Fundamental O-mode ECRH assisted Low-loop voltage plasma start-up in tokamak ADITYA-U

The EC assisted low-loop voltage plasma start-up experiments have been carried in Tokamak Aditya-U. The 42GHz ECRH system is used for off-axis breakdown in tokamak, which is operated at a toroidal magnetic field of ~ 1.2T to 1.4T. The EC power in fundamental O-mode is launched from low field side of the tokamak. The EC power and duration for breakdown are varied from 75kW to 150kW and from 50 ms to 100 ms respectively. The ECRH power is launched around 25ms before the start of the loop voltage and successful plasma start-up is achieved with 40% reduction in the peak loop voltage. In ADITYA-U, the gas breakdown and successful plasma start-up is normally achieved at peak loop-voltage of ~20V (Electric field ~ 4.5V/m). In these EC-assisted lowloop voltage plasma start-up experiments, the peak loop voltage is reduced to ~40 % (~12V) by reducing the resistance values in the ohmic circuit and successful EC-assisted plasma discharges with plasma current ~115kA and discharge duration of ~250ms has been achieved at ~12V loop-voltage.