Fast control of depressed collector gyrotrons

High power gyrotrons for plasma heating utilize a single stage depressed collector potential in order to reduce the collector load and to recover a large fraction of the remaining energy of the spent electron beam. This operation mode requires two high voltage power supplies which usually possess different characteristics. In the case of RF modulation, both power supplies must nevertheless operate synchronously and with a certain timing. In addition, the power must be shut down instantaneously when the collector load exceeds a certain limit, e.g. due to a dropout of the RF output. This paper discusses the realization of the above functionality in a single FPGA and describes the implementation at the W7-X stellarator.