Electron Heating in Magnetosheath Turbulence: Dominant Role of the Parallel Electric Field Within Coherent Structures. Issue 6 (28th March 2023)

• Record Type: Journal Article
• Authors: Xu, Qianyun; Zhou, Meng; Ma, Wenqing; He, Jiansen; Huang, Shiyong; Zhong, Zhihong; Pang, Ye; Deng, Xiaohua
• Is Part Of: Geophysical research letters. Volume 50:Issue 6(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-28
• Subjects: turbulence -- energy dissipation -- parallel electric field -- electron acceleration; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL102523
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: How particles are being energized by turbulent electromagnetic fields is an outstanding question in plasma physics and astrophysics. This paper investigates the electron acceleration mechanism in strong turbulence (δB/B0 ∼ 1) in the Earth's magnetosheath based on the novel observations of the Magnetospheric Multiscale mission. We find that electrons are magnetized in turbulent fields for the majority of the time. By directly calculating the electron acceleration rate from Fermi, betatron mechanism, and parallel electric field, it is found that electrons are primarily accelerated by the parallel electric field within coherent structures. Moreover, the acceleration rate by parallel electric fields increases as the spatial scale reduces, with the most intense acceleration occurring over about one ion inertial length. This study is an important step toward fully understanding the turbulent energy dissipation in weakly collisional plasmas. Plain Language Summary: The magnetosheath is one of the most turbulent environments in near‐Earth space, which is very beneficial to the study of collisionless turbulent plasma. The mechanism of turbulent energy dissipation and the consequent plasma heating is not fully understood. The Magnetosphere Multiscale mission provides high‐time cadence data and simultaneous multi‐spacecraft measurements at very small inter‐spacecraft separations, that can measure important quantities related to dissipation and heating at kinetic scales. This paper investigates how electrons are being accelerated through the dissipation of magnetic energy in nonlinear turbulence in the Earth's magnetosheath. We classify the acceleration mechanisms into three types: Fermi mechanism, betatron mechanism, and E|| acceleration. By directly calculating and comparing these mechanisms, we find electrons are predominantly accelerated by parallel electric fields within coherent structures. The E|| acceleration is the most effective around the ion inertial length. Key Points: Electrons are primarily accelerated by the parallel electric field in the magnetosheath turbulence The E|| acceleration mostly occurs within the coherent structures through Joule‐type dissipation The average E|| acceleration rate increases with the decreasing local spatial scale