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Sökning: WFRF:(Stenflo Lennart)

  • Resultat 1-10 av 211
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  • Bingham, Robert, et al. (författare)
  • Ion acceleration by Alfven waves on auroral field lines
  • 2013
  • Ingår i: Physica Scripta. - Institute of Physics. - 0031-8949. ; 87:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Observations of ion acceleration along auroral field lines at the boundary of the plasma sheet and tail lobe of the Earth show that the energy of the ions increases with decreasing density. The observations can be explained by ion acceleration through Landau resonance with kinetic Alfven waves (KAWs) such that k(A) . v(i) = omega(A), where k(A) is the wave vector, v(i) is the ion resonance velocity and omega(A) is the Alfven wave frequency. The ion resonance velocities are proportional to the Alfven velocity which increases with decreasing density. This is in agreement with the data if the process is occurring at the plasma sheet tail lobe boundary. A quasi-linear theory of ion acceleration by KAWs is presented. These ions propagate both down towards and away from the Earth. The paths of the Freja and Polar satellites indicate that the acceleration takes place between the two satellites, between 1Re and 5Re. The downward propagating ions develop a horseshoe-type of distribution which has a positive slope in the perpendicular direction. This type of distribution can produce intense lower hybrid wave activity, which is also observed. Finally, the filamentation of shear Alfven waves is considered. It may be responsible for large-scale density striations.
  • Bingham, Robert, et al. (författare)
  • Solar coronal heating by plasma waves
  • 2010
  • Ingår i: Journal of Plasma Physics. - Cambridge university. - 0022-3778. ; 76:2, s. 135-158
  • Tidskriftsartikel (refereegranskat)abstract
    • The solar coronal plasma is maintained at temperatures of millions of degrees, much hotter than the photosphere, which is at a temperature of just 6000 K. In this paper, the plasma particle heating based on the kinetic theory of wave–particle interactions involving kinetic Alfvén waves and lower-hybrid drift modes is presented. The solar coronal plasma is collisionless and therefore the heating must rely on turbulent wave heating models, such as lower-hybrid drift models at reconnection sites or the kinetic Alfvén waves. These turbulent wave modes are created by a variety of instabilities driven from below. The transition region at altitudes of about 2000 km is an important boundary chromosphere, since it separates the collision-dominated photosphere/chromosphere and the collisionless corona. The collisionless plasma of the corona is ideal for supporting kinetic wave–plasma interactions. Wave–particle interactions lead to anisotropic non-Maxwellian plasma distribution functions, which may be investigated by using spectral analysis procedures being developed at the present time.
  • Brodin, Gert, et al. (författare)
  • A new decay channel for compressional Alfven waves in plasmas
  • 2008
  • Ingår i: Journal of Plasma Physics. - 0022-3778. ; 74:1, s. 99-105
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a new efficient wave decay channel involving nonlinear interactions between a compressional Alfv´en wave, a kinetic Alfv´en wave, and a modified ion sound wave in a magnetized plasma. It is found that the wave coupling strength of the ideal magnetohydrodynamic (MHD) theory is much increased when the effects due to the Hall current are included in a Hall–MHD description of wave–wave interactions. In particular, with a compressional Alfv´en pump wave well described by the ideal MHD theory, we find that the growth rate is very high when the decay products have wavelengths of the order of the ion thermal gyroradius or shorter, in which case they must be described by the Hall–MHD equations. The significance of our results to the heating of space and laboratory plasmas as well as for the Solar corona and interstellar media are highlighted.
  • Brodin, G., et al. (författare)
  • A new decay channel for upper-hybrid waves
  • 2016
  • Ingår i: Physica Scripta. - IOP PUBLISHING LTD. - 0031-8949. ; 91:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We look here at a three-wave interaction process involving only electrostatic waves in an electron plasma with stationary ions. Special attention is given to the case with an upper-hybrid wave as a pump wave, where a new decay channel is pointed out. The corresponding growth rate is calculated.
  • Brodin, G., et al. (författare)
  • A simple electron plasma wave
  • 2017
  • Ingår i: Physics Letters A. - ELSEVIER SCIENCE BV. - 0375-9601. ; 381:11, s. 1033-1035
  • Tidskriftsartikel (refereegranskat)abstract
    • Considering a class of solutions where the density perturbations are functions of time, but not of space, we derive a new exact large amplitude wave solution for a cold uniform electron plasma. This result illustrates that most simple analytical solutions can appear even if the density perturbations are large. (C) 2016 Elsevier B.V. All rights reserved.
  • Brodin, Gert, et al. (författare)
  • Alfven wave interactions within the Hall-MHD description
  • 2013
  • Ingår i: Journal of Plasma Physics. - Cambridge University Press (CUP). - 0022-3778. ; 79, s. 909-911
  • Tidskriftsartikel (refereegranskat)abstract
    • We show that comparatively simple expressions for the Alfven wave coupling coefficients can be deduced from the well-known Hall-magnetohydrodynamics (MHD) model equations.
  • Brodin, Gert, et al. (författare)
  • Anomalous reflection and excitation of surface waves in metamaterials
  • 2007
  • Ingår i: Physics Letters A. - 0375-9601. ; 367:3, s. 233-236
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider reflection of electromagnetic waves from layered structures with various dielectric and magnetic properties, including metamaterials. Assuming periodic variations in the permittivity, we find that the reflection is in general anomalous. In particular, we note that the specular reflection vanishes and that the incident energy is totally reflected in the backward direction, when the conditions for resonant excitation of leaking surface waves are fulfilled.
  • Brodin, Gert, et al. (författare)
  • Dispersion relation for electromagnetic wave propagation in a strongly magnetized plasma
  • 2006
  • Ingår i: New Journal of Physics. - Bristol, UK : Institute of Physics Pub.. - 1367-2630. ; 8:January, s. 16
  • 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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