Scrape-Off Layer characterization and detachment integration in Negative Triangularity discharges in DIII-D

Negative triangularity (NT) experiments on DIII-D simultaneously achieved divertor detachment, an ELM-free edge, and tolerance to extrinsic impurities for divertor dissipation, demonstrating the potential for a core-edge integrated scenario. Detachment without impurity seeding was achieved via an increase in plasma density for the first time in NT discharges. Detachment onset conditions in the outer divertor were sustained with H-mode level confinement H_98-y2~1 and normalized pressure levels β_N~2. Energy confinement degradation (~30%) was observed with deeper detachment, which correlated with the loss of the edge electron temperature pedestal and the movement of the radiation front in contact with closed flux surfaces. Parametric dependence of access to detachment on plasma current and injected power was consistent with expectations from detachment scalings. However, densities higher than in positive triangularity (PT) (Greenwald fraction f_GW>0.9), were needed to achieve detachment, due to the shorter parallel connection length and narrowing of the scrape-off layer heat flux width at the strongest NT, approaching values typical of PT H-mode discharges. Impurity seeding with nitrogen and neon reduced the detachment density up to 30% at the expense of core dilution. Detachment onset density was 40% higher with ion B×▽B drift into the divertor compared to out of the divertor in NT (f_GW~1.3 vs. 0.9), while this difference is typically less than 15% in PT. The effect of cross-field drifts on divertor profiles was larger than observed in PT discharges due to the lower toroidal field at the X-point in NT shapes. Edge fluid simulations (UEDGE, SOLPS) quantitatively reproduce the observed drift dependences and high densities needed for detachment, increasing confidence in extrapolation to future NT divertor design.