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Published March 31, 2017 | Published + Supplemental Material
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Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave


Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

Additional Information

© 2017 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received: 01 September 2016; Accepted: 20 January 2017; Published online: 31 March 2017. We thank the members of the FPI ground operations and science team for their feedback and support and Lynn Wilson for his insights about wave properties. This research was supported by the NASA Magnetospheric Multiscale Mission in association with NASA contract NNG04EB99C and by NSF award 1059519, AFOSR award FA9550-11-1-0184 and DOE awards DE-FG02-04ER54755 and DE-SC0010471. S.J.S. is grateful to the Leverhulme Trust for its award of a Research Fellowship. Author Contributions: D.J.G. conducted the majority of the scientific and data analysis and was responsible for initial preparation of the manuscript text. A.F-V. assisted with the interpretation of wave signatures, plasma wave modeling and with the preparation of the manuscript text. J.C.D., S.A.B. and L.A.A. assisted with the interpretation of plasma wave signatures, detailed analysis of plasma data and with the preparation of the manuscript text. P.M.B. assisted with the implementation of the wavevector determination method and with the preparation of the manuscript text. S.J.S. assisted with the Liouville mapping of electron data and preparation of the manuscript text. B.L., V.N.C., M.O.C., Y.S. and W.R.P. provided and ensured quality of high-resolution plasma data and assisted with the preparation of the manuscript text. S.A.F. provided and ensured the quality of the plasma composition data. R.E.E. and R.B.T. provided and ensured the quality of high-resolution electric field data and assisted with the preparation of the manuscript text. R.J.S. and C.T.R. provided and ensured the quality of high-resolution fluxgate magnetometer data. B.L.G., C.J.P. and J.L.B. provided institutional and mission-level support of the analysis and ensured overall quality of MMS and FPI data. The authors declare no competing financial interests.

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