Stellarator island divertor shape optimization for reduced peak heat fluxes

Abstract

Abstract An automated algorithm to construct island divertors for stellarators is presented and is used to find divertors that meet heat load requirements determined by material limits. The algorithm uses just two initial conditions: two starting coordinates on the island separatrix chosen by the user. We leverage the simplicity of the algorithm to explore the divertor parameter space in a fixed magnetic equilibrium. Heat loads are approximated using the field line diffusion model implemented in the FLARE code. Divertor solutions that satisfy heat load requirements while maintaining a high power fraction captured are found using a parameter scan and a Bayesian optimization routine. The optimization finds divertors that perform the same as the parameter scan, but with a 75% reduction in computational cost. The resulting divertors satisfy heat load requirements across varying cross-field heat diffusivities. Optimization over various islands in the equilibrium shows that low-elongation islands are the easiest to find divertors that satisfy heat flux requirements. This algorithm presents a simple parameterization for island divertors and facilitates further physics and optimization studies.