Axisymmetric multistage cavity resonators

We study theoretically multistage cavity resonators as well as the gyrotrons manufactured on their basis. Coupled cavities with mode conversion and echelette cavities are particular cases of such devices. The possibilities of reducing the diffraction Q-factor of the operating mode of a cavity, with the preservation of its selective properties and significant increase in the gyrotron radiation power, and provision of high efficiency and acceptable heat ohmic load of the cavity at the first harmonic of the gyrofrequency are considered. Achievable parameters of the gyrotrons at the second and third harmonics with typical electron guns and cryomagnetic systems are analyzed.