Microstructures and Deuterium-Retention Behavior of Tungsten Exposed to D+(He and/or Be) Mixture Plasmas

Abstract

ITER-relevant mixed species (D, He, Be) plasma exposure experiments on microstructural changes and their impacts on D retention behavior in W are reviewed. It was observed that seeding of He into pure D plasma resulted in a significant reduction of D retention and suppression of surface blistering. TEM observations and ellipsometric measurements revealed that nano-sized high-density He bubbles were formed and percolated in the near surface region. Based on the experimental results, a mechanism to explain the reduced D retention was proposed, i.e., implanted D atoms can easily diffuse back to the surface through the percolating bubbles and escape from the surface during plasma exposure. Additional Be seeding to D+He mixture plasma suppressed this He seeding effect. Thus, it is considered that Be seeding has a more dominant influence than He seeding on microstructures and D retention in plasma-exposed W.