Modeling Solar Wind Interaction with the Local Interstellar Medium using Kinetically-Derived Rankine-Hugoniot Conditions for Pickup Ions

Non-thermal, pickup ions (PUI) are born when interstellar neutral atoms experience charge exchange charge with the solar wind (SW) ions. PUIs created in the supersonic SW quickly acquire the velocity of ambient ions, but are never in equilibrium with them. The PUI pressure soon becomes dominant as compared with the thermal SW ion pressure and magnetic pressure. While there were several attempts to model the SW interaction with the local interstellar medium (LISM) with PUIs treated on different levels of sophistication, they are not entirely satisfactory because of the very approximate description of their crossing of the (collisionless, quasi-perpendicular) heliospheric termination shock (TS). The challenging aspect of this process is that the PUI distribution function becomes anisotropic in the shock vicinity. We have used test-particle and full PIC simulations to describe such boundary conditions and parameterize them using the shock angle and magnetic compression across the shock. This allows us to model the 3-D SW-LISM interaction and compare our new results with those obtained with the traditional approaches that ignore the kinetics of ions crossing the TS. Simulations are performed using our Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS), which is capable of modeling PUIs as an ion component separate from the thermal SW plasma. This is done by treating PUIs as a separate fluid, the distribution function of which is isotropic away from the TS. With our new boundary conditions, we are able to improve the accuracy of simulations and make them physically consistent. Our new results are compared with those obtained with the traditional approaches that ignore the ion kinetics near the TS.