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| Titel |
Large-amplitude electromagnetic waves in magnetized relativistic plasmas with temperature |
| VerfasserIn |
V. Muñoz, F. A. Asenjo, M. Domínguez, R. A. López, J. A. Valdivia, A. Viñas, T. Hada |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 21, no. 1 ; Nr. 21, no. 1 (2014-02-14), S.217-236 |
| Datensatznummer |
250120887
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| Publikation (Nr.) |
 copernicus.org/npg-21-217-2014.pdf |
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| Zusammenfassung |
Propagation of large-amplitude waves in plasmas is subject to several sources
of nonlinearity due to relativistic effects, either when particle quiver
velocities in the wave field are large, or when thermal velocities are large
due to relativistic temperatures. Wave propagation in these conditions has
been studied for decades, due to its interest in several contexts such as
pulsar emission models, laser-plasma interaction, and extragalactic jets.
For large-amplitude circularly polarized waves propagating along a constant
magnetic field, an exact solution of the fluid equations can be found for
relativistic temperatures. Relativistic thermal effects produce: (a) a
decrease in the effective plasma frequency (thus, waves in the
electromagnetic branch can propagate for lower frequencies than in the cold
case); and (b) a decrease in the upper frequency cutoff for the Alfvén
branch (thus, Alfvén waves are confined to a frequency range that is
narrower than in the cold case). It is also found that the Alfvén speed
decreases with temperature, being zero for infinite temperature.
We have also studied the same system, but based on the relativistic Vlasov
equation, to include thermal effects along the direction of propagation. It
turns out that kinetic and fluid results are qualitatively consistent, with
several quantitative differences. Regarding the electromagnetic branch, the
effective plasma frequency is always larger in the kinetic model. Thus,
kinetic effects reduce the transparency of the plasma. As to the Alfvén
branch, there is a critical, nonzero value of the temperature at which the
Alfvén speed is zero. For temperatures above this critical value, the
Alfvén branch is suppressed; however, if the background magnetic field
increases, then Alfvén waves can propagate for larger temperatures.
There are at least two ways in which the above results can be improved.
First, nonlinear decays of the electromagnetic wave have been neglected;
second, the kinetic treatment considers thermal effects only along the
direction of propagation. We have approached the first subject by studying
the parametric decays of the exact wave solution found in the context of
fluid theory. The dispersion relation of the decays has been solved, showing
several resonant and nonresonant instabilities whose dependence on the wave
amplitude and plasma temperature has been studied systematically. Regarding
the second subject, we are currently performing numerical 1-D particle in
cell simulations, a work that is still in progress, although preliminary
results are consistent with the analytical ones. |
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