Heat Load Inside the Gaps of Castellated Tungsten Blocks with Different Shapes in KSTAR

Five configurations of chamfered and sharp leading edge blocks are selected to study the heat load on leading edge at KSTAR central divertor using a 2D3V particle-in-cell (PIC) code PICS2, including ions and electrons with self-consistent electric fields. Results of the PIC simulations demonstrate that the height of the misalignment determines the peak heat flux and the sheath potential near the castellated tiles. Moreover, in the case of a negative misalignment, i.e., a block edge shadowed by the adjacent upstream block, the heat flux distribution is affected mainly by the spatial structure of the monoblock. When the monoblocks are chamfered to a depth of 2 mm in the toroidal direction, more electrons are attracted to the poloidal leading edge with little magnetic shadowing found in the calculation, bringing additional heat load to the beveled side. Therefore, applying a toroidal chamfer of 2 mm at the poloidal block edges turned out to be an ineffective way to reduce the peak heat load. The influence of gap geometries on the heat load and the relations among the ion Larmor radius, the misalignment height, and the gap width are discussed. These calculation results in KSTAR on different shapes of castellated tiles are helpful for understanding the physics of the heat load on the leading edge.