Theoretical studies of high power millimeter wave quasi-optical gyro-amplifiers

Summary form only given. The quasi-optical gyro travelling wave amplifier is a novel concept for generating high power, high frequency coherent microwave radiation. For high frequency operation, conventional gyrotron amplifiers operating in low order modes are susceptible to absolute instabilities and have minimal beam clearance. Quasi-optical gyrotron amplifiers can avoid these problems, and also have low ohmic loss and a high quality Gaussian beam output. We present a linear and a non-linear theory of a 95 GHz quasi-optical gyrotron amplifier. The concept employs two sets of mirrors parallel to each other with a small offset so that a Gaussian beam can bounce between mirrors in a serpentine path along the beam line. A gyrotron electron beam propagates through the center of the radiation spot almost perpendicular to the Gaussian beam. Theoretical study shows that as the angle between the beam and the radiation changes from normal to parallel. The gait, mechanism changes between two regimes, namely gain nearly proportional to l/sup 3/ (l is the interaction length) for large angles and gain nearly proportional to l/sup 2/ for small angles. The linear theory of the quasi-optical gyrotron amplifier is derived using Floquet´s theorem, and assuming unperturbed distribution function at each of the periodicity length.