Mode Discrimination by Lossy Dielectric Rods in Cavities of Second-Harmonic Gyrotrons

The influence of a coaxial dielectric rod on eigenvalues, ohmic losses, transverse field structure, and beam-wave coupling coefficients is investigated for TE modes of a gyrotron cavity. It is shown that such dielectric insert, when made from a moderate-loss material, results in strong attenuation of all cavity modes, with the exception of those having caustic radii much larger than the insert radius. It is proposed to employ such dielectric loading for selective suppression of competing modes in cavities of second-harmonic gyrotrons. The high performance and flexibility of the proposed method of mode discrimination are demonstrated for the example of the cavity of the high-power 0.39-GHz second-harmonic gyrotron developed at the University of Fukui. In addition, some fascinating capabilities enabled by coaxial inserts made of ultralow-loss dielectrics are discussed.

Automated summary

The study investigates the influence of a coaxial dielectric rod on various aspects of a gyrotron cavity. It demonstrates that using a moderate-loss material for the dielectric insert can strongly attenuate cavity modes, except for those with much larger caustic radii. The proposed method for mode discrimination shows high performance and flexibility in cavity applications.