Gyrokinetic Analysis of Influence of Electron Beam Eccentricity on Operation of Higher-Order Mode in a Coaxial Cavity Gyrotron

A gyrokinetic analysis is presented to the influence of the electron beam eccentricity on the power and starting current of a coaxial cavity gyrotron, which operates in a higher-order mode TE_{31, 17, 1} with a frequency of 165 GHz. It is found that the starting current becomes larger because of the existence of the electron-beam eccentricity. Especially, the power will be decreased substantially by the electron beam eccentricity, for example, down to 93% of the power without any eccentricity even if the eccentricity is 1% of the outer conductor radius. The acceptable range of the electron beam voltage and operating magnetic field for the establishment of the electromagnetic oscillation is narrowed by the electron-beam eccentricity.