First experiments with negative triangularity shape in DIII-D[1]

For the first time on DIII‑D, discharges with a negative triangularity shape ${(\delta = -0.4)}$ were created to investigate the effects of this shape on transport and turbulence. Significant shape control development was required with unconventional patch panel configurations and a new startup scenario to successfully establish the discharge. These ‘reverse D’ discharges were ${L-mode}$, inner-wall limited with 1 MA current, 3.8 MW NBI, and 2.7 MW ECH. $H_{98,y2}$ factors up to 0.85 and $\beta_N$ values up to 1.7 were attained in ELM-free stationary discharges. The confinement behavior mimics Alcator scaling[2], with confinement increasing with density. Other interesting features of the experiment were a higher than typical intrinsic $co-\textit{I}_p$ edge rotation and an increase in density with ECH power. This behavior contrasts with the ECH-induced drop in rotation and density pump-out effects observed in standard ${\delta\hspace{1.5 mm}\textgreater\hspace{1.5 mm}0}$ ECH-dominated DIII-D discharges. A full set of turbulence data was obtained over low, intermediate, and high $\textit{k}$ ranges. $^1$Work supported by USDOE - DE-FG02-97ER54415 and DE-FC02-04ER54698. $^2$ Gondhalekar, A. et al, Proc. 7th IAEA Int’l Conf, Innsbruck, 1978, Vol 1, 199. IAEA, Vienna (1979).