High quality operation of a submillimeter wave gyrotron

The outputs (cw operation, f=301 GHz, P∼20W) of the Gyrotron FU IV are stabilized up to ΔP/P∼1% and Δf∼50 kHz by decreasing the fluctuations of the cathode voltage and the anode voltage (ΔV_k ∼ 0.6V, ΔV_a ∼ 0.2 V), via introducing smoothing circuits consisting of resistors, induction coils and capacitors. Further stabilization of output frequency (Δf< 1 kHz, Δf/f<3×10^-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 TE₀₃ and TE₁₃ modes are converted into bi-Gaussian beams by a quasioptical system.