Selective Excitation of Symmetric Modes in Gyrotrons with Azimuthally-Asymmetric Cavities

An electrodynamic method based on azimuthally asymmetric cavities is proposed to provide selective excitation of symmetric TE waves in fundamental-harmonic gyrotrons. The presence of small azimuthal inhomogeneities in a cavity with a "close-to-circular" cross-section does not affect on excitation of the operating TE0,p mode, but increases the starting current of excitation of the parasitic TE2,p mode. This approach can ensure also mechanical adjustment of the frequency of the operating TE0,p mode.