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A simulation approach of high-frequency electrostatic waves found in Saturn's magnetosphere
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, 042102- p.Article in journal (Refereed) Published
Abstract [en]

Using a particle-in-cell simulation, the characteristics of electron plasma and electron acoustic waves are investigated in plasmas containing an ion and two electron components. The electron velocities are modeled by a combination of two kappa distributions. The model applies to the extended plasma sheet region in Saturn's magnetosphere where the cool and hot electron velocities are found to have low indices, kappa(c) similar or equal to 2 and kappa(h) similar or equal to 4. For such low values of kappa(c) and kappa(h), the electron plasma and electron acoustic waves are coupled. The model predicts weakly damped electron plasma waves while electron acoustic waves should also be observable, although less prominent.

Place, publisher, year, edition, pages
2012. Vol. 19, no 4, 042102- p.
Keyword [en]
Electron acoustic waves, Electron component, Electron plasma waves, Electron plasmas, Electron velocity, Electrostatic waves, High frequency HF, Low index, Particle-in-cell simulations, Plasma sheet region, Simulation approach, Acoustic waves, Acoustics, Ion beams, Plasma waves, Plasmas, Electrons
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-98470DOI: 10.1063/1.3695404ISI: 000309592100002Scopus ID: 2-s2.0-84860487765OAI: oai:DiVA.org:kth-98470DiVA: diva2:537234
Note

QC 20120626

Available from: 2012-06-26 Created: 2012-06-26 Last updated: 2017-12-07Bibliographically approved
In thesis
1. A Simulation Approach to High-Frequency Plasma Waves
Open this publication in new window or tab >>A Simulation Approach to High-Frequency Plasma Waves
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Electrostatic waves in the form of Broadband Electrostatic Noise (BEN) have been observed in the Earth's auroral region associated with high geomagnetic activity. This broad frequency spectrum consists of three electrostatic modes, namely electron plasma, electron acoustic and beam-driven modes. These modes are excited in a plasma containing three electron components: hot, cool and beam electrons.

A 1D Particle-in-Cell (PIC) simulation was developed to investigate the characteristics of the electrostatic waves found in such a plasma. Dispersion, phase space and spatial electric field diagrams were constructed from the output of the PIC simulation which were used to describe the wave dispersion and spatial field structures found in a plasma. The PIC code used a three electron component plasma with Maxwellian distributions to describe the electron velocity distributions. Beam-driven waves were found to dominate the frequency spectrum while electron plasma and electron acoustic waves are damped for a high beam velocity. Furthermore, for a high beam velocity, solitary waves are generated by electron holes (positive potentials), giving rise to a bipolar spatial electric fi eld structure moving in the direction of the beam. Increasing the beam temperature allows the beam electrons to mix more freely with the hot and cool electrons, which leads to electron plasma and electron acoustic waves being enhanced while beam-driven waves are damped. Decreasing the beam density and velocity leads to damping of beam-driven waves, while electron plasma and electron acoustic waves are enhanced.

Measurements in Saturn's magnetosphere have found the co-existence of two electron (hot and cool) components. The electron velocities are best described by a kappa-distribution (instead of a Maxwellian) which has a high-energy tail. Using an adapted PIC simulation the study of electron plasma and electron acoustic waves was extended by using a kappa-distribution to describe the electron velocities with low indices. Electron acoustic waves are damped over most wave number ranges. Electron plasma waves are weakly damped at low wave numbers and damped for all other wave numbers.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. x, 33 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:64
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-106822 (URN)
Presentation
2012-12-13, Seminarierum, Teknikringen 31, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121205

Available from: 2012-12-05 Created: 2012-12-05 Last updated: 2012-12-05Bibliographically approved
2. 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)
Opponent
Supervisors
Note

QC 20140922

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

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