New observations of ion beams in the plasma sheet boundary layer

Abstract

The Wind perigee passes covered tail distances from 6–24 RE. By use of bulk quantities and the parent distributions, we have found new features in the PSBL that had been missed previously. The PSBL consists of a unidirectional earthward streaming ion beam at the edge and another unidirectional beam inside this edge streaming in the tailward direction. Bidirectional beams are observed with higher densities, further inside the PSBL. The plasma in the region supporting the tailward streaming beams consists of the beam distribution plus an isotropic component, whereas the earthward streaming beams consists mainly of the beam distribution. These distributions yield fast flows (>400 km/s) in the earthward direction and slower flows (≈ 150 km/s) in the tailward direction. Both regions support counter streaming electron beams superposed on an isotropic component. These new findings are substantially different from previous observations and the interpretation of fast flows and ion beams in terms of a neutral line model needs to be reexamined.