Properties and Acceleration Mechanisms of Electrons Up To 200 keV Associated With a Flux Rope Pair and Reconnection X‐Lines Around It in Earth's Plasma Sheet

Abstract

The properties and acceleration mechanisms of electrons (<200 keV) associated with a pair of tailward traveling flux ropes and accompanied reconnection X‐lines in Earth's plasma sheet are investigated with MMS measurements. Energetic electrons are enhanced on both boundaries and core of the flux ropes. The power‐law spectra of energetic electrons near the X‐lines and in flux ropes are harder than those on flux rope boundaries. Theoretical calculations show that the highest energy of adiabatic electrons is a few keV around the X‐lines, tens of keV immediately downstream of the X‐lines, hundreds of keV on the flux rope boundaries, and a few MeV in the flux rope cores. The X‐lines cause strong energy dissipation, which may generate the energetic electron beams around them. The enhanced electron parallel temperature can be caused by the curvature‐driven Fermi acceleration and the parallel electric potential. Betatron acceleration due to the magnetic field compression is strong on flux rope boundaries, which enhances energetic electrons in the perpendicular direction. Electrons can be trapped between the flux rope pair due to mirror force and parallel electric potential. Electrostatic structures in the flux rope cores correspond to potential drops up to half of the electron temperature. The energetic electrons and the electron distribution functions in the flux rope cores are suggested to be transported from other dawn‐dusk directions, which is a 3‐dimensional effect. The acceleration and deceleration of the Betatron and Fermi processes appear alternately indicating that the magnetic field and plasma are turbulent around the flux ropes.

Electron Energization With Bursty Bulk Flows: MHD With Embedded Particle‐In‐Cell Simulation

“…The different energization mechanisms at the different locations of BBFs have also been suggested and discussed by Sun et al. (2022).…”

“…Overall, the agreements between the observed and simulated electron VDFs at the leading and trailing parts of the BBF are very good. The different energization mechanisms at the different locations of BBFs have also been suggested and discussed by Sun et al (2022).…”

Ion‐Scale Magnetic Flux Ropes and Loops in Earth's Magnetotail: An Automated, Comprehensive Survey of MMS Data Between 2017 and 2022

“…While the ensemble of identifications is crucial for understanding the formation, global contribution and dynamics of the structures, it is also fundamentally important to understand the physics within such magnetic structures, determining their contribution to plasma heating (e.g., Drake et al., 2006; Sun et al., 2022) and their evolution (e.g., Akhavan‐Tafti et al., 2019).…”

“…On a more local scale, reconnection also causes significant plasma heating. Additional plasma heating also occurs within the coherent magnetic structures ‐ plasmoids ‐ for example, from Fermi and Betatron‐type acceleration processes (e.g., Chen et al., 2007; Dahlin et al., 2015; Drake et al., 2006; Li et al., 2019; Sun et al., 2022) or the through the generation of electrostatic waves (Chen et al., 2023). Magnetotail plasmoids have been studied at many solar system bodies including Earth (Borg et al., 2012; Hasegawa et al., 2007; Lepping et al., 1995, 1996; Moldwin & Hughes, 1992; Poh et al., 2019; Richardson et al., 1987; Scholer et al., 1984; Sibeck et al., 1984; Slavin, Lepping, et al., 2003; Stawarz et al., 2018; Sun et al., 2019), Mercury (Di Braccio et al., 2015; Slavin et al., 2012; Smith, Slavin, Jackman, Poh, & Fear, 2017; Sun et al., 2016), Mars (Briggs et al., 2011; Eastwood, Videira, et al., 2012; Hara, Brain, et al., 2017; Hara, Harada, et al., 2017), Saturn (Garton, Jackman, & Smith, 2021; Jackman et al., 2014; Smith et al., 2016; Smith, Jackman, Thomsen, et al., 2018), Jupiter (Sarkango et al., 2022; Vogt et al., 2014), and Uranus (DiBraccio & Gershman, 2019).…”

Quantitative Analysis of Electron Heating and Acceleration in Coalescing Magnetic Flux Ropes at Earth's Magnetopause

“…Sun et al. (2022) conducted comprehensive analyses of electron heating in and near MFRs in the magnetotail. They found that Fermi acceleration has the most pronounced effect on adiabatic electrons between the downstream of reconnection X‐lines and the edges of MFRs.…”