Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam

The use of two-dimensional Bragg resonators of planar geometry, realizing t wo-dimensional (2D) distributed feedback, is considered as a method of prod ucing spatially coherent radiation from a large sheet electron beam. The sp ectrum of eigenmodes is found for a 2D Bragg resonator when the sides of th e resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-do main analysis of the excitation of an open 2D Bragg resonator by a sheet el ectron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. N evertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonat or, a steady-state regime can also be realized if the beam width does not e xceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg r esonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described. [S1063-651X(9 9)04207-5].