Effects of "Sharpness" of the plasma cross-section on the stability of peeling-ballooning modes in tokamaks

Aiba, Nobuyuki; Tokuda, Shinji; Takizuka, Tomonori; Kurita, Genichi; Ozeki, Takahisa

Stabilities of peeling, ballooning and peeling-ballooning modes, which relate to edge-localized modes (ELMs), are investigated numerically with the linear ideal magnetohydrodynamic (MHD) stability code MARG2D. Effects of "sharpness" on the stability of the peeling-ballooning mode are examined, where the sharpness is defined in terms of the curvature at the top and bottom of the outermost flux surface. It is found for the first time that the stable pressure gradient significantly improves as the sharpness increases even when the ellipticity and the triangularity are unchanged. The sharpness is an important parameter for high performance H-mode operations with high pedestal pressure.