Separatrices: the Key Region for Electron Acceleration during Magnetic Reconnection

Abstract:

The collisionless magnetic reconnection theory proposed that electrons can only be accelerated in the so-called electron diffusion region. The spacecraft observations confimed that a significant part of (up to 50%) the released magnetic energy is converted into energetic electrons in reconnection. So, where and how the electrons are accelerated during reconnection is still poorly understood. By using the spacecraft measurements in the magnetotail, we demonstarted that electrons can be accelerated up to 100 keV before they get into the electron diffusion region. The electrons are generally streaming toward the electron diffusion region along the separatrices. In this process, they are accelerated by the parallle electric field pointing away from the X-line. Moreover, the fast propagating Double Layers (DLs) can accelerate electrons also. The electric field carried by the DLs is pointing away from the X-line and the DLs are moving away from the X-line. Therefore, they will accelerate electrons and lead the electrons moving to the X-line.