Study of Core and Edge Gradients in Positive and Negative Triangularity Shaped Discharges in DIII-D

Plasma shaping, in particular triangularity ($\delta$), has been shown to influence turbulence levels and energy confinement in experimental tokamak plasmas. The effects of triangularity on gradients and edge transport in DIII-D have been studied using precise equilibrium reconstructions created with the EFIT code with constraints from ONETWO modeling. It has been observed that, in matched negative (NT) and positive triangularity (PT) L-mode discharges, NT plasmas have on average similar $a/L_{Te}$ and 65\% higher $a/L_{Ti}$ in the region $0.6 < \rho < 1.0$. For L-mode NT compared to H-mode PT discharges with comparable heating input, NT plasmas have on average 40\% higher $a/L_{Te}$ and 85\% higher $a/L_{Ti}$ in the same region, which may indicate a higher critical gradient and gives the same $T_e$ and $T_i$ values at the core. Instead of the exponential profile shape expected for stiff transport models with $a/L_{Te}$ independent of radius, we observe regions at the edge of L-mode plasma with a linear dependence of $T_e$ on $\rho$ that have been characterized as depicting non-stiff transport.\footnote{Sauter O., et al., \textbf{Phys. Plasmas} 21, 055906 (2014)} Consequently, these results offer an insight to the improved confinement obtained in NT discharges.