Parametric instabilities in gyro-devices at cyclotron harmonics

Abstract A theory is developed which demonstrates the importance of three-photon processes for parametric instabilities of radiation in gyro-devices when a beam of gyrating electrons can resonate simultaneously with several modes at different cyclotron harmonics. The equations obtained describe both processes: the parametric excitation of parasitic modes at high cyclotron harmonics by the working mode operating at the fundamental resonance as well as the decay instability of the radiation at high cyclotron harmonics with respect to excitation of parasitics at the fundamental resonance. The results presented illustrate the possibility of transition from static stabilization of the decay instability to periodic automodulation and, then, to pulsations of parasitic wave envelopes.