Multicomponent plasma distributions in the tail current sheet associated with substorms

The 3D plasma instrument on the Wind spacecraft has obtained new features of plasma distributions in the region of the geomagnetic tail current sheet (CS) that have not been previously reported. In addition to the isotropic plasma sheet component, ion beams of energy 1-3 keV are observed. The beams are generally counter streaming but unidirectional beams are also observed streaming parallel and antiparallel to the direction of the magnetic field. In addition, a low energy (a few hundred eV) ion component appears in close association with B-z increases. The electron distributions have bidirectional anisotropy with T-parallel to/T-perpendicular to approximate to 1.5, and they are often accompanied by counter streaming beams. However, a few keV unidirectional electron beam is also observed with bidirectional anisotropic distributions. These keV electrons are streaming away from the CS, suggesting they have been accelerated in the CS and subsequently ejected. The plasma distribution in the CS is multicomponent and thus requires a kinetic description of the dynamics.