Entropy generation at the multi-fluid solar wind termination shock producing anomalous cosmic ray particles

Abstract

Different from other work the solar wind termination shock is described here as a multi-fluid phenomenon taking into account the wavefield-induced, magnetohydrodynamic self-interaction of a multi-species plasma, consisting of solar wind ions, pick-up ions and shock-generated anomalous cosmic ray particles. Caused by the diffusive interaction of the low- and high-energy plasmas, an extended transition structure of the shock is formed consisting of a precursor region and a gas dynamic sub-shock. The innerheliospheric pick-up ions, when convected with the solar wind plasma towards the sub-shock, will serve there as a local source, and all over the precursor region as a continuous source, of high energy particles via first-order Fermi acceleration in the shock-induced wave turbulences, thereby being energized from keV up to MeV energies and thus will operate as an entropy generator. The spatial diffusion of these high energy particles relative to the resulting, pressure-modified solar wind flow structure is described by a coupled system of differential equations describing mass-, momentum-, and energy-flow continuities for all plasma components. The energy loss due to escape of energetic particles (MeV) from the precursor into the inner heliosphere is taken into account. The hydrodynamic properties of the anomalous cosmic ray gas and the low-energy solar wind are determined in a consistent manner both for solutions with existing sub-shocks and for shock-free solutions. Also the variation of the compression ratio within the shock structure is quantitatively determined and is related to the pick-up ion energization efficiency and to the mean energy of the downstream anomalous cosmic ray particles. The variation of the resulting shock structure and of the extent of solar wind sheath plasma beyond the shock is discussed with respect to its consequences for the LISM neutral gas filtration and to the three-dimensional shape of the heliosphere.