“…That article also claims that on the rough, mechanically polished sample the retention of D is reduced. A recent study by Zayachuk et al [8] reports suppression of blistering on recrystallized W exposed to high-flux plasma already due to minor imperfections caused by mechanical polishing. An orientation-dependence became obvious particularly under conditions where the suppression occurred only on some of the grains.…”
Up to now, blister formation on rough or technical tungsten surfaces exposed to hydrogen isotope plasma was believed to be completely suppressed. The few dedicated experiments on this issue that can be found in literature appear to support that claim. Using a novel technique of three-dimensional difference imaging of tungsten surfaces, we now demonstrate that roughness introduced by chemical etching, i.e., without the associated mechanical deformation layer introduced by grinding, only moderately reduces blistering. A technical surface with comparable roughness produced by precision grinding (R a 1.6 µm) led to a strong reduction in blister size and density, but blisters were found nevertheless. In this article we give a detailed description of the investigated rough W surfaces and present a statistical evaluation of blistering on these surfaces after exposure to a low-temperature deuterium plasma.
“…That article also claims that on the rough, mechanically polished sample the retention of D is reduced. A recent study by Zayachuk et al [8] reports suppression of blistering on recrystallized W exposed to high-flux plasma already due to minor imperfections caused by mechanical polishing. An orientation-dependence became obvious particularly under conditions where the suppression occurred only on some of the grains.…”
Up to now, blister formation on rough or technical tungsten surfaces exposed to hydrogen isotope plasma was believed to be completely suppressed. The few dedicated experiments on this issue that can be found in literature appear to support that claim. Using a novel technique of three-dimensional difference imaging of tungsten surfaces, we now demonstrate that roughness introduced by chemical etching, i.e., without the associated mechanical deformation layer introduced by grinding, only moderately reduces blistering. A technical surface with comparable roughness produced by precision grinding (R a 1.6 µm) led to a strong reduction in blister size and density, but blisters were found nevertheless. In this article we give a detailed description of the investigated rough W surfaces and present a statistical evaluation of blistering on these surfaces after exposure to a low-temperature deuterium plasma.
“…This suggests that with increasing fluence the deuterium concentration, blistering and thermal diffusivity reduction saturate. The fluence at which this saturation occurs may vary and depends on a number of factors such as the crystallography, heat treatment and surface polishing [7,8]. Since we observe little change in thermal diffusivity when fluence is increased by more than one order of magnitude, it is likely that our fluences are within this saturation regime.…”
Graphical AbstractAbstract Using transient grating spectroscopy, we measure thermal diffusivity and surface acoustic wave speed in tungsten exposed to different fluences of deuterium plasma. Scanning electron microscopy (SEM) shows the formation of surface blisters that have similar morphology for all fluences considered. A significant reduction in thermal diffusivity and surface acoustic wave speed occurs as a result of plasma exposure. A saturation of the thermal diffusivity reduction with fluence is seen. Deuterium ion flux density appears to play a more important role in thermal diffusivity reduction than exposure time. These observations have important implications for plasma facing components in future fusion reactors.
“…A detailed discussion of the responsible mechanisms is provided elsewhere. [31][32][33] Our previous work showed a significant degradation of thermal diffusivity and reduction in SAW speed in the exposed area. 16 Using the mapping capability of the TGS setup, we have measured a map of thermal diffusivity and SAW speed that spans the entire sample [Figs.…”
We present new developments of the laser-induced transient grating spectroscopy (TGS) technique that enable the measurement of large area 2D maps of thermal diffusivity and surface acoustic wave speed. Additional capabilities include targeted measurements and the ability to accommodate samples with increased surface roughness. These new capabilities are demonstrated by recording large TGS maps of deuterium implanted tungsten, linear friction welded aerospace alloys, and high entropy alloys with a range of grain sizes. The results illustrate the ability to view the grain microstructure in elastically anisotropic samples and to detect anomalies in samples, for example, due to irradiation and previous measurements. They also point to the possibility of using TGS to quantify grain size at the surface of polycrystalline materials.
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