Examining the effects of plasma facing component geometries on thermal loads using HEAT simulations

Particle exhausts from the scrape-off layer (SOL) region of tokamak plasmas are notorious for delivering dangerous heat fluxes to solid plasma facing components (PFCs). These heat fluxes deliver severe thermal and mechanical damage to the PFCs, and introduce impurities that degrade plasma power output. Robust simulations of PFC heat fluxes are needed to inform the fusion community of tokamak operation scenarios to mitigate PFC damage. We use optical heat flux simulations from the Heat flux Engineering Analysis Toolkit (HEAT) on the graphite divertors of the NSTX-U tokamak [Fusion Sci. Technol. 78, 10-27(2022)]. HEAT informs us of the locations of the PFC "hot spots," where heat fluxes are particularly high, enabling the analysis of surface flux profiles. Our study focuses on NSTX-U's inboard divertor horizontal PFC, which contains geometric features such as bevels and castellations that alleviate thermal loads via magnetic shadowing. To assess the thermal effects of these geometric features, we first design a "control PFC" with a featureless flat surface. We then run HEAT on both designs, and compare the thermal evolution of each design. This allows us to inform PFC designs in future tokamaks by examining the relationship between surface geometry and thermal loads.