Invited paper. Powerful millimetre-wave gyrotrons

Abstract

The gyrotron is a promising powerful source of millimetre and submillimetre waves. This paper is devoted to the State-of-thc-art of theoretical and experimental gyroton investigations. The theory of the gyrotron permits one to determine self-excitation conditions and optimum values of gyrotron parameters which provide high efficiency, taking into account electron velocity spread and an unfixed axial structure of the RF field in open cavities with low Q. The theory of intense helical electron beams formed by gyrotron electron guns of the magnetron type has been developed. The methods of analysis and synthesis of electron-optical systems permit one to form, taking into account the beam space charge, intense electron beams with a small velocity spread. The methods of clectrodynamic selection of modes consist in cavity profiling for axial mode selection, application of azimuthal slots for azimuthal mode selection and use of coaxial cavities for radial mode selection. Experiments on gyrotrons with coxial and two mirror open cavities, as well as on gyrotrons operating at the second harmonic have been carried out. A gyroton with output of 200 KW at the wavelength 3⋅5 mm operating under pulse duration up to U-1 s has been developed for experiments on electron-cyclotron plasma heating. In conclusion the possibilities of microwave energy increase in gyrotrons have been considered.