| 1. |
- Guio, P., et al.
(författare)
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Phase space vortices in collision-less plasmas
- 2003
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Ingår i: Nonlinear processes in geophysics. - 1023-5809 .- 1607-7946. ; 10:1/2, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- Results on the formation and propagation of electron phase space vortices from laboratory experiments are summarized. The electron phase space vortices were excited in a strongly magnetized Q-machine plasma by applying a pulse to a segment of a waveguide surrounding the plasma. Depending on the temporal variation of the applied pulse, one or more phase space vortices can be excited, and their interaction can be followed in space and time. We were able to demonstrate, for instance, an irreversible coalescence of two such vortices. These results are extended by numerical simulations, showing how electron phase space vortices can also be formed by beam instabilities. Furthermore, a study of ion phase space vortices is performed by numerical simulations. Both codes allow for an externally applied magnetic field in three spatial dimensions. Ion phase space vortices are formed by the nonlinear saturation of the ion-ion two-stream instability, excited by injecting an ion beam at the plasma boundary. By following the evolution of the ion distribution of the velocity perpendicular to the direction of propagation of the injected ion beam, we find a significant ion heating in the direction perpendicular to the magnetic field associated with the ion phase space vortices being formed. The results are relevant, for instance, for the interpretation of observations by instrumented spacecraft in the Earth's ionosphere and magnetosphere.
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| 2. |
- Kjus, SH, et al.
(författare)
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Statistics of the lower hybrid wave cavities detected by the FREJA satellite
- 1998
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. ; 103:A11, s. 26633-26647
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Localized electrostatic wave packets in the frequency region of lower hybrid waves have been detected by the instruments on the FREJA satellite and also earlier by instrumented rocket payloads. These waves are often associated with local density depletion
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| 3. |
- Pecseli, HL, et al.
(författare)
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Lower hybrid wave cavities detected by the FREJA satellite
- 1996
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. ; 101:A3, s. 5299-5316
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Localized electrostatic wave packets in the frequency region of lower hybrid waves have been detected by the instruments on the FREJA satellite. These waves are often associated with local density depletions indicating that the structures can be interpret
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| 4. |
- Daldorff, Lars K. S., et al.
(författare)
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Nonlinearly generated plasma waves as a model for enhanced ion acoustic lines in the ionosphere
- 2007
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 34:18, s. L18101-
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Tidskriftsartikel (refereegranskat)abstract
- Observations from the EISCAT Svalbard Radar, for instance, demonstrate that the symmetry of the naturally occurring ion line can be broken by an enhanced, non-thermal, level of fluctuations, i.e., Naturally Enhanced Ion-Acoustic Lines (NEIALs). In a significant number of cases, the entire ion spectrum can be distorted, with the appearance of a third line, corresponding to a propagation velocity significantly below the ion acoustic sound speed. By numerical simulations, we consider one possible model accounting for the observations, suggesting that a primary process can be electron acoustic waves excited by a cold electron beam. Subsequently, an oscillating two-stream instability excites electron plasma waves which in turn decay to asymmetric ion lines. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation.
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| 5. |
- Hoymork, SH, et al.
(författare)
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Cavitation of lower hybrid waves in the Earth's ionosphere: A model analysis
- 2000
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : AMER GEOPHYSICAL UNION. - 0148-0227. ; 105:A8, s. 18519-18535
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Tidskriftsartikel (refereegranskat)abstract
- Lower hybrid wave cavities detected by the Freja satellite are analyzed. On the basis of simple statistical arguments by use of signals from two density probes, it is possible to obtain rather general results concerning the individual shapes of these cavi
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| 6. |
- Hoymork, SH, et al.
(författare)
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The shape and evolution of Lower Hybrid density cavities observed by FREJA
- 2001
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Ingår i: PHYSICS AND CHEMISTRY OF THE EARTH PART C-SOLAR-TERRESTIAL AND PLANETARY SCIENCE. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1464-1917. ; 26:1-3, s. 213-217
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Tidskriftsartikel (refereegranskat)abstract
- A large number of narrow density cavities (50 m wide in the direction perpendicular to the magnetic field) are observed by the FREJA satellite. These cavities are correlated with electric field enhancements in the frequency range of Lower Hybrid waves. By
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| 7. |
- Pecseli, HL, et al.
(författare)
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Lower-hybrid wave cavities detected by instrumented spacecrafts
- 1997
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Ingår i: PLASMA PHYSICS AND CONTROLLED FUSION. - : IOP PUBLISHING LTD. - 0741-3335. ; 39:5A, s. 227-236
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Localized electrostatic wave packets in the frequency region of lower-hybrid waves have been detected by instrumented rocket payloads and recently also by the instruments on the FREJA satellite. These waves are often associated with local density depletio
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| 8. |
- Stenflo, Lennart, et al.
(författare)
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Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines
- 2011
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 18:15, s. 052107-1-052107-14
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Tidskriftsartikel (refereegranskat)abstract
- Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.
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