Ion temperature gradient-driven ballooning mode in tokamaks

Abstract

It is shown that an ion temperature gradient (η_i) induces a collisionless ballooning mode in the MHD (magnetohydrodynamic) second stability regime. Both two‐fluid and fully kinetic analyses predict the instability, in qualitative agreement, indicating that the ion magnetic drift resonance plays a key role in destabilization. The instability is characterized by broad eigenfunctions in the ballooning space and at a small magnetic shear has a growth rate comparable with that of the MHD mode. Trapped electrons, the ion transit effect, and magnetosonic perturbation have stabilizing influences, but are unable to suppress the mode.