Electron Acceleration in a Magnetotail Reconnection Outflow Region Using Magnetospheric MultiScale Data

Abstract

We study Magnetospheric MultiScale observations in the outflow region of magnetotail reconnection. We estimate the power density converted via the three fundamental electron acceleration mechanisms: Fermi, betatron, and parallel electric fields. The dominant mechanism, both on average and the peak values, is Fermi acceleration with a peak power density of about +200 pW/m3. The magnetic field curvature during the most intense Fermi acceleration is comparable to the electron gyroradius, consistent with efficient electron scattering. The peak power densities due to the betatron acceleration are a factor of 3 lower than that for the Fermi acceleration, the average betatron acceleration is close to zero and slightly negative. The contribution from parallel electric fields is significantly smaller than those from the Fermi and betatron acceleration. However, the observational uncertainties in the parallel electric field measurement prevent further conclusions. There is a strong variation in the power density on a characteristic ion time scale.

Energy Dissipation via Magnetic Reconnection Within the Coherent Structures of the Magnetosheath Turbulence

“…The electron scattering may also explain the local increase of the perpendicular temperature and decrease of the parallel temperature. This result is consistent with recent MMS observations about electron scattering in the X-line and outflow region (e.g., Eriksson et al, 2020;Lavraud et al, 2016).…”

“…To determine the intensity of electron dissipation, an adiabatic parameter at different energies was calculated. This adiabatic parameter has been used to study the scattering in the reconnection diffusion region and outflow region (e.g., Eriksson et al., 2020; Lavraud et al., 2016). is defined as the ratio between the local magnetic field curvature radius and the electron's Larmor radius (Büchner & Zelenyi, 1989).…”

Electron Acceleration and Thermalization at Magnetotail Separatrices

“…Observations suggest that magnetic reconnection and subsequent processes can accelerate electrons to energies of tens or even hundreds of kiloelectron volts (e.g., Fu et al, 2019;Hoshino et al, 2001;Øieroset et al, 2002;Vaivads et al, 2011). The particle energization associated with magnetic reconnection is known to take place in several regions: in the inflow region and along the separatrices (e.g., Egedal et al, 2008;Eriksson et al, 2018;Hesse, Norgren, et al, 2018;Nagai et al, 2001), inside the ion and electron diffusion regions (e.g., Khotyaintsev et al, 2020;Torbert et al, 2018;Wang et al, 2018), in the magnetic reconnection exhaust (e.g., Bessho et al, 2015;Eriksson et al, 2020), in the vicinity of magnetic islands (Chen et al, 2008;Huang et al, 2012), both during island coalescence (Pritchett, 2008) and contraction (Drake et al, 2006), and at dipolarization fronts (e.g., Fu et al, 2011;Vaivads et al, 2011). Where, how, and to what extent the particles are accelerated depend not only on fundamental properties such as the particle species and the relative composition of species but also on changing properties, such as the particle's velocity.…”

Adiabatic Acceleration in a Magnetotail Flux Rope

“…The general agreement with developments in theory and simulations is encouraging. Several other investigations published in the last year have made similar use of the high‐resolution MMS data to calculate local energization in a reconnection exhaust (Eriksson et al, 2020) and perform a statistical study of heating in flux transfer events (Akhavan‐Tafti et al, 2019), indicating rising interest in this topic. Such studies are highly useful for testing predictions from kinetic reconnection studies, which have disagreed upon which processes are most important among Fermi reflection (Dahlin et al, 2014; Li et al, 2015; Wang et al, 2016), parallel electric fields (Egedal et al, 2012, 2015; Wang et al, 2016), or betatron acceleration (Huang et al, 2015).…”