Model for large scale electron heating applied to MMS observations in the Earth's magnetotail.

Magnetic reconnection is the process by which stress in the field of a magnetized plasma is reduced by a topological rearrangement of its magnetic-field lines. In the Earth’s magnetotail, reconnection energizes electrons up to hundreds of keV and solar-flare events can channel up to 50% of the magnetic energy into the electrons, resulting in superthermal populations in the MeV range. Electron energization is also fundamentally important to astrophysical applications yielding a window into the extreme environments. Using kinetic simulations it has been shown that magnetic-field aligned electric fields can be present over large spatial scales in reconnection exhausts [1,2]. The largest values of E|| are observed within double layers. The electron confinement allows sustained energization by perpendicular electric fields. The energization is a consequence of the confined electrons’ chaotic orbital motion that includes drifts aligned with the reconnection electric field. The mechanism is effective in an extended region of the reconnection exhaust allowing for the generation of superthermal electrons in large scale reconnection scenarios, including those with only a single x-line. The model is applied to new observations by the NASA’s MMS mission of large scale electron heating during reconnection in the Earth’s magnetosphere [3].



[1] Egedal J, Daughton W, and Le A, “Large scale electron energization by parallel electric fields during magnetic reconnection”, (2012) Nature Physics, 8, 321-324, doi: 10.1038/NPHYS2249.



[2] Egedal J, Daughton W, Le A, and Borg AL, “Double layer electric fields aiding the production of energetic flat-top distributions and superthermal electrons within magnetic reconnection exhausts”, (2015) Phys. Plasmas 22, 101208.



[3] Ergun, RE et al, “Observations of Particle Acceleration in Magnetic Reconnection-driven Turbulence” (2020), Astrophysical Journal, 898, 154.