EFFECTS OF IMPURITIES RELEASED FROM HIGH-Z TEST LIMITER ON PLASMA PERFORMANCE IN TEXTOR

To investigate the feasibility of high Z metals as plasma facing mater ials, a Mo test limiter was inserted into the TEXTOR edge plasma and t he Mo content in the core plasma and its flux from the limiter have be en observed. In OH plasma the additional radiation due to Mo impuritie s increased with line averaged density (n) over bar(e). Beyond (n) ove r bar(e) of about 3 x 10(19) m(-3), the central radiation increased st rongly with time and a hollow temperature profile appeared. In contras t, Mo impurity radiation decreased with (n) over bar(e) in NBI (co-inj ection) plasma and no clear Mo accumulation in the plasma center was o bserved. However, when the edge plasma was cooled by neon injection in NBI plasma, the Mo concentration in the plasma center substantially i ncreased. The Mo flux from the limiter showed no remarkable change dur ing the OH and NBI density scan or with neon cooling. The possible rea sons for the Mo behavior in the core plasma are discussed.