Charge exchange in plasmas with temperature anisotropy

Resonant charge-exchange fluid-dynamic expressions are derived for a partially ionized monatomic hydrogen gas with an isotropic neutral component and a bi-Maxwellian ionized component. The expressions are based on published results for the cross section and are valid for arbitrary ratios between thermal and bulk velocities and values of the temperature anisotropy. Although the exact analytic expressions are unwieldy, an approximate formalism allows one to quickly and efficiently compute the moments of the charge-exchange source term with a minimum loss in accuracy. The errors in the source terms are reported for a range of parameters covering most space and astrophysical environments. The paper discusses possible effects of charge exchange on the anisotropy of solar-wind and interstellar protons in the heliosphere and the surrounding interstellar space.