Enhancement of cavity selectivity in relativistic gyrotrons operated at axisymmetric modes

Mode selection is a key problem from the viewpoint of maintaining the single-mode generation regime in high-power gyrotrons operated at axisymmetric modes. In this paper, we propose several electrodynamic methods of mode selection, which allow separating the electrically strong axisymmetric higher-order mode from spurious modes. The possibility of suppressing the nearest spurious modes efficiently, by using either wide slits in the cavity, or azimuthal corrugations on the walls of the tapered cavity, is shown. A method of mode selection at cyclotron frequency harmonics is proposed. The results of studying two types of gyrotron cavities experimentally at a low power level confirmed their high selective properties. The cavities were calculated aiming at using them as the basis for creation of a gyrotron operated at the TE0.3 mode and producing a power of 5–10 MW in 1 μs long pulses at a wavelength of 1 cm. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 10, pp. 837–849, October 2008.