Toward a realistic macroscopic parametrization of space plasmas with regularized κ-distributions

¹ Centre for Mathematical Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven, Belgium
² Institute for Theoretical Physics IV, Ruhr-University Bochum, 44780 Bochum, Germany
e-mail: mlazar@tp4.rub.de
³ Research Dept. Plasmas with Complex Interactions, Ruhr-University Bochum, 44780 Bochum, Germany
⁴ Space Physics Department and STCE, Royal Belgian Institute for Space Aeronomy, 1180 Brussels, Belgium
⁵ ELI-C (Earth Life Institute), Université Catholique de Louvain (UCLouvain), 1348 Louvain-La-Neuve, Belgium

Received: 7 October 2019
Accepted: 20 December 2019

Abstract

So-called κ-distributions are widely invoked in the analysis of nonequilibrium plasmas from space, although a general macroscopic parametrization as known for Maxwellian plasmas near thermal equilibrium is prevented by the diverging moments of order l ≥ 2κ − 1. To overcome this critical limitation, recently novel regularized κ-distributions (RK) have been introduced, including various anisotropic models with well-defined moments for any value of κ >  0. In this paper, we present an evaluation of the pressure and heat flux of electron populations, as provided by moments of isotropic and anisotropic RKs for conditions typically encountered in the solar wind. We obtained finite values even for low values of κ <  3/2, for which the pressure and heat flux moments of standard κ-distributions are not defined. These results were also contrasted with the macroscopic parameters obtained for Maxwellian populations, which show a significant underestimation especially if an important suprathermal population is present (e.g., for κ <  2), but ignored. Despite the collisionless nature of solar wind plasma, a realistic characterization as a fluid becomes thus possible, retaining all nonthermal features of plasma particles.