Achievement of Reactor-Relevant Performance in Negative Triangularity Shape in the DIII-D Tokamak

Abstract

Plasma discharges with a negative triangularity (delta = -0.4) shape have been created in the DIII-D tokamak with a significant normalized beta (beta(N) = 2.7) and confinement characteristic of the high confinement mode (H-98y2 = 1.2) despite the absence of an edge pressure pedestal and no edge localized modes (ELMs). These inner-wall-limited plasmas have a similar global performance as a positive triangularity (delta = +0.4) ELMing H-mode discharge with the same plasma current, elongation and cross sectional area. For cases both of dominant electron cyclotron heating with T-e/T-i > 1 and dominant neutral beam injection heating with T-e/T-i = 1, turbulent fluctuations over radii 0.5 < rho < 0.9 were reduced by 10-50% in the negative triangularity shape compared to the matching positive triangularity shape, depending on the radius and conditions.