Betatron

The betatron (clearly also called electron spin ) is charged for light particles such as electrons or positrons suitable circular accelerator. It has been used for radiation therapy and radiographic examination, but supplanted by the more controllable electron linear accelerator.

The betatron is similar to the cyclotron, as the accelerated particles are retained by a magnetic field on a spiral-like path. However, it has no acceleration electrodes; Instead, the magnetic field varies with time. According to the law of induction, one of Maxwell's equations, a time change of the induced magnetic flux of an annular electric field. With this, the electrons are accelerated. The energy limit of the betatron is about 200 MeV, the electrons have nearly the speed of light.

To accelerate the free electrons originating from a thermionic cathode, and not from a radioactive preparation. The betatron has therefore nothing to do with radioactivity ( beta decay ), but was apparently so named because of the similarity with beta radiation of the accelerated beam.

The first functional betatron was developed in 1935 by Max Steenbeck in the research laboratory of the Siemens Schuckert Berlin, but initially kept secret and not pursued because of other priorities. Regardless of a betatron 1940 by Donald William Kerst at the University of Illinois was built. Kerst referred to in his publication in Physical Review explicitly to Rolf Wideröe who had had the idea for the betatron already in the 1920s.