Ion-temperature-gradient sensitivity of the hydrodynamic instability caused by shear in the magnetic-field-aligned plasma flow

Abstract

The cross-magnetic-field (i.e., perpendicular) profile of ion temperature and the perpendicular profile of the magnetic-field-aligned (parallel) plasma flow are sometimes inhomogeneous for space and laboratory plasma. Instability caused either by a gradient in the ion-temperature profile or by shear in the parallel flow has been discussed extensively in the literature. In this paper, (1) hydrodynamic plasma stability is investigated, (2) real and imaginary frequency are quantified over a range of the shear parameter, the normalized wavenumber, and the ratio of density-gradient and ion-temperature-gradient scale lengths, and (3) the role of inverse Landau damping is illustrated for the case of combined ion-temperature gradient and parallel-flow shear. We find that increasing the ion-temperature gradient reduces the instability threshold for the hydrodynamic parallel-flow shear instability, also known as the parallel Kelvin-Helmholtz instability or the D'Angelo instability. We also find that a kinetic instability arises from the coupled, reinforcing action of both free-energy sources. For the case of comparable electron and ion temperature, we illustrate analytically the transition of the D'Angelo instability to the kinetic instability as (a) the shear parameter, (b) the normalized wavenumber, and (c) the ratio of density-gradient and ion-temperature-gradient scale lengths are varied and we attribute the changes in stability to changes in the amount of inverse ion Landau damping. We show that near a normalized wavenumber k⊥ρi of order unity (i) the real and imaginary values of frequency become comparable and (ii) the imaginary frequency, i.e., the growth rate, peaks.

Drift-Alfven instabilities of a finite beta plasma sheared flow along a magnetic field with inhomogeneous ion temperature

“…It was found in Ref. 6 , that the electrostatic instability exists by virtue of the coupled action of parallel velocity shear, ion Landau damping and a ion temperature gradient, which reinforce each other in the development of the ion kinetic instability. In this paper we undertake the investigation of the electromagnetic counterpart of that instability: the DA instability of the parallel shear flow with inhomogeneous ion temperature.…”

“…In parallel shear flows with hot ions, T i T e , the ion kinetic effects play the decisive role in the development the instabilities of the parallel shear flows. In particular, such plasma is prone to the excitation of the shear-flow driving instabilities 6,7 . It was obtained 7 , that in plasma with inhomogeneous density the ion kinetic drift-Alfven (DA) instability develops from the coupled action of the parallel-flow shear and ion Landau damping.…”