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Slow electron holes in multicomponent plasmas
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.
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.ORCID iD: 0000-0002-1046-746X
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 18, 7264-7272 p.Article in journal (Refereed) Published
Abstract [en]

Electrostatic solitary waves (ESWs), often interpreted as electron phase space holes, are commonly observed in plasmas and are manifestations of strongly nonlinear processes. Often slow ESWs are observed, suggesting generation by the Buneman instability. The instability criteria, however, are generally not satisfied. We show how slow electron holes can be generated by a modified Buneman instability in a plasma that includes a slow electron beam on top of a warm thermal electron background. This lowers the required current for marginal instability and allows for generation of slow electron holes for a wide range of beam parameters that covers expected plasma distributions in space, for example, in magnetic reconnection regions. At higher beam speeds, the electron-electron beam instability becomes dominant instead, producing faster electron holes. The range of phase speeds for this model is consistent with a statistical set of observations at the magnetopause made by Cluster.

Place, publisher, year, edition, pages
2015. Vol. 42, no 18, 7264-7272 p.
Keyword [en]
Multi-component plasma, Modified Buneman instability, Ion-electron instability, Slow electron holes
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-267330DOI: 10.1002/2015GL065390ISI: 000363412400004OAI: oai:DiVA.org:uu-267330DiVA: diva2:873642
Funder
Swedish Research Council, 23/12:2
Available from: 2015-11-24 Created: 2015-11-20 Last updated: 2017-12-01Bibliographically 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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Norgren, CeciliaAndré, MatsGraham, Daniel. B.Khotyaintsev, Yuri. V.Vaivads, Andris

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