Suppression of Initial Energy Spreads by Transient Beam Loading Effect in Pulsed RF Linacs for Intense Electron Beam

Abstract

For intense irradiation applications, an L-band electron linac is developed incollaboration with PAL/POSTECH and KAPRA. It is capable of producing 10-MeVand average 30-kW electron beams adopting an L-band traveling-wave acceleratingstructure. This linac is operated under the fully beam-loaded condition for powerefficiency. Under this condition, the initial energy spread becomes a maximumgenerated by the transient beam loading effect. Since irradiation sources require a beamenergy of less than 10 MeV for radiation safety, those energy spreads are suppressed inorder to maintain the beam energy at a safe level but maximize the beam power. In thisstudy, beam current modulation with RF power modulation is adopted for thesuppression method. As a result, the average beam energy and the corresponding beampower are improved by nearly 60% compared with the case without any modulations.The temporal profile of beam energy is numerically calculated from the time-dependentbeam loading relationship, and it is verified with measurement using aluminium plates.The effects of beam current modulation on the bunching and acceleration are alsodiscussed.