Flute Mode Instability Driven by an E×B Drift Shear of a Nonuniform Radial Electric Field

Abstract

Flute mode instability driven by a nonuniform radial electric field is investigated in the local theory. From the analysis of the local dispersion equation derived from the profiles of Gaussian density and parabolic ambipolar potential, it is shown that a flute mode is reactively destabilized in the case of a well-type potential and that this mode can be stabilized by the Landau damping caused from the velocity shear of the E×B drift for a stronger electric field. The flute mode propagates in the direction of the ion diamagnetic drift in the E×B drifting frame of the electron. The threshold for the instability is obtained analytically, which is in good agreement with that obtained numerically. The physical mechanism of the instability is explained. The effect of the velocity shear of the E×B drift on flute interchange modes is also discussed.