Iwanenko, D.D.; Pomeranchuk, I.Y.; On the Maximal Energy Attainable in a Betatron
Doklady Akad. Nauk SSSR 44 (1944) 364;
Phys. Rev. 65 (1944) 343;
Reprinted in The Physical Review - the First Hundred Years, AIP Press (1995) CD-ROM.
By means of a recently constructed induction accelerator-betatron, Kerst succeeded in obtaining electrons up to 20 MeV. The principle of operation of the betatron is the acceleration of electrons by a tangential electric field produced by a changing magnetic flux, which is connected with the magnetic field keeping electrons on the orbit by a simple relation. In contrast to a cyclotron, whose applicability is essentially limited to the non-relativistic region on the ground of defocusing of orbits
due to the change of mass at high energies, there is no such limitation for the betatron. We may point out, however, that quite another circumstance would lead as well to the existence of a limitation for maximal energy attainable in a betatron. This is the radiation of electrons in the magnetic field. (Extracted from the introductory part of the paper.).
Related references See also D. W. Kerst, Phys. Rev. 61 (1942) 93;
D. W. Kerst and R. Serber, Phys. Rev. 60 (1941) 53;
I. Y. Pomeranchuk, J. Phys. 2 (1940) 65;
Limitation of the maximal energy attainable in a betatron.