Kinetic theory of the stability of the inhomogeneous plasmas with shear flows

Kinetic theory of the stability of the inhomogeneous plasmas with shear flows.

V.S. Mikhailenko, M.O. Azarenkov, D.V. Chibisov, K. N. Stepanov, V.V. Mikhailenko Kharkov National University, 61108 Kharkov, Ukraine

Abstract. The stability of a magnetized inhomogeneous plasma with transverse and field-aligned shear flows is analyzed by using a kinetic formalism. The perpendicular shear flow is shown to be stabilizing, but the field-aligned shear flow is destabilizing. New types of the ion cyclotron and drift-type instabilities are found. A renormalized nonlinear dispersion equation for the transverse plasma shear flow is derived and applied to the determining of the saturation level of the instabilities. A review of sheared flows in ionosphere and laboratory experimental investigations is presented.
Keywords: <Enter Keywords here> PACS: 03.40.G, 52.35.K

The existence of inhomogeneous flows and currents along and across magnetic fields is a fundamental characteristic of space plasmas. One important element of the ionospheric flows appears to be velocity shear. Tsunoda et al.[1] reported that strong thermal ion upwelling, i.e. ion heating, occurs in regions of finite velocity shear. Localized static (or quasi–static) electric fields both perpendicular [2, 3] and parallel [4] to the magnetic field were found to be colocated with waves and coherent structures as well as with enhanced ion temperatures [5], [6], [7], [8]. Compared to the homogeneous plasma case, sheared flows introduce significant modifications to plasma stability. In this report we present the results of the analytical research of the stability of the inhomogeneous plasma shear flows transverse and along with respect to magnetic field, grounded on the Vlasov-Poisson system of equation.

In Ref.[9] we obtain the following renormalized local dispersion equation for Maxwellian plasma immersed into homogeneous magnetic and transverse inhomogeneous electric fields:

We obtain, that ion cyclotron and drift-cyclotron instabilities are destabilized by a field-aligned shear flow. Inverse ion cyclotron damping of ion cyclotron waves and inverse electron Landau damping of ion cyclotron waves are potential sources for the excitation of the ion cyclotron instabilities due to shear of the field-aligned flow. The growth rates of new kinetic and hydrodynamic ion cyclotron instabilities, which are excite due to slow shear appeared to be proportional to the parameter kyV00/kzwci. These instabilities disappear in the shearless plasma.
Thus, the flow shears in magnetized plasmas are found to be important for controlling both the drift-wave and ion-cyclotron instabilities, where the parallel and perpendicular shears play different roles in these instabilities. The parallel flow shear can excite the drift-wave and ion-cyclotron instabilities, while the perpendicular flow shear suppress these instabilities regardless of the sign of the shear.
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