Generation of hundred joules pulses at 4-mm wavelength by FEM with sheet electron beam

Results of experimental investigations of a powerful millimeter-band free-electron maser (FEM) oscillator driven by a sheet electron beam are presented. A Bragg resonator of planar geometry was used for mode selection. Microsecond pulses of radiation at a wavelength of 4 mm with a peak power of 200 MW were generated. This corresponds to a record energy per pulse of 200 J. Future experiments designed to increase the energy of the millimeter-wave pulse into the tens of kilojoules range are discussed.