Stabilization of kink/peeling modes by coupled rotation and ion diamagnetic drift effects in quiescent H-mode plasmas in DIII-D and JT-60U

Abstract

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.

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

“…The other is that both K/PM and PBM are stabilized by plasma rotation in the QH-mode plasma although those stability boundaries change little in the ELMy H-mode plasma. Such the stabilization of both K/PM and PBM by rotation with the ion diamagnetic drift was also observed numerically in other QH-mode discharges [15]. It should be noted that we assume that a QH-mode can be obtained in case the operation point or its error bars exist in the region between the K/PM stability boundaries identified in the static and rotating conditions, as suggested in [14]; in this study, the error bars determined to be ±20% of j ped,max and α max are drawn on the operation point.…”

“…To confirm this trend more quantitatively, we performed numerical experiments analyzing the impacts of these physics features on MHD stability properties with other QH-mode experimental results in DIII-D. The MHD stability in four QH-mode equilibria was analyzed in the same manner as performed in previous sections; the shot number/time are #153440@1.725 s, #157102@2.42 s, #157188@2.06 s, and #163518@2.35 s. In all the discharges, B t and I p are clockwise from the top view of the torus, and the toroidal rotation of the impurity carbon is in the counter-I p direction, as the #163477 discharge; the results of MHD stability analysis in these discharges are shown in [15]. Figure 8 shows the p and j ∥ profiles of these discharges, and figure 9 is for the Ω v×B and ω * i profiles; both the original and inward shifted profiles with C * i = 0.5 are plotted.…”

“…Hence, to discuss whether or not QH-mode plasmas can always be realized in case satisfying them, it is necessary to perform a validation study with at least several pairs of QH-mode and ELMy H-mode plasmas; if possible, the study with the experimental data in not only DIII-D but also other experiments is desirable to make the results more reliable. For example, as discussed in [15,23], both PBM stability in ELMy H-mode plasmas in JT-60U and K/PM stability in QH-mode plasmas in DIII-D and JT-60U depend on the direction of toroidal rotation in case the coupled rotation and ω * i effects are considered. It is known that the QH-mode plasmas in both DIII-D and JT-60U favor the rotation direction counter to the plasma current, and the above validation study will help to clarify physics reasons of this trend.…”

“…Here E (B) is the electric (magnetic) field. These experimental conditions in QH-mode plasmas imply both plasma rotation and ω * i can affect the K/PM stability, and in fact, our recent works identified that a low-n (n being toroidal mode number) K/PM in QH-mode plasmas in DIII-D and JT-60U experiments can be stabilized by the coupled rotation and ω * i effects although the mode is destabilized when considering only rotation effect [14,15]. It was also found that the stabilizing effect by the coupled effects becomes more effective in case using the rotation profile of main ion species evaluated by assuming radial force balance with the profile of measured impurity ion species [15].…”

On the possibility of limit-cycle-state of peeling mode near stability boundary in the quiescent H-mode

“…From experimental point of view, the parameter region where the QH-mode appears is close to the instability boundaries of peeling mode or peeling-ballooning mode [24,25], so that the EHO is considered to be related with the peeling mode or peeling-ballooning mode. Theories of the peeling mode and peeling-ballooning mode have been elaborated by taking into account of the effects of E × B flow [26][27][28][29][30][31] and of ion diamagnetic drift [32][33][34].…”