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Bilbao PJ, Silva LO. Radiation Reaction Cooling as a Source of Anisotropic Momentum Distributions with Inverted Populations. PHYSICAL REVIEW LETTERS 2023; 130:165101. [PMID: 37154664 DOI: 10.1103/physrevlett.130.165101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 03/14/2023] [Accepted: 03/28/2023] [Indexed: 05/10/2023]
Abstract
Under the presence of strong electromagnetic fields and radiation reaction, plasmas develop anisotropic momentum distributions, characterized by a population inversion. This is a general property of collisionless plasmas when the radiation reaction force is taken into account. We study the case of a plasma in a strong magnetic field and demonstrate the development of ring momentum distributions. The timescales for ring formation are derived for this configuration. The analytical results for the ring properties and the timescales for ring formation are confirmed with particle-in-cell simulations. The resulting momentum distributions are kinetically unstable and are known to lead to coherent radiation emission in astrophysical plasmas and laboratory setups.
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Affiliation(s)
- P J Bilbao
- GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
| | - L O Silva
- GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
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Speirs DC, Bingham R, Cairns RA, Vorgul I, Kellett BJ, Phelps ADR, Ronald K. Backward wave cyclotron-maser emission in the auroral magnetosphere. PHYSICAL REVIEW LETTERS 2014; 113:155002. [PMID: 25375713 DOI: 10.1103/physrevlett.113.155002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Indexed: 06/04/2023]
Abstract
In this Letter, we present theory and particle-in-cell simulations describing cyclotron radio emission from Earth's auroral region and similar phenomena in other astrophysical environments. In particular, we find that the radiation, generated by a down-going electron horseshoe distribution is due to a backward-wave cyclotron-maser emission process. The backward wave nature of the radiation contributes to upward refraction of the radiation that is also enhanced by a density inhomogeneity. We also show that the radiation is preferentially amplified along the auroral oval rather than transversely. The results are in agreement with recent Cluster observations.
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Affiliation(s)
- D C Speirs
- Department of Physics, SUPA, University of Strathclyde, Glasgow, Scotland G4 0NG, United Kingdom
| | - R Bingham
- Department of Physics, SUPA, University of Strathclyde, Glasgow, Scotland G4 0NG, United Kingdom and Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England OX11 0QX, United Kingdom
| | - R A Cairns
- School of Mathematics and Statistics, University of St. Andrews, Fife, Scotland KY16 9SS, United Kingdom
| | - I Vorgul
- School of Mathematics and Statistics, University of St. Andrews, Fife, Scotland KY16 9SS, United Kingdom
| | - B J Kellett
- Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England OX11 0QX, United Kingdom
| | - A D R Phelps
- Department of Physics, SUPA, University of Strathclyde, Glasgow, Scotland G4 0NG, United Kingdom
| | - K Ronald
- Department of Physics, SUPA, University of Strathclyde, Glasgow, Scotland G4 0NG, United Kingdom
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