Plasma-facing components damage and its effects on plasma performance in EAST tokamak

Abstract

Abstract During the tokamak operations, plasma-wall interactions (PWI) can severely damage the plasma-facing components (PFCs), which will lead to degradation of plasma performance due to radiation losses by the impurities released from the damaged PFCs surfaces. The PFCs damage and its effects on the plasma performance are studied experimentally for the EAST tokamak. Substantial dusts were generated from the hot spots at the guard limiter of LHCD antenna and the tungsten (W) melting processes from the W upper divertor, which results in disruption due to high radiation losses. Two methods can be effectively used to recover the plasma discharges after tungsten melting induced disruptions, reducing the auxiliary heating power or moving away the position of strike point from the melting site. Statistics analysis indicate that about 12.0 % and 38.3 % of disruptions were due to severe impurity burst from the strong PWI processes in 2017 and 2018 campaign, respectively. In 2018 campaign, the plasma disruption due to tungsten impurity burst is about 26.3 %, which is much higher than 4.8 % in 2017 campaign. This is due to the higher auxiliary heating power, larger misalignment on W PFCs and the new W guard limiter. The main features on the effects of PFC damage on plasma operation are shown.