Magnetic contractor mechanism in betatrons and synchrotrons

Abstract

A comparative study of different types of magnetic transients (contractors and magnetic “bumps”), carried out on the 8-MeV betatron of the Institute of Atomic Physics, showed that their mechanism of operation cannot be thought of a simple orbit contraction, but merely as a convenient means of altering the parameters of the collision between the injected beam and the chamber walls. The actual orbit radius contraction was found experimentally much lower that the one necessary for the electrons to miss the injection gun. Moreover, a similarity of effects of contractor-type transient and of sectorial magnetic bump was pointed out, although the former does contract the orbit and the latter does not. These facts fit best with the central shift mechanism (CSM) theory of electron capture. The effect of relative injection and contraction timing was also studied and conclusions were drawn on the higher efficiency of injecting electrons with instantaneous radii near the equilibrium radius, and on the most convenient form of contractor pulse.