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Energetic electron acceleration by unsteady magnetic reconnection

Nature Physics volume 9, pages 426–430 (2013)Cite this article

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Abstract

The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares1,2, substorms3,4, and disruptions in fusion experiments5,6. Observations in the solar chromosphere1 and the Earth’s magnetosphere7,8,9,10 indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent11. Here we show that energetic electron acceleration is caused by unsteady reconnection. In the Earth’s magnetosphere and the solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady12, so energetic electrons are absent11. The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain for the peak observed fluxes.

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Figure 1: Sketch of unsteady reconnection in the Earth’s magnetotail.
Figure 2: Cluster 1 observations of electron acceleration by unsteady reconnection.
Figure 3: Modelling of electron acceleration by unsteady reconnection.

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Acknowledgements

We thank the Cluster Active Archive for providing the data for this study. Fruitful discussions with P. L. Pritchett and other members of the team ‘Particle Acceleration at Plasma Jet Fronts in the Earth’s Magnetosphere’ at the ISSI are appreciated. This research is supported by the Swedish Research Council under grants 2007-4377, 2009-3902 and 2009-4165. H.S.F. is in part supported by NSFC Grant 40931054 and 973 program 2011CB811404.

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Authors and Affiliations

  1. Swedish Institute of Space Physics, Box 537, Uppsala 75121, Sweden

    H. S. Fu, Yu. V. Khotyaintsev, A. Vaivads & M. André

  2. Space Science Institute, School of Astronautics, Beihang University, 37 Xueyuan Road, Beijing 100191, Haidian District, China

    H. S. Fu

  3. Laboratoire de Physique des Plasmas, CNRS—Ecole Polytechnique—Université Pierre et Marie Curie—Université Paris-Sud, Route de Saclay, F-91128 Palaiseau, France

    A. Retinò

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  1. H. S. Fu
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Contributions

H.S.F. conducted the majority of the data processing, analysis and writing for this study. Y.V.K., A.V., A.R. and M.A. gave suggestions on the unsteady reconnection concept, and participated in the interpretation of the data and the preparation of the figures. A.V. and Y.V.K. developed the software for the data analysis. All the authors discussed the results and commented on the paper.

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Correspondence to H. S. Fu.

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The authors declare no competing financial interests.

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Fu, H., Khotyaintsev, Y., Vaivads, A. et al. Energetic electron acceleration by unsteady magnetic reconnection. Nature Phys 9, 426–430 (2013). https://doi.org/10.1038/nphys2664

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