Electron dynamics in guide-field magnetic reconnection

Magnetic reconnection is a fundamental process that rapidly converts energy from the magnetic field to plasma. Recent studies have shown that a large parallel electric field (E) can appear in guide-field reconnection, and its magnitude can be several times larger than the reconnection electric field. However, the generation of this large E is still not fully understood, and the reaction of electrons to this E has not been fully investigated. In this study, we focus on these issues in a strong guide-field reconnection event (the normalized guide field is ~ 1.5) from Magnetospheric Multiscale (MMS) observations. With the presence of a large E in the electron current sheet, electrons are accelerated when streaming into this E region from one direction, and decelerated from the other direction. Some decelerated electrons can reduce the parallel speed to ~ 0 to form relatively isotropic electron distributions at one side of the electron current sheet, as the estimated acceleration potential (Φ ~ 2 kV) satisfies the relation eΦ ≥ kT, where T is the electron temperature parallel to the magnetic field. Therefore, a large E is generated to balance the parallel electron pressure gradient across the electron current sheet, since electrons at the other side of the current sheet are still anisotropic. Based on these observations, we further show that the electron beta is an important parameter in guide-field reconnection, providing a new perspective to solve the large parallel electric field puzzle in guide-field reconnection.