Studies of material deposition on the graphite divertor tile after the 2019 experimental campaign in EAST

Material erosion and deposition are one of the important topics related to plasma-wall interaction in tokamaks. Detailed analysis of the deposits on the surface of the graphite tile from the divertor dome region has been made after the 2019 experimental campaign. It is indicated that the deposits exhibited porous globular in morphology which were mainly stacked by columnar grains with size of 2–5 μm and small crystal particles with several hundreds of nanometers in size. The thickness of the deposits varied from several micrometers to about 120 μm. As the SiC coating on the graphite tile has a rough surface and exhibited valleys and hills, the deposits on the valleys were typically thicker than that on the hills. The deposits consisted of Li, C, O, W, Mo, Fe, Cu, Ni, et. mainly from the wall conditioning materials and plasma-facing materials. It was noted that Li was in the form of Li2CO3. And Mo and W were in MoO3 and WO3 respectively. The total content of Li2CO3 was found to be higher than 90 wt% with a corresponding Li density in deposits of about 7.22 μg/mm−2 in average due to the routine Li wall conditioning. The depth profile of Li exhibited differently from the other elements. And W has a higher density than Mo, which could be due to the high W erosion from the upper divertor.