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Finite gyroradius effects in the electron outflow of asymmetric magnetic reconnection
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0002-1046-746X
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 13, 6724-6733 p.Article in journal (Refereed) Published
Abstract [en]

We present observations of asymmetric magnetic reconnection showing evidence of electron demagnetization in the electron outflow. The observations were made at the magnetopause by the four Magnetospheric Multiscale (MMS) spacecraft, separated by approximate to 15km. The reconnecting current sheet has negligible guide field, and all four spacecraft likely pass close to the electron diffusion region just south of the X line. In the electron outflow near the X line, all four spacecraft observe highly structured electron distributions in a region comparable to a few electron gyroradii. The distributions consist of a core with T-vertical bar>T and a nongyrotropic crescent perpendicular to the magnetic field. The crescents are associated with finite gyroradius effects of partly demagnetized electrons. These observations clearly demonstrate the manifestation of finite gyroradius effects in an electron-scale reconnection current sheet.

Place, publisher, year, edition, pages
2016. Vol. 43, no 13, 6724-6733 p.
Keyword [en]
magnetic reconnection, electron demagnetization, finite gyroradius effects, electron diffusion region
National Category
Geophysics Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-304453DOI: 10.1002/2016GL069205ISI: 000380901600006OAI: oai:DiVA.org:uu-304453DiVA: diva2:1033006
Funder
Swedish National Space Board, 23/12:2 175/15
Available from: 2016-10-05 Created: 2016-10-05 Last updated: 2017-11-30Bibliographically approved
In thesis
1. Electron-scale physics in space plasma: Thin boundaries and magnetic reconnection
Open this publication in new window or tab >>Electron-scale physics in space plasma: Thin boundaries and magnetic reconnection
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Most of the observable Universe consists of plasma, a kind of ionized gas that interacts with electric and magnetic fields. Large volumes of space are filled with relatively uniform plasmas that convect with the magnetic field. This is the case for the solar wind, and large parts of planetary magnetospheres, the volumes around the magnetized planets that are dominated by the planet's internal magnetic field. Large plasma volumes in space are often separated by thin extended boundaries. Many small-scale processes in these boundaries mediate large volumes of plasma and energy between the adjacent regions, and can lead to global changes in the magnetic field topology. To understand how large-scale plasma regions are created, maintained, and how they can mix, it is important understand how the processes in the thin boundaries separating them work.

A process in these thin boundaries that may result in large scale changes in magnetic field topology is magnetic reconnection. Magnetic reconnection is a fundamental process that transfers energy from the magnetic field to particles, and occurs both in laboratory and astrophysical plasmas. It is a multi-scale process involving both ions and electrons, but is only partly understood

Space above the Earth's ionosphere is essentially collisionless, meaning that information, energy, and mass transfer have to be mediated through means other than collisions. In a plasma, this can happen through interactions between particles and electrostatic and electromagnetic waves. Instabilities that excites waves can therefore play a crucial role in the energy transfer between fields and particles, and different particle populations, for example between ions and electrons.

In this thesis we have used data from ESA's four Cluster and NASA's four Magnetospheric Multiscale (MMS) satellites to study small-scale – the scale where details of the electron motion becomes important – processes in thin boundaries around Earth. With Cluster, we have made detailed measurements of lower-hybrid waves and electrostatic solitary waves to better understand what role these waves can play in collisionless energy transfer. Here, the use of at least two satellites was crucial to estimate the phase speed of the waves, and associated wavelength, as well as electrostatic potential of the waves. With MMS, we have studied the electron dynamics within thin boundaries undergoing magnetic reconnection, and found that the current is often carried by non-gyrotropic parts of the electron distribution. The non-gyrotropy was caused by finite gyroradius effects due to sharp gradients in the magnetic field and plasma density and temperature. Here, the use of four satellites was crucial to deduce the spatial structure and thickness of the boundaries. Before the MMS mission, these observations of electron dynamics have never been possible in space, due to instrumental limitations of previous missions. All these findings have led to better understanding of both our near-space environment and plasma physics in general.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 68 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1453
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-307955 (URN)978-91-554-9755-2 (ISBN)
Public defence
2017-01-20, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-12-21 Created: 2016-11-23 Last updated: 2016-12-28

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