Stabilization of Drift Waves by Shear

Abstract

The stabilization by magnetic shear of drift (universal) instabilities in a nonuniform, collision-free plasma is reconsidered. The description of the instabilities in terms of normal modes is abandoned in favor of a description in terms of local perturbations which are wave packets of normal modes, and this provides a more appropriate analysis of the effect of shear. The small shear required for stability is found to be of order (m/M)⅓ (where m and M are the electron and ion masses) for the short wavelength instability driven by a density gradient only, and results are also obtained for the instabilities driven by electron temperature gradients and longitudinal currents; the instabilities driven by ion temperature gradients are not stabilized by a small shear.