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 gyroresonance. With the experiment configured as a superradiant amplifier, the effects of the gyroresonance on beam dynamics and the beam-wave interaction have been studied. Measurements indicate a peak power production of 35 MW at 4 mm with an electronic efficiency of 2.5 percent. 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 non-linear effects in the experiment. The results of these calculations are shown to be in good agreement with laboratory measurements.