A study of parametric instability in a harmonic gyrotron: designs of third harmonic gyrotrons at 94 GHz and 210 GHz

Summary form only given, as follows. Mode competition can present a major hurdle in achieving stable, efficient operation of a gyrotron at the cyclotron harmonics. A type of mode interaction in which, three modes at different cyclotron harmonics are parametrically coupled together is analyzed here. This coupling can lead to parametric excitation or suppression of a mode, cyclic mode hopping, or the coexistence of three modes. Simulation results are presented for the parametric instability involving modes at the fundamental, second harmonic and third harmonic of the cyclotron frequency. It is shown that the parametric excitation can lead to stable, efficient operation of a high power gyrotron at the third harmonic. Based on this phenomenon, two practical designs are presented here for third harmonic operation at 94 GHz and 210 GHz.