Confinement in DIII-D negative triangularity discharges*

DIII-D discharges with negative triangularity (-δ) shape and an L-mode edge have been shown to have the same stored energy and global confinement as matching positive triangularity discharges (+δ) that are in H mode and have an edge pressure pedestal. Detailed profile analysis has been carried out to determine how the transport compares in the two shapes. It is seen that while the -δ shape has lower edge confinement, it has higher confinement in the region 0.3 < r/a < 0.8 which makes up the difference. The improved core confinement is attributed to reduced turbulent transport (consistent with measured turbulence reduction), due to effect of shape on the dominant TEM modes and also on the increased Shafranov shift and higher plasma rotation. Profile studies also show that the negative triangularity has significantly higher bootstrap current than the comparison positive triangularity discharge. TRANSP runs indicate as much as 30% higher bootstrap current in negative over positive discharges consistent with loop voltage analysis of these shots.