Hybrid model of inhomogeneous solar wind plasma heating by Alfvén wave spectrum: Parametric studies

Abstract

Observations of the solar wind plasma at 0.3 AU and beyond show that a turbulent spectrum of magnetic fluctuations is present. Remote sensing observations of the corona indicate that heavy ions are hotter than protons and their temperature is anisotropic (T⊥/T∥ ≫ 1). We study the heating and the acceleration of multi‐ion plasma in the solar wind by a turbulent spectrum of Alfvénic fluctuations using a 2‐D hybrid numerical model. In the hybrid model the protons and heavy ions are treated kinetically as particles, while the electrons are included as neutralizing background fluid. This is the first two‐dimensional hybrid parametric study of the solar wind plasma that includes an input turbulent wave spectrum guided by observation with inhomogeneous background density. We also investigate the effects of He++ ion beams in the inhomogeneous background plasma density on the heating of the solar wind plasma. The 2‐D hybrid model treats parallel and oblique waves, together with cross‐field inhomogeneity, self‐consistently. We investigate the parametric dependence of the perpendicular heating, and the temperature anisotropy in the H+‐He++ solar wind plasma. It was found that the scaling of the magnetic fluctuations power spectrum steepens in the higher‐density regions, and the heating is channeled to these regions from the surrounding lower‐density plasma due to wave refraction. The model parameters are applicable to the expected solar wind conditions at about 10 solar radii.