Design and operation of a collective millimeter-wave free-electron laser

A new free-electron laser experiment has been designed at NRL to operate at millimeter wavelengths using a collective beam-wave interaction. Critical features of the experiment include an apertured diode which provides a low emittance electron beam, a wiggler magnet with adiabatic entrance and exit, and an operational domain centered around the wiggler-guide field gyroresonnance. With the experiment configured as a superradiant amplifier, the effects of the gyroresonnance on beam dynamics and the beamwave interaction have been studied. Measurements indicate a peak power production of 35 MW at 4 mm with an electronic efficiency of 2.5%. Aspects of the experimental design are discussed, and the results of a parametric study of the power dependence on the fields are presented. Detailed calculations (both analytic and computational) have been performed to analyze the linear and nonlinear effects in the experiment. The results of these calculations are shown to be in good agreement with laboratory measurements.