Design of a high order volume mode cavity for a l MW/140GHz gyrotron

A high-power cylindrical cavity gyrotron operating at 140 GHz is studied. The possible working modes TE22,4, TE22,5, and TE22,6,are compared. The output power envisaged is 1 MW. The influence of the space charge effect of the electron beam and the RF losses in the resonator are discussed. Results of numerical calculations of the interaction of the electron beam and the RF wave are presented. The problem of single-mode excitation is addressed in mode competition calculations. Stability regions of the working modes are shown for some interesting parameter ranges. From these plots an optimized variation of the parameters during start-up of the gyrotron can be deduced in order to ensure single-mode operation. On the basis of kinetic theory the influence of misalignment of the electron beam and resonator axis (eccentricity) on the starting currents and frequency shifts of the operating and parasitic modes is studies for several values of eccentricity.