Mode Competition in the Gyro-Peniotron Oscillator

The gyro-peniotron oscillator holds great promise for generating microwave radiation with efficiencies far greater than those obtainable through the electron cyclotron-maser interaction. Theoretical modeling has shown that extremely high efficiencies (>90 percent) may be possible for the gyro-peniotron. Stable operation of the gyro-peniotron oscillator requires, however, that mode competition from the electron cyclotron-maser interaction be avoided. This mode competition can be quite serious since the cyclotron-maser start-oscillation currents are generally much smaller than those from the peniotron interaction. We examine here the start-oscillation conditions for the peniotron and the electron cyclotron-maser interactions from linear theory. Both large-orbit axis-encircling and small-orbit off-axis electron beams are investigated. Conditions under which a gyro-peniotron oscillator may be operable are presented, including the important limitations on the spread of the beam guiding center. The results of this study indicate that mode competition for the gyro-peniotron can be easily avoided for TE211 and other low-order azimuthal modes when a large-orbit axis-encircling beam is used. Serious mode competition and gyro-peniotron suppression is found for small-orbit off-axis beams.