Fast pulse and glow discharge cleaning on the HT-6B tokamak

Abstract

Tokamak discharges with Zeff ≅ 1 have been achieved on the HT-6B tokamak after several days of vacuum cleaning by DC glow discharge (GDC) and fast pulse discharge (FPD). During 140 h of cleaning the total removal of carbon atoms was determined to be 1.7 × 1021 atoms and of oxygen 1.6 ×1021 atoms. In tokamak discharges, the hydrogen recycling coefficient was found to be less than unity. Since oxygen is removed through the pumping out of discharge products of CO, thus, limits the cleaning efficiency on a carbonless surface during GDC. Moreover in High Power Discharge (HPD) there is a strong trapping of H2O in a clean surface (α = 2 × 10−3). This effect can be improved by reducing the power of discharge. Transient analysis of gas components was used to explain cleaning processes and mechanisms under different wall and plasma conditions.