title: Regimes of the electron diffusion region in magnetic reconnection.
abstract: The electron diffusion region during magnetic reconnection lies in different regimes depending on the pressure anisotropy, which is regulated by the properties of thermal electron orbits. In kinetic simulations at the weakest guide fields, pitch angle mixing in velocity space causes the outflow electron pressure to become nearly isotropic. Above a threshold guide field that depends on a range of parameters, including the normalized electron pressure and the ion-to-electron mass ratio, electron pressure anisotropy develops in the exhaust and supports extended current layers. This new regime with electron current sheets extending to the system size is also reproduced by fluid simulations with an anisotropic closure for the electron pressure. It offers an explanation for recent spacecraft observations.
authors.affiliation: Department of Physics, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: A
authors.initials: A
authors.lastname: Le
authors.forename: J
authors.initials: J
authors.lastname: Egedal
authors.forename: O
authors.initials: O
authors.lastname: Ohia
authors.forename: W
authors.initials: W
authors.lastname: Daughton
authors.forename: H
authors.initials: H
authors.lastname: Karimabadi
authors.forename: V S
authors.initials: VS
authors.lastname: Lukin