Multifluid equilibrium model of current sheets with interpenetrating ion beams

The solar wind plasma is replete with transient, intense current sheets—also known as solar wind discontinuities—that play a crucial role in solar wind heating and energetic particle scattering. While these discontinuities share similarities with the classical magnetohydrodynamic (MHD) model of rotational discontinuities, they also exhibit complex kinetic behavior beyond single-species fluid models. In particular, spacecraft observations frequently reveal counterstreaming ion populations traversing these structures, suggesting that a multi-component plasma description is needed. This study presents a multifluid model of current sheets in which the stress balance and velocity difference are described by the kinetics of interpenetrating ion beams crossing the current sheet. Incorporating a nonzero normal and a guide magnetic field, this multifluid model bridges the gap between overly simplified single-fluid MHD descriptions and fully kinetic treatments, providing an analytically tractable framework that captures key features such as the partitioning between thermal and drift energy in each ion population. We derive equilibrium profiles for the magnetic field, density, current, and velocity and demonstrate how the relative densities of counterstreaming ion populations control the structure of the current sheet.