Suppression of initial energy spreads in electron radio frequency linacs for intense irradiation applications

Abstract

RF linacs for high-power beams are operated under the fully beam-loaded condition for power efficiency. Under this condition, initial energy spreads are generated by the transient beam-loading effect. Irradiation sources require a beam energy of less than 10MeV for radiation safety. In order to maximize the beam power and maintain the beam energy at a safe level, we need to suppress the initial energy spreads. In an L-band traveling-wave linac for irradiation applications, the initial high-energy electrons are suppressed by beam current modulation with RF power modulation. In this study, the temporal profile of beam energy is calculated by a numerical method and verified by measurement. As a result, the average beam energy and the corresponding beam power are improved by nearly 60% compared with the case without any modulations. The effect of beam current modulation on bunching and acceleration is also discussed in this paper. (C) 2011 The Japan Society of Applied Physics