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Modeling of CLUSTER's electric antennas in space: application to plasma diagnostics
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
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2005 (English)In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 40, no 6, RS6008- p.Article in journal (Refereed) Published
Abstract [en]

[1] The main characteristics of the long-boom electric antennas installed on board the Cluster satellites are derived from finite element modeling in a kinetic and isotropic space plasma, in the frequency range of about 1–100 kHz. The model is based on the surface charge distribution method in quasi-static conditions. The impedances of both types of antenna, i.e., the double-wire and the double-probe, are computed versus the frequency normalized with respect to the local plasma frequency and for several different Debye lengths. Most of the code outputs are checked using analytic estimations for better understanding of the involved physical mechanisms. As a by-product, the effective length of the double-probe antenna and the mutual impedance between the two antennas are computed by the code. It is shown that if it had been possible to implement such measurements on board, one would have been able not only to determine accurately the electric characteristics of the antennas but also to estimate the local plasma parameters. Nevertheless, an interesting feature predicted by the model has been checked recently in orbit by running a special mode of operation for testing the mutual impedance measurement. The preliminary results are globally consistent with the predictions, except that they suggest that our Maxwellian model for the electron distribution should be revised in order to explain the unexpected low-frequency response. After analysis of the electron flux measurements obtained simultaneously, it appears that a rough adjustment of the electron distribution with a two-component distribution allows us to account for the observations.

Place, publisher, year, edition, pages
2005. Vol. 40, no 6, RS6008- p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-93686DOI: 10.1029/2005RS003264OAI: oai:DiVA.org:uu-93686DiVA: diva2:167236
Available from: 2005-11-03 Created: 2005-11-03 Last updated: 2013-06-18Bibliographically approved
In thesis
1. Space Plasma Dynamics: Instabilities, Coherent Vortices and Covariant Parametrization
Open this publication in new window or tab >>Space Plasma Dynamics: Instabilities, Coherent Vortices and Covariant Parametrization
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The magnetospheric cusps are two funnel-like regions of Earth's magnetosphere where solar wind plasma can have direct access to the ionosphere. The cusps are very dynamic regions where wave-particle interactions continuously take place and redistribute energy among different particle populations. In this thesis, both low and high frequency plasma waves in the cusp have been studied in detail using data from the Cluster spacecraft mission. The waves were studied with respect to frequency, Poynting flux and polarization. Wavelengths have also been estimated using multi-spacecraft techniques. At low frequencies, kinetic Alfvén waves and nonpotential ion cyclotron waves are identified and at high frequencies, electron cyclotron waves, whistler waves, upper-hybrid and RX-waves are observed. A common generation mechanism called the shell-instability is proposed for several of the wave modes present in the cusp, both at low and high frequencies.

The plasma in the cusp is shown to be strongly inhomogeneous. In an inhomogeneous low-frequency magnetoplasma, kinetic Alfvén waves couple to drift-waves. Such drift-kinetic Alfvén waves have long been believed to nonlinearly self-interact and form coherent structures in the form of drift-kinetic Alfvén vortices. In this thesis the first unambiguous direct measurements confirming the existence of such vortices in a turbulent space plasma are presented. Some of the crucial parameters such as the vortex radius are determined.

Plasma theory is electrodynamics applied to a large collection of charged particles. In this thesis a new way of looking at the fundamental Maxwell tensor is presented. A covariant spectral density tensor containing information on electromagnetic waves is formed. This tensor is then decomposed into irreducible components by using the spinor formalism for an arbitrary metric. The obtained fundamental tensors are shown to correspond both to well known tensors in Maxwell's theory, as well as several physically interesting new tensors.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. vii + 57 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 113
Space and plasma physics, space physics, plasma, instabilities, turbulence, coherent structures, vortex, self-organization, magnetosphere, waves, electromagnetism, covariant, space instrumentation, Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
urn:nbn:se:uu:diva-6051 (URN)91-554-6386-X (ISBN)
Public defence
2005-11-25, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00
Available from: 2005-11-03 Created: 2005-11-03Bibliographically approved

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