foils")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 33

Tabletop: Explains why bought powder pressed into a pellet will not roll thin; the melt-and-decant-impurities step is what makes sub-mg/cm2 foils possible.

We noticed that material with a thickness of 0.5 mm or below gave the best results (Kellner & Maier-Komor, "Rolling Thin Uranium Foils")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 35

Tabletop: The foil replicates every flaw of the jacket, not the rolls — jacket steel selection is the dominant quality variable in pack rolling.

at a temperature below 930 K, which was chosen to prevent phase transitions (Kellner & Maier-Komor, "Rolling Thin Uranium Foils")

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

Tabletop: Interpass and final annealing is what keeps a work-hardened foil rollable and flat; the phase-transition ceiling matters for any allotropic metal (Ti, Fe, U), not just uranium.

Even, tough films, easy thickness control and production of self supporting targets are other advantages inherent to the process (Stinson, "Nitrogen Targets Produced by Reactive Sputtering of Tantalum and Titanium")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 68

Tabletop: Sputter deposition is the durable-target counterpart to the ORNL-3021 evaporation recipes — slower, but the film adheres and survives beam heating on whatever backing the cooling design wants.

Evaporated films of carbon, titanium, nickel, or gold of 0.01 to 0.2 mg cm-2 are used to protect the uranium layers from oxidation (Folger & Klemm, "Uranium Sandwich Targets of 0.1 to 100 mg-cm-2")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 70

Tabletop: Two transferable patterns — a tens-of-ug/cm2 cover layer buys shelf life and in-beam oxidation resistance for negligible energy loss, and a thick copper backing chip is the simplest conductive heat sink for a high-power target.

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

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

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

small impurities of nearly all metals in the order of magnitude of a few hunderd [sic] ppm largely enhance the brittleness (Friebel, Frischke, Grossmann & Maier, "Preparation of Isotopically Enriched, Self Supporting Chromium Targets")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 112

Tabletop: When a foil cracks in the mill, suspect chemistry before technique — the reduction route chosen upstream fixes the ductility available downstream.

in equilibrium the maximum tolerable water content of the hydrogen atmosphere is 540 ppm (Friebel et al., "Preparation of Isotopically Enriched Chromium Targets")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 110

Tabletop: The template calculation for judging whether tank-grade gas is good enough for any reduction or annealing atmosphere — compute the equilibrium ratio at your furnace temperature before blaming the furnace.

a cooling system for the target material post is required (Baumann & Wirth, "A Heavy Ion Sputtering System with a Penning-Ion-Source")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 127

Tabletop: 100 W/cm2 is the order of loading a mm-scale beam spot delivers at tens of uA and tens of kV — the same arithmetic that sizes cooling for beam stops, probes, and targets on a small machine.

they are less fragile than those made by evaporation in that they withstand the accelerator beam better (Saettel, "Preparation of Self-Supporting Platinum Targets by Electrodeposition")

Proceedings of the Sixth Annual Conference of the International Nuclear Target Development Society — LBL-7950, Lawrence Berkeley Laboratory (1978) — p. 133

Tabletop: Electroplating joins rolling on the durable side of the durable-vs-evaporated divide, and it works at milligram scale with a beaker and a regulated supply.

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

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

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

This improved energy transfer tended to significantly increase target lifetime under bombardment.

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 140

Tabletop: Two transferable ideas — treat the frame as the heat sink and design the film-to-frame conduction path deliberately; and watch the elastic-scattering (or yield) peak width online as a melt detector rather than waiting for visible failure.

it was observed to take five minutes before any significant amounts of oxygen or moisture were detected

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 140

Tabletop: Sets the realistic scale for handling windows on Li/Ca/lanthanide targets moved from evaporator to chamber in air — minutes, not hours — and shows overcoat choice is coupled to the experiment (overcoat nuclei scatter too).

they would slowly curl and fracture

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 100

Tabletop: Plan target fabrication against the run schedule, not the calendar — a self-supported evaporated or reduced film is a perishable. Vacuum/argon storage and use-within-weeks discipline belong in the ops checklist.

no method seems superior to the arc evaporated foil.

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 16

Tabletop: Two lessons — pick fabrication method by thickness regime, and distrust any foil-lifetime claim not measured under your own beam and current density. The same skepticism applies to target-durability claims generally.

NO QUOTE — paper IV-1 is reprinted from Nucl. Instr. and Meth. 206 (1983) 361-366 with North-Holland permission; finding paraphrased, cite the journal article.

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 210

Tabletop: Marginal technically for a proton machine, but present as the worked example of matching host-material physics (crystal symmetry, conductivity, heat sinking) to what the measurement needs — and as the rights-boundary marker for this volume.

Typical lifetimes of filaments had ranged from 15 to 30 hours. The first filament installed in the new source was intact, though thin, when removed after 109 hours of operation.

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

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

after a few days of operation, it was found to have become somewhat enlarged in the direction of ion rotation.

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

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

Cyclotron beam currents were found to be of the order of 1/10 those obtained with our standard helium ion source, which is also of the hooded type

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

Tabletop: Mostly a scoping warning for any future gas change: a source tuned for hydrogen is not a universal source. The tantalum-button-on-quartz construction detail is also this collection's only sketch of a helium-specific hooded source, useful if alphas are ever on the menu.

the corresponding permeability would drop to 118, which is dangerously low. In certain localized regions it might even be lower.

Wakerling & Guthrie (eds.), Magnets and Magnetic Measuring Techniques — TID-5215, Radiation Laboratory, University of California (1949) — p. 151

Tabletop: Gives this collection a quantitative "too far": mu ~ 100-150 at the working point is the failure territory, and the audit must use the actual steel''s curve — the same reason a FEMM model of an H-frame is only as good as the 1010/1018 B-H table fed to it.

The permeability of the material of the full-scale unit is higher than that of the model. This indicates that a slightly better performance could be expected from the full-scale unit than from the model.

Wakerling & Guthrie (eds.), Magnets and Magnetic Measuring Techniques — TID-5215, Radiation Laboratory, University of California (1949) — p. 146

Tabletop: The sign-audit habit transfers to simulation directly — list every model-vs-hardware difference (B-H table provenance, fillets, packing factor, gaps at joints) with the direction it biases the prediction, so measured-vs-predicted discrepancies arrive pre-explained.

Apparently the control of the magnetic properties in the manufacture of steel is rather uncertain.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 14

Tabletop: For a next machine's magnet, low-carbon steel chemistry is worth a mill cert, and a sample ring (or bar) from the same stock measured on a cheap B-H rig turns FEMM's material curve from a guess into a measurement. Same measure-your-own-steel discipline as nyo-780.

The steel for both the cyclotron magnet and the model was poured from the same heat and it can be assumed magnetic properties are identical.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (c. 1950) — p. 18

Tabletop: The transferable rule is identity of material between test article and final article — a next machine's FEMM model should use a B-H curve measured on the actual purchased steel, not a library curve for its nominal grade.

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

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

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

For accelerator applications, a tube should have a sufficiently heavy grid to absorb several joules of energy in an area determined by the cross section of the spark.

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. 6

Tabletop: The solid-state translation: LDMOS gates tolerate NO spark energy — the joule-absorbing ruggedness must move into the coupling network (series blocking, clamping, circulator/isolator) because it no longer lives inside the active device. Budget those parts as the modern "shield tees."