Modeling the temperature anisotropies and differential acceleration of protons and heavy ions in the expanding, turbulent solar wind: comparing numerical simulations with spacecraft observations.

The fast solar wind is the outflow of hot ionized gas, called plasma, which originates at the Sun and travels in the interplanetary space with a typical speed of 600-800 km/s. It consists mainly of electrons, protons and a small fraction of heavy ions, such as double ionized helium nuclei. The solar wind medium is permeated by different electromagnetic waves, which are believed to play important role for particle heating and energization. Heavy ions in the fast solar wind are known to be hotter and travel faster than their lighter companions, the protons. What causes this preferential heating and acceleration is still an open question, so far unanswered by the solar community. In this study we propose to perform computer simulations to study the effect of wave-particle interactions and their consequences for ion heating and acceleration in the fast solar wind. The aim is to investigate whether certain types of waves can preferentially heat and accelerate the heavy ions. Combining observations and simulations we will study the highly nonlinear (turbulent) evolution of electromagnetic waves, how they are emitted and absorbed by the solar wind plasma, and how this changes the ion properties, like temperatures, outflow velocities, etc. The solar wind is also known to expand throughout the interplanetary space and to have different temperatures along and across the ambient magnetic field. Our model takes into account the solar wind expansion and the anisotropic ion heating.