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Electrostatic plasma waves associated with collisionless magnetic reconnection: Spacecraft observations
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: 0000-0002-5861-1643
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic reconnection is a fundamental plasma process where changes in magnetic field topology result in explosive energy conversion, plasma mixing, heating, and energization. In geospace, magnetic reconnection couples the Earth’s magnetosphere to the solar wind plasma, enabling plasma transport across the magnetopause. On the sun, reconnection is responsible for coronal mass ejections and flares, which can affect everyday life on Earth, and it influences the evolution of the solar wind. Although collisionless magnetic reconnection has been studied for a long time, some fundamental aspects of the process remain to be understood. One such aspect is if/how plasma waves affect the process. Simulations and spacecraft observations of magnetic reconnection have shown that plasma waves are ubiquitous during reconnection. Particularly interesting are simulation results which show that electrostatic waves can affect the rate at which reconnection occurs, but this has not yet been experimentally verified. The recently launched Magnetospheric Multiscale (MMS) mission was designed to investigate the smallest scales of collisionless magnetic reconnection, making it an excellent mission to study small-scale waves as well. In this thesis, we use MMS to study electrostatic waves associated with magnetic reconnection in geospace. Our first two studies are devoted to the properties of electron holes (EHs), believed to play an important role in collisionless reconnection. Using MMS, we analyze EHs in unprecedented detail, and compare their properties to theory and previous studies. Importantly, we find evidence of EHs radiating whistler waves in the reconnection separatrices, a process which might modulate the reconnection rate. In our third study, we show that the presence of cold ions at the reconnecting magnetopause can lead to the growth of the ion-acoustic instability. This instability leads to dissipation and cold ion heating. The fourth study compares different techniques for determining the velocity of electrostatic waves. Accurate velocity estimates are important, since they are needed to understand how the wave interacts with the plasma. Finally, in our fifth study, we calibrate the E-field measurements made in the solar wind by the Solar Orbiter spacecraft, to aid future studies of solar wind processes, including magnetic reconnection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2022. , p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2150
Keywords [en]
Magnetic reconnection, Plasma waves, Electron holes, Solar wind, Magnetosphere, Magnetospheric Multiscale, Solar Orbiter
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
URN: urn:nbn:se:uu:diva-472803ISBN: 978-91-513-1499-0 (print)OAI: oai:DiVA.org:uu-472803DiVA, id: diva2:1652254
Public defence
2022-06-08, Room 101195, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2022-05-18 Created: 2022-04-18 Last updated: 2022-06-15Bibliographically approved
List of papers
1. Multispacecraft Analysis of Electron Holes
Open this publication in new window or tab >>Multispacecraft Analysis of Electron Holes
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 1, p. 55-63Article in journal (Refereed) Published
Abstract [en]

Electron holes (EHs) are nonlinear electrostatic structures in plasmas. Most previous in situ studies of EHs have been limited to single‐ and two‐spacecraft methods. We present statistics of EHs observed by Magnetospheric Multiscale on the magnetospheric side of the magnetopause during October 2016 when the spacecraft separation was around 6 km. Each EH is observed by all four spacecraft, allowing EH properties to be determined with unprecedented accuracy. We find that the parallel length scale, l, scales with the Debye length. The EHs can be separated into three groups of speed and potential based on their coupling to ions. We present a method for calculating the perpendicular length scale, l. The method can be applied to a small subset of the observed EHs for which we find shapes ranging from almost spherical to more oblate. For the remaining EHs we use statistical arguments to find l/l≈5, implying dominance of oblate EHs.

Plain Language Summary: Electron holes are positively charged structures moving along the magnetic field and are frequently observed in space plasmas in relation to strong currents and electron beams. Electron holes interact with the plasma, leading to electron heating and scattering. In order to understand the effect of these electron holes, we need to accurately determine their properties, such as velocity, length scale, and potential. Most earlier studies have relied on single‐ or two‐spacecraft methods to analyze electron holes. In this study we use the four satellites of the Magnetospheric Multiscale mission to analyze 236 electron holes with unprecedented accuracy. We find that the holes can be divided into three distinct groups with different properties. Additionally, we calculate the width of individual electron holes, finding that they are typically much wider than long, resembling

Keywords
Electron holes
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-377361 (URN)10.1029/2018GL080757 (DOI)000456938600007 ()
Funder
Swedish Research Council, 2016-05507Swedish National Space Board, 2016-05507
Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2022-04-18Bibliographically approved
2. Observations of Electromagnetic Electron Holes and Evidence of Cherenkov Whistler Emission
Open this publication in new window or tab >>Observations of Electromagnetic Electron Holes and Evidence of Cherenkov Whistler Emission
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 25, article id 255101Article in journal (Refereed) Published
Abstract [en]

We report observations of electromagnetic electron holes (EHs). We use multispacecraft analysis to quantify the magnetic field contributions of three mechanisms: the Lorentz transform, electron drift within the EH, and Cherenkov emission of whistler waves. The first two mechanisms account for the observed magnetic fields for slower EHs, while for EHs with speeds approaching half the electron Alfven speed, whistler waves excited via the Cherenkov mechanism dominate the perpendicular magnetic field. The excited whistler waves are kinetically damped and typically confined within the EHs.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-402379 (URN)10.1103/PhysRevLett.123.255101 (DOI)000503245200010 ()31922784 (PubMedID)
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Available from: 2020-01-29 Created: 2020-01-29 Last updated: 2022-04-18Bibliographically approved
3. Large Amplitude Electrostatic Proton Plasma Frequency Waves in the Magnetospheric Separatrix and Outflow Regions During Magnetic Reconnection
Open this publication in new window or tab >>Large Amplitude Electrostatic Proton Plasma Frequency Waves in the Magnetospheric Separatrix and Outflow Regions During Magnetic Reconnection
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2021 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 5, article id e2020GL090286Article in journal (Refereed) Published
Abstract [en]

We report Magnetospheric Multiscale observations of large amplitude, parallel, electrostatic, proton plasma frequency waves on the magnetospheric side of the reconnecting magnetopause. The waves are often found in the magnetospheric separatrix region and in the outflow near the magnetospheric ion edge. Statistical results from five months of data show that these waves are closely tied to the presence of cold (typically tens of eV) ions, found for 88% of waves near the separatrix region, and that plasma properties are consistent with ion acoustic wavegrowth. We analyze one wave event in detail, concluding that the wave is ion acoustic. We provide a simple explanation for the mechanisms leading to the development of the ion acoustic instability. These waves can be important for separatrix dynamics by heating the cold ion component and providing a mechanism to damp the kinetic Alfven waves propagating away from the reconnection site.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)AMER GEOPHYSICAL UNION, 2021
Keywords
cold ions, ion acoustic instability, kinetic Alfv&#233, n wave, separatrix dynamics
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-441974 (URN)10.1029/2020GL090286 (DOI)000627892100036 ()
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Available from: 2021-05-07 Created: 2021-05-07 Last updated: 2024-01-15Bibliographically approved
4. On the Applicability of Single-Spacecraft Interferometry Methods Using Electric Field Probes
Open this publication in new window or tab >>On the Applicability of Single-Spacecraft Interferometry Methods Using Electric Field Probes
2022 (English)In: Journal of Geophysical Research: Space Physics, Vol. 127, no 3Article in journal (Refereed) Published
Abstract [en]

When analyzing plasma waves, a key parameter to determine is the phase velocity. It enables us to, for example, compute wavelengths, wave potentials, and determine the energy of resonant particles. The phase velocity of a wave, observed by a single spacecraft equipped with electric field probes, can be determined using interferometry techniques. While several methods have been developed to do this, they have not been documented in detail. In this study, we use an analytical model to analyze and compare three interferometry methods applied on the probe geometry of the Magnetospheric Multiscale spacecraft. One method relies on measured probe potentials, whereas the other two use different E-field measurements: one by reconstructing the E-field between two probes and the spacecraft, the other by constructing four pairwise parallel E-field components in the spacecraft spin-plane. We find that the potential method is sensitive both to how planar the wave is, and to spacecraft potential changes due to the wave. The E-field methods are less affected by the spacecraft potential, and while the reconstructed E-field method is applicable in some cases, the second E-field method is almost always preferable. We conclude that the potential based interferometry method is useful when spacecraft potential effects are negligible and the signals of the different probes are very well correlated. The method using two pairs of parallel E-fields is practically always preferable to the reconstructed E-field method and produces the correct velocity in the spin-plane, but it requires knowledge of the propagation direction to provide the full velocity.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)American Geophysical Union (AGU), 2022
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-472507 (URN)10.1029/2021JA030143 (DOI)000776515200001 ()
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Available from: 2022-04-12 Created: 2022-04-12 Last updated: 2024-01-15Bibliographically approved
5. Solar wind current sheets and deHoffmann-Teller analysis: First results from Solar Orbiter's DC electric field measurements
Open this publication in new window or tab >>Solar wind current sheets and deHoffmann-Teller analysis: First results from Solar Orbiter's DC electric field measurements
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2021 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 656, article id A9Article in journal (Refereed) Published
Abstract [en]

Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields.

Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter’s DC electric and magnetic field data to estimate the solar wind speed.

Methods. We used a deHoffmann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the effective antenna length, Leff of the E-field probes. We then used the HT method to estimate the speed of the solar wind.

Results. Using the HT method, we find that the observed variations in Ey are often in excellent agreement with the variations in the magnetic field. The magnitude of Ey, however, is uncertain due to the fact that the Leff depends on the plasma environment. Here, we derive an empirical model relating Leff to the Debye length, which we can use to improve the estimate of Ey and, consequently, the estimated solar wind speed.

Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHoffmann-Teller analysis, Solar Orbiter’s magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.

Place, publisher, year, edition, pages
EDP SciencesEDP Sciences, 2021
Keywords
solar wind, plasmas, magnetic reconnection, methods, data analysis
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-464441 (URN)10.1051/0004-6361/202140855 (DOI)000730246400018 ()
Funder
Swedish Research Council, 2016-05507Swedish Research Council, VR 2018-03569Swedish National Space Board, 20/136Swedish National Space Board, SNSA 144/18Swedish Civil Contingencies Agency, 2016-2102
Available from: 2022-01-18 Created: 2022-01-18 Last updated: 2024-01-15Bibliographically approved

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