Study of deuterium reflection on tungsten material with lithium coating in EAST tokamak

• The D reflection rate on W with Li overlayer is quantitatively calculated which can be used for particle recycling analysis during EAST tokamak operation. • A non-monotonic relationship between the D reflection rate and the impact energy is found to be exist on W material with certain thickness of Li coating. • The minimal thickness of the Li overlayer required to maintain a low D reflection is evaluated based on different EAST divertor operation conditions. Lithium (Li) coating of the first wall has been used as a routine way of wall conditioning on EAST and proved to have a significant influence on particle recycling. Whereas the deuterium (D) reflection process on tungsten (W) with Li coating is not well understood. The SDTrim.SP code is employed to investigate the D reflection process on the Li-W mixed material wall surface for EAST tokamak. The study reveals that the existence of Li coating can reduce the deuterium reflection rate significantly. This reduction in reflection is influenced by both the D impact energy and the thickness of the Li overlayer. Unlike the D reflection on pure metal materials, the D reflection rate shows a non-monotonic relationship with the D impact energy. Detail analysis shows that with the increase of D impact energy, the fraction of D which can penetrate through the Li overlayer and interact with the W substrate increases, leading to a significant increase of D reflection rate. For normal EAST divertor operation conditions, a Li overlayer thickness of 30 nm is required to keep the D reflection rate at a low level. The D reflection on W with a Li-W mixed overlayer has also been investigated and discussed in this work.