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Commissioning of the 28-GHz Electron Cyclotron Resonance Heating System on ADITYA Tokamak

Abstract An electron cyclotron resonance heating system is commissioned on Aditya tokamak to carry out pre-ionization, start-up, and heating experiments. A high-power microwave source (gyrotron), capable of delivering 200-kW cw power at 28 ± 0.1 GHz, is commissioned successfully using a water dummy load for pulsed operation. The output mode of the gyrotron is TE02. The output power of the gyrotron is measured using microwave probe couplers, a spectrum analyzer, and calorimetric techniques. A hardwired interlock operates a rail-gap-based crowbar system in less than 10 μs under fault condition and protects the gyrotron. The rail-gap crowbar operation has been qualified with the high-voltage power supply by performing a 10-J wire-burn test prior to energizing the gyrotron. A transmission line consisting of matching optic units, dc break, polarizer, miter bend, and corrugated waveguides terminates with a boron nitride window. The total attenuation in the line is measured to be less than 1.1 dB. Based on quasi-optical theory, a beam launcher is designed, fabricated, and tested for ultrahigh-vacuum compatibility prior to commissioning on tokamak. After successful operation of the gyrotron on the dummy load, the gyrotron output has been coupled to the ADITYA tokamak, and successful breakdown of neutral gas is observed without assistance from an ohmic transformer.