Boundary Conditions at the Heliospheric Termination Shock with Pickup Ions

Abstract

In a collisionless shock the directed flow energy is converted mainly in thermal energy of the plasma species. At the termination shock (TS) a substantial portion of energy goes into heating of pickup ions (PUIs), while heating of the solar wind protons (SW) is weaker than it would be without PUI. Heating of both species is nonadiabatic. Downstream pressure of the mixture is determined by conservation laws for the whole mixture. SW heating is sensitive to the details of the shock front, while heating of PUI is not. The profile is an analytical approximation of the observed TS. Here the downstream temperature and pressure of PUIs are obtained for the first time using test particle analysis in a model shock profile for various magnetic compression ratios and shock angles. The profile is an analytical approximation of the observed TS. The results of the analysis are used in the pressure balance equation and the corresponding SW heating is estimated. The analysis is supported by full particle simulations, except for the SW heating that was not studied using test particle data due to its apparent dependence on fine structure of the shock front.