Study of Plasma Startup on HL-2A Tokamak

For pure Ohmic drive both plasma breakdown and startup on HL-2A are on the low field side where the field null configuration is located, and the intensity of Dα emission confirms the plasma formation area. The current of vertical field coils is an important factor to facilitate plasma breakdown and a certain value is required for prompt plasma formation. The effect of the prefill pressure on plasma breakdown has been studied by scanning the prefill pressure. High and low prefill pressure will cause failure of the discharge and only in an appropriate range of the pressure can obtain a reproducible prompt discharge. A new plasma startup scenario has been introduced for bad wall conditions using early formation of a divertor configuration, the result demonstrates that it can be successful startup even if the plasma facing components have absorbed a lot of impurities.