η i-mode in toroidal plasmas with anisotropic ion temperature and its gradient

Abstract

The gyrokinetic integral eigenmode equation is applied to study Ion-Temperature-Gradient (ITG) mode in toroidal plasmas with magnetic shear, where the ion temperature and its gradient are anisotropic. The numerical studies demonstrate that instability of ITG mode is reduced by a ion temperature anisotropy of higher perpendicular temperature $T_{i\perp}$ or high enough parallel temperature $T_{i\parallel}$, in which Landau damping plays an important role. The temperature gradient in the perpendicular (parallel) direction is stronger to drive ITG mode for large $T_{i\perp}$ ($T_{i\parallel}$). These effects are directly related to the temperature gradient threshold for excitation of ITG mode. In addition, the synergy effect of magnetic shear and anisotropy of ion temperature and its gradient is studied in detail, where the combination of magnetic shear and large parallel temperature has the most obvious inhibitory effect on ITG mode.