Correlation of the deuterium retention and defect densities in tungsten

Tungsten is a promising candidate plasma-facing material for future fusion devices. One major advantage of tungsten is its generally low retention for hydrogen isotopes. However, due to the comparatively high diffusivity of hydrogen isotopes in metals, hydrogen isotopes can reach the whole volume of a tungsten plasma-facing component. This may lead to a considerable total amount of hydrogen isotopes retained in the plasma-facing walls. A thorough understanding of hydrogen isotope retention in tungsten is therefore necessary. This presentation will show a broad survey where tungsten samples from the same base material were subjected to different heat treatments in order to achieve different defect densities. The defect densities were then quantified by scanning and transmission electron microscopy. After deuterium plasma exposure under a wide variety of different conditions the deuterium inventory in the samples was determined by nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS). It will be shown that there is a strong correlation of the deuterium retention with the initial dislocation density, whereas the density of grain boundaries appears to play only a minor role. Furthermore, the initial microstructure has a strong impact on the formation of deuterium gas-filled blisters near the irradiated surface.