Evolution of longitudinal modulation in electron beams

Electron beams with periodic longitudinal density modulation may produce terahertz radiation in linear accelerators. In this study, simulations are used to understand how the density and energy modulations of an electron bunch evolve as the beam is transported through a linac system. It is instructive to simulate beams that have only density modulation and beams that have only energy modulation. The former is useful for learning how to keep the desired density modulation for beams intended to create terahertz radiation, the latter for learning how to suppress unwanted energy modulation, which may have originated as density modulation. The simulations in this study are performed using PARMELA in conujnction with other software codes. The study investigates energy ranges that are higher than those studied in the authors' previous work. Parameters in the simulations are chosen to correspond to existing accelerator systems so that the results may be used to support an experimental study.