Design Guide › Controls & instrumentation
Cyclotron controls & instrumentation design rules
12 of the guide’s 1545 rules carry the controls tag.
Rules for instrumenting and running the machine: gauge coverage and interlocks, mass-flow gas feeds, Hall-probe field readout, RF signal sources, and the measurements a control desk needs to identify what the machine is doing.
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 2 (2) · level 3 (10) — levels rank breadth, never license to skip (method). Related domains, by shared rules: Beam measurement (3), RF (3), Vacuum (3), Magnet (2), Pedagogy (2). 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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No single gauge covers the nine-decade pressure range, so combine technologies: on COLUMBUS a Pirani (thermal-conductivity) head covers atmosphere down to its floor and a cold-cathode head takes over for high vacuum - the specific ranges, the Pirani's end-conduction/radiation floor mechanism, and placement limits being gauge-model matters to take from the manufacturer's data.
Source quote & editorial note
gibt es auch bei der Druckmessung kein Messgerät, das über den gesamten Druckbereich von neun Zehnerpotenzen messen kann [tr.: no single gauge covers the nine-decade range]
Editorial note, tabletop extrapolation: Both gauge types are gas-species dependent: a Pirani reads hydrogen differently from nitrogen and a cold cathode needs a hydrogen correction factor, so the pressure that enters the mean-free-path budget should always carry its gas correction; and keep magnetically sensitive heads out of the stray field or shield them per their spec.
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Gas-feed chain for a thermionic source, as built: cartridge -> pressure reducer to 300 mbar -> mass-flow controller at 0.10-0.20 ml/min -> directly into the source chimney; the reducer pressure enters the book's gas-load balance q_G = 300 mbar * V_dot_G, with V_dot the ACTUAL volumetric flow at the reducer pressure.
q = p_in * Q_actual (actual inlet volume) or q = p_std * Q_std for an MFC reading sccm - one convention, consistently; mixing 300 mbar with an sccm reading understates throughput ~3.4xSource quote & editorial note
Dieser Druck wird durch einen Druckminderer auf pH2 = 300 mbar reduziert [tr.: the pressure is reduced by a regulator to 300 mbar]
Editorial note, tabletop extrapolation: Fix the reducer pressure and log it - it is a term in the balance. Whatever meters the flow, state its reference conditions and take accuracy and repeatability from its specification rather than assuming a resolution.
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Identify the accelerated species by specific charge without extraction: hold the RF fixed, ramp the magnet slowly (COLUMBUS: a 0.005 Hz triangle wave), plot Faraday-cup current against the Hall-probe field, and read candidate q/m values from the peak fields via q/m = 2*pi*f_RF/(h*B) with h the harmonic number (h=1 for fundamental operation).
q/m = 2*pi*f_RF/(h*B_eff), B_eff the orbit-relevant (calibrated, orbit-averaged) field; peaks are q/m CANDIDATES pending harmonic assignmentSource quote & editorial note
Wir legen uns also mit einem geeigneten Detektor auf die Lauer und verändern das Magnetfeld solange, bis wir ein Signal erhalten [tr.: lie in wait with a detector and vary the field until a signal appears]
Editorial note, tabletop extrapolation: Slow ramps help but don't grant immunity: characterize the electrometer/amplifier settling time and pick a sweep rate that resolves the narrowest expected peak - then confirm by comparing up- and down-sweeps (hysteresis and lag shift peaks in opposite directions). Correct the Hall reading to the median plane: a probe in the lid recess reads a different field than the orbit (the 1-7.5 percent class errors below), which moves every q/m assignment.
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Instrument the guide field with a fixed Hall probe whose controller outputs a voltage proportional to B, used directly for evaluation - on COLUMBUS the probe sits at the chamber-lid centre (in the pole recess, dg-1381) and the proportional output drives the I(B) recording.
Source quote & editorial note
Ein Steuergerät liefert eine zur Flussdichte proportionale Spannung, die für die weitere Auswertung verwendet wird [tr.: a controller supplies a voltage proportional to B used for evaluation]
Editorial note, tabletop extrapolation: A fixed probe reads ITS OWN location's field, not the median plane's: map the probe output against a median-plane measurement across the full operating range and both ramp directions (saturation and hysteresis bend the relation), fit the transfer curve, and carry its uncertainty into every specific-charge assignment - a one-point offset calibration is the minimum, not the goal.
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Use a mass-flow-controlled feed and the steady-state pressure as a CONSISTENCY check of the vacuum model: COLUMBUS's measured chamber pressure agreed well with p_H2*V_G/S_eff at its operating point.
S_eff(in-situ) = delta-q / delta-p: step a calibrated throughput onto a steady baseline, apply the gauge's hydrogen correction, and divide - a differential measurement that separates the background termSource quote & editorial note
ein Wert der in guter Übereinstimmung mit dem gemessenen Druck steht [tr.: a value in good agreement with the measured pressure]
Editorial note, tabletop extrapolation: One-point agreement checks consistency; to actually MEASURE the pump stand's hydrogen speed at the chamber, do the differential version (baseline, step the flow, gauge-corrected delta-p) and repeat after every plumbing change or pump swap, logging the result.
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A digital programmable RF signal source was chosen as the oscillator because it made frequency tuning easy (HP8165), later replaced by an HP8656B 'which had greater frequency resolution than the HP8165' (Rutgers).
Source quote & editorial note
The oscillator used an HP8165 digital programmable RF signal source, which offered an easy method of tuning the frequency. ... [Later the] signal was produced using a HP8656B signal source, which had greater frequency resolution than the HP8165.
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 17
Editorial note, tabletop extrapolation: Resonance hunting rewards fine, repeatable frequency steps - the documented upgrade was FOR resolution, so check any candidate source's step size against the measured resonance width (Q of the loaded resonator) before buying; whether the first unit's resolution actually limited tuning is our inference from the upgrade, not the thesis's statement.
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Cooling and protection budget for a 1.1 T-class magnet plus diffusion pump on one small chiller (3.8 L/min at 20 C total), 3 L/min to the magnet at 50 A (6 L/min would be needed at the 70 A rating) and 0.75 L/min to the diffusion pump, with an interlock that powers down the magnet below 2.5 L/min of flow or above 50 C on any coil.
Source quote & editorial note
an interlock which shuts down the magnetic if less than 2.5 liters per minute of chilled water are supplied
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 36
Editorial note, tabletop extrapolation: The transferable pattern is the method, not the numbers: independent low-flow and over-temperature interlocks wired to POWER DOWN the load, with trip points derived from the coil's insulation limits or measured thermal performance (including sensor lag) - Houghton's 2.5 L/min floor and their coil ceiling are that machine's settings, not defaults.
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Personnel protection as built: the accelerator sits in a concrete brick room with an interlock control system preventing the machine from being turned on while a person is in the room.
Source quote & editorial note
in a concrete brick room with an interlock control system to prevent the accelerator from being turned on when a person is in the room
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 29
Editorial note, tabletop extrapolation: The documented access-control arrangement of the source machine - occupancy interlock plus (per its electronics chapter) remote operation - is a COMPONENT of protection, not a certified minimum: shielding calculations, surveys, monitors, fail-safe interlock design and applicable regulatory requirements decide sufficiency for any neutron-capable machine, and the thesis presents no dose analysis.
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Remote-control architecture, as documented: all electronics except the floating filament power supply are monitored and controlled remotely over GPIB, reaching the network through a National Instruments GPIB-enet; gauges concentrate through an SRS FGC 100 controller, the RGA joins via an RS232-GPIB converter, the Powerten magnet supply connects natively - and the filament floats on a 0-100 V supply.
Source quote & editorial note
All of the electronics, with the exception of the floating filament power supply, are monitored and controlled remotely through the general purpose interface bus. The National Instruments GPIB-enet allows these instruments to be controlled through an Ethernet network. ... The 1-100-K Ion gauge and CVT-272-101 Convectron gauge are connected to an SRS FGC 100 Ion Gauge Controller ... The SRS RGA 100 connection is RS232, and so it needs the National Instruments RS232-GPIB Converter ... The Powerten R62B-4050 magnet power supply supports a GPIB connection ... The voltage on the filament floats on the voltage provided by 0-100V power supply
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 47
Editorial note, tabletop extrapolation: Full remote operation is what makes an occupancy interlock workable. The floating-filament exception carries the real lesson: a floated circuit must not connect directly to ground-referenced instrumentation - it needs an isolated interface (or manual presetting outside the run), which is an implementation choice, not an impossibility.
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As-built RF drive chain with named commodity parts: an HP 33120A function generator feeds an ENI 155LCRH RF power amplifier into the transmatch, with the transmatch-primary power monitored by a Bird 43A RF power meter.
Source quote & editorial note
The power in the primary coil of the transmatch is monitored by a Bird 43A RF power meter, and supplied by the ENI 155LCRH RF power amplifier. The RF signal is provided by the HP 33120A function [generator]
Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 47
Editorial note, tabletop extrapolation: A bench function generator + lab RF amplifier + ham-style through-line wattmeter is a complete drive-and-monitor chain from commodity gear. Meter honestly: a directional wattmeter at the transmatch primary reads forward power at that point - net delivered power is forward minus reflected, and network losses sit downstream of the meter, so pair it with the dee-voltage pickup (dg-1392's two-readout rule).
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Beam-species spectroscopy by field sweep, as COLUMBUS practices it: fix the detector position and RF frequency, continuously increase the magnetic field, and log beam current - peaks appear at very specific fields, from which q/m follows via q/m = 2*pi*f/(h*B).
q/m = 2*pi*f / B (peak assignment from known f and measured B)Source quote & editorial note
the detector is set to a specific position and the magnetic field is continuously increased. With very specific magnetic fields, there are peaks in the beam current
Editorial note, tabletop extrapolation: A B-sweep at fixed frequency is a q/m RESONANCE SURVEY - the cheapest species diagnostic a small machine has, not a full mass spectrometer: state the harmonic number, calibrate the field reading (dg-1428), and resolve the q/m degeneracies and harmonic ambiguities by field-ratio checks or frequency scaling (dg-1422/dg-1423) before naming species.
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Instrument the RF chain at both ends: a directional coupler in the matchbox input circuit to monitor and minimize the reflections back into the RF source, and a separate RF pick-up in the output circuit (a diode-detector probe feeding a meter) which the paper uses to check whether the machine is tuned to its 5.63 MHz cyclotron frequency.
Source quote & editorial note
A directional-coupler in the input-circuit of the matchbox makes it possible to control and minimize the reflections back into the RF-source and a RF pick-up, i.e. Fig. 6, in the output-circuit allows to check whether the cyclotron is tuned to the cyclotron-frequency of 5.63 MHz
Editorial note, tabletop extrapolation: Two independent indications, reflected power at the input and detected RF at the dee side, help separate matching problems from resonance problems during tune-up - though both respond to coupling and resonance, so neither is unambiguous alone, and the pick-up reads amplitude: the drive frequency itself should be known independently (a counter is cheap) and compared against qB/2πm.