Recent results of the step-tunable 105-140 GHz, 1MW gyrotron development at Forschungszentrum Karisruhe

A multifrequency step-tunable 1MW-gyrotron for controlling plasma instabilities in fusion tokamaks has been designed. It operates in the TE/sub 22.8/ mode at 140 GHz and the TE/sub 17.6/ mode at 105 GHz and 7 other modes in between. In the final stage for long pulse operation, this gyrotron should be equipped with an advanced synthetic diamond Brewster window and an optimized beam forming system. The last design results of the Brewster window and the quasi-optical mode converter are presented.