Construction Classics

General Recommendations for Design of Small Cyclotrons

Why this document can be hosted

UCRL-476 is an AEC contractor report, produced by the University of California Radiation Laboratory under AEC contract W-7405-Eng-48 and issued and distributed by the AEC; such reports are treated as US Government works, which carry no copyright. It was also publicly distributed before 1978 without a copyright notice — an independent public-domain basis. Both were verified against the document’s title page and the OSTI and DTIC records; determination made August 2026.

Reading guide

This is the one document in the collection written for someone about to build a small cyclotron. Wouters walks through every subsystem of a working 6-inch machine in fifteen pages of text, and nearly every page carries a number a tabletop builder can use unchanged. Page references below are the report’s own printed numbers (in the hosted PDF, add one).

Magnet design opens the report, pp. 3–5. The iron rules are stated as recipes: run the iron near saturation (soft iron starts saturating near 16 kG, some irons reach 21 kG), multiply gap flux by a leakage factor read from the gap-height-to-diameter ratio (2.0 at 1/2, 1.5 at 1/4, 1.2 at 1/10), make pole cores two to three times the gap height, give the return yoke 25% more cross-section than the cores, and machine every mating surface flush. The coil rules follow on pp. 4–5: a squarish winding cross-section, 750 A/in² of conductor for continuous air-cooled running, and the cautionary example of the 6-inch machine’s 6,000-turn coils, which saturated the iron below 10 A yet overheated in minutes. Page 6 covers excitation supplies, including the standing warning never to open a charged coil circuit without surge protection across it.

Tank, ion source, and dee construction fill pp. 7–9: vacuum thresholds (10⁻⁵ mm Hg before starting, operation at 10⁻⁴ or below), hydrogen admission through a long-taper needle valve or heated palladium leak, a 0.025-inch tungsten filament, a glass sleeve insulating the dee stem past its vacuum seal, and single-dee construction with a grounded dummy edge. The oscillator and grounding practice on pp. 9–10 — grounded-grid Hartley, a copper ground sheet at grid level, chokes and bypasses on every line leaving the tank, interlocks and grounding hooks — remain sound RF hygiene. Operation, pp. 11–12, describes RF bakeout in short bursts, finding the beam by rocking field or frequency against a probe, and proving real acceleration with prompt gammas from a LiF target. The tables on pp. 14–15 collect the design formulas (NI = 2.02 × B × gap, pole-face force, conductor heating), and four schematic plates at the end show the magnet, tank cross-section, oscillator, and wiring.

Nothing here needs scaling down — the 6-inch example is tabletop scale. What has aged is the 1949 electronics: selenium rectifiers and motor-generator sets date the power-supply pages, and modern silicon replaces them outright. The magnet, vacuum, and commissioning content does not age. One honesty note on the copy itself: this is a DTIC microfilm scan with an OCR text layer that is searchable but rough, so read the page images and treat text extraction as an index, not a transcript.

Design rules extracted from this document

32 Design Guide rules cite UCRL-476 — the most-cited hosted document in the collection. Representative examples:

• dg-122 — magnet excitation from NI = 2.02 × B × gap
• dg-125 — leakage-flux factor from the gap height-to-diameter ratio
• dg-214 — current-density limits for air-cooled coils
• dg-279 — grounded-grid Hartley oscillator for the RF drive
• dg-517 — proving acceleration with a LiF prompt-gamma target

Used by the magnet design, ion sources, and beam quality deep dives.