High quality operation of a submillimeter wave gyrotron

The outputs (cw operation, f=301 GHz, P/spl sim/20W) of the Gyrotron FU IV are stabilized up to /spl Delta/P/P/spl sim/1% and /spl Delta/f/spl sim/50 kHz by decreasing the fluctuations of the cathode voltage and the anode voltage (/spl Delta/V/sub k/ /spl sim/ 0.6V, /spl Delta/V/sub a/ /spl sim/ 0.2 V), via introducing smoothing circuits consisting of resistors, induction coils and capacitors. Further stabilization of output frequency (/spl Delta/f< 1 kHz, /spl Delta/f/f<3/spl times/10/sup -9/) is attained by applying phase lock control. A carefully designed cavity resonator with nonlinear up-taper has been developed and implemented in Gyrotron FU VA. The measurements of the radiation patterns have confirmed high-purity mode operations. The output radiation of TE/sub 03/ and TE/sub 13/ modes are converted into bi-Gaussian beams by a quasioptical system.