PRECIPITATION OF FAST ION-BEAMS FROM THE PLASMA SHEET BOUNDARY-LAYER

This paper presents a model of precipitated fluxes from the PSBL and C PS. Simulation results and data from Aureol-3 spacecraft indicate the presence of velocity dispersed precipitated ion structures (VDIS) at t he poleward edge of the auroral oval. These structures are associated with fast ion beams in the PSBL region of the Earth's magnetotail, con firming previous experimental results. The simulations also reveal pos sible substructuring of the VDIS. The bulk of the PSBL population whic h is not precipitated is very effectively thermalized and quasi-isotro pized after multiple interactions with the magnetotail current layer. After each reflection cycle some part of the distribution is precipita ted and forms multiple 'echoes' of VDIS. The CPS distributions occurri ng as a result of scattering, convection, multiple reflections and Fer mi acceleration appear isotropic in the simulation model. This paper p ortrays the important role of the VDIS auroral region medium for compl icated and energetically significant processes occurring in different regions of the distant magnetotail.