| 1. |
- 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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| 2. |
- Anderson, D., et al.
(författare)
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Collapse of optical vacuum pulses due to QED nonlinearities
- 2002
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Ingår i: Nonlinear Guided Waves and Their Applications, 1–4 September 2002, Stresa, Italy. - : Optics Info Base, Optical Society of America. - 1557527237
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to quantum electrodynamical (QED) effects there are nonlinear corrections to Maxwell's equations in vacuum. We show that stationary two-dimensional light bullets can form, which are unstable and exhibit, the possibility of self-focusing collapse.
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| 3. |
- Brodin, Gert, 1963-, et al.
(författare)
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Stimulated Brillouin scattering in magnetized plasmas
- 2013
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Ingår i: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 79:Special Issue 06, s. 983-986
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Tidskriftsartikel (refereegranskat)abstract
- Previous theory for stimulated Brillouin scattering is reconsidered and generalized. We introduce an effective ion sound velocity that turns out to be useful in describing scattering instabilities.
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| 4. |
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| 5. |
- Eliasson, Bengt, et al.
(författare)
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Full-scale simulation study of the initial stage of ionospheric turbulence
- 2008
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 113:0148-0227, s. A02305-1-A02305-9
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Tidskriftsartikel (refereegranskat)abstract
- We present a full-scale simulation of the nonlinear interaction between an intense electromagnetic wave and the Earth's ionosphere, by means of a generalized Zakharov model. The radio wave propagates from the neutral atmosphere into the ionospheric plasma layer and reaches the turning points of the ordinary and extraordinary wave modes. At the turning point of the ordinary mode, a parametric instability takes place in which the electromagnetic wave decays into an electron plasma wave and an ion acoustic wave with a typical wavelength of one meter. This is followed by collapse and caviton formation and trapping of the intense electron plasma wave. The cavitons lead to an efficient excitation of slow X (or Z) waves that propagate further into the denser ionospheric layer at higher altitudes. We use a realistic ion (oxygen) mass, length scales, and other plasma parameters. This numerical study should be useful for understanding the nonlinear interaction between intense radio waves and the ionosphere.
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| 6. |
- Gradov, O.M., et al.
(författare)
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Non-linear effects in a cold electron plasma with non-uniform density profile
- 2008
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 77, s. 055503-1-055503-3
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Tidskriftsartikel (refereegranskat)abstract
- A new step forward on the theory for two-dimensional wave propagation is outlined for a non-uniform plasma with a smooth density profile. A way to excite envelope solitary waves with certain shapes is described. The corresponding wave space structure is calculated, and the restrictions on the wave profile along the direction of wave propagation are noticed.
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| 7. |
- Kaladze, T. D., et al.
(författare)
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Zonal flow interaction with Rossby waves in the Earth's atmosphere : A numerical simulation
- 2008
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 372:31, s. 5177-5180
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Tidskriftsartikel (refereegranskat)abstract
- A numerical simulation of the Charney-Obukhov equation modified by the presence of a sheared zonal flow is carried out. The zonal flow is assumed to propagate longitudinally and is sheared along the meridians. It is shown that owing to the nonlinear interaction of the sheared zonal flow with the initially given disturbances the energy of the zonal flow is accumulating into the formations which are broken into several pieces. As a result new solitary vortex structures arise to produce the structural turbulence
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| 8. |
- Karimov, AR, et al.
(författare)
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Flow oscillations in radial expansion of an inhomogeneous plasma layer
- 2011
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 375:27, s. 2629-2636
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Tidskriftsartikel (refereegranskat)abstract
- The cylindrically symmetric radial evolution of an inhomogeneous plasma layer expanding into vacuum is investigated nonperturbatively by first determining the spatial structure of the plasma flow structure. The evolution is then governed by a set of ordinary differential equations. The effect of the plasma inhomogeneity on the nonlinear coupling among the electron and ion flow components and oscillations is investigated
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| 9. |
- Lundin, Joakim, 1978-, et al.
(författare)
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Circularly polarized waves in a plasma with vacuum polarization effects
- 2007
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Ingår i: Physics of Plasmas. - : American Institute of Physics. - 1070-664X .- 1089-7674. ; 14:6, s. 064503-3 sidor
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Tidskriftsartikel (refereegranskat)abstract
- The theory for large amplitude circularly polarized waves propagating along an external magnetic field is extended in order to also include vacuum polarization effects. A general dispersion relation, which unites previous results, is derived.
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| 10. |
- Marklund, Mattias, 1970-, et al.
(författare)
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Nonlinear propagation of partially coherent dispersive Alfvén waves.
- 2006
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Ingår i: Physica Scripta. - : INSTITUTE OF PHYSICS PUBLISHING. - 0031-8949 .- 1402-4896. ; 74:3, s. 373-376
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Tidskriftsartikel (refereegranskat)abstract
- The effects of partial coherence on the propagation of dispersive Alfvén waves in a magnetoplasma are investigated. In particular, nonlinear interactions between dispersive Alfvén waves and ion-acoustic perturbations are considered by means of a Wigner formalism. A set of governing equations consisting of a kinetic equation for dispersive Alfvén waves coupled nonlinearly to a ponderomotive force driven ion-acoustic wave equation is obtained. The governing nonlinear equations are used to derive a nonlinear dispersion relation that is appropriate for investigating the modulational instability of broadband Alfvén wavepackets. The spectral broadening of the Alfvén waves gives rise to new regimes for the growth rate of the modulational instability.
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