Hydrogen isotopes transport in sputter-deposited tungsten coatings

For a DEMO reactor, surface coatings made of tungsten are necessary to protect the plasma-facing wall made of reduced activation ferritic steels such as F82H. In this study, hydrogen and deuterium transport parameters for sputter-deposited tungsten coatings have been evaluated by the gas-driven permeation technique in the temperature range from 200 °C to 550 °C. The evaluated permeability for sputter-deposited tungsten is comparable with the literature data for bulk polycrystalline tungsten. However, the apparent diffusivity and solubility are different from that of bulk polycrystalline tungsten by several orders of magnitude, which is attributed to the presence of trapping sites resulting from the characteristic microstructure of sputter-deposited tungsten coatings. The trapping effects on hydrogen migration have been discussed.