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A betatron is a cyclic particle accelerator developed by Donald Kerst at the University of Illinois in 1940 to accelerate electrons, but the concepts ultimately originate from Rolf Widerøe,〔 〕 whose development of an ''induction accelerator'' failed due to the lack of transverse focusing. Previous development in Germany also occurred through Max Steenbeck in the 1940s.〔("Physics and national socialism: an anthology of primary sources" ), Klaus Hentschel. Birkhäuser, 1996. ISBN 3-7643-5312-0, ISBN 978-3-7643-5312-4. p. 350.〕 The betatron is essentially a transformer with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electrons in the vacuum around a circular path. The betatron was the first important machine for producing high energy electrons. ==Operation principle== In a betatron, the changing magnetic field from the primary coil accelerates electrons injected into the vacuum torus, causing them to circle round the torus in the same manner as current is induced in the secondary coil of a transformer (Faraday's Law). The stable orbit for the electrons satisfies : where : is the flux within the area enclosed by the electron orbit, : is the radius of the electron orbit, and : is the magnetic field at . In other words, the magnetic field at the orbit must be half the average magnetic field over its circular cross section: : This condition is often called ''Widerøe's condition''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「betatron」の詳細全文を読む スポンサード リンク
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