Effect of equilibrium properties on the structure of the edge MHD modes in tokamaks

Aiba, Nobuyuki; Hayashi, Nobuhiko; Takizuka, Tomonori; Tokuda, Shinji; Ozeki, Takahisa

We investigate numerically the effects of the equilibrium properties on the structure of the edge MHD modes in tokamaks. In particular, we focus on the effects of the plasma shape and the pressure profile inside the top of the pedestal. As the results of numerical analyses, we find that the structure of the unstable MHD mode expands to the plasma core region even when the width of the edge pedestal region, and the mode structure can expand deeply in strongly-shaped plasmas. This deeply expansion in strongly-shaped plasma is because the difference of the stabilizing effect of the ideal ballooning mode between the plasma edge region (including the edge pedestal region) and the region inside the pedestal in strongly shaped plasma is larger than that in weakly shaped plasma. This difference allows to destabilize the MHD mode whose structure extend from the edge pedestal region to the region inside the pedestal in strongly shaped plasma.