Computational and Theoretical study of the acceleration and heating of ions in the Solar Wind

The problem of acceleration and heating of minor ions in the solar wind has received a special attention during the last decades. Recent observations and theoretical results seem to indicate that most of the acceleration process occurs within a few solar radii from the Sun and the main mechanism is due to resonant absorption of ion-cyclotron waves. However, the detailed processes for the energy transfer between waves and different particle species is still an open question. To address these issues, we investigate the wave-particle interaction and evolution of circularly polarized electromagnetic ion-cyclotron waves propagating parallel to the background magnetic field. The analysis presented follow two approaches: (1) we have developed a quasi-linear theory to understand the energy cascade in which there is a transfer of wave energy from longer to shorter wave modes, with the subsequent acceleration of ions with increasing q/m ratio; and (2) we preformed one-dimensional hybrid simulations of the system using a spherically expanding box model where a thin box of plasma moves away from the Sun, in a moving frame at the local solar wind speed to investigate the fully non-linear wave-particle interaction of the cascade process. All these effects, i.e., energy cascade, expansion and non-linear wave-particle interaction, are included in the study to show how the shape of the particle velocity distribution functions are controlled and regulated in the solar wind.