Comparison of MHD stability properties between QH-mode and ELMy H-mode plasmas by considering plasma rotation and ion diamagnetic drift effects

Abstract

Magnetohydrodynamic (MHD) stability at tokamak edge pedestal in a quiescent H-mode (QH-mode) and type-I ELMy H-mode plasmas in DIII-D experiment was analyzed by considering plasma rotation and ion diamagnetic drift effects. QH- mode plasma is marginally stable to kink/peeling mode (K/PM), but ELMy H-mode one is almost unstable to peeling ballooning mode (PBM). It was identified that there are three physics features responsible for the difference in the MHD stability properties between QH-mode plasma and ELMy H-mode one. These are the distance of pedestal foot from the last closed flux surface (LCFS), the amount of the ion diamagnetic drift frequency at pedestal, and impact of coupled rotation and ion diamagnetic drift effects. These features were confirmed through the numerical experiments that the stability properties of the QH-mode plasma can be changed to that of the ELMy H- mode by shifting the plasma profiles inward in the radial direction and halving the ion diamagnetic drift frequency. The reasons of the change in the stability properties are thought as that K/PM is stabilized due to the inward shift of the bootstrap current profile, and PBM is destabilized due to the reduction of the coupled rotation and ion diamagnetic drift stabilizing effect. Importance of these features was validated through numerical experiments with experimental data of other QH-mode plasmas in DIII-D. All the results show that MHD stability properties of QH-mode plasma can be obtained in case that pedestal foot is close to LCFS, large ion diamagnetic drift frequency due to high ion temperature, and strong rotation shear near pedestal.

Effects of diamagnetic drift on nonlinear interaction between multi-helicity neoclassical tearing modes

“…For example, studies have been carried out on the control of NTMs by resonant magnetic perturbations, [41][42][43] on the suppression of the onset of neoclassical double tearing modes by diamagnetic drift, [44] on the systematic numerical simulation of the mode penetration in NTMs, [45] on the influence of Hall effect on TMs [46,47] and on the influence of diamagnetic drift on MHD stability in DIII-D experiments. [48] Despite great progress having been made in two-fluid studies, further research is still required to simulate multi-helicity NTMs based on two-fluid theory.…”