Progress of understanding negative triangular tokamak configuration

Kikuchi, Mitsuru; Fasoli, A.*; Takizuka, Tomonori*; Diamond, P.*; Medvedev, S.*; Duan, X.*; Zushi, Hideki*; Furukawa, Masaru*; Kishimoto, Yasuaki*; Wu, Y.*; Sauter, O.*; Villard, L.*; Brunner, S.*; Merlo, G.*; Kwom, J. M.*; Zheng, G.*; Mishra, K.*; Honda, Mitsuru; Urano, Hajime; Pueschel, M. J.*; Told, D.*; Fujisawa, Akihide*; Nagasaki, Kazunobu*; Sano, Fumimichi*

Power and particle control is challenging for standard D-shaped H-mode scenario in tokamak. Possibility of negative triangularity as innovative tokamak concept is discussed by Kikuchi et al. Experimental and numerical studies of negative triangular plasma at CRPP-EPFL success-fully demonstrated improved connement and the weakening of the SOL flow acceleration is implied for the negative triangularity. Recent studies on mechanism of type II and grassy ELM show importance of closure of second stability access to achieve small ELM regimes and also kinetic effects. Medvedev showed that closure of second stability also occurs for negative triangularity. But the MHD stability in negative triangularity is a bit more complicated so that closure of second stability does not imply easy access to small ELM regimes. We discuss critical elements behind.