A Multi-ion Model of the Heliosphere with Secondary Charge Exchange

Charge exchange between the solar wind (SW) and local interstellar medium (LISM) involves a complicated mixture of the unperturbed SW and LISM, primary pick-up ions (PUIs), and secondary PUIs and neutral atoms produced from multiple charge exchange processes. Furthermore, these processes are qualitatively different in each heliospheric region (supersonic SW, heliosheath, and LISM), potentially yielding over a dozen categories of charged and neutral particles with distinct properties as shown by kinetic simulations. We present a 3D multi-fluid MHD model with one primary and two secondary neutral fluids, an ion fluid for the mixture of SW and PUIs, and additional source terms for PUI pressure and density. Some charge exchanges produce hot ions which are grouped together as PUIs, while others produce ions with similar properties to the SW. This approach is supposed to bring the accuracy of the fluid model closer to that of kinetic models, in addition to reproducing phenomena observed by spacecraft, e.g., Voyager and IBEX.