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Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts
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.
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.
2011 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, L16104- p.Article 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
2011. Vol. 38, L16104- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-158591DOI: 10.1029/2011GL048528ISI: 000294130400002OAI: oai:DiVA.org:uu-158591DiVA: diva2:440367
Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08Bibliographically approved

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