a Metal-Grating Free-Electron Maser

The development of a class of mildly relativistic electron beam driven open resonator oscillators is summarized. The devices are based on a grating loaded parallel plate waveguide structure which, together with terminating cylindrical mirrors or a cylindrical mirror/horn antenna combination, form an open resonator. Electron beam voltages between 30 and 150 kV and currents between 1 and 20 A have been used to achieve 20-30 kW output levels in the 7 mm wavelength range and approximaty 10 kW in the 4 mm region. Theory describing the operating characteristics of these devices; small signal gain, tuning range, and saturation levels has been developed. We will present a detailed summary of the theory and the results of an extensive series of measurements.