Effects of Radial Expansion, Collisions, and Wave-Particle Interactions on Protons, Electrons, and Alpha Particles in the Solar Wind

The solar wind is replete with non-thermal features, which includes various temperature anisotropies associated with the charged particles. Observations made in the near-Earth environment as well as close to the Sun, as evidence from the recent Parker Solar Probe (PSP) mission, show that the solar wind is characterized by a broad distribution in 2D phase space defined by the plasma beta and the ratio of perpendicular versus parallel plasma temperatures. The outer boundaries of such a 2D data distribution is partially encompassed by various marginal stability conditions associated with temperature anisotropy instabilities. The remaining boundaries may be associated with collisional effects as well as heating by finite-amplitude EM fluctuations. The present paper discusses the latest model of the solar wind in which the combined effects of solar wind radial expansion, the spiraling magnetic field, collisional processes among different charged-particle species, and wave-particle interaction processes, which includes various kinetic instabilities driven by the temperature anisotropy and/or the heat flux, as well as resonant heating, are modeled in a comprehensible manner. The basic theoretical framework utilizes the model of the solar wind density, magnetic field, and quasi-constant average solar wind speed, combined with the quasilinear theory of kinetic instabilities and resonant heating. The model calculation will be compared against the 1AU observations as well as the recent PSP dataset.