Investigations on the Output System of 300-GHz Gyrotrons

This article presents the comprehensive design studies of the output systems consisting of nonlinear taper (NLT), quasi-optical launcher (QOL), RF window, and matching optics unit (MOU) for gyrotrons operating at 0.5 and 1 MW, respectively, for their potential application in the DEMOnstration tokamak. Two distinct designs of NLTs and QOLs are considered for these gyrotrons, along with the common design of RF window and MOU. The NLTs are optimized using our in-house code gyrotron design suite (GDS-2018). The transmission efficiency achieved for the NLT design of the 0.5 MW gyrotron is 99.48% and the 1 MW gyrotron is 99.53%. The initial design studies of dimpled wall QOLs are carried out using GDS-2018 and optimized through the commercial code launcher optimization tool (LOT). The QOL design for the 0.5 MW gyrotron contains 99.32% Gaussian content factor (GCF) in the output beam, while the QOL design for the 1 MW gyrotron contains 99.58% GCF. A single-disk RF window (made of chemically vapor deposited (CVD) diamond) and MOUs are designed using GDS-2018. The RF window separates the very low-pressure vacuum environment of the gyrotron from the external environment. MOU with two beam-shaping mirrors couples the synthetic Gaussian beam (SGB) to the corrugated waveguide, rectifying the off-axis incidence of the Gaussian beam while reducing beam astigmatism.