Cyclotron controls & instrumentation design rules

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

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

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

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

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

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

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 69-71

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.

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]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 36, 70

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.

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

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

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

The 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.

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.

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.

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.

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).

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

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

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.

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

Wolf, Frank & Held, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — WE1PB03, Proceedings of Cyclotrons2013 (2013) — p. 2

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.

Thermal cut-off switches (fully insulated in a screw on housing type), set to open an electrical circuit at 40°±5°C shall be fitted on the external lead (return lead of water circuit) of each pancake ... Suitable thermal switches will be placed on outer terminals of the coils to prevent over-heating of the coils (cut-off value: > 40 oC) by shutting off the power supply ... [spec table:] Thermal sensors (cut-off value) — > 400 C (8 nos. of sensors to be mounted on each coil); Interlocks — overload, high temperature cut-off

IUAC, e-Tender 09/GOR/2024–25 — H-Dipole Water-Cooled DC Electromagnet for the Table-Top Cyclotron: Engineering Specification and Acceptance Tests (2024) — p. 19, 24, 25

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: hardware thermal switches on every pancake's return water lead, dropping the supply through an interlock, is a simple, software-free protection pattern for a water-cooled coil stack — with two cautions. An outlet-mounted switch lags stagnant-water and winding hot spots when flow is lost, so pair it with flow or pressure detection; and the interlock must command the supply's controlled shutdown or energy-dump path, never break magnet current mechanically — an inductive circuit interrupted dry arcs.

Stability of power supply, at least 100 ppm ... [compliance sheet:] Equipment required for field mapping: a) 3D magnet field mapping system with Hall probe, associated control software for the field mapping ... DC Power supply rating: Voltage: 20V, Current: 200 Amps ... CMM and allied measuring instruments ... In-house electrical testing facilities: Insulation Resistance, Hipot Test, Inductance ... Inhouse Hydraulic Testing Facility for Coils ... Note: Final Testing of assembled magnet will be performed at supplier premises, hence supplier is required to provide a list of testing facility available in-house.

IUAC, e-Tender 09/GOR/2024–25 — H-Dipole Water-Cooled DC Electromagnet for the Table-Top Cyclotron: Engineering Specification and Acceptance Tests (2024) — p. 40, 41

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: the equipment list doubles as a checklist of what a serious small-magnet test stand contains, and 100 ppm shows what a professional team asks of a mapping/energizing supply. It is one machine's specification, not a universal requirement: derive the allowable current stability from the machine's own B-I slope, field tolerance and RF phase-slip budget — the answer is usually far tighter than an unregulated bench supply but need not be 100 ppm.

IUAC, New Delhi, India, operates accelerators with RF structures in the range of 12.125-97 MHz, in both normal and superconducting modes ... this controller has been tested as a Sawtooth Waveform Generator for the Multi-Harmonic Buncher (MHB), as a generator-driven (GDR), and as a self-excited loop (SEL)-based LLRF for various RF cavities at IUAC ... It is a compact, frequency-reconfigurable, standalone device controlled by an EPICS IOC ... The main feature of our design is the hardware configuration, which remains the same regardless of the cavity type, without the need for FPGA reprogramming. In addition to the LLRF algorithm, the same FPGA contains logic for the motorized Frequency Tuner Control, considerably lowering the system's cost ... The major blocks of the system as shown in the overall physical block diagram (Fig. 1a) are a wideband Analog Front-End (AFE), microcontroller programmed PLL Multiplier, and a SoC-FPGA-based digital board.

Sharma, Kar, Dabas, Sahu, Singh, Mathur, Satyanarayana & Venkatramanan, Design and Testing of a Universal Embedded Feedback Controller for RF Cavities — MOP6698, Proceedings of IPAC2026 (2026) — p. 1, 2

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: one reconfigurable digital controller replacing a zoo of structure-specific analog LLRF chassis is exactly the maintainability trade a small lab faces. Folding the mechanical tuner drive into the same FPGA as the feedback loop removes a separate controller box — the motor's power stage still exists, but its logic does not need its own electronics.

Long-term RMS stability of ~1% in amplitude and a < ±0.4∘ in phase locks have been obtained ... [Table 1, long-term performance:] MHB-DPLL — phase ± 0.40∘; GDR — ± 0.5%, ± 0.45∘; SEL-AP — ± 1.2%, ± 0.35∘ ... The loop allows phase corrections of up to 35∘ and amplitude corrections of ±3 dB, as verified using an additional phase shifter and attenuator.

Sharma, Kar, Dabas, Sahu, Singh, Mathur, Satyanarayana & Venkatramanan, Design and Testing of a Universal Embedded Feedback Controller for RF Cavities — MOP6698, Proceedings of IPAC2026 (2026) — p. 1, 3

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: sets a benchmark for what percent/sub-degree RF regulation looks like from a compact digital controller — and, more transferably, shows how to verify a loop's correction range by deliberately injecting known phase and amplitude disturbances. Bench figures of this style are the right pre-beam acceptance evidence for any home-built dee drive.

this mode also features a PWM-controlled motorized frequency tuner in the same FPGA ... It compares the phase error (between the FWD signal and the PU signal) with a threshold value and, based on that, it decides the direction of motion of the tuner

Sharma, Kar, Dabas, Sahu, Singh, Mathur, Satyanarayana & Venkatramanan, Design and Testing of a Universal Embedded Feedback Controller for RF Cavities — MOP6698, Proceedings of IPAC2026 (2026) — p. 2

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: the forward-versus-pickup phase comparison is the classic resonance-tracking criterion, stated here in an implementable threshold-and-direction form suitable for a microcontroller and a stepper on a trimmer capacitor. Separating slow mechanical tuning from the fast electronic loop is the standard division of labour worth copying — and the on-resonance phase setpoint must be calibrated for the actual coupling, pickup placement and cable delays, not assumed to be zero.

Several implementations invoke backplane-based methods, such as VME, cPCI, and microTCA. These solutions are often costly, bulky, and difficult to adopt due to a customized design goal. Standalone, non-crate-based systems provide a more versatile, fast, and cost-effective alternative ... The local oscillator signal for the mixer is generated by a Si5356-based I2C-programmable PLL multiplier, synchronized with an external reference signal. Apart from the LO signal, it is used to generate a 125 MHz system clock signal for the FPGA ... This board [13] houses the main signal processing algorithm ... [reference 13:] Red Pitaya, "Red pitaya STEMlab 125-14" ... A lightweight digital PLL (DPLL) ... helps the Si5356-based PLL multiplier mitigate long-term sub-millihertz-level errors which were experimentally observed and caused by accuracy issues with the manual setting of its phase increment word

Sharma, Kar, Dabas, Sahu, Singh, Mathur, Satyanarayana & Venkatramanan, Design and Testing of a Universal Embedded Feedback Controller for RF Cavities — MOP6698, Proceedings of IPAC2026 (2026) — p. 1, 2, 4

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: a national accelerator centre building its cyclotron LLRF around a hobbyist-priced software-defined-radio board shows amateur-accessible hardware can anchor serious RF field control at these frequencies — as one component of a system whose performance also hangs on the analog front end, clock reference, firmware and interlocks. The DPLL fix for the clock chip's long-term drift (sub-millihertz-level, from manual phase-increment setting) is a practical gotcha worth knowing before trusting a cheap synthesizer unsupervised.

Frequency is fine tunes with vacuum variable capacitor. A capacitive pick-up built-in the Cyclotron chamber is used as feedback in order to control and maintain the RF voltage and frequency of the system using a digital LLRF controller and a motorized tuner.

IUAC, Annual Report 2024–25, Chapter 3 — Research Support Facilities (table-top cyclotron RF system) — p. 18

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: building the capacitive pick-up into the chamber from the start — rather than improvising one later — is the design habit to copy: early provision simplifies every scheme that reads the cavity field from a pick-up, including the dee-voltage calibration chain on this machine. Other feedback routes exist (directional-coupler signals, other probe types); a motor-driven vacuum variable capacitor is an amateur-accessible tuner implementation.