Ion Heating Due to Plasma Microinstabilities in Coronal Holes and the Fast Solar Wind

Abstract

There is growing evidence that the heating of ions in coronal holes and the fast solar wind is due to cyclotron resonant damping of ion cyclotron waves. At the same time, the origin of these waves is much less understood. We suggest that the source of the waves in the coronal holes is a heat flux coming from the Sun. The heat flux generates ion cyclotron waves through plasma microinstability, and then the waves heat the ions. We use a new view according to which the heat flux is launched intermittently by small‐scale reconnection events (nanoflares) at the coronal base. This allows the heat flux to be sporadically large enough to drive the instabilities, while at the same time to satisfy the time‐averaged energy requirements of the solar wind. Depending on the plasma parameters, the heat flux can excite shear Alfven and electrostatic ion cyclotron waves. We show that, for reasonable parameters, the heat flux is sufficient to drive the instability that results in significant heating of protons and heavy io...