Multiplet structure of acceleration processes in the distant magnetotail

Abstract

We have studied ion distributions measured in the Plasma Sheet Boundary Layer (PSBL) of the Earth's magnetotail by the Cluster spacecraft at X ~ -15Re. Field-aligned ion beams (beamlets) accelerated in the magnetotail to energies of ~30keV are typically observed within the interface region between the Plasma Sheet (PS) and the magnetotail lobes. PSBL beamlets are produced by non-adiabatic ion acceleration in the vicinity of X-line which is located, during quiet periods, in the distant parts of the tail. Earlier kinetic models attributed the filamentary and/or bursty nature of these processes to Current Sheet (CS) resonances and predicted the scaling law for the velocity of subsequent structures as V_N ~ N^2/3. Cluster-2 provides experimental evidence from the PSBL from of the existence of such resonant structures in ion velocity space and provides the first statistically proven identification of such a scaling law for quiet and moderately disturbed periods.