Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

Abstract

Neon (Ne) seeding is used to cool the edge plasma by radiation to protect the divertor tungsten (W) target in the Experimental Advanced Superconducting Tokamak (EAST). The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system. It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature. After reaching a maximum around 25 eV, the W sputtering rate starts to decrease, presenting a suppression effect. The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed. The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering. Moreover, ELM suppression is observed when Ne and W impurities enter the core plasma, which could be correlated to the enhanced turbulence transport in the pedestal.