Cluster Observations of Energetic Electron Acceleration Within Earthward Reconnection Jet and Associated Magnetic Flux Rope

We study acceleration of energetic electrons in an earthward plasma jet due to magnetic reconnection in the Earth magnetotail for one case observed by Cluster. The case has been selected based on the presence of high fluxes of energetic electrons, Cluster being in the burst mode and Cluster separation being around 1,000 km that is optimal for studies of ion scale physics. We show that two characteristic acceleration mechanisms are operating during this event. First, significant acceleration is achieved inside the magnetic flux pile-up of the jet, the acceleration mechanism being consistent with betatron acceleration. Second, strong energetic electron acceleration occurs in magnetic flux rope like structure forming in front of the magnetic flux pile-up region. Energetic electrons inside the magnetic flux rope are accelerated predominantly in the field-aligned direction and the acceleration can be due to Fermi acceleration in a contracting flux rope.