The betatron , also known as an electron spinner, is a circular accelerator suitable for electrically charged particles such as electrons or positrons and is an early type of electron accelerator . It became the radiotherapy and radiographic testing used, but in a row by the better controllable electron linear accelerator displaced.
The betatron is similar to the cyclotron in that the accelerated particles are kept on a spiral-like path by a magnetic field . However, it has no acceleration electrodes; instead, the magnetic field is variable over time. According to the law of induction , a change in the magnetic flux over time creates a ring-shaped electric field . This accelerates the electrons. The ring-shaped electron beam represents the secondary coil of a transformer . The energy limit of the Betatron is around 200 MeV , the electrons then have almost the speed of light .
The free electrons for acceleration come from a hot cathode and not from a radioactive preparation. The betatron has nothing to do with beta decay, but was named because of the similarity between the accelerated beam and beta radiation .
The first functional betatron was developed in 1935 by Max Steenbeck in the research laboratory of Siemens-Schuckertwerke Berlin, but initially kept secret and not pursued because of other priorities. In 1940 a betatron was built by Donald William Kerst at the University of Illinois . In his publication in the Physical Review, Kerst referred explicitly to Rolf Wideröe , who had the idea for the betatron back in the 1920s, but did not mention Steenbeck's work, although he probably knew it, since General Electrics was in contact with Siemens at the time and Steenbeck's work at GE was known.
In 1942 Konrad Gund began developing the first 6 MeV betatron industrially produced in Germany at Siemens-Reiniger in Erlangen (see illustration). It was used in cancer therapy and basic physics in Göttingen after the war in 1946.
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