So You Want to Build a Cyclotron

It can be done. High-school students, undergraduates, and garage builders have produced working cyclotrons since the 1940s, and the build census documents the ones we know about. But the same record shows most attempts never reach beam. This page is the honest version of what the project takes — skills, money, years, and the decisions that determine whether a build finishes — so that anyone starting one starts with open eyes.

First, read Safety. All of it. A cyclotron project is a high-voltage, RF, radiation, and heavy-rigging project before it is anything else.

What it actually takes: the skills inventory

A cyclotron is not one project but five overlapping ones. A builder — or a team — needs working competence in each, and "working competence" means being able to debug it at 2 a.m., not having read about it:

• Vacuum. Reaching and holding ~10⁻³–10⁻⁴ Pa (10⁻⁵–10⁻⁶ torr): pump selection, seals, leak hunting, cleanliness discipline. Most first-time schedule overruns die here — a chamber that held pressure yesterday and doesn't today.
• RF. Building or adapting an oscillator or amplifier that delivers hundreds of watts at 5–20 MHz into a resonant dee, and matching it. Amateur-radio experience transfers almost directly; its absence is expensive.
• Magnetics. Designing an iron circuit, winding or specifying coils, and — the part that surprises people — measuring and shimming the field to the ~0.1% uniformity the resonance demands.
• Machining. Poles, chamber, dees, feedthroughs, and a hundred brackets. Access to a lathe and mill (and a friendly machinist) is close to a prerequisite.
• HV electronics and instrumentation. Kilovolt supplies, ion-source drivers, and the Faraday cups and picoammeter-class measurements needed to know whether the faint first beam exists at all.
• Patience. Not a joke. The documented builds that finished were multi-year efforts sustained through long stretches of no visible progress. Project discipline — logs, one variable at a time — separates finished machines from garage shrines.

What it costs

Documented amateur builds have typically landed in the range of several thousand to low tens of thousands of US dollars, spread over the life of the project. The big-ticket items are the magnet (iron and copper, often the single largest line), vacuum pumps and gauging, and RF power; the long tail of feedthroughs, fittings, gauges, and rebuilt mistakes adds up to a comparable sum. The used and surplus market is the difference between feasible and not: transformer iron, surplus diffusion or turbo pumps, ham-fest RF hardware, and scrapped equipment routinely cut costs several-fold, at the price of time spent hunting and refurbishing.

For calibration of what "real" machines cost: a 2005 study for the US Department of Energy priced commercial 45 and 70 MeV isotope-production cyclotrons at $14.8M and $17.0M respectively, before the building (JUPITER Corp. cost/benefit study for DOE, 2005). An amateur machine is not a small version of that — it is a different object, built from a different economy. Budget accordingly, and budget honestly: a figure that assumes zero mistakes is a figure that assumes a builder who has done it before.

How long it takes — and the completion rate

The documented builds that reached beam took on the order of two to four years, and several took longer; "one summer" appears in many plans and no completions. More sobering: across the attempts documented in the build census, only roughly one in five reached a working beam. The failure modes are rarely exotic physics — they are underestimated vacuum work, an RF system that never quite made voltage, a field that never got shimmed flat, and above all, life intervening in year two. Plan for the long middle, and pick a first milestone (ion source glowing, chamber at pressure, resonance on a signal generator) that pays off early.

The decision points

Four choices, made early, shape everything downstream:

• Pole size. 8–12 inch poles is the classic tabletop class: iron and copper a person can afford and lift (barely), fields of 0.5–1 T, and enough radius for a demonstrable beam. Bigger poles buy energy quadratically — T ∝ B²r² — and cost, weight, and power at least as fast.
• Target energy. Sub-MeV is the realistic first goal, and it is not a consolation prize: it demonstrates every part of cyclotron physics, while staying below activation thresholds and (in many jurisdictions) below regulatory attention — verify in Legal. Chasing MeV-class energy on the first machine multiplies every subsystem's difficulty.
• RF approach. A self-excited oscillator built around the dee as its tank circuit is the traditional, forgiving route — it follows the resonance it drives. A signal-generator-plus-amplifier chain gives control and measurement at the cost of matching-network complexity. The RF matching calculator shows the numbers behind the choice.
• Used vs. new. Surplus pumps, transformers, and RF gear against new catalog hardware is a time-versus-money slider. The documented pattern: builds that finished mixed both — surplus for the heavy iron and pumps, new for seals, gauges, and anything where a mystery failure would burn months.

The reading order

A path through this site and the literature that matches how the project actually unfolds:

1. How a Cyclotron Works — the physics you'll be debugging.
2. Safety — before any hardware exists.
3. The Library — start with the classic small-cyclotron papers and Livingston & Blewett; the annotations flag what's readable and what's reference.
4. The Design Guide — 560 sourced rules; read your subsystem's rules before designing it, not after.
5. The Builds census — what people with the same budget actually did, and where they stalled.
6. Legal — your jurisdiction's registration rules, before first beam, ideally before first purchase.
7. The Calculators — as design partners throughout: energy/field/radius, turns and vacuum, magnet power, lid safety, RF matching.

Where to ask questions

No cyclotron-only forum currently exists, but the adjacent communities have deep, directly transferable expertise (links checked August 2026):

• Fusor.net forums — the amateur fusion community; the strongest concentration of hands-on high-voltage, vacuum, and radiation-measurement experience anywhere online, with a history of cyclotron build threads in its advanced-projects section.
• Physics Forums — long-running general physics community; good for theory questions and sanity checks.
• r/Physics — large (millions of members) and general-purpose; useful reach, less hands-on depth.

Wherever you ask: post numbers, not vibes. "8-inch poles, 0.7 T, 1.2 kV on the dee, 3×10⁻⁵ torr, no beam on the probe at r = 5 cm" gets answers that "my cyclotron doesn't work" never will.

Sources

• Documented amateur builds compiled in this site's build census — cost bands, timelines, and the observed completion rate.
• JUPITER Corporation, Cost/Benefit Comparison for 45 MeV and 70 MeV Cyclotrons, study for the US DOE Office of Nuclear Energy, May 2005 — commercial machine costs.
• M. S. Livingston & J. P. Blewett, Particle Accelerators, McGraw-Hill, 1962 — the standard reference underlying the skills and subsystem framing.
• Community links checked August 2026.