The influence of N on the D retention within W coatings for fusion applications

Plasma facing components (PFC) in a fusion device are subjected to a harsh operating environment involving high heat fluxes and exposure to high fluxes of hydrogen isotopes. This exposure can lead to high fuel retention that can raise serious concern from the safety point of view. One of the reasons for the use of W as a material for the construction of the first wall is to reduce fuel retention compared to carbon wall. Nitrogen seeding, used during the operation of fusion reactors, represents a method to cool the divertor plasma and to reduce the W source in the divertor due to ELMs. However an exposure of the PFC to a combination of hydrogen isotopes and nitrogen can lead to changes in properties of exposed surfaces or to unexpected material behavior. In this work, the influence of nitrogen on the deuterium content within tungsten coatings produced by reactive high power impulse magnetron sputtering (HIPIMS) was investigated. The deposition process of W coatings in a nitrogen deuterium environment leads to a significant retention of deuterium. Coatings with a deuterium content up to 54 at.% were obtained in the presence of nitrogen compared with a deuterium content of 25 at.% measured for the coatings produced in absence of nitrogen from the deposition atmosphere.