Kinetic Behavior of Pickup Ions at Shocks and its Incoporation into Global MHD Simulations

Interstellar neutral atoms can penetrate deeply into the heliosphere, where they can be ionized by diffrent physical process, of which charge exchange with the solar wind (SW) plasma plays a major role. The newly created ions quickly acquire the bulk speed of the ambient SW ions, but have no time to reach thermal equilibrium with them. These nonthermal, pickup ions (PUIs) gain energy from SW and decelerate it. PUI-generated turbulence heats up the primary SW ions through wave-particle interaction. PUIs and their effect on the SW are observed in situ. On the other hand, the behavior of PUIs at collisionless shocks is a subject of intense theoretical studies and kinetic simulations, which reavealed a sophisticated structure of shocks and strong anisotropies in the PUI distribution functions. Unfortunately, due to the necessity of extreme computational resources, the kinetic behavior of PUIs at shocks cannot be performed in the framework of global MHD simulations. We propose a systematic approach to incorporate the kinetic behavior of PUIs at the heliosphereic termination shock into a global MHD model of the SW interaction with the local interstellar medium as boundary conditions. We also discuss full PIC and hybrid simulations used in our new model. The results show better agreement with observational data behind the termination shock. They are also in agreement with New Horizons measurements in the supersonic SW.