THE WIGGLER-FREE FREE-ELECTRON LASER - A SINGLE-PARTICLE MODEL

A general single-particle formalism is developed that is applicable for describing thermal and nonlinear effects both in the wiggler-free free-electron laser (WFFEL) and in the cyclotron autoresonance maser (CARM). The general formalism is used in the present paper for a linear analysis. The WFFEL interaction is shown to result from the coupling of the electromagnetic wave to two slow waves: a left-hand polarized wave and a longitudinal wave. This coupling results from the spatial periodicity of the electron flow in the WFFEL which follows the gyrophase coherence of the beam. The comparison between the WFFEL and the CARM is extended to the case where the wave phase velocity is different from the velocity of light in vacuum, and conditions are found for the gain in the WFFEL to be larger. An exact dispersion relation is derived for the WFFEL which employs an electron beam with thermal spread in the transverse velocity.