Vlasov simulations of multi-ion plasma turbulence in the solar wind

TL;DR

This study uses hybrid Vlasov-Maxwell simulations to explore kinetic effects and non-Maxwellian features in multi-ion plasma turbulence, revealing ion anisotropies, preferential heating, and distribution distortions consistent with solar wind observations.

Contribution

It introduces a multi-ion Vlasov model to accurately simulate kinetic effects and non-Maxwellian features in turbulent solar wind plasma, advancing understanding of ion-specific behaviors.

Findings

Ion velocity distributions deviate from thermal equilibrium.

Alpha particles show more pronounced anisotropy and perpendicular heating.

Distribution functions exhibit bumps along magnetic field lines.

Abstract

Hybrid Vlasov-Maxwell simulations are employed to investigate the role of kinetic effects in a two-dimensional turbulent multi-ion plasma, composed of protons, alpha particles and fluid electrons. In the typical conditions of the solar-wind environment, and in situations of decaying turbulence, the numerical results show that the velocity distribution functions of both ion species depart from the typical configuration of thermal equilibrium. These non-Maxwellian features are quantified through the statistical analysis of the temperature anisotropy, for both protons and alpha particles, in the reference frame given by the local magnetic field. Anisotropy is found to be higher in regions of high magnetic stress. Both ion species manifest a preferentially perpendicular heating, although the anisotropy is more pronounced for the alpha particles, according with solar wind observations. Anisotropy of the alpha particle, moreover, is correlated to the proton anisotropy, and also depends on the local differential flow between the two species. Evident distortions of the particle distribution functions are present, with the production of bumps along the direction of the local magnetic field. The physical phenomenology recovered in these numerical simulations reproduces very common measurements in the turbulent solar wind, suggesting that the multi-ion Vlasov model constitutes a valid approach to the understanding of the nature of complex kinetic effects in astrophysical plasmas.