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Low Frequency Waves in Space Plasma

#4044


Low Frequency Electromagnetic Waves in Anisotropic High Pressure Space and Astrophysical Plasmas

Tech Area / Field

  • PHY-PLS/Plasma Physics/Physics
  • SAT-AST/Astronomy/Space, Aircraft and Surface Transportation

Status
3 Approved without Funding

Registration date
19.03.2010

Leading Institute
VNIITF, Russia, Chelyabinsk reg., Snezhinsk

Supporting institutes

  • Institute of Physics of the Earth, Russia, Moscow

Collaborators

  • Observatoire de Paris / Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique, France, Meudon\nCNRS / Laboratoire de Physique et Chemie de L'Environnement, France, Orleans\nUniversity of Sheffield / Department of Automatic Control and Systems Engineering, UK, Shiffield

Project summary

The main goal of the present proposal is to extend the theoretical achievements gained during the realization of the ISTC grant #3520 to a wider class of physical problems related to the development of a fully kinetic theory of magnetic field generation in space plasmas. This theory may then be applied to interpret observations in such key regions of intergalactic environment as active galactic nucleus (AGNs), microquasars, gamma-ray bursts (GRBs), giant flares and pulsar wind nebulae.

Cosmic ray and gamma-ray astrophysics provides an arena where concepts drawn from many branches of plasma physics can assist in answering questions of fundamental cosmological significance. In recent years, striking advances have been made in the quality and resolution of the data available in this field. The generation of cosmic ray detection arrays and space-based x-ray and gamma-ray observatories, coupled to measurements in other wavebands, are yielding information, which invites detailed quantitative interpretation in terms of plasma processes. In parallel with these developments, a systematic picture of behavior of energetic particle populations on JET, Z-pinches, and the acceleration of electrons to highly relativistic energies has been demonstrated in laser-plasma interaction experiments.

Motivations for such a theoretical study result from:

  • In-situ satellite observations
  • Importance of a link between processes in solar-terrestrial and astrophysical plasmas
  • Evidence for the plasma mediation by Weibel-type instabilities during shock propagation from astrophysical sources.

Plasma physics input is required, to understand both the acceleration mechanisms and the propagation of cosmic rays through the interstellar medium, particularly with regard to magnetic fields. An important subtlety is that a pre-acceleration (`injection') mechanism is required to raise particle energies from background to mildly relativistic levels, from which they can further accelerated to much higher energies in supernova shocks.

Magnetic fields with an energy density close to equipartition with the kinetic energy density of the plasma can be generated during the nonlinear development of electromagnetic wave modes driven by electron temperature anisotropy. Such modes in an unmagnetized plasma are known as "Weibel instabilities". The Weibel instability results in the breakdown of the plasma into current filaments. Strong anisotropy arises in collisions in which charged particles interpenetrate. This has led to suggestions that the Weibel instability is responsible for the growth of magnetic fields in unmagnetized collisionless shocks. In this scenario, magnetic fields generated in the shocks provide effective collisionality in the collisionless transitional layer of the shock. The magnetic fields may also be responsible for diffusive particle acceleration in the shock. In terms of the mathematical description the Weibel instability is somewhat similar to the magnetic mirror instability.

Another important application of the Weibel-type instabilities is related to the collisionless magnetic reconnection at the Earth's magnetopause and in the terrestrial magnetotail. Theory predicts that this phenomenon, triggered by the tearing instability, is a sensitive function of the electron temperature anisotropy. Computer simulations of the tearing mode have confirmed this prediction, suggesting that the electron temperature anisotropy is a critical parameter for determining the onset and collisionless saturation. The particle-in-cell simulations of a current sheet in a collisionless plasma show that the growth of the lower hybrid drift instability heats electrons in the direction perpendicular to the external magnetic field. These considerations imply that to provide the proper context for the application of electron temperature anisotropies to the tearing mode instability, it is appropriate to reexamine and compare both the linear and nonlinear theory properties of the various resonant instabilities driven by the electron anisotropy.

The flute waves and related Rayleigh - Taylor instability (RTI) are of interest for the interpretation of the astrophysical phenomena occurring in a number astrophysical settings, including supernovae, in the shells of young supernova remnants, magnetized radio jets and another objects where in accordance of modern representation exist inhomogeneous plasma with high beta. The gravity may be a real or an effective one due to the plasma motion along the curved magnetic field lines or due to plasma acceleration along the direction of the plasma inhomogeneity.

The proposed theory will take into account such important factors known from experimental measurements in the regions of interest as the dynamic of nonlinear waves in high beta plasmas, nonlinear structures and turbulent spectra, substantial gradients, non-Maxwellian plasma distributions and gravitational fields modulating shock wave acceleration or deceleration.

The main goal of the project is to develop a kinetic theory of waves in space plasmas, incorporating all these features. The present proposal assumes the productive use of the experience gained and results obtained under ISTC grant #3520.

The main objectives of the project are:

  • To perform a theoretical investigation of the various Weibel-type wave modes that exist in space plasmas (dispersion relations, growth rates, instability thresholds etc.) including finite collision less skin depth, effects due to non-Maxwellian (waterbag and kappa velocity distributions etc.) electron and ion velocity distributions etc.
  • To study the effects of stabilization of the Weibel instability due the final value of the external magnetic field.
  • To provide an analytical and numerical analysis of the nonlinear evolution of Weibel-type instabilities in two different cases of weak and strong drive.
  • To elucidate the role of trapped particles in the nonlinear saturation of the instability.
  • To investigate nonlinear dynamics of flute-drift waves with arbitrary ratio of the wave length to the ion Larmor radius in a plasma with finite ion temperature gradient (ITG).
  • To generalize the theory of the Rayleigh - Taylor (drift-flute, interchange) instability on arbitrary wave-length and finite ITG.
  • To provide an analytical study and numerical simulation of the mechanism of spontaneous generation of large-scale structures by flute turbulence.
  • To apply the developed theory to the physics of remote astrophysical objects. Special attention will be paid to the particle acceleration in space and astrophysical objects.

The majority of the project participants were involved earlier in the development of military technologies. The proposed project will provide the work for these highly skilled scientists, in the past taking participation in the military researches and developments. The members of two teams, which are working on the project, will participate in international conferences and publishing the papers in international journals and, thus be integrated into the works of international scientific community.


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