Theory of Aftercavity Interaction in Gyrotrons

The theory describing the cyclotron resonance interaction between electrons in a spent beam exiting the cavity and traveling electromagnetic waves propagating from the cavity exit into the output part of a gyrotron is developed At present, it is recognized that this parasitic effect may lead to the gyrotron efficiency degradation. First, a simple theory is developed which allows one to analyze the role of aftercavity interaction on gyrotron operation. Then, the simulations done with the use of the self-consistent code MAGY are described. It is shown that when the profile of the output waveguide and the axial distribution of the magnetic field are properly optimized, the effect of aftercavity interaction on the efficiency degradation can be significantly diminished.