Self-Consistent Modeling of Beam-Wave Interaction in Complex Gyrotron Cavities with Azimuthal Slots

A fast theoretical approach is extended to take into account mode conversion induced by an azimuthal slot in a complex gyrotron cavity excited by a helical electron beam. As an example, a modified complex cavity with intermediate slot for a second-harmonic 0.4-THz gyrotron is considered. For this gyrotron, the influence of the slot on starting current of the operating mode and output mode purity of the complex cavity is investigated. The obtained results are found to be in contrast to what might be expected from the cold-cavity calculations. The reason is related to the effect of the electron beam on formation of the combined operating mode of the complex-cavity gyrotron.