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Dust-driven and plasma-driven currents in the inner magnetosphere of Saturn
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
2012 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 4, 042903- p.Article in journal (Refereed) Published
Abstract [en]

General equations for dust-driven currents and current systems J(D) in magnetized plasmas are derived and, as a concrete example, applied to the E ring of Saturn at radial distances 3R(S) < R < 5R(S). An azimuthal ring current J(D,phi) acts as a current generator and is coupled to two secondary dust-driven current systems down to the ionosphere of Saturn, both rotating with the magnetospheric plasma. One of these closes across the polar cap, and the other over a limited range in latitude. These dust-driven current systems are embedded in three systems of plasma-driven currents J(p): a ring current, a cross-polar-cap current system, and an ion pickup current system. Both the J(D) and the J(p) current systems have been quantitatively assessed from a data set for the E ring of Saturn in which the unknown distribution of small dust is treated by a power law extrapolation from the known distribution of larger dust. From data on the magnetic perturbations during a crossing of the equatorial plane, an approximate constraint on the fraction of the electrons that can be trapped on the dust is derived. For this amount of electron capture, it is demonstrated that all three types of dust-driven currents are, within somewhat more than an order of magnitude, of the same strength as the corresponding types of plasma-driven currents. Considering also that both plasma and dust densities vary with the geyser activity at the south pole of Enceladus, it is concluded that both the dust-driven and the plasma-driven contributions to the current system associated with the E ring need to be retained for a complete description.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012. Vol. 19, no 4, 042903- p.
Keyword [en]
saturn, magnetosphere, current system, field-aligned current, dusty plasma
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-93980DOI: 10.1063/1.3701995ISI: 000309592100035Scopus ID: 2-s2.0-84860477047OAI: oai:DiVA.org:kth-93980DiVA: diva2:524798
Note

QC 20120504

Available from: 2012-05-03 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Plasma and dust interaction in the magnetosphere of Saturn
Open this publication in new window or tab >>Plasma and dust interaction in the magnetosphere of Saturn
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Cassini spacecraft orbits Saturn since 2004, carrying a multitude of instruments for studies of the plasma environment around the planet as well as the constituents of the ring system. Of particular interest to the present thesis is the large E ring, which consists mainly of water ice grains, smaller than a few micrometres, referred to as dust. The first part of the work presented here is concerned with the interaction between, on the one hand, the plasma and, on the other hand, the dust, the spacecraft and the Langmuir probe carried by the spacecraft. In Paper I, dust densities along the trajectory of Cassini, as it passes through the ring, are inferred from measured electron and ion densities. In Paper II, the situation where a Langmuir probe is located in the potential well of a spacecraft is considered. The importance of knowing the potential structure around the spacecraft and probe is emphasised and its effect on the probe's current-voltage characteristic is illustrated with a simple analytical model. In Paper III, particle-in-cell simulations are employed to study the potential and density profiles around the Cassini as it travels through the plasma at the orbit of the moon Enceladus. The latter part of the work concerns large-scale currents and convection patterns. In Paper IV, the effects of charged E-ring dust moving across the magnetic field is studied, for example in terms of what field-aligned currents it sets up, which compared to corresponding plasma currents. In Paper V, a model for the convection of the magnetospheric plasma is proposed that recreates the co-rotating density asymmetry of the plasma.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiii, 40 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:018
Keyword
saturn, dusty plasma
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-93983 (URN)978-91-7501-343-5 (ISBN)
Public defence
2012-05-28, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120507Available from: 2012-05-07 Created: 2012-05-03 Last updated: 2012-05-07Bibliographically approved

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