Three-dimensional electron magnetohydrodynamic reconnection. III. Energy conversion and electron heating

Abstract

Further observations are presented of a magnetic reconnection experiment with three-dimensional fields in the parameter regime of electron magnetohydrodynamics. The initial magnetic configuration is imposed via a Helmholtz coil, whose field is added to or subtracted from a uniform background magnetic field. Energy is transferred from the coil’s external power supply into thermal energy of electrons and kinetic energy of ions via the decay of the imposed magnetic field configuration. For the case when the Helmholtz coil field opposes the background field, thus creating a field-reversed configuration, the magnetic energy convects in the whistler mode and dissipates over large distances resulting in negligible heating. For the case when the Helmholtz coil field is added to the background field, magnetic field annihilation leads to strong localized electron heating and acceleration of unmagnetized ions via space-charge electric fields. The energy conversion to electron heat is observed in regions away from magnetic nulls and a new mechanism for breaking the frozen-in condition is proposed.