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Ann. Geophys., 24, 3041-3057, 2006
www.ann-geophys.net/24/3041/2006/
© European Geosciences Union 2006
Nonlinear 1-D stationary flows in multi-ion plasmas – sonic and critical loci – solitary and "oscillatory" waves
E. M. Dubinin1, K. Sauer1, and J. F. McKenzie1,2,3
1Max-Planck-Institute für Sonnensystemforschung, Lindau, Germany
2School of Pure and Applied Physics, University of Natal, Durban, South Africa
3University of California, Riverside, CA, USA
Abstract. One-dimensional stationary flows of a plasma consisting of two ion
populations and electrons streaming against a heavy ion cloud are
studied. The flow structure is critically governed by the position
of sonic and critical points, at which the flow is shocked or
choked. The concept of sonic and critical points is suitably
generalized to the case of multi-ion plasmas to include a
differential ion streaming. For magnetic field free flows, the
sonic and critical loci in the (upx, uhx) space coincide.
Amongst the different flow patterns for the protons and heavy ions,
there is a possible configuration composed of a "heavy ion shock"
accompanied by a proton rarefaction. The magnetic field introduces a
"stiffness" for the differential ion streaming transverse to the
magnetic field. In general, both ion fluids respond similarly in the
presence of "ion obstacle"; the superfast (subfast) flows are
decelerated (accelerated). The collective flow is choked when the
dynamic trajectory (upx, uhx) crosses the critical loci. In
specific regimes the flow contains a sequence of solitary structures
and as a result, the flow is strongly bunched. In each such
substructure the protons are almost completely replaced by the
heavies. A differential ion streaming is more accessible in the
collective flows oblique to the magnetic field. Such a flexibility
of the ion motion is determined by the properties of energy
integrals and the Bernoulli energy functions of each ion species.
The structure of flows, oblique to the magnetic field, depends
critically
on the velocity regime and demonstrates a rich
variety of solitary and oscillatory nonlinear wave structures. The
results of the paper are relevant to the plasma and field
environments at comets and planets through the interaction with the
solar wind.
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