MHD stability at edge pedestal in a QH-mode plasma in DIII-D was analyzed by taking into account plasma rotation and ion diamagnetic drift effects. We have found that the coupled rotation and ion diamagnetic drift effects can stabilize a kink/peeling mode in the QH-mode plasma rotating in the direction counter to the plasma current, although it has been recognized the rotation alone destabilizes the mode regardless of its direction. The physics mechanism responsible for the stabilization was identified as reduction of the destabilizing effect by dynamic pressure through the coupling between the rotation and the ion diamagnetic drift. The coupling effect can be harnessed to both stabilize and destabilize the kink/peeling mode by switching the rotation direction, the trend which could be the reason that the QH-mode plasmas in DIII-D favor toroidal rotation counter to the plasma current direction.

Magnetohydrodynamic stability at the edge pedestal in several quiescent H-mode (QH-mode) plasmas in DIII-D and JT-60U experiments was analyzed by considering plasma rotation and ion diamagnetic drift effects. It was identified that a kink/peeling mode, which is a prime candidate for a trigger of edge harmonic oscillation in QH-mode, is stabilized by plasma rotation when considering the ion diamagnetic drift simultaneously in both experiments. The stabilizing effect by rotation becomes more effective in case using the rotation profile of the main ion species evaluated by assuming radial force balance. In addition, when inverting the rotation direction, it was found that the kink/peeling mode is more stabilized when considering the rotation of the main ion species, though the mode is less stabilized by the rotation of impurity ion species. The result implies that the kink/peeling mode stability in QH-mode plasmas is sensitive to how the rotation profile is evaluated, but it is shown that a qualitative trend stabilizing the kink/peeling mode by rotation can be reproduced with the poloidal rotation profile of an impurity predicted numerically based on the neoclassical theory.