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Interaction between Electromagnetic Waves and Localized Plasma Oscillations
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Växelverkan mellan elektromagnetiska vågor och lokaliserade plasmaoscillationer (Swedish)
Abstract [en]

This thesis treats interaction between electromagnetic waves and localized plasma oscillations. Two specific physical systems are considered, namely artificially excited magnetic field-aligned irregularities (striations) and naturally excited lower hybrid solitary structures (LHSS). Striations are mainly density depletions of a few percent that are observed when a powerful electromagnetic wave, a pump wave, is launched into the ionosphere. The striations are formed by upper hybrid (UH) oscillations that are localized in the depletion where they are generated by the linear conversion of the pump field on the density gradients. However, the localization is not complete as the UH oscillation can convert to a propagating electromagnetic Z mode wave. This process, termed Z mode leakage, causes damping of the localized UH oscillation. The Z mode leakage is investigated and the theory predicts non-Lorentzian skewed shapes of the resonances for the emitted Z mode radiation. Further, the interaction between individual striations facilitated by the Z mode leakage is investigated. The LHSS are observed by spacecraft in the ionosphere and magnetosphere as localized waves in the lower hybrid (LH) frequency range that coincides with density cavities. The localized waves are immersed in non-localized wave activity. The excitation of localized waves with frequencies below LH frequency is modelled by scattering of electromagnetic magnetosonic (MS) waves off a preexisting density cavity. It is shown analytically that an incident MS wave with frequency less than the minimum LH frequency inside the cavity is focused to localized waves with left-handed rotating wave front. In addition, the theory is shown to be consistent with observations by the Freja satellite. For frequencies between the minimum LH frequency inside the cavity and the ambient LH frequency, the MS wave is instead mode converted and excites pressure driven LH oscillations. This process is studied in a simplified geometry.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 43
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 985
Keywords [en]
Space and plasma physics, space physics, plasma physics, radio waves, ionospheric modification, density depleations, field-aligned irregularities, lower hybrid solitary structures, lower hybrid cavities, Z mode waves, magnetosonic waves, scattering, mode conversion
Keywords [sv]
Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-4282ISBN: 91-554-5982-X (print)OAI: oai:DiVA.org:uu-4282DiVA, id: diva2:164694
Public defence
2004-06-03, Häggsalen (Room 10132), Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15
Opponent
Supervisors
Available from: 2004-05-12 Created: 2004-05-12Bibliographically approved
List of papers
1. Conversion of trapped upper hybrid oscillations and Z mode at a plasma density irregularity
Open this publication in new window or tab >>Conversion of trapped upper hybrid oscillations and Z mode at a plasma density irregularity
2003 In: Physics of Plasmas, ISSN 1070-664X, Vol. 10, no 6, p. 10-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91832 (URN)
Available from: 2004-05-12 Created: 2004-05-12Bibliographically approved
2. Electromagnetic interaction of localized upper hybrid oscillations in a system of density depletions
Open this publication in new window or tab >>Electromagnetic interaction of localized upper hybrid oscillations in a system of density depletions
2006 (English)In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 38, no 11, p. 2516-2517Article in journal (Refereed) Published
Abstract [en]

We present the results of the investigation of interaction of different depletions of plasma density by Z-mode radiation. It is shown that more profitable disposition of cavities in space is random. The amplitude of the radiated Z-mode in this case is of the order of the amplitude of the pumping ordinary wave, but the amplitude of trapped into cavities upper hybrid wave is maximum and can be significantly higher than the amplitude of the pumping wave.

Keywords
electromagnetic waves, ionospheric disturbances and modifications
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-91833 (URN)10.1016/j.asr.2005.02.039 (DOI)000202988800034 ()
Available from: 2004-05-12 Created: 2004-05-12 Last updated: 2017-12-14Bibliographically approved
3. Excitation of localized rotating waves in plasma density cavities by scattering of fast magnetosonic waves
Open this publication in new window or tab >>Excitation of localized rotating waves in plasma density cavities by scattering of fast magnetosonic waves
2004 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 25 pt.1, p. 255002-Article in journal (Refereed) Published
Abstract [en]

An analytic description of electromagnetic waves in an inhomogeneous plasma is applied to investigate excitation of localized rotating waves below the lower hybrid frequency through scattering of fast magnetosonic waves on a density cavity. The magnetosonic wave is focused to left-handed rotating oscillations. We find the amplitude of the localized oscillations, resonance frequencies, and the width of the resonances. The theory is relevant for the lower hybrid solitary structures observed in space plasmas and is shown to be consistent with observations by the Freja satellite.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-91834 (URN)10.1103/PhysRevLett.92.255002 (DOI)15245017 (PubMedID)
Available from: 2004-05-12 Created: 2004-05-12 Last updated: 2017-12-14Bibliographically approved
4. Conversion of localized lower hybrid oscillations and fast magnetosonic waves at a plasma density cavity
Open this publication in new window or tab >>Conversion of localized lower hybrid oscillations and fast magnetosonic waves at a plasma density cavity
In: Physics of Plasmas, ISSN 1070-664XArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-91835 (URN)
Available from: 2004-05-12 Created: 2004-05-12Bibliographically approved

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