Simulation of negative triangularity plasmas on DIII-D using SOLPS-ITER*

Boundary plasma simulations constrained against experimental data of DIII-D negative triangularity (NT) plasmas with SOLPS-ITER are used to inform the design of dedicated divertor components. Across a range of plasma conditions and triangularities (delta_avg=-0.2/-0.5), the upstream kinetic profiles and heat flux widths are well matched. The measured trend in improved edge thermal confinement with increasing plasma current is reproduced from the inferred cross-field diffusivities. Divertor target profiles are reproduced withing a factor of ~2x, with further refinement likely requiring activation of cross-field drifts. It is found that the narrow heat flux width, open divertor shape, and short connection length make access to detachment without degradation of the core conditions challenging, consistent with experimental results. The dedicated NT divertor aims to increase the closure such that the beneficial properties of NT plasmas can be achieved along with detached divertor conditions. Using predictive simulations, it is found that a closed divertor reduces the upstream density at which rollover occurs by a factor of 2, with a significant reduction in the target electron temperatures. About half of the change comes from the increased connection length and the other half from closure, consistent with two-point model scalings.