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

A 42-GHz electron cyclotron resonance heating (ECRH) system will be used to carry out preionization and start-up experiments on tokamaks SST-1 and Aditya. The system would give reliable start-up in the SST-1 tokamak at 1.5-T operating toroidal magnetic field. The fundamental O-mode will be launched from the low-field side of the tokamak. The same system will be used in tokamak Aditya to carry out second-harmonic ECRH-assisted breakdown experiments at 0.75-T operation. The gyrotron capable of delivering 500-kW power will be installed such that it will deliver power to both the tokamaks without dismantling any component. An approximately 50-m-long transmission line will be used to transmit power from the gyrotron to each tokamak. 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 the fundamental and second harmonics. 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 the second harmonic. In the SST-1 tokamak, there are two options to launch ECRH power: 1) from the radial port and 2) from the top port. From the radial port, a conventional ECRH launcher consisting of two mirrors (one focusing and one plane) would be used; however, from the top port, one mirror would be used along with a corrugated waveguide. The VME-based data acquisition and control system will be used for the 42-GHz ECRH system. The slow interlocks would be activated through software while the fast interlocks would be hardwired to remove the high voltage within 10 . This paper discusses the physics and technical aspect of the 42-GHz ECRH system and preliminary design of launchers for SST-1 and Aditya.