During World War II, Kerst took a leave of absence in 1940 and 1941 to work on it with the engineering staff at General Electric, and he designed a portable betatron for inspecting dud bombs.

[2] He entered the University of Wisconsin, where he earned a Bachelor of Arts (BA) degree in 1934, and then his Doctor of Philosophy (PhD) in 1937,[3] writing his thesis on "The Development of Electrostatic Generators in Air Pressure and Applications to Excitation Functions of Nuclear Reactions".

In 1938 he accepted an offer of an instructorship at the University of Illinois at Urbana Champaign, where the head of the physics department, F. Wheeler Loomis encouraged Kerst in his efforts to create a better particle accelerator.

[7] In December 1941 Kerst decided on "betatron", using the Greek letter "beta", which was the symbol for electrons, and "tron" meaning "instrument for".

Its success was due to a thorough understanding of the physics involved, and painstaking design of the magnets, vacuum pumps and power supply.

[7] During World War II, Kerst took a leave of absence from the University of Illinois to work on the development of the betatron with the engineering staff at General Electric in 1940 and 1941.

[1] Kerst's engineering and physics background placed him near the top of the list of scientists that Robert Oppenheimer recruited for the Manhattan Project's Los Alamos Laboratory, which was set up to design the atomic bomb.

Primarily drawn from Purdue University, his group included Charles P. Baker, Gerhart Friedlander, Lindsay Helmholtz, Marshall Holloway, and Raemer Schreiber.

A sufficient quantity of enriched uranium arrived at Los Alamos by April 1944, and the Water Boiler commenced operation in May.

As early as November 1943, Kerst suggested using a betatron employing 20 MeV gamma rays instead of x-rays to study implosion.

[14] In the August 1944 reorganization, he became joint head, with Seth Neddermeyer, of the G-5 Group, part of Robert Bacher's G (Gadget) Division specifically charged with betatron testing.