Kinetic Theory of waves in space and astrophysical plasmas

Lead Research Organisation: University of Sheffield
Department Name: Automatic Control and Systems Eng


The main goal of the present proposal is to extend the theoretical achievements gained during realization of the existing PPARC grant (PP/D002087/1) 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. 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 and contribution to fundamental plasma physics. Collisionless plasmas with anisotropic velocity distributions drive a wide class of instabilities such as ion-cyclotron instability, magnetic mirror instability, whistler and Weibel instabilities, thereby generating magnetic fields. The Weibel instability present in homogeneous or nearly-homogeneous plasmas which possess an anisotropy in momentum (velocity) space. In the linear limit the instability causes exponential growth of electromagnetic fields in the plasma which restore momentum space isotropy. In the limit of an extremely anisotropic distribution the Weibel instability is related to one or two-dimensional stream instabilities. In this situation, the Weibel instability is beam-driven, and is sometimes referred to as the filamentation instability. Recently, this instability has attracted considerable attention for both astrophysical and laboratory plasmas. For example, it is considered that this instability can be driven in strong collisionless shock waves associated with various astrophysical phenomena, e.g., pulsar winds, gamma-ray bursts, and/or theirafterglows or gravitational collapse of large-scale structures in the universe. It can also be driven if temperature gradients are present in plasmas. The magnetic field generated by the instability is responsible for synchrotron and or 'jitter' radiation from the existing high-energy particles. Furthermore, such magnetic fields can provide an effective scattering mechanism for charged particles. For example, it would affect the dissipation process of collisionless shock waves and efficiency of the Fermi acceleration or heat conductivity by charged particles. In all these cases, the amplitude of the magnetic field is of primary importance. 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 PPARC grant PP/D002087/1. 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 collisionless 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 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.


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Description Quasi-linear dynamics of Weibel and Mirror instabilities has been investigated.
Growth of filaments and saturation of the filamentation instability in relation to collisionless shocks in the vicinity of gamma ray bursts has been investigated.
It was shown that magnetic holes observed in the vicinity of dipolarisation fronts are not related to the mirror instability as was suggested by others earlier.
Exploitation Route Findings are published in refereed research journals
Sectors Other