PROPAGATION CHARACTERISTICS OF A PREMODULATED ELECTRON-BEAM

The propagation properties of an electron beam whose energy and curren t are simultaneously premodulated at the cathode are investigated by c omputer simulation using the two-dimensional particle-in-cell code, MA GIC. The simulation is carried out to investigate the influence of the initial energy modulation and phase difference between current and en ergy modulation. With appropriate initial energy modulation, amplitude of the downstream current modulation can be kept as high as the initi al modulation level. Appreciable growth of high harmonic components is observed as the electron beam debunches. The maximum amplitude of the fundamental mode (m = 1) occurs at the propagation distance, where al l the other modes vanish or have a very small amplitude. (C) 1998 Amer ican Vacuum Society. [S0734-211X(98)04702-7].