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Abstract. The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X ∼ −7-−9 R E ) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the B Z magnetic field lasted ∼ 13 min and it was comprised of several B Z pulses or dipolarization fronts (DFs) with duration ≤ 1 min. Multipoint observations have shown that the beginning of the increase in suprathermal (> 50 keV) electron fluxes -the injection boundary -was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the B Z field, and it was comprised of multiple short (∼ few minutes) electron injections associated with the B Z pulses. This behavior can be explained by the combined action of local betatron acceleration at the B Z pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization.On the contrary, proton injections were detected only in the vicinity of the strongest B Z pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range ∼ 70-90 keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn-dusk electric field associated with the B Z pulses.

[1] Fortunate positioning of Cluster and TC-1 in the plasma sheet (PS) of the Earth's magnetotail has allowed studies of the current sheet (CS) structure and particle dynamics in mesoscale and microscale in both sides of the near-Earth reconnection, which took place between 03:42 and 03:55 UT on 22 September 2004. The distinctive feature of this event was the presence of a strong negative B Y field forming a "bell-like" spatial profile with the maximum absolute value near the neutral plane. The magnitude of this B Y field was almost two times larger than the interplanetary magnetic field (IMF) and therefore could not be explained solely by the IMF penetration into the magnetotail. We propose a possible intrinsic mechanism of the B Y field enhancement near the neutral plane based on peculiarities of the nonadiabatic ion interaction with the thin CS. An analysis of test particle trajectories shows that in the presence of a guide field with the "bell-like" spatial profile, a pronounced north-south asymmetry appears in the refraction/reflection properties of nonadiabatic ions from the CS. In a region tailward of the reconnection (B Z < 0), this asymmetry results in an increase of the density of the keV ions ejected into the northern PS and moving tailward. These ions can carry the tailward current which may be responsible for the strong negative B Y near the neutral plane, i.e., self-consistent enhancement of a B Y field could occur near the neutral plane.