Non-linear MHD simulations of QH-mode DIII-D plasmas and implications for ITER high Q scenarios

In nonlinear MHD simulations of DIII-D QH-mode plasmas it has been found that low n kink/peeling modes (KPMs) are unstable and grow to a saturated external kink mode. The features of the dominant saturated KPMs, which are localized toroidally by non-linear coupling of harmonics, such as mode frequencies, density fluctuations and their effect on pedestal particle and energy transport, are in good agreement with the observations of the Edge Harmonic Oscillation (EHO) typically present in DIII-D QH-mode experiments. The non-linear evolution of MHD modes with toroidal mode numbers n from 0 to 10, including both kink-peeling modes and ballooning modes, is investigated through MHD simulations by varying the pedestal current and pressure relative to the initial conditions of DIII-D QH-mode plasma. The edge current and pressure at the pedestal are key parameters for the plasma either saturating to a QH-mode regime or a ballooning mode dominant regime. The influence of E×B flow and its shears on QH-mode plasma has been investigated. The behavior of QH-mode with different flow shear shows E×B rotation has strong stabilization effects on the medium to high-n modes but destabilizing for n=2. The QH-mode extrapolation results of an ITER Q=10 plasma show that the pedestal currents are large enough to destabilize an n=1-5 kink/peeling mode, leading to a saturated kink-peeling mode.