Heating of coronal holes and generation of the solar wind by ion-cyclotron resonance

We discuss a new model to describe the heating of the magnetically open solar corona and the acceleration of the fast solar wind by the cyclotron resonant interaction of coronal ions with ion-cyclotron waves. This 'kinetic shell' model includes important details of the wave-particle interaction which are not present in most other treatments. In this model, we approximate the evolution of the collisionless coronal ion distribution through the assumption that the pitch-angle scattering by the resonant ion-cyclotron waves is much faster than the other processes taking place. Under this assumption, the resonant ions uniformly populate velocity-space surfaces, or shells, of constant energy in the frame moving with the wave phase speed. We show that a fast solar wind can be generated by this process. Furthermore, we present a number of properties of the resonant interaction that are implied by this model: (1) The amount of wave energy that can be absorbed by the proton distribution at a given radial position is limited. (2) The proton distribution generated by the interaction with outward-propagating waves will necessarily be unstable to the generation of inward-propagating waves, so a complete description must include waves of both propagation directions. (3) The structure of the resonant shells for ions heavier than protons indicates that these ions will be perpendicularly heated by the second-order Fermi process, an energization channel that is not available to the protons. This last point is particularly intriguing, and may lead to a fundamentally new way to produce the preferential effects on heavy ions in the fast solar wind.