--- title: "Knowing before building — four hosted reports · Cyclotron Info" canonical: https://cyclotroninfo.com/library/classics/model-and-computation/ description: "Four hosted public-domain reports on predicting a cyclotron's behaviour before committing metal: a 1947 RF system proposal and the half-scale model tests that checked it three months later, plus two 1961 computational studies of extraction optics and dee field geometry." generated: 2026-11-12 note: "Markdown rendering of the canonical HTML page, generated at build for AI assistants and text tools. Figures and interactive elements are described, not reproduced. On Design Guide rules the source quote, this site's paraphrase and this site's editorial note are labelled separately and must not be conflated." licence: "Datasets CC BY 4.0, census snapshot CC BY-NC 4.0 (https://cyclotroninfo.com/data/); cite as Cyclotron Info, cyclotroninfo.com" --- [Construction Classics](https://cyclotroninfo.com/library/classics/) # Knowing before building One question, answered two ways, fourteen years apart. In 1947 you found out what an RF system would do by **building half of one and measuring it**. By 1961 you found out by **writing an orbit code and running it**. All four reports exist for the same reason: metal is expensive and a mistake in the magnet gap is expensive twice. The first two are a matched pair, and finding the second half of it is why this page now has four documents. In **September 1947** MacKenzie proposed the “three quarter wave” RF system and set out its theory with early model results. In **December 1947**, three months later and at the same laboratory, Anderson reported the half-scale model tests of that same system. **The collection now holds the proposal and its verification.** MacKenzie is candid in the introduction about which half of his own report he expects to last: > By the time it is available, the experimental results quoted in the report will be superseded, it is hoped, by much more recent and encouraging data. However, the theory should apply, and may help to clarify some of the improvements found by empirical methods. The design he is arguing for puts the rotating condenser about a third of the way along the dee line from the shorted end, which gets it **outside the magnetic field** — no eddy current losses, room to build it ruggedly, and, as he notes, the ability to service it without much danger of an overdose of radiation from a ‘hot’ dee. He states the costs just as plainly: bulkier than a condenser mounted on the dee, more power, and many more possible modes of oscillation. A 2.5:1 frequency swing was achieved against a theoretical 3:1, and the limit was how to couple the oscillator tube across the range. ## The documents - **Preliminary Report on the “Three Quarter Wave” R.F. System for Frequency Modulated Cyclotrons** proposal + model MacKenzie, Kenneth. Preliminary Report on the “Three Quarter Wave” R.F. System for Frequency Modulated Cyclotrons, AECD-1850. University of California. Manuscript 12 September 1947; declassified 16 March 1948. Issued by the Technical Information Branch, Oak Ridge. Record: [DTIC AD-A320280](https://archive.org/details/DTIC_ADA320280) · [Download PDF — 3.6 MB, 24 pages](https://cyclotroninfo.com/classics/aecd-1850.pdf) - **Half-Scale Model Tests on the Three Quarter Wave R.F. System** physical model Anderson, Robert L. Half-Scale Model Tests on the Three Quarter Wave R.F. System, UCRL-31. Radiation Laboratory, University of California, Berkeley, under AEC contract W-7405-Eng-48, 30 December 1947. Record: [OSTI 971255](https://www.osti.gov/biblio/971255) · [Download PDF — 10.0 MB, 39 pages](https://cyclotroninfo.com/classics/ucrl-31.pdf) - **Computational Study of Factors Determining the Optical Characteristics of a Resonant Extraction System for a 3 Sector Cyclotron** computation Blosser, H. G., and M. M. Gordon. Computational Study of Factors Determining the Optical Characteristics of a Resonant Extraction System for a 3 Sector Cyclotron, MSUCP-9. Michigan State University Cyclotron Project, January 1961. Record: [OSTI 4791728](https://www.osti.gov/biblio/4791728) · [Download PDF — 5.8 MB, 45 pages](https://cyclotroninfo.com/classics/msucp-9.pdf) - **Computation of Electric Field and Potential of an Idealized Dee Geometry** computation Beal, J. W. Computation of Electric Field and Potential of an Idealized Dee Geometry, MSUCP-12. Michigan State University Cyclotron Project, October 1961. Record: [OSTI 4769713](https://www.osti.gov/biblio/4769713) · [Download PDF — 0.7 MB, 19 pages](https://cyclotroninfo.com/classics/msucp-12.pdf) ## Why these documents can be hosted AECD-1850 is a **declassified AEC report** — manuscript September 1947, declassified March 1948, issued by the Commission's Technical Information Branch at Oak Ridge — the same basis as the MDDC memoranda hosted elsewhere here. Its 24 pages carry no copyright notice, no residual classification marking and no journal-reprint marking. UCRL-31 is a University of California Radiation Laboratory report under AEC contract W-7405-Eng-48, carrying no copyright notice, no classification marking and no journal-reprint marking — the same basis as every other UCRL report in this collection. **The two MSU reports need a different argument, and it is worth stating rather than borrowing.** MSUCP is a *university* series whose footnote reads “Research supported *in part* by U. S. Atomic Energy Commission Contract AT(11-1)-872.” Supported in part, by university employees, is not the same as a work produced under contract by a laboratory operator, so the US-Government-work argument is weaker here than it is for an Oak Ridge or Berkeley report. The load-bearing basis for these two is therefore **pre-1978 distribution with no copyright notice** — verified absent from both scans — with the AEC sponsorship and the standard government-sponsorship disclaimer as support rather than as the claim. Determinations made August 2026, by reading the scans. ## 1947: build half of it UCRL-31 tests a **half-scale model of the RF system for the 184-inch cyclotron** — the three-quarter-wave system for frequency-modulated machines. It follows a preliminary report by Kenneth MacKenzie from September 1947 and states its own scope precisely: to present the apparatus and the results of tests performed on the half-scale model since that date. The sentence to take away is the one about what happens next: Further tests will be made on the full size r.f. system prior to its actual installation in the 184-inch cyclotron. That is a **three-stage validation chain** — half-scale model, then full-size system on the bench, then installation — and each stage exists to catch what the previous one could not. Berkeley did not model instead of testing, or test instead of modelling. MacKenzie’s name is the connective tissue here. He co-authored the already-hosted [UCRL-64](https://cyclotroninfo.com/library/classics/ucrl-64/), the design history of that same 184-inch RF system, and [MDDC-1045](https://cyclotroninfo.com/library/classics/mddc-1045/) on the 37-inch FM conversion that preceded it. Read in order — MDDC-1045, UCRL-31, UCRL-64 — the three give one RF system from prior art through scale model to as-built design. Scale modelling is the method the collection keeps returning to. [NYO-780](https://cyclotroninfo.com/library/classics/nyo-780/) ran magnet models at 2, 6 and 9 inches before committing forgings; [TID-454](https://cyclotroninfo.com/library/classics/tid-454/)’s sixth report is a three-quarter-scale model oscillator; [ORNL-2648](https://cyclotroninfo.com/library/classics/ornl-2648/) established the model-magnet method for AVF machines. UCRL-31 is the RF instance, and the earliest. ## 1961: compute it instead The two MSU reports are the same instinct with a computer behind it, from the Michigan State cyclotron project as it was being designed. **MSUCP-12** is the one to read first, and the more useful of the two at small scale: analytic solutions for the electric field and potential of an *idealized dee geometry*, obtained by transforming the dee cross-section into a geometry whose field is already known, and tabulated for several dee arrangements. Nineteen pages. Because the result is analytic rather than a machine-specific field map, the formulas do not care how big your dees are — which is exactly why it was worth acquiring for a site about small machines. It builds on earlier work on fields within cyclotron dees, with annotations and corrections stated as such. **MSUCP-9** is Blosser and Gordon on resonant extraction optics for a medium-energy three-sector cyclotron, studied by orbit tracking — the Fixed Point Code and the General Orbit Code, run on MISTIC, with a linear transfer-matrix method for the well-behaved cases. It is candid about the limits of the approach: reading design conclusions out of orbit plots and phase diagrams “is not however an easy” matter, so both static and accelerated orbit behaviour had to be computed. Blosser is the same author as [ORNL-2648](https://cyclotroninfo.com/library/classics/ornl-2648/), three years earlier at Oak Ridge. ## Why the pairing matters now An amateur builder in 2026 has both methods available and cheaper than either was then. The computation is free — see [modeling tools](https://cyclotroninfo.com/learn/modeling-tools/) for the open-source field solvers and orbit codes that do what MISTIC did. The physical model is a weekend of aluminium and a network analyser. What these reports supply is the judgement about *which* to use. UCRL-31 models the RF system, where the awkward quantities are contact resistance, joint behaviour and standing-wave patterns in real conductors — things a field solver still models badly. The MSU reports compute orbits and electrostatic fields, where geometry is exact and measurement is hard. The 1947 answer and the 1961 answer are not competing; they were applied to different subsystems, and mostly still should be. ## Design rules extracted from these documents **47 Design Guide rules** come from these reports. Representative examples: - [dg-999](https://cyclotroninfo.com/design-guide/#dg-999) — retire RF-system risk with a scaled electrical model before cutting full-size metal - [dg-1003](https://cyclotroninfo.com/design-guide/#dg-1003) — tune with every electrode in place — the dummy dee alone detuned the model by ~9% - [dg-1002](https://cyclotroninfo.com/design-guide/#dg-1002) — three parasitics set a dee system's resonant range and deserve first attention - [dg-1011](https://cyclotroninfo.com/design-guide/#dg-1011) — a scale model's known infidelities must be listed alongside its results - [dg-1028](https://cyclotroninfo.com/design-guide/#dg-1028) — the peak accelerating field saturates at V₀/h — set by the aperture, not the gap - [dg-1030](https://cyclotroninfo.com/design-guide/#dg-1030) — do not use the parallel-plate V/d estimate for dee-gap fields - [dg-1031](https://cyclotroninfo.com/design-guide/#dg-1031) — Table 1 is a ready-made verification dataset for anyone implementing the solution Used by the [modeling tools](https://cyclotroninfo.com/learn/modeling-tools/) and [dee RF coupling](https://cyclotroninfo.com/learn/dee-coupling/) pages. > **Page provenance.** Last reviewed: 17 August 2026 · Hosted copies verified against the OSTI originals; rights review August 2026 · [Methodology](https://cyclotroninfo.com/about/methodology/) · [Report a correction](mailto:info@cyclotroninfo.com?subject=Correction%3A%20Knowing%20before%20building%20%E2%80%94%20three%20hosted%20reports) · [Changelog](https://cyclotroninfo.com/changelog/)