Three-dimensional analysis of self-field effects in free-electron lasers

Abstract

Summary form only given. A model of the self-fields associated with the charge density and current of the electron beam is incorporated into three-dimensional nonlinear formulations of the interaction in free-electron lasers for both planar and helical wiggler configurations. The model assumes the existence of a cylindrically symmetric electron beam with a flat-top density profile and a uniform axial velocity, and the self-electric and self-magnetic fields are determined from Poisson's equation and Ampere's law. The nonlinear formulations are based on the ARACHNE and WIGGLIN codes which represent slow-time-scale formulations for the evolution of the amplitudes and phases of a multimode superposition of vacuum waveguide modes. The results of the simulations have been compared directly with an experiment at Lawrence Livermore National Laboratory based upon a planar wiggler and experiments at the Massachusetts Institute of Technology and the Naval Research Laboratory which employed helical wigglers. The simulations are in reasonable agreement with the experiments, and indicate that the self-fields tend to reduce saturation efficiencies and enhance beam spreading depending upon the magnitude of external beam focusing.