A Novel Complex Cavity for Second-Harmonic Subterahertz Gyrotrons: a Tradeoff Between Engineering Tolerance and Mode Selection

Using a simplified approach, a self-consistent modeling of beam–wave interaction in a complex cavity is performed to evaluate the performance of the complex cavity second-harmonic 0.4-THz gyrotron developed at the University of Fukui. For this gyrotron, the quantitative analysis of an adverse effect of small manufacturing errors of the complex cavity on mode selection, output power, and output mode purity is done. To improve the robustness of gyrotron operation to manufacturing errors, a novel complex cavity formed by coupled smooth-walled and corrugated cylindrical resonators is considered. The novel cavity is a hybrid between conventional cylindrical and standard complex cavities and therefore offers the benefit of a tradeoff between engineering tolerance and mode selection.