Deuterium (D) retention in Tungsten (W) under plasma heat loads relevant to edge localized modes in ITER was experimentally investigated at the QSPA-T plasma gun facility. Samples were exposed to 1.0 ms D plasma pulses with different heat loads in the range of 0.4−3.7 MJm−2 (heat flux factor P√t = 13.3−123 MJm−2s−0.5). A significant D retention was observed already after one pulse. Moreover, the D retention grew up continuously with increasing the power load, although the surface was melted at highest loads (above 1.4 MJ m−2). The D retention was higher than that in the case of stationary plasma irradiation at 600–700 K, indicating possible significant contribution of ELM’s-like events to the total D retention. All stages of the experiments (irradiation, storage time and TDS) have been simulated using the TMAP 7 code.

Modification of the surface layer and deuterium accumulation in tungsten targets under plasma irradiation in a quasi-stationary plasma accelerator with an intrinsic magnetic field QSPA-T, which reproduces the conditions (plasma thermal load of 0.2-5 MJ/m 2 , pulse duration of 0.1-1.2 ms) typical of ELM events in ITER, are studied. Using a scanning electron microscope, structure modifications at the surface and in the bulk after deuterium plasma irradiation are analyzed. The observed changes in the near-surface layer are compared with the calculated data on the change in the internal structure of tungsten under intense thermal action obtained as a result of the numerical solution of the heat conduction problem. The total deuterium retention in the samples was measured using thermal desorption spectroscopy, and it was in the range of (3-4) × 1016 particles/cm 2 for the samples melted during plasma exposure. These numbers exceed by an order of magnitude the values obtained for samples without traces of melting.

The trapping of helium in tungsten irradiated with He+ ions with an energy of 3 keV and fluence of 1019–1022 He/m2 at room temperature was studied by thermal desorption spectroscopy and scanning electron microscopy. Both as-prepared and recrystallized (at 2000 K for 30 min prior to irradiation) tungsten foils with a thickness of 50 μm were used. It was found that the initial structure of tungsten affects both the dynamics of helium accumulation and the size of defects formed in the process of irradiation and subsequent heating. At low irradiation fluences, helium desorption proceeds primarily at 2000–2500 K in recrystallized tungsten and at 1100–1900 K in as-prepared tungsten samples. At high fluences (higher than 1021 He/m2), a considerable amount of helium is released at low temperatures (starting from 400 K), but a significant fraction of it remains in the samples even after heating to maximum temperatures. Analysis of cross-section of the samples performed after thermal desorption revealed pores 10–75 nm in diameter. The largest pores were formed in the samples that were recrystallized prior to irradiation.

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 similar to 4 and similar to 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. (C) 2018 Elsevier B.V. All rights reserved.

The deuterium release from reduced activation Eurofer steel samples is investigated by measuring the re-emission directly during ion irradiation and via thermal desorption spectroscopy without contact with air. A part of the experiments are carried out using a sample previously subjected to high-power pulsed thermal action using the QSPA-T setup, Troitsk Institute of Innovative and Thermonuclear Research. Subsequent irradiation is performed using a 5-keV D 3 + ion beam to a fluence of up to 1021 m–2 at room temperature. In all cases, a major part of the implanted deuterium is released from the sample already at the irradiation stage. A significant part of the deuterium also desorbs in the interval between irradiation and spectroscopic measurements. Deuterium re-emission from damaged samples reaches a maximum value more slowly than that from undamaged ones, and deuterium release during holding is more intense. This can be explained by the structure of the damages caused by the heat flux: the hydrogen-trap concentration grows in the material, and the surface area participating in desorption increases.