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Enhancement in the electromagnetic beam-plasma instability due to ion streaming
GoLP/Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisboa, Portugal.
GoLP/Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisboa, Portugal.
GoLP/Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisboa, Portugal.
GoLP/Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisboa, Portugal.
2012 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 78, 181-187 p.Article in journal (Refereed) Published
Abstract [en]

We investigate the Weibel instability in counterpropagating electron-ion plasmas with the focus on the ion contribution, considering a realistic mass ratio. A generalized dis- persion relation is derived from relativistic theory by assuming an initially anisotropic temperature, which is represented by a waterbag distribution in momentum space which shows an enhanced growth rate due to the ion response. Two-dimensional particle-in- cell simulations support the theoretical analysis, showing a further amplification of the magnetic field on the ion time scale. The effect of an initially anisotropic temperature is investigated showing that the growth rate is monotonously decreased if the transverse spread is increased. Nevertheless, the presence of ions generates that the instability can develop for significantly higher electron temperatures. Suppression of the oblique mode is also explored by introducing a parallel velocity spread. 

Place, publisher, year, edition, pages
Cambridge University Press, 2012. Vol. 78, 181-187 p.
National Category
Physical Sciences
Research subject
URN: urn:nbn:se:umu:diva-52679DOI: 10.1017/S0022377811000559OAI: diva2:506378
Available from: 2012-02-29 Created: 2012-02-28 Last updated: 2012-03-13Bibliographically 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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