Electron Heating During Magnetic Reconnection: The Interplay of Parallel Electric Fields and Fermi-Bounce Acceleration

The heating of electrons due to magnetic reconnection plays an important role throughout the heliosphere, but is currently not well understood. A systematic simulation study of antiparallel reconnection is performed with the kinetic PIC code P3D. Electrons are energized and heated through reflection across contracting magnetic field lines in the center of the outflow exhaust. Parallel electric fields form to keep electrons trapped in the exhaust and to maintain quasi-neutrality. These parallel fields act as an electron pre-acceleration mechanism which makes the contracting field line energization more efficient. Although the energy gain for each electron pass through the exhaust is weaker for smaller electron mass, the increase in bounce frequency leads to a heating prediction that is independent of the electron to ion mass ratio. Ultimately, this parallel heating isotropizes due to several different scattering mechanisms leading to nearly isotropic heating several 10s of ion inertial lengths downstream of the x-line.