Influence of surface structure on D retention and erosion behaviours of RAFM steel with D-plasma exposure

Abstract

As the first wall candidate material in the future fusion device, Reduced Activation Ferritic/Martensitic (RAFM) steel represented by CLF-1 steel was further investigated on the deuterium (D) erosion and retention behaviours. The influences of the surface conditions, including surface morphology, W-enriched structure and the original surface roughness, of the surface conditions including the sample temperature, W-enriched structure and the original surface roughness are mainly discussed. The results showed that with the increase of the sample temperature of CLF-1 steel during D-plasma exposure, the surface morphology changed obviously, and the grooves/pits formed by the erosion on the sample surface are deepened and the boundary becomes obvious. Then, the granular nanostructures appeared at the erosion edges and covered the grooves, eventually forming the nanoclusters structure on the surface. At the same time, TEM results showed that the thickness and content of W atoms on the surface increased. Under the combined action of the above surface conditions, both the sputtering rate and total D retention amount of CLF-1 steel decrease. Under the current experimental parameters, with the increase of the initial surface roughness, the sputtering morphology and the surface roughness of CLF-1 steel changed to different degrees after erosion of D, which eventually led to the slightly increase of the sputtering rate. The effect of incident D-plasma angle on the sputtering and redeposition behaviour of the material may explain this phenomenon. Besides, both the specific surface area of the contact plasma and the erosion behaviour of the material by D-plasma increased with the original surface roughness. The D releasing peak, thermal desorption temperature and total D retention amount of CLF-1 steel samples decrease with the original roughness of CLF-1 steel, which is mainly caused by the increase of D diffusion on the surface. At present, it can be found that the W-enriched surface behaviour induced by D-plasma exposure as well as the change of roughness and morphology lead to the decrease of the sputtering rate of RAFM steel with fluence, energy and sample temperature.