Knudsen number as a non-thermal parameter: possible origin of skewness in space plasma distributions

Abstract

Non-Maxwellian distributions and their origins in space plasma have attracted significant attention due to their prevalence and impact on various astrophysical and space-related phenomena. This paper presents a theoretical study of the consequences of incorporating a Skew-Kappa distribution to describe the non-thermal electron distribution in the solar wind. By introducing a Krook-like term into the Boltzmann equation to represent collision effects, we investigate the dependence of the skewness parameter on plasma macro-dynamics. Our analysis focuses on understanding the departure from thermal equilibrium and the statistical behavior of the plasma under the influence of collisional processes. By analyzing the Boltzmann transport equation adapted to space plasma, we derive expressions for the skewness parameter as a function of plasma parameters and the collision effect. Our results provide valuable information on the relationship between skewness, collisional dynamics, and the statistical properties of space plasmas, namely $\delta \sim K_N$, the relationship between the skewness parameter and the effective Knudsen number. This study contributes to a deeper understanding of non-Maxwellian distributions and their role in astrophysical and space plasma phenomena.