Impact of ion diamagnetic drift effect on MHD stability at edge pedestal of rotating tokamaks

Aiba, Nobuyuki; Honda, Mitsuru; Kamiya, Kensaku

We derived a linearized drift MHD equation derived with Frieman-Rotenberg formalism and an incompressible assumption. A linearized drift MHD code, MINERVA-DI, was developed to solve this equation, and has been applied to the stability analysis of MHD modes at tokamak edge pedestal. As the result, it was found that plasma rotation can cancel the well-known stabilizing effect by an ion diamagnetic drift. The impact of plasma rotation on the ion diamagnetic drift effect depends on the ion species due to changing effective mass and effective charge. Based on these understandings, the MHD stability of type-I ELMy H-mode plasmas in JT-60U was analyzed with MINERVA-DI. When the plasma is assumed as static, the MHD stability boundary is far from the operation point observed experimentally, and the ion diamagnetic effect kept the boundary away further. However, by taking into account plasma rotation, the stability boundary shifts close to the operation point even when the ion diamagnetic drift effect is taken into account.