Abstract
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.
Highlights
The multi-ion nature of the solar wind and planetary/cometary plasmas gives rise to new and interesting effects
Space measurements near the nonmagnetized planets with extended ionospheric/atmospheric shells have shown the appearance of unexpected boundaries (e.g. pile-up boundaries at Mars and Venus (Acuna et al, 1998; Bertucci et al, 2005; Boesswetter et al, 2004). The nature of these boundaries remains unclear, it is suggested that the multi-ion origin of the interacting plasmas may be a key element. Another interesting feature of the plasma environment of comets and nonmagnetized planets is the observations of strongly nonlinear coherent wave structures which often fill the broad regions of the interaction between different plasmas (Reme et al, 1987, 1993)
Compression of the protons is followed by a sudden rarefaction and acceleration, while the oxygen ions continue to be decelerated. Such unusual behavior of different ion species hints that the inclusion of dissipation may lead to the appearance of the peculiar heavy ion shock characterized by a proton rarefaction (Fig. 6d)
Summary
The multi-ion nature of the solar wind and planetary/cometary plasmas gives rise to new and interesting effects. The nature of these boundaries remains unclear, it is suggested that the multi-ion origin of the interacting plasmas may be a key element Another interesting feature of the plasma environment of comets and nonmagnetized planets is the observations of strongly nonlinear coherent wave structures which often fill the broad regions of the interaction between different plasmas (Reme et al, 1987, 1993). 3 we include a magnetic field transverse to the plasma flow In this case a sonic point translates to a locus in the (upx, uhx) plane, which corresponds to a superfast-subfast transition, and the value of speed which generalizes the fast magnetosonic speed in a bi-ion plasma, is evaluated. It is shown that the characteristics of a flow may be strongly influenced by the possible existence of solitary and oscillatory structures
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