Towards a realistic evaluation of transport coefficients in non-equilibrium space plasmas

TL;DR

This paper estimates transport coefficients in non-equilibrium space plasmas using regularised Kappa distributions, revealing significant differences from Maxwellian assumptions especially for low ppa values, which are relevant for suprathermal particles.

Contribution

It introduces a method to compute finite, well-defined transport coefficients in space plasmas using regularised Kappa distributions, addressing divergences in standard models.

Findings

Transport coefficients are finite for all ppa > 0.

Low ppa values lead to much higher transport coefficients than Maxwellian predictions.

Ignoring suprathermal electrons can cause significant underestimations of transport properties.

Abstract

Recent studies have outlined the interest for the evaluation of transport coefficients in space plasmas, where the observed velocity distributions of plasma particles are conditioned not only by the binary collisions, e.g., at low energies, but also by the energisation of particles from their interaction with wave turbulence and fluctuations, generating the suprathermal Kappa-distributed populations. This paper provides a first estimate of the main transport coefficients based on regularised Kappa distributions (RKDs), which, unlike standard Kappa distributions (SKDs), enable macroscopic parameterisation without mathematical divergences or physical inconsistencies. All transport coefficients derived here, i.e., the diffusion and mobility coefficients, electric conductivity, thermoelectric coefficient and thermal conductivity, are finite and well defined for all values of $\kappa > 0$. Moreover, for low values of $\kappa$ (i.e., below the SKD poles), the transport coefficients can be orders of magnitudes higher than the corresponding Maxwellian limits, meaning that significant underestimations can be made if suprathermal electrons are ignored.