Modes selection of the dual-frequency operation terahertz coaxial gyrotron with two electron beams

It is important to keep the frequency of higher-frequency operating mode twice or triple as large as that of the lower-frequency operating mode in the dual-frequency operation terahertz coaxial gyrotron with two electron beams. From the practical point of view, the effects of a possible tilted or shifted inner rod of a coaxial gyrotron cavity on the ohmic loss distribution, the resonant frequency, the diffractive quality factor and the longitudinal field distribution for axially symmetric TE modes with zero caustic radii, asymmetric volume TE modes and whispering-gallery TE modes with nonzero caustic radii should be considered in mode selection and coaxial gyrotron cavity design due to the misalignment error in the terahertz coaxial gyrotron cavity fabrication.