High-harmonic gyrotrons with irregular microwave systems

A natural way to increase the gyrotron frequency is the use of operation at higher cyclotron harmonics. However, at moderate voltages, the intensity of the electron-wave coupling decreases rapidly with the increasing harmonic number. Due to this fact, the danger of excitation of parasitic close-to-cutoff waves at lower harmonics becomes a serious problem. This is true especially in low-relativistic gyrotrons with low output powers (and, therefore, low operating currents) at least due to two reasons. First, low-harmonic waves possess bigger electron-wave coupling factors. Second, longer operating cavities are required, in general, to excite high-harmonic operating waves. The latter results also in extremely high diffraction Qfactors for the operating near-cutoff waves and, therefore, a great share of ohmic losses. In this work, we describe several schemes of cavities with short irregularities designed to improve operation of lowrelativistic high-harmonic gyrotrons.