Construction Classics

A Proposal for the Mc² Isochronous Cyclotron

Why this document can be hosted

ORNL-3540 is an Oak Ridge National Laboratory report prepared for the US Atomic Energy Commission by Union Carbide Corporation as operating contractor, and is marked Unclassified throughout. AEC contractor reports are treated as US Government works and carry no copyright; pre-1978 distribution without a copyright notice is an independent public-domain basis. No copyright notice, publisher imprint, or journal-reprint marking appears anywhere in the 327-page scan. Verified against the scan and the OSTI record; determination made August 2026.

Reading guide

This is the most unusual document in the collection: a complete engineering design for a machine that was never built. Oak Ridge proposed an isochronous eight-sector proton cyclotron delivering an extracted beam in excess of 100 μA at 810 MeV — primary protons plus secondary meson and neutron beams — for nuclear structure, elementary-particle, biomedical and space-oriented research. The Mc² was never funded. What survives is 327 pages of the reasoning, worked to construction standard and then shelved.

That makes it valuable in a way a built-machine report is not. Construction reports tell you what a laboratory settled on; a proposal at this depth shows the alternatives being weighed, because a proposal has to justify itself to a funding agency. The fourteen chapters run from the research programme and beam-optics system through extraction and the accelerating system to shielding, buildings, costs and schedule — a full-lifecycle document rather than a machine description.

Three parts repay a small-machine builder’s attention despite the scale. The accelerating system (ch. 10) is AVF-era RF design worked out at length. Shielding (ch. 11) is one of this corpus’s documented gaps, and the chapter is a rare treatment of it as an engineering deliverable with a budget attached rather than as a regulatory afterthought; the residual-radiation studies elsewhere in the volume address what a machine leaves behind after it is switched off. And costs and schedule (chs. 13–14) are the sections almost no accelerator document contains at all — an explicit review of estimating procedures, which is the closest thing in the collection to an honest account of what building an accelerator takes in money and time.

The extraction material is worth pairing with UCRL-10654: the volume includes a study of beam extraction from Cyclotron Analogue II, the model machine Oak Ridge used to test AVF behaviour before committing to a full design. Modelling first and extracting from the model is the transferable discipline, not the geometry.

A caution on scale. At 810 MeV this is a relativistic machine with eight spiral sectors and a building designed around it; nothing here scales down by arithmetic. Read it for how a complete design was assembled and defended — including the parts most reports omit — rather than for numbers to copy.

Design rules extracted from this document

36 Design Guide rules cite ORNL-3540, and they land where this page argued the volume was unusual rather than where a machine report normally pays out. 8 of them are shielding rules, in a collection that had exactly one before this document was mined; the rest are concentrated in project estimating, scheduling, and the discipline of a trade study. Magnet and RF contributed less than the shielding and cost chapters did.

• dg-914 — build a shield estimate as an explicit chain — dose limit, source term, attenuation, secondary buildup
• dg-917 — design mazes and penetrations by multiplying per-element transmissions
• dg-919 — use stepped labyrinth joints on shield doors so ordinary construction tolerances are acceptable
• dg-912 — assume your shielding estimate is low and your experiment space too small; design the expansion room in
• dg-921 — structure an estimate as basic cost plus explicit adders — engineering ~15%, contingency ~20%
• dg-922 — ground every cost line in evidence: several bids with the median taken, or a documented basis
• dg-892 — build a cheap scaled analogue before committing to the full machine
• dg-893 — when rejecting an alternative in a trade study, write down its specific defects

Used by the shielding deep dive, whose method section is built on this report's chapter 11. Worth noting what the extraction confirmed: a proposal has to justify itself to a funding agency, so it documents the estimating and shielding reasoning that built-machine reports omit — which is why a design for a machine that was never built earns its place here.