42GHz 0.5MW ECRH system for Tokamaks SST-1 and Aditya

A 42GHz ECRH system would be used to carry out pre-ionization and start-up experiments on Tokamaks SST-1 and Aditya. The system would give reliable start-up in SST-1 Tokamak at 1.5T operating toroidal magnetic field. Fundamental O-mode would be launched from low field side of tokamak. The same system would also be used in Tokamak Aditya to carry out second harmonic ECRH assisted breakdown experiments at 0.75T operation. The Gyrotron capable to deliver 500 kW power would be installed such that it will deliver power to both the tokamaks without dismantling any component. It will be achieved by using two waveguide switches in the transmission line. First switch will divert power either to dummy load for Gyrotron testing or to launch power in the tokamaks. The second switch will give the option to transmit power either to tokamak Aditya or SST1. Approximately 50-meter long transmission line will be used to transmit power from Gyrotron to each tokamak. The transmission line consists of a matching optic unit, DC break, mitre-bends, polarizer, 63.5mm ID circular corrugated waveguide and bellows. The total transmission loss in the line is less than 20%, in this case we can launch ~ 400 kW power to carry out reliable ECRH assisted breakdown experiments at fundamental and second harmonic. The launcher design is different for both the tokamaks. In Aditya, due to space restriction, a simple waveguide type launcher is used to launch ECRH power in X-mode at second harmonic. However, in SST-1 tokamak, a conventional ECRH launcher consisting of two mirrors (one focusing and one plane) is used to launch focused beam for breakdown in tokamak. The VME based data acquisition and control (DAC) system would be used for 42GHz ECRH system. The slow interlocks would be activated through software while fast interlocks would be hardwired to remove the high voltage within lOμs. The paper discusses the physics and technical aspect of 42GHz ECRH system and preliminary design of launchers- - for SST-1 and Aditya.