Gyrokinetic theory of slab ion temperature gradient mode in negative sheartokamaks

In a slab configuration modeling the negative shear tokamak, a linear analy sis of the ion temperature gradient (ITG) mode is performed based on a gyro kinetic integral eigenvalue equation with retaining the full finite Larmor radius (FLR) effect. Numerical results show that characteristics of the sla b ITG mode are greatly changed in the negative shear configuration. When a single mode-rational surface exists at the q(min)-surface, the steep ion te mperature gradient and the associated FLR effect produce an asymmetric mode structure with respect to the mode-rational surface. In the weak magnetic shear region near the q(min)-surface, an unstable region of the ITG mode is divided into two separate regions, which are located in both sides of the mode-rational surface. Since the ion Larmor radius varies significantly bet ween these regions, low-k(y) (high-k(y)) modes appear in the high-T-i (low- T-i) side due to the asymmetric FLR effect, where k(y) corresponds to the w avenumber in the poloidal direction. When double mode-rational surfaces exi st near the q(min)-surface, it is found that the ITG mode becomes unstable in the interior region between the two mode-rational surfaces. Since the sh ear stabilization disappears in this region, the unstable k(y) region sprea ds up to an extremely short wavelength region or k(y)rho(ti)less than or eq ual to 10, where rho(ti) is the ion Larmor radius. (C) 1999 American Instit ute of Physics. [S1070-664X(99)01212-4].