Deuterium retention in tungsten pre-damaged by ELM-like high heat flux plasma and sequentially irradiated with deuterium ions

The interaction of deuterium (D) with defects produced by high heat flux (HHF) in tungsten relevant to Edge Localized Mode (ELM-like) transient events in ITER was studied using thermal desorption spectroscopy (TDS). Defects in tungsten were created by 10 pulses of D plasma HHF with a duration of 1 ms each. The energy density of the pulses was 0.7 and 1.7 MJ/m2, which is below and above the tungsten melting threshold, respectively. Using TDS up to 1800K, D was completely removed from HHF damaged samples, and then the remaining defects were decorated by D 3 + ion beam irradiation (667 eV/D+) to a fluence of 1022 D/m2 at a temperature of 470 K with sequential in-situ TDS. Deuterium retention after exposure to a power load of 1.7 MJ/m2 is almost two times higher than in the case of 0.7 MJ/m2. Cracks appear on the tungsten surface under a load of 1.7 MJ/m2, and closed cracks similar to elongated voids are found in deeper layers in the tungsten bulk. The formation of the cracked surface increases the effective surface area for D trapping after ion beam irradiation which leads to significant D retention by a factor of 8 compared to a crack-free surface. It is expected that after ELM-like events, D retention in tungsten will be increased during subsequent steady-state plasma operation.