Donald W. Kerst

Donald Kerst was a physicist who worked as a professor at the University of Illinois for almost 20 years. During his time at Illinois, Kerst made several contributions in the field of physics. One innovation that he is most famous for is the Betatron, the world’s first magnetic induction accelerator in 1940. Branded as the “World’s Most Powerful X-Ray Machine,” the betatron could accelerate electrons at speeds of more than 158,000 miles per second and give them energy of more than 2.5 million electron volts. At the time, this was the highest velocity ever produced by any machine. 

Born in Galena, Illinois, on November 1, 1911, Donald William Kerst quickly discovered a passion for physics, in which he earned a bachelor’s degree in 1934 and a doctorate in 1937 from the University of Wisconsin. After graduating, he became an instructor, assistant professor, and then professor at the University of Illinois. He remained at the University from 1938 to 1957, with the exception of brief periods at General Electric (1937-1938, 1940), Los Alamos, New Mexico (1943-1945), and the General Atomic Laboratory, La Jolla, California (1957-1962).

Donald Kerst, ca. 1950, wielding a soldering gun and drill.

Before coming to Illinois, Kerst wrote to F. L. Loomis, then the department head of Physics at Illinois, describing a “small electron accelerator which will go to very high voltages” and would “increase the flux within the robot of an electron and so induce an E.M.F. along its orbit which causes an acceleration.” Loomis encouraged Kerst to work on this project at Illinois. It would become his most famous invention: the betatron. Created in 1940, the betatron was a particle accelerator that used a revolutionary method that “pushed” particles, rather than “kicking” them for the purpose of acceleration. So great was its impact, that it not only influenced every single particle accelerator that came after it, but also made significant contributions to the field of medicine for the more powerful x-rays it could produce.

A true experimentalist, Kerst stayed committed to his project despite only having a $500 budget for it, and completed the first implementation of his invention in a little under a year, according to Loomis. However, both the betatron and Kerst himself garnered interest from the military for defense purposes. Dr. J. Oppenheimer personally requested that Kerst come to work on a special military project. 

It was a power struggle between the military and the University of Illinois on where Kerst would work in 1943. President Willard at the University of Illinois did not want Kerst to leave as he saw the betatron project as too valuable to the war efforts, and believed Kerst, as the creator, as the best person to continue working on it. Twice the university denied Kerst release from his work at Illinois to work on this “special project” (although the University had let many other physicists be released for other war efforts).

To complicate matters, Kerst, who was willing to help at Los Alamos, was hospitalized for viral pneumonia making it difficult for him to argue to be released. He even suggested to General L. R. Groves, Dr. James B Conant, and Dr. Oppenheimer that he should stay at Illinois since the University did not seem willing to release him from his current work and the National Defense Research Committee wanted to expand and extend his contracted betatron work at Illinois. 

Shortly after, the Board of Trustees received a request from Secretary of War, Henry L. Stimson, to release Kerst from his University contract and they overruled Willard’s decision after hearing both sides from officials in the War Department and President Willard and other Illinois faculty. In 1943, Kerst joined many other great scientists at Los Alamos to begin work on scientific advancements for the Second World War, most notably the atomic bomb.

Kerst returned to Illinois in 1945, when the Illinois legislature granted $1,500,000 for funding the betatron project. Back at Illinois, Kerst designed bigger and more powerful versions of his invention, along with working on other key Illinois innovations, such as ILLIAC.


Prof. Gerald P. Kruger (left), Prof. Donald W. Kerst (center), and Prof. James N. Snyder (right) examine some of the computations made by the ILLIAC, University of Illinois electronic computer, September 5th, 1957


Eventually, Kerst made the move back to his alma mater in 1962. This was largely a result of the efforts L. R. Ingersoll, Department of Physics head at Wisconsin, who for years sent letters reinforcing the wish for Kerst to return to Wisconsin to teach. In one of the letters, Ingersoll goes so far as to nominate Kerst for the Nobel Prize in Physics, reminding Kerst that, should he win, to “please have some kind thoughts in your head towards us here at Wisconsin.” Evidently he did, for Kerst remained at Wisconsin until his retirement to Florida with his wife, Dorothy.

Even while retired, Kerst never forgot the research he helped develop, always making sure to call regularly and get updates. Donald W. Kerst died at age 81 on August 19th, 1993.


This text has been corrected and updated as of 02/19/2024. The original text stated that Kerst had been ill after arriving at Los Alamos and asked to be released from the Los Alamos project. Kerst in fact had been ill while asking to be released from his work at the University of Illinois to go to Los Alamos and the text now accurately reflects this.


– Loomis Laboratory. You can see Kerst’s work, the cyclotron, at Loomis Lab. Directions: the display is located in the northwest corner near the study tables.


Betatron Correspondence, 1938-1970. Record Series 11/10/11, University of Illinois Archives.

Correspondence. Donald W. Kerst Papers, 1937-1959, 1983-85, 1987. Record Series 11/10/30, University of Illinois Archives.

Donald W. Kerst. (1950). Photographic Subject File. Record Series 39/2/20, Box FAC – 4, Folder FAC – Kerst, Donald. University of Illinois Archives.

ILLIAC, University of Illinois Electronic Computer. (1957, September 5). Photographic Subject File. Record Series 39/2/20, Box 135, Folder FAC – 4 SM – SN. University of Illinois Archives.

Kerst to Loomis, Nov. 28, 1938, Betatron Correspondence, 1938-1970. Record Series 11/10/11, University of Illinois Archives.

Sessler, A., & Symon, K.R. (1997). Donald William Kerst. In Biographical Memoirs, v. 72. Washington D.C: The National Academies Press.

Sprott, J.C. (1993). Eulogy to Donald W. Kerst. Retrieved September 3, 2013 from

Contributors: Maggie McNaughton and Anonymous