Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm51b0822s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM51B-0822
Other
2712 Electric Fields (2411), 2772 Plasma Waves And Instabilities
Scientific paper
The role of velocity shear-driven instabilities in space plasmas has recently received considerable attention. Broadband extremely low frequency waves (BBELF) are frequently observed in both the ionosphere and the laboratory. In space the BBELF waves have frequencies from nearly DC to above the H+ cyclotron frequency with electric fields which are oriented mostly perpendicular to the magnetic field, but may have a significant component along the magnetic field. Frequently the parallel current in these situations is below the critical threshold for the current driven ion-cyclotron instability. However, BBELF waves are frequently coincident with quasi-DC small-scale transverse electric fields which suggests that the inhomogeneous transverse electric field is a free energy source which may assist in producing BBELF waves. We shall discuss several instabilities driven by a structured transverse electric field in a warm fluid plasma. The inhomogeneous energy density driven instability has recently received a significant amount of theoretical and experimental attention. This instability is driven by a negative energy ``well'' localized within the inhomogeneous plasma flow. The growth rate of this instability is independent of shear (V'=dV/dx, where V is the plasma velocity) in the simplified theoretical models studied to date. We derive growth rates and thresholds for this instability in a warm fluid plasma within a simplified fluid model. A true shear driven instability in a linearly sheared electric field is characterized. We find that the growth rate is a function of both the shear scale Ls and the normalized shear frequency α =V'/Ω i i. The critical threshold for this instability is approximately α ~0.5 or lower. Lastly we consider another instability driven by the curvature (d2V/dx2) of the plasma flow. This work has been supported by ONR and NASA.
Ganguli Gurudas I.
Schuck Peter W.
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