The competition of electron and ion heating during magnetic reconnection

Abstract

The physical processes that control the partition of released magnetic energy between electrons and ions during reconnection is explored through particle‐in‐cell simulations and analytical techniques. We demonstrate that the development of a large‐scale parallel electric field and its associated potential controls the relative heating of electrons and ions. The potential develops to restrain heated exhaust electrons and enhances their heating by confining electrons in the region where magnetic energy is released. Simultaneously, the potential slows ions entering the exhaust below the Alfvénic speed expected from the traditional counterstreaming picture of ion heating. Unexpectedly, the magnitude of the potential and therefore the relative partition of energy between electrons and ions is not a constant but rather depends on the upstream parameters and specifically the upstream electron normalized temperature (electron beta). These findings suggest that the fraction of magnetic energy converted into the total thermal energy may be independent of upstream parameters.

Three‐scale structure of diffusion region in the presence of cold ions

“…The heating is in a good agreement with the analytical estimate: ΔT (i) ∼ m i V 2 A(up) ∼ 0.2 for ∼ 0.1 [Haggerty et al, 2015]. The global evolution of the magnetic reconnection (reconnection rate and Hall fields) is nearly unchanged in the presence of cold ions and depends on upstream parameters (B and n).…”

Pseudo-3D PIC modeling of drift-induced spatial inhomogeneities in planar magnetron plasmas

“…They implicitly assume the localtype Speiser motion, while the relevant self-consistent orbits have not been investigated. In fact, Haggerty et al 21 showed in Figure 2(d) of their paper that the electron jet region, flanked by the bipolar E k layers, extends 40d i 's away from the X-line. This is favorable for the noncrossing electrons.…”

“…Second, the electron heating mechanisms have been actively studied in the last few years. 21,43,51 These works reported electrons parallel heating outside the ECL inside the outflow exhaust. They implicitly assume the localtype Speiser motion, while the relevant self-consistent orbits have not been investigated.…”

The role of three-dimensional transport in driving enhanced electron acceleration during magnetic reconnection

“…We propose the following explanation: in order for a charged particle to accelerate multiple times, it must propagate upstream against the Alfvénic outflow that ejects plasma β ≪ 1, reconnection heats electrons to an appreciable fraction of the available magnetic energy density 47,48 : ∆T e ≈ 0.03m e c 2 Ae , corresponding to v th,e /c A ≈ 0.06m i /m e ≈ 10 so that essentially all reconnection-heated electrons will satisfy the criterion, independent of the initial temperature. In contrast, ions are typically sub-Alfénic and would require an injection mechanism (e.g.…”