Thesis (M.S.)--Baylor University, 2005. / Includes bibliographical references (p. 80-82).

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. / QC 20120507

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

No description available.

The kinetic dispersion relation for a magnetized dusty plasma comprising of ions, electrons and massive, charged dust particles is solved for low frequency electrostatic instabilities in the dust plasma frequency regime. The free energy is provided by the drifting ion beam. The effect of varying parameters such as ion drift speed, particle densities, ion temperature and magnetic field strength on the real frequency and growth rate is examined. Initially light and heavy dust species of different charge are separately considered. This procedure is then repeated for a four-component plasma in an attempt to study the effect of the presence of both the dust species on low frequency electrostatic phenomena. Using a different plasma model, instabilities generated by an equal E x B drift of both the magnetized ions and electrons relative to the unmagnetized dust grains of both the heavy and light dust species is also investigated. The latter instabilities are applicable to the planetary ring plasmas of Saturn. Throughout our studies, numerical solutions of the full dispersion relation for the real frequency and growth rate are compared with approximate analytical solutions. / Thesis (M.Sc.)-University of Durban-Westville, 1999.

To ensure safety regarding dust explosion hazards, it is important to study the dust lifting process experimentally and identify important parameters that will be valuable for development and validation of numerical predictions of this phenomenon. A new shock tube test section was developed and integrated into an existing shock tube facility. The test section allows for shadowgraph or laser scattering techniques to track dust layer particle motion. The test section is designed to handle an initial pressure of 1 atm with an incident shock wave velocity up to Mach 2 to mimic real world conditions. The test section features an easily removable dust pan and inserts to allow for adjustment of dust layer thickness. The design allows for the changing of experimental variables including initial pressure, Mach number, dust layer thickness and characteristics of the dust itself. A separate vacuum manifold was designed to protect existing equipment from negative side effects of the dust. A study was performed to demonstrate the capabilities of the new facility and to compare results with experimental trends formerly established in the literature. Forty-micron limestone dust with a layer thickness of 3.2 mm was subjected to Mach 1.22 and 1.38 shock waves, and a high-speed shadowgraph was used for flow visualization. Dust layer rise height was graphed with respect to shock wave propagation. Dust particles subjected to a Mach 1.38 shock wave rose more rapidly and to a greater height with respect to shock wave propagation than particles subjected to a Mach 1.22 shock wave. These results are in agreement with trends found in the literature, and a new area of investigation was identified.

Thesis (Ph. D.)--University of Sydney, 2009. / Includes graphs and tables. Cotutelle thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Complex Plasma Laboratory, School of Physics, Faculty of Science, University of Sydney and the degree of Docteur de l'Université Orléans. Title from title screen (viewed May 5, 2009) Degree awarded 2009; thesis submitted 2008. Includes bibliographical references. Also available in print form.

Recently, experimental observations have shown that Polar Mesospheric Summer Echoes PMSE may be modulated by radio wave heating the irregularity source region with a ground-based ionospheric heating facilities. It is clear from these past investigations that the temporal behavior of PMSE during ionospheric heating shows promise as a diagnostic for the associated dust layer. To investigate the temporal behavior of plasma irregularities thought to produce PMSE, this work describes a new model that incorporates both finite diffusion time effects as well as dust charging. The hybrid model utilizes fluid ions described by continuity and momentum equations, electrons whose behavior is determined from quasi-neutrality, and charged dust described by the standard Particle-In-Cell PIC method. The model has been used to investigate the temporal behavior of charged dust associated electron irregularities during electron temperature enhancement associated with radio wave heating. The model predicts that the temporal behavior of the irregularities depends on the ratio of the electron-ion ambipolar diffusion time to the dust particle charging time Td/Tc. The results indicate that typically for Td/Tc << 1, an enhancement in electron irregularity amplitude occurs for a period after turn-off of the radio wave heating. The work also predicts that for Td/Tc >> 1, an enhancement in electron irregularity amplitude occurs for a time period after the turn-on of the radio wave heating. Due to the dependence of Td on irregularity scale-size, these results have important implications for observations of PMSE modification at different radar frequencies. Both continuous and discrete charging model were embedded into this computational model, the results were compared and analyzed. It is evident that significant diagnostic information may be available about the dust layer from the temporal behavior of the electron irregularities during the heating process which modifies the background electron temperature. Particularly interesting and important periods of the temporal behavior are during the turn-on and turn-off of the radio wave heating. Although a number of past theoretical and experimental investigations have considered both these on and off period, this dissertation considers further possibilities for diagnostic information available as well as the underlying physical processes. Approximate analytical models are developed and compared to a more accurate full computational model as a reference. Then from the temporal behavior of the electron irregularities during the turn-on and turn-off of the radio wave heating, the analytical models are used to obtain possible diagnostic information for various charged dust and background plasma quantities. Finally, two experiment campaigns have been performed at HAARP, Gakona, Alaska. Preliminary observation results look promising for the existence of PMSE turn-on overshoot. However, more careful experiments need to be done before firm conclusions can be drawn. The new designed Echotek digital receiver is ready for use now. It will be much superior to the experimental setup used for measurements in the previous campaign.Therefore, future experimental campaigns are planning next year to support the theoretical research. / Ph. D.

There has been a great deal of interest in investigating numerous unique types of electrostatic and electromagnetic waves and instabilities in dusty plasmas. Dusty plasmas are characterized by the presence of micrometer or submicrometer size dust grains immersed in a partially or fully ionized plasma. In this study, a two-dimensional numerical model is presented to study waves and instabilities in dusty plasmas. Fundamental differences exist between dusty plasmas and electron-ion plasmas because of dust charging processes. Therefore, a primary goal of this study is to consider the unique effects of dust charging on collective effects in dusty plasmas. The background plasma electrons and ions here are treated as two interpenerating fluids whose densities vary by dust charging. The dust is treated with a Particle-In-Cell PIC model in which the dust charge varies with time according to the standard dust charging model. Fourier spectral methods with a predictor-corrector time advance are used to temporally evolve the background plasma electron and ion equations. The dust charge fluctuation mode and the damping of lower hybrid oscillations due to dust charging, as well as plasma instabilities associated with dust expansion into a magnetized background plasma are investigated using our numerical model. Also, an ion acoustic streaming instability in unmagnetized dusty plasmas due to dust charging is investigated. The numerical simulation results show good agreement with theoretical predictions and provide further insight into dust charging effects on wave modes and instabilities in dusty plasmas. / Ph. D.

Dusty plasmas, defined as plasmas of ions, electrons, neutrals, and charged micron to sub-micron dust particles, support a rich diversity of physical states. These states (ranging from solids to liquids to gas) are determined by the ratio of the Coulomb potential energy between dust particles to the particles kinetic energy and allow for a broad range of phenomena, from crystallization to dust acoustic waves. Due to various dusty plasma interactions, dust acoustic waves can be nonlinear and exhibit various wave phenomena, from topological wave defects to shock waves to structure formations. In this thesis, I investigate a spectrum of plasma and wave interactions in liquid-like dusty plasmas and focus on a range of dust acoustic wave phenomena observed experimentally in a dc discharge dusty plasma. By developing various experimental techniques, dust acoustic wave diffraction and topological wave defects, dust acoustic shock waves, temporal dust acoustic wave growth, and structure forming dust acoustic waves were observed. I begin in Chapter 2 with the diffraction of dust acoustic waves, which I investigated by introducing a glass rod into the dusty plasma. The resulting diffraction pattern was compared to acoustic wave diffraction in a neutral gas. In addition to the diffraction pattern, topological wave defects were observed to form. I continue Chapter 2 with a preliminary investigation into topological wave defects in dust acoustic waves. Chapter 3 follows with three nonlinear dust acoustic wave experiments. I created a shock tube like profile for dust acoustic waves using a single slit. The shock-tube like potential resulted in two sets of nonlinear dust acoustic waves, coalescing high and low amplitude waves and dust acoustic waves that developed into dust acoustic shock waves. The self-excited dust acoustic shock waves were compared to theoretical models. The third nonlinear dust acoustic wave phenomenon that I investigated was a reverse drift mode that appears in high amplitude dust acoustic waves. I propose a wave process based on dust particle dynamics in high amplitude dust acoustic waves to explain the observations. In Chapter 4, I describe an experimental technique that I developed to create a quiescent drifting dusty plasma. The drifting dusty plasma was used to observe dust acoustic wave growth from thermal density fluctuations. The observed growth rate and frequency were compared kinetic and fluid models. In Chapter 5, I describe experimental observations of a structure forming instability in dusty plasmas. By increasing the discharge current, transient and aperiodic dust density striations formed. I characterized the transient and stationary modes and compared the stationary mode to an ionization/ion-drag instability and a polarization instability.