The Generation of Kappa distributions At Perpendicular Shocks And The Heliospheric Termination Shock

Abstract:

Although wave-particle interactions may maintain a pre-existing kappa distribution throughout the solar wind once formed, an important question is to identify the origin of a quasi-kappa distribution. It transpires that the dissipation mechanism at quasi-perpendicular shocks and the so-called injection problem at shock waves may be of particular relevance to the formation of initial quasi-kappa distributions throughout the solar wind. In particular, the question of how particles are injected into the diffusive shock acceleration (DSA) mechanism at a perpendicular shock can be addressed on the basis of a kappa distribution. We discuss briefly the possible formation of a kappa distribution at interplanetary shocks and show how this is then accelerated at a quasi-perpendicular shock. These results are related to observed energetic particle spectra downstream of an interplanetary shock. The related question of the dissipation mechanism at the quasi-perpendicular heliospheric termination shock is discussed, focusing particularly in the important role of the pickup ion distribution upstream and downstream of the heliospheric termination shock. We show that the downstream proton distribution in the inner heliosheath closely resembles a kappa distribution.