The design of a 100-GHz CARM oscillator experiment

The design of a 10-20-MW 40-ns cyclotron autoresonance maser (CARM) is presented. The basic components of a CARM are a pulseline accelerator, magnetic-field coils, a novel 600-kV 200-A field-emission electron gun designed for p/sub perpendicular to //p/sub z/=0.6 and Delta p/sub z//p/sub z/<3% and a whispering-gallery mode rippled-wall cavity, designed for a high Q for the desired CARM mode and low Q for competing gyrotron modes. The Naval Research Laboratory CARM operates with a wave group velocity that is less than optimum for autoresonance, but where the cyclotron maser instability is strong. By keeping the interaction region short (less than ten cyclotron orbits), the effect of velocity spread is reduced, and the efficiency can be quite high; computer simulations indicate that the device can operate at efficiencies greater than 20%.<
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