Temperature gradient driven short wavelength modes in sheared slab plasmas

Abstract

The temperature gradient (ηi and ηe) driven instability in the short wavelength regime, |kyρi|>1, is studied in a sheared slab. An analytical analysis is performed first to clarify the physics mechanisms for the modes in a shearless slab. The correlation between the growth rate and the real frequency of the modes is discussed in detail. The electron temperature gradient is found to have strong influences on the modes in short wavelength regions. Several series of the short wavelength modes are then identified with a kinetic integral equation code in a sheared slab. The radial widths of the modes are found to be comparable with the conventional ηi modes and not short, although the poloidal wavelengths are short. The lowest odd mode usually dominates in the weak magnetic shear and low β regime. However, the fundamental mode seems to be important in tokamak plasmas because the higher order modes are easily stabilized by finite β and/or by magnetic shear. The fundamental short wavelength mode cannot be stabilized by β when the magnetic gradient drift effect is taken into account. The modes are excited by both finite ηi and ηe, and may be stabilized by magnetic shear.