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Particle-in-cell simulations of ion-acoustic waves with application to Saturn's magnetosphere
KTH, School of Electrical Engineering (EES), Communication Theory. South African National Space Agency (SANSA), South Africa.ORCID iD: 0000-0002-4030-1014
2014 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, no 072122Article in journal (Refereed) Published
Abstract [en]

Using a particle-in-cell simulation, the dispersion and growth rate of the ion-acoustic mode areinvestigated for a plasma containing two ion and two electron components. The electron velocitiesare modelled by a combination of two kappa distributions, as found in Saturn’s magnetosphere.The ion components consist of adiabatic ions and an ultra-low density ion beam to drive a veryweak instability, thereby ensuring observable waves. The ion-acoustic mode is explored for a rangeof parameter values such as j, temperature ratio, and density ratio of the two electron components.The phase speed, frequency range, and growth rate of the mode are investigated. Simulations ofdouble-kappa two-temperature plasmas typical of the three regions of Saturn’s magnetosphere are also presented and analysed.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014. Vol. 21, no 072122
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-151411DOI: 10.1063/1.4891320ISI: 000341154100024Scopus ID: 2-s2.0-84904730356OAI: oai:DiVA.org:kth-151411DiVA: diva2:748551
Note

QC 20140922

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2017-12-05Bibliographically approved
In thesis
1. A Simulation Approach to Plasma Waves
Open this publication in new window or tab >>A Simulation Approach to Plasma Waves
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrostatic waves in the form of Broadband Electrostatic Noise (BEN) have been observed inthe Earth’s auroral region associated with high geomagnetic activity. Their broad frequencyspectrum consists of three electrostatic modes, namely electron plasma, electron acoustic andbeam-driven modes.A 1D Particle-in-Cell (PIC) simulation was developed to investigate the characteristics ofthe electrostatic waves found in such a plasma. Dispersion, phase space and spatial electricfield diagrams were constructed from the output of the PIC simulation which was used todescribe the wave dispersion and spatial field structures found in a plasma. A three electroncomponent plasma was studied using a Maxwellian distribution function to model their ve-locities. Beam-driven waves were found to dominate the frequency spectrum while electronplasma and electron acoustic waves were damped for a high beam velocity. Furthermore, for ahigh beam velocity, solitary waves are generated by electron holes (positive potentials), givingrise to a bipolar spatial electric field structure moving in the direction of the beam. Increasingthe beam temperature allows the beam electrons to mix more freely with the hot and coolelectrons, which leads to electron plasma and electron acoustic waves being enhanced whilebeam-driven waves are damped. Decreasing the beam density and velocity leads to dampingof beam-driven waves, while electron plasma and electron acoustic waves are enhanced.The electron acoustic mode was studied with the addition of a static background magneticfield. When the angle of wave propagation is perfectly perpendicular to the backgroundmagnetic field, a set of harmonics, called Bernstein modes, were produced. These modesare characterized by their nodes being furtherly displaced along the wave vector axis for anincrease in the node (harmonic) number. The model was further generalized by allowing theangle of wave propagation, θ, with respect to the magnetic field to be varied, thus enabling thestudy of the obliquely propagating electron acoustic mode. Both the amplitude and frequencyof the electron acoustic mode was found to decrease as θ increases.Measurements in Saturn’s magnetosphere have shown the co-existence of two electron (hotand cool) components. The electron velocities are best described by a κ-distribution (insteadof a Maxwellian) which has a high-energy tail. Using an adapted PIC simulation, the study ofelectron plasma and electron acoustic waves was extended by using a κ-distribution to describethe electron velocities with low κ indices. Electron acoustic waves are damped over most wavenumber ranges while electron plasma waves are weakly damped at low wave numbers anddamped for all other wave numbers. Furthermore, the study was extended by introducingthe motion of ions to study the ion acoustic waves in Saturn’s magnetosphere. While the ionacoustic mode was found to be relatively insensitive to the κ indices of the electrons, it isfound to be sensitive to the electron temperature and density ratios.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xii, 43 p.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-151415 (URN)978-91-7595-274-1 (ISBN)
Public defence
2014-10-07, F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
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Note

QC 20140922

Available from: 2014-09-22 Created: 2014-09-19 Last updated: 2014-09-22Bibliographically approved

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Publisher's full textScopushttp://dx.doi.org/10.1063/1.4891320

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Koen, Etienne

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