Nonlinear Analysis of a Grating Free-Electron Laser
NAVAL RESEARCH LAB WASHINGTON DC
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A two-dimensional nonlinear model of a grating free-electron laser is formulated that includes the effects of self-field forces, finite beam emittance, energy spread and gyromotion of electrons in a guide magnetic field. The start-oscillation current and energy spread requirement for operation at either 100 microns or at 10 microns are determined. The designs call for mildly relativistic less than or equal to 12 MV electron beams. The extraction efficiency is determined by numerical simulation. Three different examples are studied in order to elucidate the nonlinear stage of the interaction. We analyze the examples of an infinitely-thin beam, a finite-thickness beam with laminar flow and a finite- thickness beam with full transverse motion. For a thick beam we find the interesting result that the effect of electron gyration about the beam axis is to enhance the extraction efficiency as compared to that for a beam with laminar flow. The numerical results for the extraction efficiency are found to be in close agreement with analytical estimates based on a model in which the electrons are trapped in the slow-wave associated with the grating structure.
- Lasers and Masers