5kHz modulation of 170 GHz gyrotron with anode-cathode short-circuited switch

A high speed modulation method is proposed for a triode gyrotron. An anode voltage modulation for on/off output RF power modulation with cathode-anode short-circuited switch is demonstrated with full beam current suppression by shorting the cathode and the anode electrodes by the switch. 5kHz modulation is successfully achieved with the power of 1.16 MW and 40 sec. The electron beam from the cathode is completely suppressed during the turn off phase. This is the first 5 kHz modulation experiments with full current suppression for high power (more than 1 MW) with long pulse. On the start up phase of the each pulse, the TE30,8 mode is generated instead of the TE31,8 of the main mode. This was caused by the slight drift of the anode-cathode voltage or/and electron beam current during the flat top of the turn on phase. In order to improve it, a new circuit configuration and a new anode power supply is proposed.