Influence of trapped backscattered electrons on parasitic oscillations in gyrotrons

Trajectories of backscattered electrons have been studied, in respect of those electrons that transit through the rf cavity toward the MIG gun. They get reflected before they reach the cathode. On the return journey they can get reflected again from the collector region and thus get trapped. The transit back and forth through the rf cavity is a potential source of parasitic oscillations. An initial estimate of the oscillation frequency is in the range of tens of megahertz. Trapping can also take place between the cathode and the rf cavity, in which case the transit time will be less and the frequency higher than for the case of reflection back from the collector region.