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A new purely growing instability in a strongly magnetized nonuniform pair plasma
Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany. (School of Physics, University of KwaZulu-Durban, Durban 4000, South Africa)
2007 (English)In: Physics Letters A, ISSN 0375-9601, Vol. 367, no 1-2, 120-122 p.Article in journal (Refereed) Published
Abstract [en]

It is shown that a strongly magnetized nonuniform electron–positron (hereafter referred to as e–p or pair) plasma is unstable against low-frequency (in comparison with the electron gyrofrequency) electrostatic oscillations. For this purpose, a dispersion relation is derived by using the Poisson equation as well as the electron and positron continuity equations with the guiding center drifts for the electron and positron fluids. The dispersion relation admits a purely growing instability in the presence of the equilibrium density and magnetic field inhomogeneities. Physically, instability arises because of the inhomogeneous magnetic field induced differential electron and positron density fluctuations, which do not keep in phase with the electrostatic potential arising from the charge separation in our nonuniform pair plasmas.

Place, publisher, year, edition, pages
Elsevier, 2007. Vol. 367, no 1-2, 120-122 p.
National Category
Physical Sciences
URN: urn:nbn:se:umu:diva-53018DOI: 10.1016/j.physleta.2007.02.064OAI: diva2:508890
Available from: 2012-03-12 Created: 2012-03-10 Last updated: 2012-03-12Bibliographically approved
In thesis
1. Generation of magnetic fields in plasmas
Open this publication in new window or tab >>Generation of magnetic fields in plasmas
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Relativistic and non-relativistic plasma outflows are quite ubiquitous in astrophysical scenarios, as well as in laboratory plasmas. The propagation of relativistic and non- relativistic charged particle beams in background plasmas provides return currents in the opposite direction and interactions between the currents then drive several plasma instabilities involving the longitudinal (electrostatic instabilities) and trans- verse (electromagnetic instability) modes. Such instabilities have been accepted as possible mechanisms for generating spontaneous magnetic fields in extreme astrophysical environments, such as the gamma-ray bursts (GRBs), pulsar magnetosphere, active galactic nuclei (AGN), as well as in laboratory plasmas such as those in inertial confinement fusion schemes.

In the present thesis, we have studied several aspects of waves and instabilities in both unmagnetized and magnetized plasmas. We have calculated the linear growth rates of the plasma instabilities that can occur in the presence of counter-propagating anisotropic plasmas (the Weibel instability/filamentation instability) in an unmagnetized plasma, due to the counter-streaming of electrons and positrons in uniform and nonuniform magnetoplasmas, and by a nonstationary ponderomotive force of an electromagnetic wave in a warm plasma.

Comprehensive analytical and numerical studies of plasma instabilities have been made to understand possible mechanisms for purely growing magnetic fields in the presence of mobile/immobile ions and (or) cold/mildly hot electron beams. The theory has been developed for a proper understanding of fast as well as slow phenomena in plasmas by using the kinetic, fluid and magnetohydrodynamic (MHD) approaches. Specific applications are presented, including inertial confinement fusion; Gamma- rays bursts (GRBs), and pulsar magnetosphere.

We have also studied new and purely growing modes in quantum-plasmas, which happen to be a rapidly growing emerging subfield of plasma physics. We have investigated an oscillatory instability involving dust acoustic-like waves due to a relative drift between the ions and the charged dust particles in quantum dusty magneto-plasma. This study can be of importance in semiconductor plasmas or in astrophysical plasmas, such as those in the cores of white dwarfs.

Abstract [sv]

Relativistiska och icke-relativistiska partikelflöden är vanliga inom astrofysikaliska scenarier lika väl som i laboratorieplasmor. Utbredningen av relativistiska och icke-relativistiska laddade partikel-strålar i bakgrunds plasmat genererar strömmar i den motsatta riktningen, och växelverkan mellan dessa strömmar kan sedan driva olika sorters plasma instabiliteter,

inklusive longitudinella (elektrostatiskt instabila) och transversella (elektromagnetiskt instabila) moder. Sådana instabiliteter har lagts fram som möjliga mekanismer för spontan generering av magnetfält i astrofysikaliska miljöer, såsom gammablixtar (GRB), pulsar magnetosfärer, aktiva galaxkärnor, lika väl som i laboratorie-plasmor, exempelvis i samband med tröghetsfusion.

I denna avhandling har flera aspekter av vågor studerats, både i magnetiserade och omagnetiserade plasmor. Den linjära tillväxthastigheten har beräknats för mot-strömmande anisotropa plasmor (Weibelinstanilitet/Filamentations instabilitet) i ett icke-magnetiserat plasma, p. g. a. driften mellan elektroner och positroner i homogena såväl som inhomogena plasmor, samt p. g. a den ponderomotiva kraften från en elektromagnetisk våg i ett varmt plasma.

Omfattande analytiska och numeriska studier av plasma instabilitieter har gjorts för att förstå möjliga mekanismer för magnetfältsförstärkning i närvaro av rörliga/orörliga joner och/eller kalla/varma elektronstrålar. Teorin har utvecklats för att nå en djupare förståelse av snabba såväl som långsamma fenomen i plasmor genom användande av kinetiska modeller, vätskemodeller och magnetohydrodynamiska (MHD) modeller.

Specifika tillämpningar presenteras mot tröghetsfusion, gammablixtar and pulsar magnetosfärer. Tillväxten hos nya vågmoder i kvantplasmor studeras också, vilket är ett nytt snabbt växande delområde av plasmafysiken. Slutligen studeras en oscillerande instabilitet hos damm-akustiska vågor orsakad av en drift mellan joner och laddade damm-partiklar i ett kvantplasma. Denna studie kan vara av betydelse för halvledar-plasmor och astrofysikaliska plasmor, exempelvis i de centrala delarna av en vit dvärg.

Place, publisher, year, edition, pages
Umeå Universitet, 2012. 60 p.
National Category
Physical Sciences
urn:nbn:se:umu:diva-53026 (URN)978-91-7459-394-5 (ISBN)
Public defence
2012-04-04, Naturvetarhuset, N450, Umeå Universitet, Umeå, 13:15 (English)
Available from: 2012-03-14 Created: 2012-03-12 Last updated: 2012-03-12Bibliographically approved

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