| 1. |
- Stenflo, Lennart, et al.
(author)
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Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines
- 2011
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In: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 18:15, s. 052107-1-052107-14
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Journal article (peer-reviewed)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.
(author)
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Collapse of optical vacuum pulses due to QED nonlinearities
- 2002
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In: Nonlinear Guided Waves and Their Applications, 1–4 September 2002, Stresa, Italy. - : Optics Info Base, Optical Society of America. - 1557527237
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Conference paper (other academic/artistic)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.
(author)
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Stimulated Brillouin scattering in magnetized plasmas
- 2013
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In: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 79:Special Issue 06, s. 983-986
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Journal article (peer-reviewed)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.
(author)
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Full-scale simulation study of the initial stage of ionospheric turbulence
- 2008
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In: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 113:0148-0227, s. A02305-1-A02305-9
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Journal article (peer-reviewed)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.
(author)
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Non-linear effects in a cold electron plasma with non-uniform density profile
- 2008
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In: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 77, s. 055503-1-055503-3
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Journal article (peer-reviewed)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.
(author)
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Zonal flow interaction with Rossby waves in the Earth's atmosphere : A numerical simulation
- 2008
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In: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 372:31, s. 5177-5180
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Journal article (peer-reviewed)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.
(author)
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Flow oscillations in radial expansion of an inhomogeneous plasma layer
- 2011
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In: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 375:27, s. 2629-2636
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Journal article (peer-reviewed)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.
(author)
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Circularly polarized waves in a plasma with vacuum polarization effects
- 2007
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In: Physics of Plasmas. - : American Institute of Physics. - 1070-664X .- 1089-7674. ; 14:6, s. 064503-3 sidor
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Journal article (peer-reviewed)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.
(author)
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Nonlinear propagation of partially coherent dispersive Alfvén waves.
- 2006
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In: Physica Scripta. - : INSTITUTE OF PHYSICS PUBLISHING. - 0031-8949 .- 1402-4896. ; 74:3, s. 373-376
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Journal article (peer-reviewed)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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| 11. |
- Shukla, Nitin, et al.
(author)
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Ion streaming instability in a quantum dusty magnetoplasma
- 2008
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 15:1070-664X, s. 044503-1-044503-3
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Journal article (peer-reviewed)abstract
- It is shown that a relative drift between the ions and the charged dust particles in a magnetized quantum dusty plasma can produce an oscillatory instability in a quantum dust acousticlike wave. The threshold and growth rate of the instability are presented. The result may explain the origin of low-frequency electrostatic fluctuations in semiconductors quantum wells. (C) 2008 American Institute of Physics.
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| 12. |
- Shukla, Padma Kant, et al.
(author)
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Magnetization of plasmas
- 2010
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In: New Frontiers in Advanced Plasma Physics. - : AIP. ; , s. 1-6
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Conference paper (other academic/artistic)abstract
- Wecritically examine and evaluate several physical mechanisms that are responsiblefor the seed magnetic fields in plasmas. The plasma magnetizationis attributed to sources that foster motion of the backgroundplasma electrons against the ions. The resulting space charge electricfield and currents, in turn, are detrimental for the plasmamagnetization.
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| 13. |
- Shukla, P.K., et al.
(author)
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Modulational instabilities of surface plasmons on metallic plasma surfaces with nanoparticles
- 2008
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In: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 74:03, s. 287-291
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Journal article (other academic/artistic)abstract
- The nonlinear coupling between high-frequency surface plasmons (SPs) and low-frequency ion oscillations on metallic plasma surfaces with charged nanoparticles is considered. It is shown that a finite-amplitude SP wave is modulationally unstable against the excitation of non-resonant ion oscillations. The growth rates and thresholds of the modulational instabilities are presented.
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| 14. |
- Shukla, P.K., et al.
(author)
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Quantum Hall-MHD equations for a non-uniform dense magnetoplasma with electron temperature anisotropy
- 2008
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In: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 74:05, s. 575-579
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Journal article (other academic/artistic)abstract
- Nonlinear quantum Hall-MHD equations for a warm dense magnetoplasma with an anisotropic electron pressure are derived. The nonlinear equations include the quantum force associated with electron tunneling effects. The newly found equations can be used to investigate the dense plasma stability, as well as different types of waves, instabilities, and nonlinear structures in a warm dense magnetoplasma.
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| 15. |
- Shukla, Padma, et al.
(author)
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Wake field generation and nonlinear evolution in a magnetized electron-positron-ion plasma
- 2008
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In: Physics of Plasmas. - New York : AIP Publishing. - 1070-664X .- 1089-7674. ; 15:8, s. 082305-1-082305-4
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Journal article (peer-reviewed)abstract
- The nonlinear propagation of a circularly polarized electromagnetic (CPEM) wave in a strongly magnetized electron-positron-ion plasma is investigated. Two coupled equations describing the interaction between a high-frequency CPEM wave and the low-frequency electrostatic wake field are derived. It is found that the generation of the wake fields partly depends on the presence of the ion species and the external magnetic field. The wake field generation in turn leads to deceleration and frequency down conversion of the electromagnetic pulse.
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| 16. |
- Shvartsburg, Alexander, et al.
(author)
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Superluminal tunneling of microwaves in smoothly varying transmission lines
- 2008
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In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - New York : American Physical Society through the American Institute of Physics. - 1063-651X .- 1095-3787. ; 78, s. 016601-1-016601-6
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Journal article (peer-reviewed)abstract
- Tunneling of microwaves through a smooth barrier in a transmission line is considered. In contrast to standard wave barriers, we study the case where the dielectric permittivity is positive, and the barrier is caused by the inhomogeneous dielectric profile. It is found that reflectionless, superluminal tunneling can take place for waves with a finite spectral width. The consequences of these findings are discussed, and an experimental setup testing our predictions is proposed.
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| 17. |
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| 18. |
- Stenflo, Lennart, 1939-, et al.
(author)
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Decay interactions involving two electrostatic waves and one arbitrary polarized wave in a magnetized plasma
- 2010
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In: AIP Conference Proceedings. - : AIP. - 0094-243X .- 1551-7616. ; 1306, s. 14-17
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Journal article (peer-reviewed)abstract
- We demonstrate that previously overlooked formulations of the general theory are highly useful when deriving concrete expressions for specific cases. We also point out that some previous results deduced directly from the basic plasma equations contain inappropriate approximations leading to unphysical results. Finally, the generalization to more elaborate plasma models, containing e.g. kinetic effects, is presented.
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| 19. |
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| 20. |
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| 21. |
- Stenflo, Lennart, 1939-, et al.
(author)
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Nonlinear Processes in Space Plasmas
- 2007
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In: Handbook of the Solar-Terrestrial Environment. - Berlin : Springer Berlin/Heidelberg. - 9783540463146 - 9783540463153 ; , s. 311-329
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Book chapter (other academic/artistic)abstract
- We present here a comprehensive review of some of the main nonlinear effects involving wave–wave and wave–particle interactions in space plasmas. Attention is focused on three-wave decay interactions, modulational instabilities, wave localization and the formation of structures caused by ponderomotive forces, differential electron Joule heating, and self-wave interactions of high- and low-frequency electromagnetic waves. We present nonlinear dispersion relations and their analysis, as well as the dynamics of nonlinearly interacting modes with the background plasma. The relevance of our investigation to space plasmas is discussed.
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| 22. |
- Stenflo, Lennart, 1939-, et al.
(author)
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On the parametric decay of a circularly polarized wave
- 2011
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In: Journal of Plasma Physics. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 77:4, s. 431-435
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Journal article (peer-reviewed)abstract
- The nonlinear decay of a circularly polarized wave is reconsidered. We deduce an explicit expression for the growth rate, and present it in a form which is significantly simpler than those of previous papers.
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| 23. |
- Stenflo, Lennart, 1939-, et al.
(author)
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Parametric decay of whistler waves in electron magnetohydrodynamics
- 2011
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In: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 83:3, s. 035503-035503
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Journal article (peer-reviewed)abstract
- The nonlinear interaction between three whistler waves is reconsidered. We argue that the squared growth rate of parametric decay instability has to be expressed in a form that is always positive.
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| 24. |
- Stenflo, Lennart, 1939-
(author)
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Öppna Säpo-arkiven
- 2011
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In: Axess. - 1651-0941.
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Journal article (pop. science, debate, etc.)
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| 25. |
- Stenflo, Lennart, 1939-
(author)
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Övervakad av KGB
- 2012
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In: Kungl. Skytteanska samfundets årsbok. 2012. - umeå : Kungl. Skytteanska Samfundet. - 9789186438425 ; , s. 45-51
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Book chapter (pop. science, debate, etc.)
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