Electron trajectory and growth rate in two-stream electromagnetically pumped free-electron lasers with ion-channel guiding

Abstract

A theory of the two-stream electromagnetic wave wiggler free-electron lasers (TSEMWFEL) with ion-channel guiding is proposed and investigated. An analysis of the two-stream steady-state electron trajectories is done by solving the equation of motion in the electromagnetic wave wiggler and ion-channel guiding. Numerical calculations show that there are seven groups of trajectories rather than the two groups reported for the conventional free-electron laser (FEL). The dispersion relation is derived by employing linear fluid theory. The characteristics of the dispersion relation are analyzed numerically. The results show that employing two streams rather than a single stream in an FEL with ion-channel guiding gives rise to an enhancement in the growth rate, and using ion-channel guiding instead of an axial magnetic field in a two-stream FEL causes the growth rate to increase. Our numerical study of the normalized maximum growth rate and maximum wavenumber as a function of ion-channel frequency for different trajectories is presented.