Deuterium and helium retention in W with and without He-induced W ‘fuzz’ exposed to pulsed high-temperature deuterium plasma

In the present work, helium (He) was incorporated into tungsten (W) samples by inductively coupled plasma (ICP) source above the threshold of He-induced W ‘fuzz’ formation on W surface. Then, W samples with and without nano-structured W ‘fuzz’ were exposed to pulsed heat loads using deuterium (D) plasma in quasi-stationary high-current plasma gun QSPA-T. The pulse duration was 1 ms and number of pulses was varied from one to thirty to simulate ITER transient events with surface heat load parameters relevant to edge-localized-mode (ELM) impacts. The irradiation was performed below and above the W melting threshold. The D and He retention in each irradiated sample was measured by a method of thermal desorption spectroscopy. We examined the impact of (i) ELMs-like events and (ii) formation of He-induced nano-structured ‘fuzz’ on the D retention in W. We found that the D retention was the highest for samples irradiated by plasma gun above the melting threshold after thirty pulses. Moreover, the D retention after 10 pulses of deuterium plasma gun exposure was higher than that after stationary low-energy plasma exposure at sample temperature of either 600 or 700 K indicating the dominate influence of ELM's-like events on the D retention compared to normal operation regime. The D retention in W samples with the presence of He-induced W ‘fuzz’ was slightly smaller than without that after one pulse of plasma gun exposure with heat load below the W melting temperature. The W ‘fuzz’ was not disappear in this loading conditions, only the length and thickness of nano-structured W fibres were reduced by factors of ∼4 and ∼2, respectively. The He concentration in W with W ‘fuzz’ was decreased by a factor of about 3 after one pulse of plasma gun exposure. The results obtained give possibility to assess the particle retention in divertor areas subjected to high thermal loads at different operation regimes.