Analysis of oscillation characteristics for the raman‐type free‐electron laser utilizing a two‐dimensional periodic magnetic field for the pumping source

Abstract

A two‐dimensional model of the Raman‐type free‐electron laser is considered. It is composed of a relativistic electron beam drifting in a parallel plate waveguide, immersed in a magnetostatic pump field with periodic variation in the direction of flow of the electron beam. For the model of the Raman‐type free‐electron laser specified here, a theoretical study on the oscillation characteristics is presented and the following results are obtained. First, the spatial growth rate of the scattered wave can be maximized by properly adjusting the ratio of the beamwidth to the separation between conducting plates of the waveguide. The magnetostatic pump field affects the growth rate through its magnitude on the beam surface and its wave number. Second, the growth rate of the scattered wave is enhanced and its frequency is lowered as the wave number of the periodic magnetic field decreases, while the former is reduced and the latter becomes higher as it increases. Third, the generation of higher‐order modes can be suppressed by reducing the wave number of the periodic magnetic field.