Electromagnetic Ion/Beam Instabilities In The Fast Solar Wind: Proton Core Temperature Anisotropy Effects On The Relative Drift Speed And Ion Heating

Ion velocity distributions in the fast solar wind are usually characterized by nonthermal features such as multicomponent ions, temperature anisotropies and average relative drifts. These nonthermal features lead to the growth of several electromagnetic instabilities. Here, two-dimensional hybrid simulations are used to study these instabilities in a homogeneous, magnetized collisionless plasma model. We show that for conditions typical of the fast solar wind the proton core temperature anisotropy plays a significant role in modifying the wave-particle scattering of each proton component as compared to the isotropic cases. As a consequence, the scattering reduces both the heating and anisotropy enhancement of the proton beam and decreases the relative proton/ion flow speed below the corresponding isotropic instability thresholds in agreement with recent observations and with our previous one-dimensional study. Our results are consistent with recent satellite observations and provide support to the physical scenario in which core temperature anisotropies play a regulating effect on the instability thresholds.