Commissioning of 42GHz/500kW ECRH system on tokamak SST-1

The 42GHz ECRH system on SST-1 will be used for ECRH assisted pre-ionization, startup and heating experiments at 0.75T (second harmonic) and 1.5T (fundamental harmonic) operation. The Gyrotron delivers 500kW power at 42GHz frequency at -50kV beam voltage, 20A beam current and +19kV anode voltage. The Gyrotron has been tested successfully on dummy load for full parameters. The good gaussian burn pattern at the exit of matching optic unit ensures required mode purity. The circular corrugated waveguide based transmission line consists of matching optic unit, mitre-bend with bi-directional coupler, waveguide switches, polarizer, bellows, DC breaks and an uptaper at the exit of line. Approximately 20 meter long transmission line is used to launch the power from Gyrotron to tokamak. The transmission line has been commissioned on tokamakSST1 using a switch which gives flexibility to operate the Gyrotron either on dummy load or on tokamak. The high power test of transmission line is done and burn pattern at the exit of transmission line near SST1 tokamak ensures good Gaussian beam. A composite launcher consisting of four mirrors (two profiled and two plane), two gate valves and two vacuum barrier windows is used for two ECRH systems (42GHz and 82.6GHz). The distance between plasma centre and plane mirror is 900mm. The mirror size for 42GHz ECRH systems are 170mm × 240mm, the focal length of mirror for 42GHz system is 353mm. The mirror's size for 82.6GHz launcher is 140mm × 200mm and focal length for mirror is 481mm. The beam size at plasma centre for 42GHz launcher is 35mm (1/e beam radius) and for 82.6GHz it is 20mm. The complete launcher system with low power testing has been commissioned on tokamak SST-1.