Electron heating associated with magnetic reconnection in foreshock
waves: particle-in-cell simulation analysis
Abstract
Magnetic reconnection occurs in turbulent plasmas like shock transition
regions, while its exact role in energy dissipation therein is not yet
clear. We perform a 2D particle-in-cell simulation for foreshock waves
and study electron heating associated with reconnection. The probability
distribution of Te exhibits a shift to higher values near reconnection
X-lines compared to elsewhere. By examining the Te evolution using the
superposed epoch analysis, we find that Te is higher in reconnection
than in non-reconnecting current sheets, and Te increases over the ion
cyclotron time scale. The heating rate of Te is 10%-40% miVA2, where
VA is the average ion Alfvén speed in reconnection regions, which
demonstrates the importance of reconnection in heating electrons. We
further investigate the bulk electron energization mechanisms by
decomposing under guiding center approximations. Around the reconnection
onset, E|| dominates the total energization partly
contributed by electron holes, and the perpendicular energization is
dominant by the magnetization term associated with the gyro-motion in
the inhomogeneous fields. The Fermi mechanism contributes negative
energization at early time mainly due to the Hall effect, and later the
outflow in the reconnection plane contributes more dominant positive
values. After a couple of ion cyclotron periods from reconnection onset,
the Fermi mechanism dominates the energization. A critical factor for
initiating reconnection is to drive current sheets to the de-scale
thickness. The reconnection structures can be complicated due to flows
originated from the ion-scale waves, and interactions between multiple
reconnection sites. These features may assist future analysis of
observation data.