Pulse Shape Dependence Of Vapor Shielding Efficiencies During

Erosion of first walls in tokamak fusion reactors due to transient heat loads during ELM and disruptions is a major concern and needs to be predicted. Studies have shown that the erosion amount is strongly dependent on the total energy density and duration of a transient heat pulse. Recently, it was pointed out that the erosion amount is also dependent on the pulse shape [J.H. Yu et al., Nucl. Fusion 55, 093027 (2015), and D. Motoi et al., Fusion Eng. Des. 165, 112209 (2021)]. Meanwhile, it is predicted that the erosion during the transient heat loads can be suppressed by vapor shieldings, and the efficiency of the vapor shielding may differ between the pulse shapes. Thus, in this study, we investigate the pulse shape dependence of the vapor shielding effect by a particle-in-cell based simulation code, PIXY. Two types of square shapes and three types of triangular shapes are examined. Among the triangular shapes, it is found that the vapor shielding is effective especially in "Negative Ramp" triangular shape, where the peak heat flux comes first. (C) 2021 The Japan Society of Plasma Science and Nuclear Fusion Research