Kinetic ballooning mode unstable in the 2nd stability regime as a possible source of the low-k broadband fluctuation observed in the wide-pedestal QH-mode

The kinetic ballooning mode destabilized by the ion magnetic curvature drift resonance in the 2nd ballooning stability regime is shown to be a plausible candidate for the low-k broadband fluctuation recently observed in the wide-pedestal quiescent-H (QH) mode of DIII-D. With its intrinsic real frequency approaching very closely to the ion pressure diamagnetic frequency in the pedestal-like condition with a steep gradient, this mode can be nearly free from the first-order ExB flow shear effect driven by the ion pressure gradient. As a result, it can be sensitive to the next-order one by toroidal rotation, with the possible strong excitation in the low toroidal rotation limit. The frequency in the lab frame and the peak wavenumber spectrum of the mode appear to be in the range similar to those of the observed low-k fluctuation. (paper)