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Title: Parallel electron velocity shear instability in a magnetized plasma

Abstract

It is shown that the parallel electron velocity shear can destabilize low-frequency (in comparison with the electron gyrofrequency) electrostatic waves in a magnetized plasma. A new dispersion relation is derived and solved for the parameters relevant for laboratory experiments of velocity shear instabilities in a magnetized plasma.

Authors:
; ;  [1]
  1. Institut fuer Theoretische Physik IV, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
Publication Date:
OSTI Identifier:
20782526
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 2; Other Information: DOI: 10.1063/1.2173934; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COMPARATIVE EVALUATIONS; DISPERSION RELATIONS; ELECTRONS; GYROFREQUENCY; PLASMA; PLASMA INSTABILITY; PLASMA WAVES; SHEAR; VELOCITY

Citation Formats

Eliasson, B., Shukla, P.K., and Hall, J.O. Parallel electron velocity shear instability in a magnetized plasma. United States: N. p., 2006. Web. doi:10.1063/1.2173934.
Eliasson, B., Shukla, P.K., & Hall, J.O. Parallel electron velocity shear instability in a magnetized plasma. United States. doi:10.1063/1.2173934.
Eliasson, B., Shukla, P.K., and Hall, J.O. Wed . "Parallel electron velocity shear instability in a magnetized plasma". United States. doi:10.1063/1.2173934.
@article{osti_20782526,
title = {Parallel electron velocity shear instability in a magnetized plasma},
author = {Eliasson, B. and Shukla, P.K. and Hall, J.O.},
abstractNote = {It is shown that the parallel electron velocity shear can destabilize low-frequency (in comparison with the electron gyrofrequency) electrostatic waves in a magnetized plasma. A new dispersion relation is derived and solved for the parameters relevant for laboratory experiments of velocity shear instabilities in a magnetized plasma.},
doi = {10.1063/1.2173934},
journal = {Physics of Plasmas},
number = 2,
volume = 13,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • Buneman instability is often driven in magnetic reconnection. Understanding how velocity shear in the beams driving the Buneman instability affects the growth and saturation of waves is relevant to turbulence, heating, and diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak cosine velocity shear together with Vlasov simulations, the effects of shear on the kinetic Buneman instability are studied in a plasma consisting of strongly magnetized electrons and cold unmagnetized ions. In the linearly unstable phase, shear enhances the coupling between oblique waves and the sheared electron beam, resulting in a wider range of unstable eigenmodes with common lowermore » growth rates. The wave couplings generate new features of the electric fields in space, which can persist into the nonlinear phase when electron holes form. Lower hybrid instabilities simultaneously occur at k/k{sub perpendicular{approx}{radical}}(m{sub e}/m{sub i}) with a much lower growth rate and are not affected by the velocity shear.« less
  • The nonlinear behavior of the parallel velocity shear instability in a shear magnetic field is studied. It is found that the nonlinear fluctuation levels and turbulent momentum transport depend strongly upon the direction of the magnetic shear. When the shear has the same sign as the second derivative of the parallel velocity with respect to the radial coordinate, the fluctuations grow to larger levels than if there were no magnetic shear. The physical mechanism controlling this effect is vortex merging between modes on either side of the velocity peak. It is likely that this behavior may be a general featuremore » of all modes with structure parallel to the magnetic field. {copyright} {ital 1998} {ital The American Physical Society }« less
  • A nonlocal theory of the electrostatic parallel velocity shear instability in a three-dimensional slab with a uniformly sheared magnetic field has been developed. It is shown that in the limit of a weak parallel velocity gradient, the linear growth rate can be increased depending upon the direction of the magnetic shear (s) with respect to the radial curvature of the parallel velocity profile (d{sup 2}v{sub {parallel}}/dx{sup 2}). When these parameters have the same sign, the growth rate can actually be stronger than in the limit of no magnetic shear. In this limit of increased instability, the eigenmode is broadened, thusmore » producing enhanced transport. This effect should be observable when the scale length of the curvature is of order {approx}L{sub s}{rho}{sub s}. For strong parallel velocity gradients that are more typical of flows in tokamaks, the effect of the varying Doppler shift becomes more prominent on the stability of the mode, the net result being that the sensitivity of the growth rates on the sign of the magnetic shear becomes insignificant. This effect, however, is effectively offset when a finite density gradient is included. When the density scale length is of order the scale length of v{sub {parallel}}, the growth rate is moderately reduced, but becomes dependent again upon the sign of the magnetic shear.« less
  • Finite Larmor radius (FLR) effects, originally shown to stabilize magnetized plasma interchange modes at short wavelength, are shown to assist velocity shear stabilization of long wavelength interchanges. It is shown that the FLR effects result in stabilization with roughly the same efficacy as the stabilization from dissipative (resistive and viscous) effects found earlier.