ECRH assisted helium plasma discharge in SST-1

The 42GHz ECRH (Electron Cyclotron Resonance Heating) system is an essential system for plasma start-up and current ramp-up in SST-1 tokamak. This system is suitable to operate the tokamak at 1.5T operating toroidal magnetic field. The fundamental O-mode is launched from the radial port (low field side) of tokamak. This system has been extensively used in SST-1 tokamak to carry out plasma start-up at fundamental and second harmonic. Till now the plasma start-up has been achieved with hydrogen plasma. However, plasma discharges with helium in SST-1 is carried out first time. The tokamak is operated at 1.5T operating toroidal magnetic field. The fill pressure of helium gas is maintained around 1 x 10^-5 mbar. The ECH power in O-mode is launched before the loop voltage. The ECH power is varied from 100 kW to 150 kW and pulse duration is also varied from 50 ms to 150 ms. The loop voltage is maintained around 4V, successful ECH assisted plasma discharge is achieved with helium gas. In various plasma discharges, around 50 kA plasma current is achieved with plasma shot duration varying from 100 ms to 200 ms. As the plasma discharges with helium gas is tried first time in SST-1, the successful consistent helium plasma discharges are achieved with ECRH assisted pre-ionization. The paper discusses about the role of ECRH in SST-1 plasma and explains the breakdown and start-up of helium gas with ECRH. (author)