Energy Separation Between Thermal and Pickup Ions in the Heliosheath

Abstract:

Charge exchange between the solar wind (SW) and local interstellar medium (LISM) creates a population of hot ions which do not reach thermal equilibrium with the original solar wind before exiting the heliosphere. These pickup ions (PUIs) make up the dominant contribution to the plasma thermal energy in the heliosheath despite their small number density relative to the SW plasma. The separation of energy between thermal and pickup ions therefore significantly influences the width of the heliosheath. We present a multi-fluid MHD-neutral model of the heliosphere with PUIs treated as a separate ion fluid. The contribution of PUIs is adjusted both through source terms for charge exchange and through boundary conditions at the termination shock, taking into account reflection and transmission of ions at the shock. This approach allows us to decrease the heliosheath width in accordance with Voyager 1 observations. We present results of our numerical simulation of the time-dependent heliosphere. In particular, our previous solar cycle models are upgraded with a new approach and comparison is made both between one-ion- and two-ion-fluid models and with observational data. These results are aimed to improve our understanding of Voyager and IBEX observations through numerical modeling.