Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts

Two dipolarization front (DF) structures observed by Cluster in the Earth midtail region (XGSM ≈ −15 RE), 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 de...

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Veröffentlicht in:Geophysical research letters 2011-08, Vol.38 (16), p.L16104-n/a
Hauptverfasser: Fu, H. S., Khotyaintsev, Y. V., André, M., Vaivads, A.
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Sprache:eng
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Zusammenfassung:Two dipolarization front (DF) structures observed by Cluster in the Earth midtail region (XGSM ≈ −15 RE), 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 (
ISSN:0094-8276
1944-8007
1944-8007
DOI:10.1029/2011GL048528