| 1. |
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| 2. |
- Ali, S, et al.
(författare)
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Dust acoustic solitary waves in a quantum plasma
- 2006
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Ingår i: Physics of Plasmas. - Melville : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- By employing one-dimensional quantum hydrodynamic (QHD) model for a three species quantum plasma, nonlinear properties of dust acoustic solitary waves are studied. For this purpose a Korteweg-de Vries (KdV) equation is derived, incorporating quantum corrections. The quantum mechanical effects are also examined numerically both on the profiles of the amplitude and the width of dust acoustic solitary waves. It is found that the amplitude remains constant but the width shrinks for different values of a dimensionless electron quantum parameter H-e=root(Z(d0)h(2)omega(2)(pd))/m(e)m(d)C(d)(4), where Z(d0) is the dust charge state, h is the Planck constant divided by 2 pi, omega(pd) is the dust plasma frequency, m(e) (m(d)) is the electron (dust) mass, and C-d is the dust acoustic speed.
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| 3. |
- Brodin, Gert, et al.
(författare)
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Dispersion relation for electromagnetic wave propagation in a strongly magnetized plasma
- 2006
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Ingår i: New Journal of Physics. - Bristol, UK : Institute of Physics Pub.. - 1367-2630. ; 8:January, s. 16-
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Tidskriftsartikel (refereegranskat)abstract
- A dispersion relation for electromagnetic wave propagation in a strongly magnetized cold plasma is deduced, taking photon–photon scattering into account. It is shown that the combined plasma and quantum electrodynamic effect is important for understanding the mode-structures in magnetar and pulsar atmospheres. The implications of our results are discussed.
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| 4. |
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| 5. |
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| 6. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Electron acceleration by a relativistic two stream instability with oblique B
- 2006
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Ingår i: 33rd European Physical Society Conference on Plasma Physics,2006. - Rome : European Physical Society. ; , s. P4.071-
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Konferensbidrag (refereegranskat)abstract
- Electrons that are trapped by a quasi-electrostatic wave move, on average, with the phase speed of the wave. In the presence of a magnetic field B, the trapped electrons could, in principle, be accelerated to cosmic ray energies through cross-field transport. We model this cross-field transport with a particle-in-cell (PIC) simulation for an oblique B. The electron energies at the simulation's end exceed 5 MeV for all pitch angles and they can reach GeV energies along the wavevector. We discuss environments, in which such conditions may exist and for which such an acceleration would be relevant.
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| 7. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Electron surfing acceleration by the electron two-stream instability in a weak magnetic field
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 48:October, s. 1515-1530
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Tidskriftsartikel (refereegranskat)abstract
- The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here.
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| 8. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Electron surfing acceleration in oblique magnetic fields
- 2006
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 367:3, s. 865-872
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Tidskriftsartikel (refereegranskat)abstract
- Initially, inhomogeneous plasma jets, ejected by active galactic nuclei and associated with gamma-ray bursts, are thermalized by the formation of internal shocks. Jet subpopulations can hereby collide at Lorentz factors of a few. As the resulting relativistic shock expands into the upstream plasma, a significant fraction of the upstream ions is reflected. These ions, together with downstream ions that leak through the shock, form relativistic beams of ions that outrun the shock. The thermalization of these beams via the two-stream instability is thought to contribute significantly to plasma heating and particle acceleration by the shock. Here, the capability of a two-stream instability to generate relativistic field-aligned and cross-field electron flow, is examined for a magnetized plasma by means of a particle-in-cell (PIC) simulation. The electrons interact with the developing quasi-electrostatic waves and oblique magnetic fields. The simulation results bring forward evidence that such waves, by their non-linear interactions with the plasma, produce a highly relativistic field-aligned electron flow and electron energies, which could contribute to the radio synchrotron emissions from astrophysical jets, to ultrarelativistic leptonic subpopulations propagating with the jet and to the halo particles surrounding the accretion disc of the black hole.
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| 9. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Evolution of the fastest-growing relativistic mixed mode instability driven by a tenuous plasma beam in one and two dimensions
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 13:11, s. 112110-1-112110-8
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Tidskriftsartikel (refereegranskat)abstract
- Particle-in-cell simulations confirm here that a mixed plasma mode is the fastest growing when a highly relativistic tenuous electron-proton beam interacts with an unmagnetized plasma. The mixed modes grow faster than the filamentation and two-stream modes in simulations with beam Lorentz factors Gamma of 4, 16, and 256, and are responsible for thermalizing the electrons. The mixed modes are followed to their saturation for the case of Gamma=4 and electron phase space holes are shown to form in the bulk plasma, while the electron beam becomes filamentary. The initial saturation is electrostatic in nature in the considered one- and two-dimensional geometries. Simulations performed with two different particle-in-cell simulation codes evidence that a finite grid instability couples energy into high-frequency electromagnetic waves, imposing simulation constraints.
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| 10. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Formation of electrostatic structures by wakefield acceleration in ultrarelativistic plasma flows : Electron acceleration to cosmic ray energies
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 13:6, s. 062905-1-062905-8
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Tidskriftsartikel (refereegranskat)abstract
- The ever increasing performance of supercomputers is now enabling kinetic simulations of extreme astrophysical and laser produced plasmas. Three-dimensional particle-in-cell (PIC) simulations of relativistic shocks have revealed highly filamented spatial structures and their ability to accelerate particles to ultrarelativistic speeds. However, these PIC simulations have not yet revealed mechanisms that could produce particles with tera-electron volt energies and beyond. In this work, PIC simulations in one dimension (1D) of the foreshock region of an internal shock in a gamma ray burst are performed to address this issue. The large spatiotemporal range accessible to a 1D simulation enables the self-consistent evolution of proton phase space structures that can accelerate particles to giga-electron volt energies in the jet frame of reference, and to tens of tera-electron volt in the Earth's frame of reference. One potential source of ultrahigh energy cosmic rays may thus be the thermalization of relativistically moving plasma.
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| 11. |
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| 12. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Particle-in-cell simulation studies of the non-linear evolution of ultrarelativistic two-stream instabilities
- 2006
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 367:3, s. 1072-1082
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray bursts are associated with relativistic plasma flow and intense X-ray and soft gamma-ray emissions. We perform particle-in-cell simulations to explore the growth and saturation of waves driven by the electrostatic two-stream instability that may contribute to the thermalization of the relativistic plasma flows and to the electromagnetic emissions. We evolve self-consistently the instability driven by two charge-neutral and cool interpenetrating beams of electrons and protons that move at a relative Lorentz factor of 100. We perform three simulations with the beam density ratios of 1, 2 and 10. The simulations show that the electrostatic waves saturate by trapping the electrons of only one beam and that the saturated electrostatic wave fields spatially modulate the mean momentum of the second beam, while retaining its temperature. Cavities form in the charge density of the latter beam which, in turn, compress the electrostatic waves to higher intensities. A runaway process develops that terminates with the collapse of the waves and the development of an exponential electron high-energy tail. We bring forward evidence that this energetic tail interacts stochastically with the charge density fluctuations of the relativistic proton beam. In response, an electron momentum distribution develops that follows an inverse power law up to a spectral break at four times the beam Lorentz factor.
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| 13. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Particle-in-cell simulations of plasma slabs colliding at a mildly relativistic speed
- 2006
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 8:October, s. 225-1-225-21
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Tidskriftsartikel (refereegranskat)abstract
- Plasmas collide at relativistic speeds in many astrophysical and high-energy density laboratory environments. The boundaries that develop between such plasmas and expand at much larger speeds than the ion sound speed cs are not well understood. Here, we address two identical electron-proton plasma slabs that collide with a relativistic speed and a Mach number v/cs of over 400. The collision speed, the plasma temperature and magnetic field are such that the growth rate of the two-stream instability exceeds that of all other instabilities. We model a planar turbulent boundary (TB) with one-dimensional (1D) and 2D particle-in-cell (PIC) simulations. We show that the boundary dissipates its energy via electron phase space holes (EPSHs) that accelerate electrons at the boundary to relativistic speeds and increase significantly the speed of some protons. Our results are put into the context of a dynamic accretion disc and the jet of a microquasar. It is shown that the accelerated electrons could contribute to the disc wind and to relativistic leptonic jets, and possibly to the hard radiation component of the accretion disc.
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| 14. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Phase speed of electrostatic waves : the critical parameter for efficient electron surfing acceleration
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 48:4, s. 489-508
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Tidskriftsartikel (refereegranskat)abstract
- Particle acceleration by means of nonlinear plasma wave interactions is of great topical interest. Accordingly, in this paper we focus on the electron surfing process. Self-consistent kinetic simulations, using both relativistic Vlasov and particle-in-cell (PIC) approaches, show here that electrons can be accelerated to highly relativistic energies (up to 100mec2) if the phase speed of the electrostatic wave is mildly relativistic (0.6c to 0.9c for the magnetic field strengths considered). The acceleration is strong because of relativistic stabilization of the nonlinearly saturated electrostatic wave, seen in both relativistic Vlasov and PIC simulations. An inverse power law momentum distribution can arise for the most strongly accelerated electrons. These results are of relevance to observed rapid changes in the radio synchrotron emission intensities from microquasars, gamma ray bursts and other astrophysical objects that require rapid acceleration mechanisms for electrons.
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| 15. |
- Dieckmann, Mark E, 1969-, et al.
(författare)
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Two-stream instability in collisionless shocks and foreshock
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 48:12 B, s. B303-B311
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Shocks play a key role in plasma thermalization and particle acceleration in the near Earth space plasma, in astrophysical plasma and in laser plasma interactions. An accurate understanding of the physics of plasma shocks is thus of immense importance. We give an overview over some recent developments in particle-in-cell simulations of plasma shocks and foreshock dynamics. We focus on ion reflection by shocks and on the two-stream instabilities these beams can drive, and these are placed in the context of experimental observations, e.g. by the Cluster mission. We discuss how we may expand the insight gained from the observation of proton beam driven instabilities at near Earth plasma shocks to better understand their astrophysical counterparts, such as ion beam instabilities triggered by internal and external shocks in the relativistic jets of gamma ray bursts, shocks in the accretion discs of micro-quasars and supernova remnant shocks. It is discussed how and why the peak energy that can be reached by particles that are accelerated by two-stream instabilities increases from keV energies to GeV energies and beyond, as we increase the streaming speed to relativistic values, and why the particle energy spectrum sometimes resembles power law distributions.
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| 16. |
- Eliasson, Bengt, et al.
(författare)
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Theoretical and simulation studies of relativistic ion holes in astrophysical plasmas
- 2006
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 8:April, s. 55-1-55-12
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical and numerical studies of relativistic ion holes in a relativistically hot electron-ion plasma are presented. Previous particle-in-cell (PIC) simulations have shown that the ion holes are formed as a result of relativistic beam-plasma instabilities in the foreshock region of internal shocks of gamma-ray bursts and the relativistic jets of active galactic nuclei. In this process, the electrons are heated to ultra-relativistic temperatures so that their relativistic mass becomes comparable to the proton mass, and relativistic ion holes are formed by a secondary ion beam instability. The electrostatic potentials associated with the ion holes are large enough to accelerate particles to GeV energies. We use a semi-analytical model to construct relativistic ion holes and investigate their stability by means of fully relativistic Vlasov simulations. This investigation is relevant for astrophysical settings where the ion holes may work as efficient particle accelerators.
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| 17. |
- Eliasson, Bengt, et al.
(författare)
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Theory and simulations of nonlinear kinetic structures in plasmas
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 48:12 B, s. B257-B265
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present analytical and numerical studies of the dynamics of relativistic electron and ion holes in a collisionless plasma. Electromagnetic radiation can be trapped in relativistic electron phase-space holes mainly due to the relativistic mass increase of the electrons that are accelerated by the potential of the phase-space hole and by the quivering component of the electromagnetic field. Relativistic ion holes may exist in plasmas where the electrons are thermalized to extremely ultra-relativistic energies. They may be responsible for the acceleration of particles to GeV energies in active galactic nuclei and supernova remnant shocks. The analytic solutions are employed as initial conditions for numerical simulations in which the dynamics and stability of the phase-space holes are investigated. The results have relevance for intense laser-plasma experiments and for astrophysical plasmas.
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| 18. |
- Forsberg, Mats, 1978-, et al.
(författare)
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Nonlinear interactions between gravitational radiation and modified Alfvén modes in astrophysical dusty plasmas
- 2006
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Ingår i: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 74, s. 064014-064014-5
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Tidskriftsartikel (refereegranskat)abstract
- We present an investigation of nonlinear interactions between gravitational radiation and modified Alfvén modes in astrophysical dusty plasmas. Assuming that stationary charged dust grains form neutralizing background in an electron-ion-dust plasma, we obtain the three-wave coupling coefficients and calculate the growth rates for parametrically coupled gravitational radiation and modified Alfvén-Rao modes. The threshold value of the gravitational wave amplitude associated with convective stabilization is particularly small if the gravitational frequency is close to twice the modified Alfvén wave frequency. The implication of our results to astrophysical dusty plasmas is discussed.
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| 19. |
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| 20. |
- Marklund, Mattias, et al.
(författare)
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Electrostatic pair creation and recombination in quantum plasmas
- 2006
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Ingår i: JETP Letters. - 0021-3640 .- 1090-6487. ; 83:8, s. 313-317
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Tidskriftsartikel (refereegranskat)abstract
- The production of electron-positron pairs by electrostatic waves in quantum plasmas is investigated. In particular, a semiclassical governing set of equations for a self-consistent treatment of pair creation by the Schwinger mechanism in a quantum plasma is derived.
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| 21. |
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| 22. |
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| 23. |
- Marklund, Mattias, et al.
(författare)
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Fysiken bakom monstervågor
- 2006
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Ingår i: Fysikaktuellt. - 0283-9148. ; :4, s. 6-7
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- 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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| 32. |
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| 33. |
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| 34. |
- Mendonça, J.T., et al.
(författare)
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Photon acceleration in vacuum
- 2006
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Ingår i: Physics Letters A. ; 359, s. 700-704
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Tidskriftsartikel (refereegranskat)
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| 35. |
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| 36. |
- Shukla, Padma K., et al.
(författare)
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Amplitude modulation of whistlers by modified ion-cyclotron perturbations in plasmas
- 2006
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 72:2, s. 149-152
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear interaction between a large-amplitude whistler pump and the modified ion-cyclotron perturbations is studied. A nonlinear dispersion relation for the modulation/filamentation interaction is derived and solved numerically to investigate the instability properties. We discuss the relevance of the present study with regard to recent laboratory experiments where the modulation/filamentation of a whistler pump by the modified ion-cyclotron waves has been observed.
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| 37. |
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| 38. |
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| 39. |
- Shukla, Padma K, et al.
(författare)
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Instability and dynamics of two nonlinearly coupled laser beams in a plasma
- 2006
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 13:5, s. 053104-1-053104-7
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear interaction between two laser beams in a plasma is investigated in the weakly nonlinear and relativistic regime. The evolution of the laser beams is governed by two nonlinear Schrödinger equations that are coupled with the slow plasma density response. A nonlinear dispersion relation is derived and used to study the growth rates of the Raman forward and backward scattering instabilities as well of the Brillouin and self-focusing/modulational instabilities. The nonlinear evolution of the instabilities is investigated by means of direct simulations of the time-dependent system of nonlinear equations.
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| 40. |
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| 41. |
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| 42. |
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| 43. |
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| 44. |
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| 45. |
- Shukla, Padma K, et al.
(författare)
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Nonlinear aspects of the solar coronal heating
- 2006
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 48:12 B, s. B249-B255
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The heating of the solar coronal plasma has remained one of the most important problems in solar physics. An explanation of the electron and ion heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the plasma particles. In this paper, we discuss two important nonlinear aspects of the electron and ion heating caused by finite amplitude obliquely propagating dispersive Alfvén (DA) waves and magnetic field-aligned circularly polarized electromagnetic ion-cyclotron Alfvén (EMICA) waves that may exist in the solar terrestrial environment. Specifically, DA waves may contribute to the solar coronal electron heating via Joule heating involving electron-wave interactions, and resonant ion EMICA wave interactions may contribute to differential ion heating in the solar corona.
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| 46. |
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| 47. |
- Shukla, Padma K., et al.
(författare)
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Nonlinear interaction between three kinetic Alfven waves
- 2006
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Ingår i: Physics Letters A. - Amsterdam : North-Holland. - 0375-9601 .- 1873-2429. ; 353:1, s. 73-75
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Tidskriftsartikel (refereegranskat)abstract
- Using Hall-MHD theory, we focus on the resonant interaction between three kinetic Alfvén waves. We thus derive three coupled equations which govern this process. It turns out that these equations contain the same coupling coefficient, directly showing that they satisfy the Manley–Rowe relations. The coupling coefficient can be written in a comparatively very simple form, that has not been deduced before. The decay rate, when a pump kinetic Alfvén wave decays into two similar Alfvén waves, is therefore easily estimated for plasmas of astrophysical interest.
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| 48. |
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| 49. |
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| 50. |
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