The kinetic shell model of coronal heating and acceleration by ion cyclotron waves 1. Outward propagating waves

We introduce a new kinetic treatment of the heating of the magnetically open solar corona and the acceleration of the fast solar wind by the cyclotron resonant interaction of coronal protons with ion cyclotron waves. In this kinetic shell formalism we approximate the evolution of the collisionless coronal proton distribution by the assumption that the pitch angle diffusion due to the resonant ion cyclotron waves is much faster than the other processes taking place. Under this assumption the resonant protons uniformly populate velocity space surfaces, or shells, of constant energy in the frame moving with the wave phase speed. These resonant shells then evolve slowly in response to the nonresonant large-scale forces in the system. For this initial demonstration of the kinetic shell concept, we additionally take the resonant waves to be solely outward propagating and dispersionless. In this case the resonant shells are spherical sections in velocity space which are confined to the sunward half of the proton distribution. We then calculate the radial evolution of collisionless protons in a coronal hole using this simplified system, which also includes the effects of gravity, the charge-separation electric field, and the mirror force. We find that a fast solar wind can be generated by this process using reasonable values of the physical parameters. However, we also prove that the proton distribution generated by the interaction with only outward propagating waves will necessarily be unstable to the generation of inward propagating waves. Thus this illustrative calculation is incomplete and will have to be extended to include waves in both propagation directions.