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. One caution before the riches: the examiner checks that the disclosure legally suffices to teach the claimed invention, not that the apparatus was ever built, worked as described, or is safe to operate.
Three different permissions hide in the phrase "patents are free", and they are worth separating (verified against USPTO guidance, September 2026):
- Reading and copying the document is open to everyone, for any patent, in force or not: the standard rights language in patent files authorizes "facsimile reproduction by anyone of the patent document… as it appears in the Patent and Trademark Office patent file or records" (37 CFR 1.71(d)–(e)). The same rule means a patent can contain material — software listings are the classic case — whose owner reserves copyright beyond that facsimile permission, so an old patent's content is not automatically public-domain text to republish at will.
- Practicing the claims — building what the claims cover — is restricted while the patent is in force, and not only commercially: infringement is making, using, offering to sell, selling, or importing the patented invention "without authority" (35 U.S.C. 271(a)). Suits over a hobbyist's one-off are, in practice, vanishingly rare; that is a fact about enforcement, not a permission.
- After expiry, the claims are free for anyone to practice — which is why the historic cyclotron patents below really are free engineering.
When a given patent expires takes a real check rather than a rule of thumb. The ordinary US utility term runs 20 years from the earliest effective filing date (applications filed on or after June 8, 1995; older patents get the longer of 17 years from grant or 20 from filing), USPTO delays can add adjustment on top, and unpaid maintenance fees end protection years early — the fee comes due at three points in a patent's life, and protection lapses if it is missed. So look the specific patent up: its USPTO record and its Google Patents page both show status and anticipated expiry. For the machines an amateur would actually study, the answer is comfortable under any reading: the classical, synchro-, and AVF-era patents were filed between the 1930s and the 1980s, and all of them are long expired (MPEP 2701 and USPTO maintenance-fee guidance, retrieved September 2026).
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 — their claims free for anyone to practice, their documents free to copy. 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; building or using what its claims cover without authority is infringement whether or not money changes hands (35 U.S.C. 271(a)); the enforcement note at the top of the page applies. This card is the reason "check the term and status" 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.