Analytical model of a magnetopause with countercurrents: multicomponent plasma with arbitrary particle energy distributions

We propose an analytical model for a distributed current sheet separating two regions of anisotropic collisionless plasma with different values of magnetization and different effective temperatures of the energy distributions of electrons and ions [1, 2]. Namely, we find a solution to the Vlasov–Maxwell equations in the form of a superposition of arbitrary isotropic distribution functions of particle energy, each multiplied by a Heaviside step function of one of the projections of the generalized momentum. This solution admits the shear of magnetic field lines and the presence of several ion components with different effective temperatures and localized countercurrents with arbitrary densities and spatial shifts.

It is shown that a certain choice of the energy distribution of particles (Maxwellian, kappa, and others) determine only the quantitative, not qualitative, properties of the constructed models. Sheets containing several fractions of particles with countercurrents, shifted relative to each other in space and having different scales, allow multiple non-monotonic changes in the magnetic field value and direction. The total thickness of the current sheet is determined by the values of shifts between the currents of the plasma fractions with the highest energy content and by the typical gyroradii of their particles.

We carried out particle-in-cell simulations of the analytically constructed magnetic transition layers in one-dimensional and two-dimensional geometries. The stability of the simplest models of the considered class is demonstrated, which is consistent with qualitative estimates of stability against Weibel-type perturbations.

The proposed models make it possible to interpret modern data of satellite observations of multicomponent current sheets in the regions of the magnetopause and the bow shock, solar wind magnetic clouds and high coronal magnetic structures, and to analyze their fine structure taking into account the observed suprathermal, nonequilibrium particle fractions.

The investigation of stability of current sheets was supported by the Russian Science Foundation under grant No. 20-12-00268.

1. Kocharovsky V. V., Kocharovsky Vl. V., Martyanov V. Yu., Nechaev A. A. An analytical model for the current structure of the magnetosheath boundary in a collisionless plasma // Astron. Lett. 2019. V. 45, No. 8. P. 551–564. doi:10.1134/S1063773719080048 .

2. Kocharovsky V. V., Kocharovsky Vl. V., Nechaev A. A. Analytical model of a magnetopause in a multicomponent collisionless plasma with a kappa energy distribution of particles // Doklady Physics. 2021. V. 496. In press.