Transport coefficients enhanced by suprathermal particles in nonequilibrium heliospheric plasmas

Abstract

Context. In heliospheric plasmas, such as the solar wind and planetary magnetospheres, the transport of energy and particles is governed by various fluxes (e.g., heat flux, particle flux, current flow) triggered by different forces, electromagnetic fields, and gradients in density or temperature. In the outer corona and at relatively low heliocentric distances in the solar wind (i.e., < 1 AU), particle-particle collisions play an important role in the transport of energy, momentum, and matter, described within classical transport theory by the transport coefficients, which relate the fluxes to their sources. Aims. The aim of the present paper is to improve the evaluation of the main transport coefficients in such nonequilibrium plasmas, on the basis of an implicit realistic characterization of their particle velocity distributions, in accord with the in situ observations. Of particular interest is the presence of suprathermal populations and their influence on these transport coefficients. Methods. Using the Boltzmann transport equation and macroscopic laws for the energy and particle fluxes, we derived transport coefficients, namely, electric conductivity, thermoelectric coefficient, thermal conductivity, diffusion, and mobility coefficients. These are conditioned by the electrons, which are empirically well described by the Kappa distribution, with a nearly Maxwellian (quasi-thermal) core and power-law tails enhanced by the suprathermal population. Here we have adopted the original Kappa approach that has the ability to outline and quantify the contribution of suprathermal populations. Results. Without exception, the transport coefficients are found to be systematically and markedly enhanced in the presence of suprathermal electrons (i.e., for finite values of the κ parameter), due to the additional kinetic energy with which these populations contribute to the dynamics of space plasma systems. The present results also show how important an adequate Kappa modeling of suprathermal populations is, which is in contrast to other modified interpretations that underestimate the effects of these populations.

On modeling ICME cross-sections as static MHD columns

“…Going by this comparison, it is fair to conclude that MC plasmas adhere better (than laboratory plasmas) to the basic assumptions made in MHD. Since the electrons in ICMEs can be non-Maxwellian (Nieves-Chinchilla and Viñas, 2008), we note that transport coefficients such as the conductivity might be somewhat enhanced (Husidic et al, 2021).…”

Magnetohydrodynamic Mode Conversion in the Solar Corona: Insights from Fresnel-like Models of Waves at Sharp Interfaces

“…Besides Pedersen currents, several other channels of ion-neutral interaction have been proposed to be important in the chromosphere (e.g., Khomenko et al 2018;Martínez-Sykora et al 2020). Also, the collisional transport coefficients may also be higher if the electrons, ions, and neutral atoms have non-Maxwellian velocity distributions (Husidic et al 2021). Lastly, our assumption of a simple temperature-dependent ionization-recombination equilibrium, which includes only hydrogen, should be replaced by more self-consistent physics (again, see codes like Bifrost or MuRAM; Carlsson et al 2016;Przybylski et al 2022).…”

Discussion on the transport processes in electrons with non-Maxwellian energy distribution function in partially-ionized plasmas

“…In these plasmas, the EEDFs are also measured as non-Maxwellian with populated tails, usually well-fitted with Kappa distributions [16]. The influence of the suprathermal particles on the transport coefficients has been studied by Husidic et al [17] by considering a fully-ionized plasma and a Krook-type collisional operator.…”