Cyclotron patents
Patent literature is one of the most underused resources in amateur accelerator work. A patent is written to teach "a person skilled in the art" how to build the thing — which means dimensioned drawings, operating parameters, materials, and failure modes, reviewed for completeness by an examiner. And unlike journal papers, every word and figure of an expired patent is free to read and free to use: once a patent lapses, its disclosure is public-domain engineering documentation.
For cyclotrons the timing is generous. A US patent now expires 20 years after filing (for patents filed before June 1995, the longer of 17 years from grant or 20 from filing), so every US patent granted before mid-2007 — which covers the entire classical, synchro-, and AVF cyclotron era — is long expired. The machines an amateur would actually build were patented between 1934 and the 1980s, and all of that literature is free engineering.
Where to search
Search links verified working August 2026, except as marked. A useful trick on any of these: cyclotrons have their own patent classification, CPC H05H 13/00 — searching by that class instead of by keyword finds cyclotron patents that never use the word in their titles.
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Google Patents
The easiest interface: full text, OCR'd drawings, one-click PDF of the original document, and citation graphs that lead from any patent to its ancestors and descendants. Useful starting queries: cyclotron dee, cyclotron ion source, cyclotron magnet pole.
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USPTO Patent Public Search
The authoritative US source, with the full-resolution original page images — the place to go when a Google Patents scan is too rough to read a dimension off a drawing. The query syntax is more rigid than Google's but supports proper fielded search (inventor, classification, date ranges).
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Espacenet (European Patent Office)
140+ million documents worldwide — the way into the European, Japanese, and Soviet cyclotron patent record that never passed through the USPTO. Machine translation is built in, and classification browsing (H05H 13/00 again) works well here.
Five patents worth actually reading
Each verified against its Google Patents record, August 2026. The first four are long expired — public domain in full. The fifth is included deliberately: a reminder that compact superconducting machines are the one corner of cyclotron engineering where patents are still in force.
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US 1,948,384 — "Method and apparatus for the acceleration of ions"
The cyclotron patent. Lawrence lays out the resonance principle, the dee geometry, the magnetic field requirement, and the vacuum chamber in nine pages that read remarkably like a build plan for the small machines amateurs make today. Anyone building a classical cyclotron should read the original at least once.
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US 2,615,129 — "Synchro-cyclotron"
Phase stability, from the man who discovered it (and shared a Nobel Prize for other work). The patent explains why a fixed-frequency cyclotron runs out of energy as ions go relativistic, and how modulating the RF frequency rescues synchronism — the idea behind every synchrocyclotron and, ultimately, every synchrotron.
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US 3,868,522 — "Superconducting cyclotron"
The Chalk River line of work that put superconducting coils on a cyclotron magnet — how to hold field quality when the iron is driven far into saturation, and what that does to the machine's size and cost. Background reading for understanding why modern compact machines look the way they do.
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US 4,641,057 — "Superconducting synchrocyclotron"
Blosser's compact high-field synchrocyclotron concept from the MSU cyclotron laboratory — the direct engineering ancestor of today's single-room proton-therapy machines. Unusually rich in real design numbers: fields, dimensions, RF program, extraction. Expired since the mid-2000s.
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US 8,558,485 — "Compact, cold, superconducting isochronous cyclotron"
A modern compact isochronous design in the same lineage — listed here as the counterexample. Reading an in-force patent is free and legal; practicing its claims commercially is not. For a hobby machine this is rarely a real constraint, but it is the reason "check the grant date" belongs in the workflow.
The old version of this page carried an automated patent feed; it broke years ago and is not coming back — new cyclotron patents appear at a rate best handled by running the searches above when curiosity strikes. All links on this page verified August 2026, except Espacenet as noted.