Tuesday, October 20, 2020
At full power operation, the core plasma of the SPARC tokamak will produce around 30 MW of power that must be dissipated by the walls of the device. The bulk of this power will flow to the upper and lower divertors, where unmitigated heat fluxes up to 300 MW/m^2 are expected. SPARC is being designed to withstand these extreme heat flux levels via strike-point sweeping with moderate divertor radiation levels, but a further improvement could be provided by plasma detachment, in which significant power is dissipated through impurity radiation as it travels from the core to the divertor plates. The UEDGE code, which provides a 2D fluid model of the plasma boundary in steady state, has been used in this work to explore the SPARC divertor and edge plasma parameter space. Transport coefficients were tuned to match expected midplane plasma profiles, target plate heat flux profiles, and inner/outer divertor power sharing, based on existing empirical scalings. Fully and partially detached solutions were obtained with a carbon impurity fixed to 1% of the main ion density. High levels of X-point radiation in these scenarios indicate that it could be challenging to achieve these conditions experimentally without negatively affecting core performance. Sensitivity studies were carried out to assess the robustness of the results with respect to the assumptions in the model, in particular the choice of boundary conditions at the outer walls and the resolution of the grid.