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Surface topography and deuterium retention in polycrystalline hot-rolled W and W–5%Re have been examined after exposure to a low-energy (76 eV), high flux (around 10 22 D/m 2 s) deuterium plasma to an ion fluence of 10 26 D/m 2 at various temperatures. The methods used were confocal laser scanning microscopy and the D( 3 He, p) 4 He nuclear reaction at 3 He energies varied from 0.69 to 4.0 MeV. During exposure to the D plasma at temperatures in the range from 348 to 673 K, small blisters of size in the range from about 1 to about 15 μm, depending on the exposure temperature, are formed on the W and W–5%Re surfaces. In the W–5%Re, the deuterium retention demonstrates its maximum at exposure temperature of 463 K, while in the W this maximum is shifted to 523 K. A difference in the temperature dependence of the D retention for the W and W–5%Re is explained, as a rough approximation, by temperature dependences of the ductility of these materials. [ABSTRACT FROM AUTHOR]

Abstract: Surface topography and deuterium retention in polycrystalline ITER-grade tungsten have been examined after exposure to a low-energy (38eV/D), high-flux (1022 D/m2 s) deuterium plasma with ion fluences of 1026 and 1027 D/m2 at 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 at temperatures in the range from 320 to 815K, small blisters of size in the range from 0.2 to 5μm, depending on the exposure temperature and ion fluence, are formed on the W surface. At an ion fluence of 1027 D/m2, the deuterium retention increases with the exposure temperature, reaching its maximum value of about 1022 D/m2 at 500K, and then decreases below 1019 D/m2 at 800K. [Copyright &y& Elsevier]

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: Depth profiles of deuterium trapped in tungsten exposed to a low-energy (≈200eV/D) and high deuterium ion flux (about 1×1021 D/m2 s) in clean (We use the term ‘clean’ in quotation marks having in mind the impossibility to obtain absolutely clean plasma. In our case the conception ‘clean’ D plasma means the plasma without intentionally introduced carbon impurities.) and carbon-seeded D plasmas at an ion fluence of about 2×1024 D/m2 and various temperatures have been measured up to a depth of 7μm using the D(3He,p)4He nuclear reaction at a 3He energy varied from 0.69 to 4.0MeV. The deuterium retention in single-crystalline and polycrystalline W increases with the exposure temperature, reaching its maximum value at about 500K (for ‘clean’ plasma) or about 600K (for carbon-seeded plasma), and then decreases as the temperature grows further. It is assumed that tungsten carbide formed on the W surface under exposure to the carbon-seeded D plasmas serves as a barrier layer for diffusion and prevents the outward transport of deuterium, thus increasing the D retention in the bulk of tungsten. [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: 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]

Abstract: The prediction of hydrogen isotope retention in n-irradiated tungsten (W) is an important topic for edge plasma research as it has significant implications for the operation of ITER and fusion reactors. Direct measurement of tritium retention in n-irradiated tungsten is a difficult task. The self-implantation of W is the most promising approach because it generates dense cascade with large clusters which are typical for n-irradiation and any chemical effects are avoided. Pre-damaged samples were exposed to pure and He-seeded deuterium plasmas on both front (undamaged) and rear (damaged) sides in order to separate deuterium (D) retention in plasma-induced traps and in displacement damage created by fast tungsten ions. Irradiation was done up to a damage level expected from the end-of-life neutron fluence in ITER. The diffusion model with dynamic trap formation during irradiation was validated by comparison with experiments and applied for calculation of hydrogen isotope retention in ITER in the presence of neutron irradiation. [Copyright &y& Elsevier]