Analysis and optimization of a free-electron laser with an irregular waveguide

Abstract

Using a time-dependent approach, the analysis and optimization of a planar free-electron laser (FEL) amplifier with an axial magnetic field and an irregular waveguide is performed. By applying methods of nonlinear dynamics, a self-consistent reduced model of the FEL is built in a special phase space. This reduced model is the generalization of the Colson-Bonifacio model and takes into account the intricate dynamics of electrons in the pump magnetic field and the intramode scattering in the irregular waveguide. The reduced model and concepts of evolutionary computation are used to find optimal waveguide profiles. The numerical simulation of the original nonsimplified model is performed to check the effectiveness of found optimal profiles. To demonstrate advantages of the proposed FEL configuration, the parameters are chosen to be close to the parameters of the experiment, in which a sheet electron beam with the moderate thickness interacts with the TE01 mode of a rectangular waveguide. The results strongly indicate that one can improve the efficiency by a factor of 5 or 6 if the FEL operates in the magnetoresonance regime and if the irregular waveguide with the optimized profile is used. The FEL efficiency is maximal if the initial beam energy is slightly higher than the energy that corresponds to a transition between negative- and positive-mass regimes so that the transition from the negative-mass to positive-mass regimes occurs during the beam-wave interaction. © 2011 American Physical Society.