Density jump as a function of magnetic field for switch-on collisionless shocks in pair plasmas

The properties of collisionless shocks, like the density jump, are usually derived from magnetohydrodynamics (MHD), where isotropic pressures are assumed. Yet, in a collisionless plasma, an external magnetic field can sustain a stable anisotropy. We have already devised a model for the kinetic histo...

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Bibliographic Details
Published in:Journal of plasma physics 2022-06, Vol.88 (3), Article 905880320
Main Authors: Bret, Antoine, Narayan, Ramesh
Format: Article
Language:English
Subjects:
Anisotropy
Collisionless plasmas
Density
External pressure
Laboratories
Magnetic fields
Magnetic properties
Magnetohydrodynamics
Plasma physics
Plasmas (physics)
Temperature
Upstream
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Summary:The properties of collisionless shocks, like the density jump, are usually derived from magnetohydrodynamics (MHD), where isotropic pressures are assumed. Yet, in a collisionless plasma, an external magnetic field can sustain a stable anisotropy. We have already devised a model for the kinetic history of the plasma through the shock front (J. Plasma Phys., vol. 84, issue 6, 2018, 905840604), allowing to self-consistently compute the downstream anisotropy, and hence the density jump, in terms of the upstream parameters. This model deals with the case of a parallel shock, where the magnetic field is normal to the front both in the upstream and the downstream. Yet, MHD also allows for shock solutions, the so-called switch-on solutions, where the field is normal to the front only in the upstream. This article consists in applying our model to these switch-on shocks. While MHD offers only one switch-on solution within a limited range of Alfvén Mach numbers, our model offers two kinds of solutions within a slightly different range of Alfvén Mach numbers. These two solutions are most likely the outcome of the intermediate and fast MHD shocks under our model. While the intermediate and fast shocks merge in MHD for the parallel case, they do not within our model. For simplicity, the formalism is restricted to non-relativistic shocks in pair plasmas where the upstream is cold.
ISSN:0022-3778
1469-7807
DOI:10.1017/S0022377822000605