Confinement and performance trends in DIII-D negative triangularity discharges*

DIII-D negative triangularity (NT) plasmas exhibit H-mode-like confinement with an ELM-free boundary and a tolerance for high normalized beta operation (β_N ~3). Using fits to profiles and sampling of confinement parameters of the DIII-D NT database of ~600 discharges, trends in transport are investigated and compared with more traditional positive triangularity (PT) shots. From profile fits the electron temperature gradient scale length R/LT_e increases with stronger NT shaping, but the energy confinement does not vary strongly as the average triangularity δ_avg changes from -0.1 to -0.5. However, NT discharges in general have higher values of R/LT_e for radii 0.5 < r/a < 0.8 than PT H-mode discharges with similar parameters; typical values would be ~10 for NT compared to ~5 for PT. Also noted is that, with higher T_e gradients in the confinement zone and lower NT edge pedestals, both T_e and n_e, NT has on average 10-20% higher pressure peaking factors than typical H-modes, p_e0/<p_e> ~2. This can contribute the observed neutron rates, normalized to volume, which are of the same order as other DIII‑D high performance discharges.