Propagation characteristics of a premodulated electron beam

The propagation properties of an electron beam whose energy and current are simultaneously premodulated at the cathode are investigated by computer simulation using the two-dimensional (2-D) particle-in-cell code, MAGIC. The simulation is carried out to investigate the influence of the initial energy modulation and the phase difference between current and energy modulation. With appropriate initial energy modulation, the amplitude of the downstream current modulation can be kept as high as the initial modulation level. Appreciable growth of high harmonic components is also observed as the electron beam debunches. The simulation data are compared with results obtained from a nonlinear theory of the current modulation in an electron beam propagating through a drift tube. It is shown that the simulation data agree remarkably well with the analytical theory.