Electron Energization within an Ion-scale Flux Rope Chain in Earth’s Turbulent Magnetotail Plasma Sheet

Flux ropes in space plasma can play an important role in particle acceleration. However, the mechanisms of electron energization and the resulting electron energy distribution associated with flux ropes are still not fully understood. This study examines a flux rope chain with four ion-scale flux ropes observed by the Magnetospheric Multiscale (MMS) mission in a turbulent plasma region in Earth’s magnetotail. We investigate the active electron acceleration mechanisms, including parallel electric fields, betatron acceleration, and magnetic curvature-driven Fermi-type acceleration, based on MMS’s four spacecraft in situ measurements. Our results demonstrate that Fermi acceleration is the dominant mechanism with betatron acceleration providing an important contribution. The electron energy spectra are further fitted by Kappa and Flattop distributions aiming to characterize the energy densities of thermal and suprathermal populations. It shows that although suprathermal electrons comprise only 10% of the number number density, they could contribute up to 30% of the total energy density. While the energy densities of both thermal and suprathermal electrons increase within the flux ropes, the relative portions of suprathermal electrons decrease. This suggests that flux rope could confine both thermal and suprathermal electrons; however, they are likely more efficient to energize thermal electrons.