Cluster observations of energetic electron acceleration within earthward
reconnection jet and associated magnetic flux rope
Abstract
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 due to the presence of
high fluxes of energetic electrons, Cluster being in the burst mode and
Cluster separation being around 1000\,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.