Deuterium retention in bulk tungsten exposed to the outer divertor plasma of ASDEX Upgrade

Abstract

Deuterium (D)-retention and -release behaviour from bulk solid tungsten (W) samples exposed to the outer divertor of ASDEX Upgrade were investigated. In the present plasma loading condition, no remarkable blister formation and no severe cracking/melting were observed on the W sample. D retained at the surface (up to ∼7 μm) was measured by nuclear reaction analysis (NRA) and total D retention was determined by thermal desorption spectroscopy (TDS). By comparison of the NRA and TDS results, it was found that D was dominantly retained in the bulk (up to 90% of retained D was in the bulk beyond the NRA detection range). The amount of D retention in bulk solid W increased almost in proportional to the square root of the incident fluence, which suggests that D diffusion plays a key role in the D accumulation in the bulk.