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Generation of magnetic fields in plasmas
Umeå University, Faculty of Science and Technology, Department of Physics.
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
Identifiers
URN: urn:nbn:se:umu:diva-53026ISBN: 978-91-7459-394-5 (print)OAI: oai:DiVA.org:umu-53026DiVA: diva2:509044
Public defence
2012-04-04, Naturvetarhuset, N450, Umeå Universitet, Umeå, 13:15 (English)
Opponent
Supervisors
Available from: 2012-03-14 Created: 2012-03-12 Last updated: 2012-03-12Bibliographically approved
List of papers
1. Generation of magnetic field fluctuations in relativistic electron-positron magnetoplasmas
Open this publication in new window or tab >>Generation of magnetic field fluctuations in relativistic electron-positron magnetoplasmas
2006 (English)In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 362, no 2-3, 221-224 p.Article in journal (Refereed) Published
Abstract [en]

It is shown that magnetic field aligned equilibrium relativistic plasmas flows can excite electromagnetic fluctuations in a magnetized electron–positron (e–p) plasma. For this purpose, a new dispersion relation is derived by using a relativistic two-fluid model and the Maxwell equations. The dispersion relation admits purely growing instabilities of electromagnetic perturbations across the ambient magnetic field direction. The results have relevance for understanding the origin of magnetic field fluctuations in cosmological and laser-produced plasmas.

Place, publisher, year, edition, pages
Elsevier, 2006
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-19898 (URN)10.1016/j.physleta.2006.09.095 (DOI)
Available from: 2009-03-12 Created: 2009-03-12 Last updated: 2017-12-13Bibliographically approved
2. A new purely growing instability in a strongly magnetized nonuniform pair plasma
Open this publication in new window or tab >>A new purely growing instability in a strongly magnetized nonuniform pair plasma
2007 (English)In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, 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
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-53018 (URN)10.1016/j.physleta.2007.02.064 (DOI)
Available from: 2012-03-12 Created: 2012-03-10 Last updated: 2017-12-07Bibliographically approved
3. Amplification of magnetic fields by polaritonic flows in quantum pair plasmas
Open this publication in new window or tab >>Amplification of magnetic fields by polaritonic flows in quantum pair plasmas
2007 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 73, 289-293 p.Article in journal (Refereed) Published
Abstract [en]

It is shown that equilibrium polaritonic flows can amplify magnetic fields in an ultra-cold quantum electron–positron/hole (polaritons) plasma. For this purpose, a linear dispersion relation has been derived by using the quantum generalized hydrodynamic equations for the polaritons, the Maxwell equation, and Faraday's law. The dispersion relation admits purely growing instabilities, the growth rates of which are proportional to the equilibrium streaming speeds of the polaritons. Possible applications of our work to the spontaneous excitation of magnetic fields and the associated cross-field transport of the polaritons in micromechanical systems, compact dense astrophysical objects (e.g. neutron stars), and intense laser–plasma interaction experiments are mentioned.

Place, publisher, year, edition, pages
Cambridge University Press, 2007
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-19902 (URN)10.1017/S0022377807006551 (DOI)
Available from: 2009-03-12 Created: 2009-03-12 Last updated: 2017-12-13Bibliographically approved
4. Ion streaming instability in a quantum dusty magnetoplasma
Open this publication in new window or tab >>Ion streaming instability in a quantum dusty magnetoplasma
2008 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, 044503- p.Article in journal (Refereed) Published
Abstract [en]

It is shown that a relative drift between the ions and the charged dust particles in a magnetized quantum dusty plasma can produce an oscillatory instability in a quantum dust acousticlike wave. The threshold and growth rate of the instability are presented. The result may explain the origin of low-frequency electrostatic fluctuations in semiconductors quantum wells.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2008
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-10367 (URN)10.1063/1.2909533 (DOI)
Available from: 2008-08-27 Created: 2008-08-27 Last updated: 2017-12-14Bibliographically approved
5. Magnetization of a warm plasma by the nonstationary ponderomotive force of an electromagnetic wave
Open this publication in new window or tab >>Magnetization of a warm plasma by the nonstationary ponderomotive force of an electromagnetic wave
2009 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 80, 027401- p.Article in journal (Refereed) Published
Abstract [en]

It is shown that magnetic fields can be generated in a warm plasma by the nonstationary ponderomotive force of a large-amplitude electromagnetic wave. In the present Brief Report, we derive simple and explicit results that can be useful for understanding the origin of the magnetic fields that are produced in intense laser-plasma interaction experiments.

Place, publisher, year, edition, pages
American Physical Society, 2009
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-30462 (URN)10.1103/PhysRevE.80.027401 (DOI)
Available from: 2009-12-29 Created: 2009-12-29 Last updated: 2017-12-12Bibliographically approved
6. Proton-temperature-anisotropy-driven magnetic fields in plasmas with cold and relativistically hot electrons
Open this publication in new window or tab >>Proton-temperature-anisotropy-driven magnetic fields in plasmas with cold and relativistically hot electrons
2010 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, 1-5 p.Article in journal (Refereed) Published
Abstract [en]

We present a dispersion relation for a plane-polarized electromagnetic wave in plasmas composed of cold electrons, relativistically hot electrons and bi- Maxwellian protons. It is shown that the free energy in proton-temperature aniso- tropy drives purely growing electromagnetic modes in our three-component plasma. Expressions for the growth rates and thresholds of instabilities are presented. The present results are relevant for explaining the origin of spontaneously generated magnetic fields in laboratory and astrophysical plasmas. 

Place, publisher, year, edition, pages
Cambridge University Press, 2010
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-52677 (URN)10.1017/S0022377809990298 (DOI)000274550800001 ()
Available from: 2012-02-29 Created: 2012-02-28 Last updated: 2017-12-07Bibliographically approved
7. Enhancement in the electromagnetic beam-plasma instability due to ion streaming
Open this publication in new window or tab >>Enhancement in the electromagnetic beam-plasma instability due to ion streaming
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
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-52679 (URN)10.1017/S0022377811000559 (DOI)
Available from: 2012-02-29 Created: 2012-02-28 Last updated: 2017-12-07Bibliographically approved

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