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 VN ~ N2/3. 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.