Large-scale electron acceleration by parallel electric fields during magnetic reconnection

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. The process is often accompanied by an explosive release of magnetic energy and is implicated in a range of astrophysical phenomena(1). In the Earth's magnetotail, reconnection energizes electrons up to hundreds of keV (ref. 2) and solar-flare events can channel up to 50% of the magnetic energy into the electrons, resulting in superthermal populations in the MeV range(3-5). Electron energization is also fundamentally important to astrophysical applications(6) yielding a window into the extreme environments. Here we show that during reconnection powerful energization of electrons by magnetic-field-aligned electric field (E-parallel to) can occur over spatial scales that hugely exceed previous theories and simulations(7). In our kinetic simulation E-parallel to is supported by non-thermal and strongly anisotropic features in the electron distributions not permitted in standard fluid formulations, but routinely observed by spacecraft in the Earth's magnetosphere. This allows for electron energization in spatial regions that exceed the regular d(e)-scale electron-diffusion region by at least three orders of magnitude.