Radio-Frequency Accelerators for Multi-Kiloampere Electron Beams

Abstract

Most present work on intense pulsed electron beam accelerators is aimed toward linear induction accelerators. In this paper the authors consider the application of resonant accelerators to the generation of pulsed multi-kiloampere electron beams. The main relative advantages are that low cost and high voltage gradient can be achieved by eliminating ferromagnetic isolation cores; that cavity designs are simpler (with optimum utilization of vacuum insulators); and that there are no high voltage shorting switches. The last feature implies that RF accelerators may operate at higher repetition rate and duty cycle. The authors discuss RF cavities filled with water. The high attainable dielectric constant raises the stored energy density by a factor greater than 60 for enhanced pulsed operation. The lower impedance of the cavity also permits CW operation in the 10-50 A level. The discussion treats, in order, the functions a water-filled cavity can perform and the configuration of a high current RF accelerator; the power losses in the cavity walls and dielectric medium; the effects of water heating and cavity distortion on the resonant frequency; the baseline parameters for a 750 kV cavity; and, in the last section, the problem of beam loading in CW operation.