Effect of emission inhomogeneities on low-frequency oscillations in gyrotron-type electron beams

Plasma heating in large tokamaks is one of the most attractive applications for millimeter wave gyrotrons. Gyrotrons designed and created in Russia for this purpose have megawatt microwave power level in quasi-CW regime (in single pulses with duration t>1s). Their effective operation is impeded by low-frequency (/spl sim/100 MHz) spurious oscillations of electron space charge accumulated in the trap between gun cathode and magnetic mirror. These oscillations often develop after a long-term operation of a gyrotron. Modification of cathode emission characteristics can be one of the most probable causes of this phenomenon. Our paper reports the results of the study of space charge oscillations in gyrotron trap and effect of emission inhomogeneities on their characteristics.