Complex cavity gyrotron

A complex gravity gyrotron designed for stable operation at high order modes is described. The device comprises circuitry for generating an annular electron beam, a coupled cavity disposed coaxially with the electron beam and having a first and second adjacent coaxial sections with the dimensions of these coaxial sections adjusted so that different modes with the same azimuthal eigen number but different radial eigen numbers are simultaneously resonant at approximately the same frequency in the two sections, and circuit for generating an axial magnetic field within the cavity. Few, if any, combinations of modes other than the combination chosen will simultaneously resonate in the cavity thereby effecting higher order mode suppression. The present design has a low susceptibility to beam velocity spread and its effective for any combination of modes with identical azimuthal eigen numbers.