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Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts
Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.ORCID iD: 0000-0003-1654-841x
2011 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, article id L16104Article in journal (Refereed) Published
Abstract [en]

Two dipolarization front (DF) structures observed by Cluster in the Earth midtail region (X(GSM) approximate to -15 R(E)), showing respectively the feature of Fermi and betatron acceleration of suprathermal electrons, are studied in detail in this paper. Our results show that Fermi acceleration dominates inside a decaying flux pileup region (FPR), while betatron acceleration dominates inside a growing FPR. Both decaying and growing FPRs are associated with the DF and can be distinguished by examining whether the peak of the bursty bulk flow (BBF) is co-located with the DF (decaying) or is behind the DF (growing). Fermi acceleration is routinely caused by the shrinking length of flux tubes, while betatron acceleration is caused by a local compression of the magnetic field. With a simple model, we reproduce the processes of Fermi and betatron acceleration for the higher-energy (>40 keV) electrons. For the lower-energy (<20 keV) electrons, Fermi and betatron acceleration are not the dominant processes. Our observations reveal that betatron acceleration can be prominent in the midtail region even though the magnetic field lines are significantly stretched there.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2011. Vol. 38, article id L16104
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Natural Sciences
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URN: urn:nbn:se:kth:diva-253255DOI: 10.1029/2011GL048528ISI: 000294130400002Scopus ID: 2-s2.0-80051973538OAI: oai:DiVA.org:kth-253255DiVA, id: diva2:1324657
Note

QC 20190625

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-25Bibliographically approved

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Vaivads, Andris

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