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Ion Injection At Quasi-Parallel Shocks Seen By The Cluster Spacecraft
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. UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..ORCID iD: 0000-0001-7714-1870
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.
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2016 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 817, no 1, article id L4Article in journal (Refereed) Published
Resource type
Text
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.

Place, publisher, year, edition, pages
2016. Vol. 817, no 1, article id L4
Keywords [en]
acceleration of particles, cosmic rays, shock waves, solar wind
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-279631DOI: 10.3847/2041-8205/817/1/L4ISI: 000369370900004OAI: oai:DiVA.org:uu-279631DiVA, id: diva2:910001
Available from: 2016-03-08 Created: 2016-03-02 Last updated: 2018-12-04Bibliographically approved
In thesis
1. Ion dynamics and structure of collisionless shocks
Open this publication in new window or tab >>Ion dynamics and structure of collisionless shocks
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. p. 24
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-303636 (URN)
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
2. Ion dynamics and structure of collisionless shocks in space
Open this publication in new window or tab >>Ion dynamics and structure of collisionless shocks in space
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Shock waves form when supersonic flows encounter an obstacle. Like in regular gases, shock waves can form in a plasma - a gas of electrically charged particles. Shock waves in plasmas where collisions between particles are very rare are referred to as collisionless shock waves. Collisionless shocks are some of the most energetic plasma phenomena in the universe. They are found for example around exploded supernova remnants and in our solar system where the supersonic solar wind encounters obstacles like planets and the interstellar medium. Shock waves in plasmas are very efficient particle accelerators though a process known as diffusive shock acceleration. An example of particles accelerated in shock waves are the extremely energetic galactic cosmic rays that permeate the galaxy. This thesis addresses the physics of collisionless shocks using spacecraft observations of the Earth's bow shock, particularly understanding the ion dynamics and shock structure for different shock conditions. For this we have used data from ESA's four Cluster satellites and NASA's four Magnetospheric Multiscale (MMS) satellites. The first study presents Cluster measurements from the quasi-parallel bow shock, where the angle between the magnetic field and the shock normal is less than 45 degrees. We study the first steps of acceleration of solar wind ions at short large-amplitude magnetic structures (SLAMS). We observe nearly specularly reflected solar wind ions upstream of a SLAMS. By gyration in the solar wind, the reflected ions are accelerated to a few times the solar wind energy. The second and third study are about shock non-stationarity using MMS measurements from the quasi-perpendicular shock, where the angle between the magnetic field and the shock normal is greater than 45 degrees. In the second study we show that the shock is non-stationary in the form of ripples that propagate along the shock surface. In the third study we study closer in detail the dispersive properties of the ripples and find that whether a solar wind ion will be reflected at the shock is dependent on where it impinges on the rippled shock. In the fourth study we quantify the conditions for ion acceleration shocks by using MMS measurements from many encounters with the bow shock. We find that the quasi-parallel shock is efficient with up to 10% of the energy density in energetic ions. We also find that at quasi-parallel shocks, SLAMS can restrict high-energy ions from propagating upstream and convect them back to the shock, potentially increasing acceleration efficiency.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 63
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1750
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-368091 (URN)978-91-513-0519-6 (ISBN)
Public defence
2019-02-01, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, 97/13
Available from: 2019-01-07 Created: 2018-12-04 Last updated: 2019-01-21

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Johlander, AndreasVaivads, AndrisKhotyaintsev, Yuri V.

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