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Ion dynamics and structure of collisionless shocks
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.ORCID iD: 0000-0001-7714-1870
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Shock waves are responsible for slowing down and heating supersonic flows. In collisionless space plasmas, shocks are able to accelerate particles to very high energies. We study injection of suprathermal ions at Earth’s quasi- parallel shock using high time resolution data from the Cluster spacecraft. We find that solar wind ions reflect off short large-amplitude magnetic structures (SLAMSs) and are subsequently accelerated by the convection electric field. We also use data from the closely-spaced Magnetospheric MultiScale (MMS) spacecraft to compare competing non-stationarity processes at Earth’s quasi- perpendicular bow shock. Using MMS’s high cadence plasma measurements, we find that the shock exhibits non-stationarity in the form of ripples.

Place, publisher, year, edition, pages
Uppsala University, 2016. , 24 p.
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-303636OAI: oai:DiVA.org:uu-303636DiVA: diva2:972507
Presentation
2016-09-22, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:58 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, 97/13
Available from: 2016-09-29 Created: 2016-09-21 Last updated: 2016-09-29Bibliographically approved
List of papers
1. Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft
Open this publication in new window or tab >>Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft
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2016 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 817, no 1, L4Article in journal (Refereed) Published
Abstract [en]

Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) and obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.

Keyword
acceleration of particles, cosmic rays, shock waves, solar wind
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-279631 (URN)10.3847/2041-8205/817/1/L4 (DOI)000369370900004 ()
Available from: 2016-03-08 Created: 2016-03-02 Last updated: 2017-11-30Bibliographically approved
2. Rippled quasiperpendicularshock observed by the Magnetospheric Multiscale spacecraft
Open this publication in new window or tab >>Rippled quasiperpendicularshock observed by the Magnetospheric Multiscale spacecraft
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2016 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114Article in journal (Refereed) Accepted
Abstract [en]

Collisionless shock non-stationarity arising from micro-scale physics influences shock structure and particle acceleration mechanisms. Non-stationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely-spaced (sub-gyroscale), high time-resolution measurements from one rapid crossing of Earth's quasi-perpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing non-stationarity processes. Using MMS's high cadence kinetic plasma measurements, we show that the shock exhibits non-stationarity in the form of ripples.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-303649 (URN)10.1103/PhysRevLett.117.165101 (DOI)000385641500003 ()
Funder
Swedish National Space Board, 139/12 97/13
Available from: 2016-09-29 Created: 2016-09-21 Last updated: 2017-11-21Bibliographically approved

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Swedish Institute of Space Physics, Uppsala DivisionDepartment of Physics and Astronomy
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