Kappa Distributions: The Injection Problem At Perpendicular Shocks And The Transmission Problem At The Heliospheric Termination Shock

Abstract:

The extended high-energy tail associated with kappa distributions has been exploited to model plasmas mediated by energetic particles. Two cases of particular relevance include the so-called injection problem at shock waves. 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 a shock 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 reverse question at the heliospheric termination shock is discussed viz., what form does the pickup ion distribution downstream of the heliospheric termination shock assume? We show that this closely resembles a kappa distribution. We illustrate the importance of using a kappa distribution in the context of large-scale simulations of the solar wind – local interstellar medium interaction.