The n=1 (n is the toroidal mode number) internal kink (IK) instability is numerically investigated, in both fluid and non-perturbative drift-kinetic models, for an ITER 15 MA baseline plasma with the fusion gain of Q∼10. Fluid analysis identifies two unstable branches in the absence of an ideal wall: a core-localized IK mode and a coupled IK-peeling mode. The latter is fully stabilized by the ITER-relevant conducting wall, while the core IK mode remains unstable. Crucially, the precessional drift resonance of fusion-born alpha particles is found to strongly destabilize the IK mode and trigger a secondary fishbone branch. The plasma toroidal rotation modifies the resonance condition via the Doppler shift, leading to a distinct asymmetry in the kinetic stability: the primary fishbone branch is relatively insensitive to the flow, whereas the secondary branch remains weakly unstable under co-current rotation but is significantly stabilized by countercurrent rotation. Furthermore, self-consistent inclusion of finite orbit width effects and alpha bounce resonances provides a robust stabilizing mechanism; these effects can completely suppress the secondary fishbone branch even under the baseline co-current rotation scenario. In contrast, the primary branch persists despite all considered drift-kinetic resonances. These findings suggest that while alpha particles provide the dominant kinetic drive, the stability of triggered modes in ITER can be actively manipulated by either controlling the plasma rotation or utilizing specific kinetic stabilizing mechanisms.
Zhao et al. (Fri,) studied this question.