Full high-power modulation on a 170 GHz 1 MW ITER gyrotron with a triode magnetron injection gun

Abstract

A 5 kHz full power modulation experiment is demonstrated on a 170 GHz gyrotron. 5 kHz high-power and beam on/off modulation is achieved by employing a fast short-circuited switch between the anode and the cathode of the triode-type electron gun (single anode switch). Lower heat load on the cavity and the collector compared with continuous-wave operation realizes more than 1 MW oscillation with 1 MW designed gyrotron. The maximum achieved power is 1.16 MW with an electrical efficiency of 48%. In the high-efficiency operation, an unwanted mode oscillation is observed at the start-up phase of each pulse, which is induced by the slow voltage rise time of the anode. For faster rise of the anode voltage, another fast switch is inserted between an anode voltage divider and the anode (double anode switch). In the experiment, successful fast start-up of the anode voltage and minimized unwanted mode generation are observed.