The Acceleration of Electrons by Magnetic Induction

Apparatus with which electrons have been accelerated to an energy of 2.3 Mev by means of the electric field accompanying a changing magnetic field is described. Stable circular orbits are formed in a magnetic field, and the changing flux within the orbits accelerates the electrons. As the magnetic field reaches its peak value, saturation of the iron supplying flux through the orbit causes the electrons to spiral inward toward a tungsten target. The x-rays produced have an intensity approximately equal to that of the gamma-rays from one gram of radium; and, because of the tendency of the x-rays to proceed in the direction of the electrons, a pronounced beam is formed. In the past the acceleration of electrons to very high voltage has required the generation of the full voltage and the application of that voltage to an accelerating tube containing the electron beam. No convenient method for repeated acceleration through a small potential difference has been available for electrons, although the method has been highly successful in the cyclotron for the heavier positive ions at velocities much less than the velocity of light. Several investigators2 3 4 5 have considered the possibility of using the electric field associated with a time-varying magnetic field as an accelerating force. This is a very attractive possibility because the magnetic field can be used to cause a circular or spiral orbit for the electron while the magnetic On leave at the General Electric Company Research Laboratory. G. Breit and M. A. Tuve, Carnegie Institution Year Book (1927-28) No. 27, p. 209. R. Wideroe, Arch. f. Electrotechnik 21, 400 (1928). E. T. S. Walton, Proc. Camb. Phil. Soc. 25, 469-81 (1929). W. W. Jassinsky, Arch. f. Electrotechnik 30, 500 (1936).