Physics in the 1940s: The Betatron

Professor Donald Kerst built the world's first magnetic induction accelerator at the University of Illinois in 1940. After the new machine was referred to variously as a "rheotron," an "inductron," a "Super-X-Ray Machine," and a "cosmic ray machine" in early press releases, a departmental contest was held to name it.

"Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron" was one of the more original entries. Kerst settled on "betatron." The original betatron is now on display at the Smithsonian Institution.

Donald Kerst with the first betatron, invented at the University of Illinois in 1940
Donald Kerst with the first betatron, invented at the University of Illinois in 1940
Donald Kerst with the original table-top betatron and a 25-MeV version.
A larger push-button 25-MeV device, shown behind Kerst in the photo above, was built by the Allis-Chalmers Company and was used as an x-ray lithography device for detecting flaws in metals or other materials for the war effort.
Donald Kerst and his student, H. William Koch, measuring depth-dose distributions of X-rays produced by a 20-MeV betatron
Donald Kerst (L) and his student H. William Koch (R) are shown in the photograph above measuring depth-dose ionization distributions produced by 20-MeV betatron X-rays in 1942. They carried out the first measurements of dose distributions in human-tissue-like materials, which were critical to the development of the betatron as a source of high-energy X-rays for cancer therapy.

In 1950, a 300-MeV betatron, more powerful than that called for in the original design, goes online in its own new building on the corner of Stadium Drive and Oak Street. New staff members are recruited to exploit this major new facility, including Giulio Ascoli, Gilberto Bernardini, and Edwin Goldwasser.

Turning the betatron
Turning the betatron, June 1949.

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Celia Elliott
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