Effects of impurities released from high Z test limiter on plasma performance in TEXTOR

Abstract

To investigate the feasibility of high Z metals as plasma facing materials, a Mo test limiter was inserted into the TEXTOR edge plasma and the Mo content in the core plasma and its flux from the limiter have been observed. In OH plasma the additional radiation due to Mo impurities increased with line averaged density n ̄ e . Beyond n ̄ e of about 3 × 10 19 m −3, the central radiation increased strongly with time and a hollow temperature profile appeared. In contrast, Mo impurity radiation decreased with n ̄ e in NBI (co-injection) plasma and no clear Mo accumulation in the plasma center was observed. However, when the edge plasma was cooled by neon injection in NBI plasma, the Mo concentration in the plasma center substantially increased. The Mo flux from the limiter showed no remarkable change during the OH and NBI density scan or with neon cooling. The possible reasons for the Mo behavior in the core plasma are discussed.