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Ion Energization and Thermalization in Magnetic Reconnection Exhaust Region in the Solar Wind

Wu, Ziqi; He, Jiansen; Duan, Die; Zhu, Xingyu; Hou, Chuanpeng; Verscharen, Daniel; Nicolaou, Georgios; ... Louarn, Philippe; + view all (2023) Ion Energization and Thermalization in Magnetic Reconnection Exhaust Region in the Solar Wind. The Astrophysical Journal , 951 (2) , Article 98. 10.3847/1538-4357/accf9b. Green open access

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Abstract

Plasma energization and thermalization in magnetic reconnection is an important topic in astrophysical studies. We select two magnetic reconnection exhausts encountered by Solar Orbiter and analyze the associated ion heating in the kinetic regime. Both cases feature asymmetric plasma merging in the exhaust and anisotropic heating. For a quantitative investigation of the associated complex velocity-space structures, we adopt a three-dimensional Hermite representation of the proton velocity distribution function to produce the distribution of Hermite moments. We also derive the enstrophy and Hermite spectra to analyze the free energy conversion and transfer in phase space. We find a depletion of Hermite power at small m (corresponding to large-scale structures in velocity space) inside the reconnection exhaust region, concurrent with enhanced proton temperature and decreased enstrophy. Furthermore, the slopes of the 1D time-averaged parallel Hermite spectra are lower inside the exhaust and consistent with the effect of phase mixing that creates small fluctuations in velocity space. These fluctuations store free energy at higher m and are smoothed by weak collisionality, leading to irreversible thermalization. We also suggest that the perpendicular heating may happen via perpendicular phase mixing resulting from finite Larmor radius effects around the exhaust boundary.

Type: Article
Title: Ion Energization and Thermalization in Magnetic Reconnection Exhaust Region in the Solar Wind
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/1538-4357/accf9b
Publisher version: https://doi.org/10.3847/1538-4357/accf9b
Language: English
Additional information: Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10173108
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