Hydrogenic retention in tungsten exposed to ITER divertor relevant plasma flux densities

Tungsten targets are exposed to the plasma conditions expected at the strike point of a detached ITER divertor (~1024 D/m2s, Te ~ 2 eV). The surface temperature of the target is ~1600 K at the center and decreased radially to ~1000 K at the edges. A 2-D spatial scan of the W target using nuclear reaction analysis (NRA) shows an asymmetric D retention profile with the lowest retention values at the center of the target and the highest 6 mm off-center. Even in the regions of larger retention, the D concentrations were =5 × 1015 D/cm2 as measured by NRA. Thermal desorption spectroscopy (TDS) is used to measure the global D retention. Very low retention with retained fractions ranging from 10-7 to 10-5 Dretained/Dincident were measured with TDS. Both NRA and TDS results show no clear dependence of retention on incident fluence possibly indicating the absence of plasma-driven trap production in W under these conditions.