Divertor detachment characterization in negative triangularity discharges in DIII-D via UEDGE modeling*

Edge fluid modeling of the first detachment experiments in diverted negative triangularity discharges in DIII-D is presented using UEDGE including cross-field drifts. Detachment experiments were performed at strong (baseline shape, δ~-0.5) and intermediate negative triangularity (hybrid shape, ) and intermediate negative triangularity (hybrid shape, δ~-

0.2) in DIII-D via an increase in upstream density or impurity seeding. UEDGE simulations with both the ion Grad-B drift directed into (Forward B T ) and out of (Reverse B T ) the active divertor are included for the baseline shape and the ion Grad-B drift into the active divertor in the hybrid shape. Upstream density scans are performed with UEDGE to reach a detached plasma and to quantitatively recover the experimental roll-over of the ion saturation current on the outer target by the Langmuir Probes. Consistent with experiments, simulations reproduce: a higher fraction of Greenwald density required to reach detachment onset in negative triangularity compared to positive triangularity; a ~40% higher

density to reach detachment onset with Forward B T than with Reverse B T ; deep detachment only in the Forward B T case. The effect of longer connection length and changes in radial transport in the hybrid shape compared with the baseline shape are investigated in the simulations.