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
Sun, Weijie; Turner, Drew L.; Zhang, Qile; Wang, Shan; Egedal, Jan; Leonard, Trevor; Slavin, James A.; Hu, Qiang; Cohen, Ian J.; Genestreti, Kevin; Poh, Gangkai; Gershman, Daniel J.; Smith, Andrew; Le, Guan; Nakamura, Rumi; Giles, Barbara L.; Ergun, Robert E.; Burch, James L.
2022-12
Citation
Sun, Weijie; Turner, Drew L.; Zhang, Qile; Wang, Shan; Egedal, Jan; Leonard, Trevor; Slavin, James A.; Hu, Qiang; Cohen, Ian J.; Genestreti, Kevin; Poh, Gangkai; Gershman, Daniel J.; Smith, Andrew; Le, Guan; Nakamura, Rumi; Giles, Barbara L.; Ergun, Robert E.; Burch, James L. (2022). "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." Journal of Geophysical Research: Space Physics 127(12): n/a-n/a.
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.Plain Language SummaryTheoretical physicists have been using simulations to explain the origin of energetic electrons in astrophysics and space plasma physics. The simulations and test particle calculations showed that flux ropes, an important magnetic structure generated by magnetic reconnection, can accelerate energetic electrons. Our study provides a comprehensive investigation of the properties and acceleration mechanisms associated with a pair of flux ropes and reconnection X-lines. The three fundamental acceleration mechanisms, that is, the Betatron process, the Fermi process, and the parallel electric field, have been directly assessed and are shown to be important in different regions. The results of our investigations should advance our understanding of the role of magnetic flux ropes in charged particle acceleration of all cosmic plasmas.Key PointsFermi and parallel potential is strong near X-lines, Betatron is strong on flux rope boundaries, and electrostatic structures in flux ropeAdiabatic electrons are to a few keV around X-line, 10’s keV downstream of X-line, 100’s keV on flux rope boundary and a few MeV in flux ropeEnergetic electrons and electron distribution function suggest that field lines in flux rope core connect to X-line in dawn-dusk directionPublisher
Imperial College Press Wiley Periodicals, Inc.
ISSN
2169-9380 2169-9402
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