Multiscale numerical study of the ELM-induced sputtering on the tungsten castellated divertor gap

Material sputtering and erosion are key issue in fusion science. In the steady state, tungsten sputtering can be maintained at a low level. However, tungsten is seriously sputtered by the hot plasma from edge localized mode (ELM) bursts. The time evolution and spatial distribution of sputtering on the divertor gap are still not clear. This unclearness influences the understanding of ELM-induced sputtering and the explanation of experimental phenomenon. In this study, the evolution of tungsten flux generated by ELM burst is obtained via hybrid multiscale simulation and a double-peak of tungsten flux is found. The first peak is produced by the ELM electrons, which provides great sheath potential, and the second peak is generated by the energetic ions from ELM. The castellated divertor gap (CDG) can influence the tungsten sputtering distribution due to the change of the impacting angle. The sputtering and erosion on CDG are more serious than that on the mono-block top, but the tungsten source from the gap is very insignificant because the gap size is small. The simulation results are compared with EAST experiments and a qualitative consistency is obtained.