Betatron energy control

Abstract

The Allis-Chalmers betatron is a high-energy induc­tion electron accelerator commercially made for taking industrial X-ray photographs. In this application, the electrons emitted from a hot filament are accelerated dur­ing the first quarter-cycle of an alternating magnetic field, which is excited by a 180 cps sine wave source. During the acceleration, the electrons are constrained to a stable orbit of constant radius by having the field of special shape. When the electrons have reached the desired energy, the orbit is expanded and the electrons strike a thin, heavy-element target. The rapid decelera­tion causes the electrons to lose their energy principally in the form of gamma rays (X-rays). The energy spectrum of these rays is continuous and ranges up to the kinetic energy of the electrons when they strike the target.

In nuclear physics work, the maximum energy of the X-ray spectrum must be accurately known and continuously variable. This means that the orbit must be expanded at the time in the cycle when the electrons have the required energy. This present work is concerned with the electronic circuitry which has been developed to cause the orbit to expand when the instantaneous electron energy reaches some adjustable preset value.