Experimental studies of a plasma with multi-phase matters on fusion PWI research fields

In the wear evaluation of plasma facing wall surface materials due to melting, evaporation, or scattering caused by the pulsed thermal load such as disruption, the proper understanding of vapor shielding (VS) effect that is evolved by the interaction between vapor phase and plasma is necessary. The melt layer containing solid bulk and bubbles (vapor cloud) constitutes a multi-phase structure. This paper firstly introduced the results of VS experiments, which have conventionally been carried out using plasma gun equipment in the research field of the plasma wall interaction (PWI) of magnetic field confinement fusion reactor. It then discussed the factors necessary for evaluating VS effect, such as plasma heat inflow process through sheath, inflow process of plasma momentum to wall, and penetration process of evaporated atoms into plasma. The VS phenomena are made up of many elementary processes that bring about these phenomena. By identifying these factors, it has become possible for the first time to understand the whole picture, to correctly evaluate material wear, and to have predictive performance. (A.O.)