Electron Beams near the Dipolarization Front Observed by THEMIS Satellites

Electron beams are found in the earth plasma sheet shortly before the occurrence of the so-called dipolarization front. These electron beams, with their peak value around 200eV-2KeV, are very cold and temperature change slightly with time and position. These beams are strong comparing with the background number density, and the field-aligned current is strong enough to generate beam instability. By comparing five THEMIS satellite observation of the electrons distribution function, as well as observations by Cluster at relatively higher latitude, the evolution of these electron beams and possible acceleration mechanisam and their relations with dipolarization current system are discussed.