Mode interaction in gyrotrons

Abstract

The developed non-linear theory of multimode gyrotrons describes such effects as mode competition (i.e. suppression of unexcited modes by the operating one), nonlinear excitation of passive modes by the active one and mode-locking. Mode competition is the dominant effect for modes with close frequencies (relatively to the cyclotron resonance band). In such a system only single-mode oscillations are stable. Non-linear excitation of passive modes whoso frequency is greater than the frequency of the operating mode, is possible due to electrons under the action of the operating mode group in the decelerative phase with respect, to the passive modes. For three (and more) modes with an equidistant spectrum of frequencies mode-lacking takes place when the beam current essentially exceeds the threshold conditions, even though one mode finds itself in the non-linear excitation band. The results obtained permit one to estimate the conditions for stable single-mode oscillation in multimode gyrotrons.