Theory of non-stationary processes in gyrotrons with low Q resonators

A non-stationary theory is developed for gyrotrons with open resonators that have a minimum diffraction Q. The gyrotron is described by a self-consistent set of equations taking into account the dependence of the axial structure of microwave oscillations on the electron beam where electron bunching is defined by the same axial structure. As a result of non-stationary processes constant-amplitude oscillations are established for a moderate value of the beam current. As the beam current grows, automodulation and stochastic oscillations take place; their spectral characteristics are presented. It is shown that in the region of parameters close to optimum for efficiency constant-amplitude oscillations are established in gyrotrons with low-Q resonators.