Using MMS high‐resolution measurements, we present the first observation of fast electron jet (Ve ~2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness (~ 0.9 di), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring‐current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron‐jet‐driven current (E ⋅ je ≈ 2 E ⋅ ji), rather than the ion current suggested in previous studies.

The rolling‐pin distribution of suprathermal electrons (40–200 keV), showing electron pitch angles primarily at 0°, 90°, and 180°, has recently been reported behind dipolarization fronts (DFs) both in observations and simulations. The formation of such type of distribution, however, has been unclear so far. In this study, we present an observation of such type of distribution by Cluster in the magnetotail behind a DF. We interpret the formation of such distribution using the global‐scale Fermi acceleration together with local‐scale betatron acceleration. We quantitatively reproduce these two processes and therefore the rolling‐pin distribution of suprathermal electrons using an analytical model. We further reveal that only at energies higher than 26 keV can such distribution be formed. This study, quantitatively explaining the formation of rolling‐pin distribution, can improve the understanding of electron dynamics behind DFs.

Dipolarization front (DF)—a sharp boundary with scale of ion inertial length (c/ωpi) in the Earth's magnetotail—can also have fine structures at electron scale (c/ωpe). Such electron‐scale structures, determining the local energy conversion, have not been revealed by multispacecraft observations so far, due to the large separation of spacecraft in previous studies. Here we report the first electron‐scale multispacecraft measurements of DF, using data from the recent Magnetospheric Multiscale mission. We find strong parallel currents only in the high‐density side of the DF but strong perpendicular currents across the whole DF. We find no parallel electric fields during the DF interval. Although DF is primarily an energy‐load region (E·J > 0), the electron‐scale currents could lead to a localized energy generation (E·J < 0). Such features are different from those reported in previous multispacecraft studies, where the currents, electric fields, and energy conversion are uniform across the DF; they also shed lights on the study of substorm current wedge, which is crucial in the magnetosphere‐ionosphere coupling.

Electrostatic solitary waves (ESWs) have been reported inside reconnection jets, but their source and role remain unclear hitherto. Here we present the first observational evidence of ESWs generation by cold ion beams inside the jet, by using high‐cadence measurements from the Magnetospheric Multiscale spacecraft in the Earth's magnetotail. Inside the jet, intense ESWs with amplitude up to 30 mV m−1 and potential up to ~7% of the electron temperature are observed in association with accelerated cold ion beams. Instability analysis shows that the ion beams are unstable, providing free energy for the ESWs. The waves are observed to thermalize the beams, thus providing a new channel for ion heating inside the jet. Our study suggests that electrostatic turbulence can play an important role in the jet dynamics.