Cyclotron pedagogy design rules

Die Endenergie der Ionen ist so etwas wie die Höhe einer Leiter und die Beschleunigungsspannung ist dann der Abstand der einzelnen Sprossen [tr.: final energy is the ladder height, voltage the rung spacing]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 41-42

Editorial note, tabletop extrapolation: Recomputed for 1000 V protons at 185 mT: r1 = 24.7 mm, matching the book. A 150 keV machine at 1 kV needs 150 ideal crossings; at 5 kV only 30 - relaxing vacuum and field-error tolerance roughly in proportion. The idealization to keep visible: real voltage also moves capture, turn separation and whether the top rung is reachable at all (dg-1376's ceiling-vs-attainability).

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.

Die Deutung der anderen, kleineren Peaks [...] ist nicht immer möglich und auch nicht ganz einfach [tr.: interpreting the other smaller peaks is not always possible nor simple]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 71, 74

Editorial note, tabletop extrapolation: Keep a running peak ledger (B, f, U0, gas flow, probe radius) across runs. Persistence at fixed B across U0 and flow changes is EVIDENCE toward species/harmonic assignments, and motion is evidence toward phase-spread or direct-ion artefacts - evidence, not a classification: confirm with frequency scaling and probe-radius scans (dg-1422, dg-1425).

Physik- und Mathematik-Kenntnisse auf dem Level der 11. Klasse der Oberstufe sollten ausreichend sein [tr.: physics and maths at class-11 level should suffice]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 13

Editorial note, tabletop extrapolation: The chapter template (dialogue, then formula, then a per-subsystem results table) is a ready-made lesson structure for an educational accelerator - our reading of the book's organization, worth copying deliberately; the author's 'should suffice' keeps its hedge.

Die Herausforderung dieses Projekts bestand demnach darin, ein Zyklotron in diesem niedrigen Energiebereich zum Laufen zu bringen [tr.: the challenge was to get a cyclotron running in this low energy range]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 7-8

Editorial note, tabletop extrapolation: Define the teaching machine's safety envelope explicitly rather than declaring it hazard-free: maximum electrode potential (X-ray endpoint), ion species and energy (reaction thresholds - remembering exothermic channels like D-D have none, so deuterium is a different machine), beam current, target and contaminant composition, plus the ordinary electrical, RF, vacuum and stored-energy hazards that exist at ANY energy. Survey, don't assume; the low-energy regime shrinks the radiological terms, not the list.

Der Teilchenstrahl braucht dabei nicht einmal ausgelenkt zu werden [tr.: the particle beam does not even need to be extracted]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 27

Editorial note, tabletop extrapolation: A radial probe drive with a Faraday cup is the first detector to build on any small machine, and extraction is properly a separate later project - which, when undertaken, teaches its own lessons (septum design, transport, external diagnostics; the COLUMBUS Wien-filter plan, dg-1512, is that next chapter). Wait until internal beam is reproducible across days.

Die spezifische Ladung ist sozusagen der Personalausweis eines Teilchens. Wenn wir diese kennen, kennen wir auch das Teilchen [tr.: specific charge is a particle's identity card]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 68-69

Editorial note, tabletop extrapolation: Connecting to the e/m fine-beam tube students already know turns first beam into an assessable experiment with a literature value and a computable error - the PROTON value being 9.58e7 C/kg. Teach the degeneracy honestly: q/m alone does not name the particle (D+, H2+ and He2+ all sit near 4.8e7 C/kg), so the identity card needs the source-gas and charge-state context too (dg-1422's candidate discipline).

Sicher hätte sich das Projekt nicht gelohnt, wenn es nach dem erfolgreichen Abschluss im Jahre 2014 beendet worden wäre [tr.: the project would not have been worth it had it ended in 2014]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 75-76

Editorial note, tabletop extrapolation: The listed follow-on improvements (magnet stand, acceleration simulation, probe translator, mechanical model) are the kind of second-year items a small-machine program should schedule rather than improvise - as this case study's pattern, adapted to local aims, not a universal checklist.

After the FZ Juelich provided a magnet, VACOM, a company for vacuum components, sponsored a suitable vacuum chamber ... the cyclotron COLUMBUS began in 2012. ... The first beam was registered in April 2014 (see Fig. 2), which was followed by the first workshop with students in autumn of the same year. ... The COLUMBUS project, started in 2012, has developed very positively in the last 10 years.

Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022) — p. 1

Editorial note, tabletop extrapolation: A realistic schedule anchor for the plan's teaching-machine ambitions: two years start-to-beam WITH a donated magnet and sponsored chamber - the in-kind support is part of the datum. And the methodological point stands: a conference paper's year dates the claim; prefer the builders' own retrospective dates when reconstructing a machine's history.

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.

The aim of this project is to deflect the ion beam and guide it through a Wien Filter to measure the speed and energy of the ions.

Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022) — p. 3

Editorial note, tabletop extrapolation: A Wien filter is a realistic first external beamline element for a low-energy machine: it measures VELOCITY directly and yields energy only once the species is known (or paired with a separate analyzer) - which is exactly why it also cross-checks species assignments. It needs crossed electric AND magnetic fields; at keV energies both are modest, but 'electrostatic-only' it is not.

The cyclotron was continuously improved and expanded with the involvement of pupils and students.

Wolf & Prechtl, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — THPO001, Proceedings of Cyclotrons2022 (2022) — p. 1

Editorial note, tabletop extrapolation: An educational machine CAN make learner projects its upgrade workforce when they are scoped as real subsystem work - a Faraday-cup translator or a field map is simultaneously curriculum and infrastructure; whether that is the fastest improvement route is a program-design judgment, not this paper's measurement.

A workshop takes place in groups with up to 6 participants. If more people register, up to 12 persons can be accepted, who will then be divided into two groups.

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

Editorial note, tabletop extrapolation: Six-per-group is the format the team settled on for one machine - a reasonable planning anchor for hands-on accelerator teaching, not a demonstrated pedagogical ceiling; whether hybrid delivery preserves learning quality is an outcomes question the paper doesn't measure. Copy the structure, evaluate your own.

In order to build such a small cyclotron one has to meet two conditions: Vacuum, magnetic field, frequency etc. must be so low that one can use standard components as far as possible, otherwise the costs will go to infinity; The final energy of the cyclotron must be small enough so that no harmful radiation can arise, so that the students can do experiments with the cyclotron. Table 1 shows the technical data of COLUMBUS. One can easily recognize that COLUMBUS meets all the conditions mentioned above.

Wolf, Frank & Held, COLUMBUS — A Small Cyclotron for School and Teaching Purposes — WE1PB03, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: A hobby-scale build benefits from the same requirements discipline; writing the cost condition and the radiation condition down first turns every later component choice into a check against them. The radiation condition itself needs its own verification, not just an energy number: whether 'no harmful radiation can arise' at a given operating point is the paper's claim for its machine, and X-rays begin when high voltage or RF is energized, before any beam.

As shown in Fig. 1 the simulation consists of three sections, the input-layer, the simulation-layer and the presentation-layer. … The input-layer incorporates three groups of parameters which define the ions, the experiment and the geometry of the cyclotron. So the simulation can be easily adapted to different situations. … The simulation engine described above has three modules for the evaluation: XY-Plot, Intensity-Plot and Spectrometer-Plot. Every module - apart from the graphical output - allows also a data export to a file so that the measured values can be processed by external programs.

Wolf, Rueß & Prechtl, Simulation and Detection of the Helical Ion-Paths in a Small Cyclotron — MOB02, Proceedings of Cyclotrons2016 (2016) — p. 1, 2

Editorial note, tabletop extrapolation: Separating ion, experiment, and geometry parameter groups lets one code serve several machine configurations and several experiments; the data-export hook is what allows direct overlay of simulated and measured detector scans.

In this experiment the beam is measured in dependence of the magnetic field at a fixed position of the detector. Here one can identify the ions in the beam … The Spectrometer-Plot (Fig. 8) shows the caluculated probability as a measure for the beam-current vs. the magnetic field and allows to simulate this experiment.

Wolf, Rueß & Prechtl, Simulation and Detection of the Helical Ion-Paths in a Small Cyclotron — MOB02, Proceedings of Cyclotrons2016 (2016) — p. 3

Editorial note, tabletop extrapolation: A fixed-cup B-sweep is a species diagnostic using hardware a small hydrogen machine already carries, separating proton from molecular-ion contributions; simulating the sweep first tells the operator which peak to expect where. The assignment rests on rigidity plus the assumed charge and energy, so overlapping peaks can stay ambiguous.

The experimental program on the Iowa State University undergraduate 1.5 Mev cyclotron is divided between cyclotron technology experiments and nuclear experiments. Beam technology work has been done in the determination of the shape of the resonance curve as a function of the magnetic field strength and radius, the determination of the tune-down at various radii, and the measurement of the vertical excursion of the protons (beam height). The experimental measurements have been compared to the theoretical calculations made for the ISU cyclotron by A. H. Mueller (1). The nuclear physics experiments are limited to the lightest elements due to the low energy of the machine. Comprehensive experiments have been performed using lithium and carbon as the target material ... [footnote:] This work was made possible in part by grants from the National Science Foundation Undergraduate Research Participation Program.

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 2

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: a low-energy machine supports a real two-track curriculum — the accelerator itself as measurement subject (tuning curves, field studies, beam optics) plus light-element nuclear physics. The machine-as-experiment track begins as soon as beam circulates; the nuclear track needs its own justification per experiment — reaction energetics, yield at the available current, detection capability, and radiation controls.

The Li7(p,Y)Be8 resonance reaction has a threshold energy of 0.441 Mev and has a large cross section ... A thick (0.5 mm) Li7 target was attached to the target and r2 was set so that the energy of the protons would be about 1 Mev ... The NaI crystal was located about fifty centimeters from the target ... The scintillation spectrometer was calibrated using the unresolved (1.25 Mev) Y-rays from Co60 ... The reaction actually yields two high energy Y-rays, the 17.5 Mev one and also one of energy of 14.5 Mev ... it had an abundance of 30%, as determined by the relative counting rates

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 7-9

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: the strong 441 keV resonance puts high yield within reach of even modest machines, and a ~17 MeV gamma is a distinctive high-energy signature — though NaI response at 15-18 MeV is pair-production-dominated and needs calibrated interpretation (the source's own 15 MeV pulse-height reading needed a +0.5 MeV pair-escape correction and still sat 2 MeV low, within their stated uncertainties). Yield versus target radius maps beam energy against the resonance once target energy-loss and beam-spread corrections are applied; a gamma-onset reading is not a threshold measurement, because capture occurs below the resonance too. Photons this energetic exceed photoneutron thresholds in nearby materials — assess shielding, dose and activation before running the experiment.

The samples to be bombarded were machined (dry) in the form of thin wafers (1 mm thick) from spectroscopic carbon. The target radius was set so the energy of the protons would be only slightly greater than the threshold energy for the reaction. This was done to minimize the absorption of the β+-particles leaving the sample, thus providing the maximum flux at the counter. The sample was then bombarded for about one half-hour. After bombardment, the activated sample was removed from the machine and taped to a two-inch NaI crystal scintillation counter located in a lead house for minimum background. The counting was done for fifteen-second periods every minute for one half-hour ... A plot of the natural logarithm of the counting rate versus elapsed time has a slope equal to 0.693/T1/2, where T1/2 is the half life for the decay ... gave T1/2 = 10.3±0.3 min. The average value of three such determinations also yielded a half life close to 10.3 min. for the N13. This is in reasonable agreement with the published value of 10.1 min.

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 9, 10

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: off-line activation counting decouples the measurement from accelerator-correlated pickup — the machine only has to run for the bombardment, and a known half-life gives a self-grading answer. Barely-above-onset bombardment as a technique for keeping activity near the surface is a subtle, transferable target-design trick.

1.2 MeV proton cyclotron proposed to be built in India by Prof. P. C. Deshmukh is currently under development at the Inter-University Accelerator Center, New Delhi. The proposal was developed by CAMOST members plus affiliate members, including Prof. G. Aravind, Prof. C. Vijayan, and Prof. T. S. Natarajan. Students from IISER/IIT Tirupati can go to IUAC and do internships using this facility.

CAMOST (IIT Tirupati / IISER Tirupati), Annual Report 2022–2024 — p. 16

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: pins the machine's stated design energy in one primary source — and institutional coverage of the same pre-beam machine varies between this 1.2 MeV figure and roughly 1 MeV-class elsewhere, a spread preserved rather than resolved, and a caution for anyone citing energies of in-progress machines. The declared purpose (student internships on a teaching cyclotron) marks the pedagogy use-case for this machine class.

The first set was a simple, pure-radial sector design of periodicity four. Their geometry was the least expensive to machine and provided the maximum field variation achievable within practical constraints. Not expected to host beam, their purpose was to benchmark simulations, measurement techniques, and test analysis code.

Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011) — p. 2

Editorial note, tabletop extrapolation: A process rule worth more than most hardware numbers: build the cheap, geometrically simple article first and use it to shake down the toolchain — solver, field mapper, analysis scripts — before spending shop time on the expensive curved part. The radial set rehearses most of the pipeline; what it cannot validate is the spiral-specific machining and edge-field modeling, which the real article still tests (the sequence that produced AKG270, dg-1717).

The cyclotron magnet features flat poles with a maximum B-field of about 1T. The magnetic field can be shaped using pole-tips that are fixed on the flat poles. ... In particular, different sets of magnet pole-tips have been designed and built. ... These different magnetic configuration illustrate the main aspects of the cyclotron focusing theory: weak focusing, radial sectors (Thomas focusing) and spiral sectors (Kerst and Laslett focusing effects)

Hernalsteens, Ponter, Beaudoin, Koeth, Ruisard & Miller, Betatron Tune Characterization of the Rutgers 12-Inch Cyclotron for Different Magnetic Poles Configurations (2016) — p. 1

Editorial note, tabletop extrapolation: A strong architectural argument for an educational tabletop machine: build the magnet with flat poles and put the field shaping entirely in separate pole-tips, so focusing schemes become swappable experiments rather than a magnet rebuild. This paper documents the sets and their purpose; the mounting/interchange practice is documented in the same program's field-mapping report (lib-006), whose four pole-tip sets were mapped on this magnet.

Fourteen pole piece conceptions were modeled during the semester long project. … After examining field profiles and particle motion, the original design was adjusted or discarded, and a new design analyzed identically. Due to the short project duration (1 semester), each of the 3 students established competency in one program and worked as a team in interpreting results.

Ruisard, Hine, Koeth & Rosenberg, The Rutgers Cyclotron: Placing Student's Careers on Target — WE1PB02, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.293. The transferable part is the loop and its discipline: CAD → field solver → profile/flutter inspection → tracking → adjust or discard, then re-analyse identically — with the labour split so nobody had to master every tool. Fourteen concepts in one semester is what three students at a university managed with that structure; treat it as an existence proof of the loop's throughput, not an amateur productivity quota.

A 30 AWG 7 cm radius wire loop was energized with 2.5 amps and placed in the magnetic gap … Four additional orbits were found at higher radii, beyond the four seen in simulation. These are likely lower energy equilibria, as the wire loop technique does not strictly correlate circumference to ion orbit energy (due to an additional degree of freedom, tension).

Ruisard, Hine, Koeth & Rosenberg, The Rutgers Cyclotron: Placing Student's Careers on Target — WE1PB02, Proceedings of Cyclotrons2013 (2013) — p. 4

Editorial note, tabletop extrapolation: PDF p.4 = printed p.294. An almost free diagnostic: hookup wire, a couple of amps and an acrylic spacer reveal a pole-tip set's equilibrium-orbit structure with no vacuum, RF or source. Run it as the controlled demonstration it was: 2.5 A through 30 AWG dissipates about 0.9 W in the fine wire, so use a fused, current-limited low-voltage supply, keep the duty short, secure the (nonmagnetic) leads, and keep hands clear while energized. Carry the authors' own caveat with the method: wire tension is an uncontrolled degree of freedom, so a loop's circumference does not map cleanly onto a beam energy — they found four MORE orbits than simulation predicted for exactly that reason.

The photos shown in Fig. 9 demonstrate betatron motion of a proton beam in a ½ Tesla field, with fRF = 7.8 MHz. … All images were gathered using the radial P-22 Phosphor probe and a DSLR camera. … In the spiral pole tips, the motion quickly reaches a focus, due to the comparatively stronger weak-focusing central region. … for DEE powered at 100 Watts.

Ruisard, Hine, Koeth & Rosenberg, The Rutgers Cyclotron: Placing Student's Careers on Target — WE1PB02, Proceedings of Cyclotrons2013 (2013) — p. 4

Editorial note, tabletop extrapolation: PDF p.4 = printed p.294 (the 100 W dee power is the Fig. 9 caption, PDF p.5 / printed p.295; the subscript in "fRF" is printed as f with subscript RF). A phosphor-tipped radial probe, a viewport and an ordinary DSLR turn a pole-tip set's vertical focusing behaviour into a photograph — at half a tesla, within amateur reach. Read it as the qualitative first check that a new taper focuses (this paper's own comparison: adiabatic tightening on the weak-focusing tips, fast focus on the spirals with their stronger central gradient), then quantify with calibrated radial scans or tune measurements before believing details of the image.

To date, 18 junior- and senior-level undergraduate physics students have gained experience with this machine … six of them have gone on to pursue accelerator physics careers in both academia and industry. The Rutgers cyclotron was the inspiration for a 1 week course at the United States Particle Accelerator School (USPAS) in January 2013. A second course (2 weeks) is in preparation for January 2015.

Ruisard, Hine, Koeth & Rosenberg, The Rutgers Cyclotron: Placing Student's Careers on Target — WE1PB02, Proceedings of Cyclotrons2013 (2013) — p. 5

Editorial note, tabletop extrapolation: PDF p.5 = printed p.295. A reported program count for a tabletop-cyclotron education effort: 18 upper-level undergraduates to 2013, six of whom went on to accelerator-physics careers — with the machine also seeding a one-week USPAS course (January 2013) and a two-week course then in preparation for January 2015, i.e. stated intent at the 2013 conference, not an accomplished fact. Use it as one program's outcome record, not a student-hours costing benchmark; the paper gives no participation-duration data.

the pole tips can be up to 1-inch thick and are easily removable – to date, we have four sets of pole tips and one of each set is shown in Fig. 2. They consist of two weak focusing (one “good” and one intentionally “bad” for educational purposes), a radial sector AVF and a spiral sector AVF, all with a maximum central axial field, Bz(r=0), of 1.2 Tesla.

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

Editorial note, tabletop extrapolation: PDF p.1 = printed p.369 (the four sets are photographed in Fig. 2). The key architectural decision for a tabletop machine intended to be experimented on: make the pole tips removable and the same magnet becomes four different machines. Budget the geometry honestly — tips up to 1 inch THICK EACH sit inside the magnet opening, and the clear beam gap that remains is a separate design number this paper does not state. 1.2 T central is the stated ceiling with tips installed, versus the "nominally 1 Tesla" working figure quoted elsewhere in this collection.

Small axial motion is initiated by a vertical electric field that imparts an upward kick to the ions immediately upon their exit of the chimney.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.370. A controlled way to excite vertical motion for diagnosis rather than waiting for it to appear as a fault: an intentional electric kick at the chimney exit launches the oscillation, which a turn-resolving diagnostic (here, the radial-draw phosphor image) then converts into a tune number. The caution reads in reverse too: a stray vertical field near the source will do the same thing uninvited.

To estimate a local average tune, Qz, the student notes the radial locations of two adjacent axial peaks and divides by the number of revolutions within that interval. When the radial beam spot is wider than the turn-to-turn spacing, overlap prevents a direct count of individual turns; peak DEE voltage is used to estimate the number of turns within the corresponding energy (radial) increment. By definition, the measured tune directly follows from the ratio of vertical oscillations to revolutions.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.370 (the printed text reads "can beam measured", a source typo for "can be measured"). A tune measurement needing only a phosphor probe, a viewport and a camera on long exposure — no gated camera, unlike we1pb04's phase method. The dee-voltage fallback is the practical part, and it is an ESTIMATE: turns-per-energy-increment follows from an energy-gain-per-turn model (effective voltage, gap crossings, phase), so calibrate that model before trusting the count on a machine where turns overlap early.

The n=0.2 point occurs at r=3.5 inches, well within the 5 inch DEE radius, so as to allow the ion displacement to grow.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.371. The inverse of a design rule and the most instructive demonstration here: a taper whose n = 0.2 point lands at 3.5 inches instead of near the 5-inch dee edge converted a working configuration into one that grows axial displacement — and in the reported simulation and experiment the growth fed on a 3 mm chamber-to-magnet offset (the difference resonance bounds axial amplitude by the initial radial offset). What transfers is the mechanism and the method — locate n = 0.2 on the measured map, track orbits through it — not a fabrication tolerance or a universal seed threshold.

Although considered obsolete in this day, the HP85 proved to be an extremely versatile piece of test equipment. It's ability to control any HPIB ready unit has made possible a flexible data control and acquisition system. The simple HP Basic language allowed even the most novice programmer to exercise complete equipment control. Although the processor is slow, speed was not an issue as the magnetic field needed to be ramped even slower. Future needs that may arise from active feedback certainly would require a faster computer.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 7

Editorial note, tabletop extrapolation: The controls-architecture lesson survives the obsolete hardware: when the acquisition loop is bounded by how fast you dare ramp the magnet, a slow, simple, well-understood controller on a standard instrument bus wins — and the logging-here, analysis-elsewhere split (HP85 logs, PC stores and analyzes, per the p.2 calibration chain) is the same split a modern builder should make. The author's own caveat carries: feedback, protection and fast diagnostics impose different timing budgets than a slow scan.