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Abstract: Surface topography and deuterium retention in tungsten have been examined after exposure to a low-energy (38eV/D), high-flux (1022 D/m2s) deuterium plasma at ion fluences of 1026 and 1027 D/m2 and various temperatures. The methods used were scanning electron microscopy equipped with focused ion beam, thermal desorption spectroscopy, and the D(3He,p)4He nuclear reaction at 3He energies varied from 0.69 to 4.0MeV. During exposure to the D plasma, blisters with various shapes and sizes depending on the exposure temperature are formed on the W surface. At the temperatures above 700K no blisters appear. The deuterium retention increases with the exposure temperature, reaching its maximum value of about 1022 D/m2 at 480–530K, and then decreases to about 1019 D/m2 at 800K. [Copyright &y& Elsevier]

Abstract: The surface topography and optical properties of recrystallized tungsten exposed to a low-energy (38eV/D), high flux (1022 D/m2 s) deuterium plasma with an ion fluence of 1026 D/m2 at various temperatures was investigated. It was found that the surface morphology weakly depends on the exposure temperature in the range 320–695K with the exception of the narrow temperature region around 535K, where large changes to all optical characteristics occurs. After plasma exposure at this temperature, the surface topography of the W sample is characterized by active blistering as has already been indicated in previous publications. The reflectance found in direct measurements at normal incidence drops in the wavelength interval 220–650nm, whereas the estimations of reflectance using the ellipsometry data demonstrate some increase. [Copyright &y& Elsevier]

Abstract: Surface and sub-surface morphology and deuterium retention in polycrystalline tungsten, undamaged and pre-damaged with 5.5MeV W2+ ions to damage levels of 0.04, 0.4, and 1.2dpa, with and without subsequent annealing at 1200K for 2h, have been examined after irradiation with low-energy deuterium ions up to a fluence of 1×1026 D/m2 at various temperatures. The morphology changes were investigated by scanning electron microscopy in combination with focused ion beam surface cutting. The different hydrogen binding states were investigated by thermal desorption spectroscopy, and the depth profile of the implanted D was measured by ion beam nuclear reaction analysis. The dependence of the D retention on the damage level and the implanted fluence was studied, and the results show saturation for 0.4dpa independent of the deuterium implantation fluence. Additionally, it was observed that self-implantation introduces high temperature traps which can almost completely be removed by annealing at 1200K. [Copyright &y& Elsevier]

Abstract: Samples of polycrystalline ITER-grade W and recrystallized W were irradiated at room temperature with 20MeV W ions to displacement damage up to 0.5dpa. The damaged W samples were then exposed to (i) D neutrals at 403–573K and (ii) D2 gas at 673–1073K and pressures of 1.2 and 100kPa. Trapping of deuterium in the damage zone was examined by the D(3He, p)4He nuclear reaction with 3He energies between 0.69 and 4.0MeV allowing determination of the D concentration up to a depth of 6μm. It has been found that generation of the W-ion-induced displacement damage leads to accumulation of deuterium in the damage zone up to concentration depending on the exposure temperature and, at temperatures ⩾673K, on the D2 gas pressure. Thermal desorption spectra allowed a conclusion that deuterium is mainly accumulated in the form of D atoms bound to inner walls of vacancy clusters. [Copyright &y& Elsevier]

Abstract: Deuterium retention in porous vacuum plasma-sprayed tungsten coating has been examined after exposure to low-energy, high-flux (1022 D/m2 s) pure D and helium-seeded D plasmas to ion fluences in the range from 1026 to 1027 D/m2 at various temperatures. The methods used were thermal desorption spectroscopy and the D(3He,p)4He nuclear reaction, allowing determination of the D concentration at depths up to 7μm. Under exposure to pure D plasma (76eV ) at 340–560K, the D concentration reaches 0.1–0.2at.% at depths of several micrometers, while at temperatures above 700K the D concentration is below 10−2 at.% and deuterium is retained over the whole thickness of the coating. Seeding of 76eV He+ into the D plasma reduces the D retention at temperatures of 400–600K. However, at temperatures above 700K, the D retention becomes comparable to that for pure D plasma exposure. [Copyright &y& Elsevier]

Abstract: Hydrogen isotope exchange in re-crystallized polycrystalline tungsten was investigated at 320 and 450K. In a first step the tungsten samples were loaded with deuterium to a fluence of 1024 D/m2 from a low-temperature plasma at 200eV/D particle energy. In a second step, H was implanted at the same particle energy and similar target temperature with a mass-separated ion beam at different ion fluences ranging from 2×1020 to 7.5×1023 H/m2. The analytic methods used were nuclear reaction analysis with D(3He,p)α reaction and elastic recoil detection analysis with 4He. In order to determine the D concentration at depths of up to 7.4μm the 3He energy was varied from 0.5 to 4.5MeV. It was found that already at an H fluence of 2×1020 H/m2, i.e. at 1/5000 of the initial D fluence, about 30% of the retained D was released. Depth profiling of D without and with subsequent H implantation shows strong replacement close to the surface at 320K, but extending to all analyzable depths at 450K especially at high fluences, leading to higher release efficiency. The reverse sequence of hydrogen isotopes allowed the analysis of the replacing isotope and showed that the release of D is balanced by the uptake of H. It also shows that hydrogen does not diffuse through a region of filled traps into a region were unfilled traps can be encounter but transport is rather a dynamic process of trapping and de-trapping even at 320K. Initial D retention in H loaded W is an order of magnitude higher than in pristine W, indicating that every H-containing trap is a potential trap for D. In consequence, hydrogen isotope exchange is not a viable method to significantly enhance the operation time before the tritium inventory limit is reached but should be considered an option to reduce the tritium inventory in ITER before major interventions at the end of an operation period. [Copyright &y& Elsevier]

Abstract: Deuterium retention in single-crystal tungsten was measured by thermal desorption spectroscopy as a function of D+ energy, fluence and specimen temperature. At 300K, D retention increased significantly with increasing ion energy but at 500K the energy dependence was weak. For both 300 and 500K implantations, the retention was significantly lower for 10eV/D+ than for 500eV/D+ over the fluence range ∼1022–1024 D/m2. Depth profiles in D-implanted SCW show D retention at 300K extending beyond 7μm while at 500K retention concentration is detectable at the surface <60nm. By comparison, D retention of 10eV/D+ at both 300 and 500K is detectable in the very near surface. Similar TDS release peaks for both 10 and 500eV/D+ indicate that trapping mechanisms are independent of incident ion energy, and the reduced D retention is likely to be due to the shallower trapping depth. [Copyright &y& Elsevier]

Abstract: Retention of D in neutron-irradiated W and desorption were examined after plasma exposure at 773K. Deuterium was accumulated at a relatively high concentration up to a large depth of 50–100μm due to the trapping effects of defects uniformly induced in the bulk. A significant D release in a vacuum continued to temperatures⩾1173K because of the small effective diffusion coefficient and the long diffusion distance. Exposure of ion-irradiated W to D2 gas showed a clear correlation between concentrations of trapped and solute D as determined by the trapping–detrapping equilibrium. These observations indicated that the accumulation of tritium in high concentrations is possible even at high temperatures if the concentration of solute tritium is high, and baking at moderate temperatures is ineffective for removal of tritium deeply penetrating into the bulk. Nevertheless, clear enhancement of D release was observed under the presence of solute H. [Copyright &y& Elsevier]