Effect of the azimuthal inhomogeneity of electron emission on gyrotron operation

Gyrotrons are typically driven by electron beams produced by magnetron-type thermionic electron guns operating in the regime of temperature limited em ission. Very often, the current density in such annular electron beams is a zimuthally nonuniform. To describe the effect of this nonuniformity on gyro tron operation, the code MAGY [M. Botton , IEEE Trans. Plasma Sci. 26, 882 (1998)], which is widely used for modeling of slow and fast microwave sourc es, was properly modified. The results of numerical simulations demonstrate the effect of azimuthal inhomogeneity of the emission on the excitation of low- and high-frequency satellites of the operating mode and on the effici ency degradation. The calculations are done for parameters typical for mega watt-class, long-pulse, millimeter-wave gyrotrons, which are currently unde r development for electron cyclotron plasma heating and current drive exper iments in controlled fusion reactors. (C) 2001 American Institute of Physic s.