Charge-Exchange in Global Heliospheric Models: A Comparison of Source Term Integration Methods

The NASA missions, Interstellar Boundary Explorer (IBEX) and Voyager I & II, provide invaluable data for studying the solar wind - local interstellar medium interactions. Simulation models of the heliosphere provide complementary views, giving additional insight into data interpretation. Current leading models facilitate a hybrid approach, i.e. a fluid magnetohydrodynamic (MHD) solver for electrons and ions coupled via charge-exchange with a kinetic Boltzmann solver for neutral atoms. The hybrid approach is necessary due to dynamics on many spatial scales and deviations from local thermal equilibrium. In this work we investigate new methods of computing the charge-exchange source terms that are vital in the MHD-kinetic coupling procedure. We compare assumptions about the heliospheric plasma distribution and integration schemes used to compute the charge-exchange source terms. These comparisons may give us insight into how the inclusion of helium into global heliospheric models can be handled with respect to charge-exchange.