Numerical Modelling of Intense Electron Beam Transport in the Spiral LineInduction Accelerator

摘要

Computer simulation is used to study issues of intense electron beam transportarising in the context of the spiral line induction accelerator (SLIA), a device in which the beam is transported along an open-ended beam pipe, making multiple passes through each accelerating cavity and traversing a 180 deg achromatic bend between passes. In the straight sections, the beam is transported on a solenoidal field; in the bends, the beam is subject to a vertical bending field and strong focusing stellarator fields, in addition to the solenoidal field. We show that the self-fields of the beam change the optimum vertical field in the bend but do not significantly affect the achromaticity of the bend. We find that magnetic matching elements are required, at the entrance and exit of each stellarator section, to minimize oscillations of the beam envelope and concomitant emittance growth. We show that matching can be accomplished satisfactorily with a single thick quadrupole lens. We determine the frequency and damping rate of envelope oscillations that result from mismatches, and resulting emittance growth. These are found to be sensitive functions of the beam radial profile. Simulation results are found to be in excellent agreement with experiments conducted recently at Pulse Sciences, Inc. Intense beam, Induction accelerator, Emittance growth.