The influence of fusion-relevant D2-0.1He plasma on Be-W mixed-materials

Compositionally homogeneous mixed-material layers of Be and W, ∼2 μm thick, and of various W contents (spanning 0-100 at.% W), are produced by thermionic vacuum arc deposition. The layers are exposed to low energy (∼50 eV), high ion flux (6-8 × 1022 m−2 s−1) D2-0.1He (10% He) mixed species plasma at 473 K and 1073 K to simulate ITER-like first wall and divertor plasma-material interaction. Surface morphological and compositional analysis is conducted prior and subsequent to plasma exposure. The action of the plasma produces almost complete depletion of Be from the near surface, and this is found regardless of the exposure temperature or initial composition. In the exposure case of 473 K, thermal desorption spectrometry reveals decreased D retention in W rich compositions compared to similar exposure in D2 plasma without He, but no discernable difference is noted in Be rich compositions. At 1073 K, surface enrichment in W, by depletion of the Be, results in He induced W “fuzz” structures for all Be-W compositions explored.