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

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

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.

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.

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.

A côté des solides, des liquides et des gaz, le plasma est le quatrième état de la matière. Il est généré en ionisant un gaz. Dans l’univers, 99% de la matière est à l’état de plasma. L’émergence de plusieurs types de plasmas artificiels est due aux multiples et différentes applications, très intéressantes les unes que les autres, des plasmas dans des secteurs aussi variés que l’industrie, l’énergie, le biomédical et la science. Très souvent, des particules solides peuvent se former dans les plasmas. Ceci a tout particulièrement été observé dans ceux utilisés dans l’industrie. La compréhension des mécanismes de leur nucléation et croissance est d’une importance capitale en vue de trouver des solutions pour inhiber leur formation ou d’éviter qu’elles ne se déposent sur les surfaces en cours de traitement. L’objectif du travail de recherche entrant dans le cadre de cette thèse est l’étude de la formation de particules dans un plasma généré par décharge électrique continue. Il a été observé que ce phénomène dépend du flux de gaz neutre injecté dans l’enceinte du réacteur. Nous avons mis en évidence que la fréquence de formation est liée à ce paramètre. Les observations enregistrées à l’aide d’un spectroscope sont complétées et corrélées aux photographies obtenues par microscopie électronique à balayage. L’injection de particules dans le plasma plutôt que de procéder à les faire croitre présente certains avantages. On peut contrôler leur taille y compris du cas de mélanges de particules. On tout particulièrement injecter des particules ayant des tailles beaucoup plus importantes que celles que l’on forme sur des gammes de durées raisonnables des plasmas utilisés. Plusieurs expériences réalisées avec des particules injectées ont mis en exergue le caractère pluridisciplinaire du milieu plasma. Afin de comprendre les interactions mutuelles entre particules il est crucial de déterminer la charge portée par les particules. Plusieurs expériences réalisées au cours de cette thèse et présentées ici ont porté sur la détermination de ce paramètre fondamental. Dans ce cadre une série d’expérience a été réalisée à bord de la Station Spatiale Internationale (ISS) dans le but de déterminer la charge résiduelle des particules dans la phase de post-décharge. Dans la dernière partie, seront présentées et discutées des expériences portant sur l’observation de la rotation de clusters de particules soumis à un confinement supplémentaire. On montre que les particules tendent à former des alignements verticaux dus au faible champ qui se forme en aval de chaque particule. Enfin, les connaissances acquises sur les possibilités de moduler le potentiel d’interaction par l’intermédiaire d’un champ électrique seront discutées. Les résultats sont comparés aux prédictions des simulations. / Plasmas are next to the solid, liquid and gaseous phase the fourth state of matter. It is established by ionizing a gas. About 99% of the visible matter in the universe is in the state of plasma. The industrial, medical and scientific benefits of plasmas led to a variety of artificially produced plasmas. In plasmas dust particles can grow. Especially in industrial plasmas particle formation in the plasma gas phase is very common. The fundamental understanding of the growth is of vital importance in order to suppress undesired particle formation or to deposit particles and films in a certain region. In terms of this thesis the particle growth in a direct current (DC) discharge by using acetylene will be discussed. It has been observed that the particle growth depends on the neutral gas flow fed into the plasma chamber. Depending on the applied flow different growth frequencies and transport phenomena are shown. The observations recorded by a spectrometer will then be complimented by pictures from the particles taken by a scanning electron microscope. Introducing artificial particles into a plasma rather than growing them there yields several advantages. The particle sizes can be controlled, including the possibility of particle mixtures. Furthermore, particles with bigger diameter can be introduced than what can be grown on reasonable time scales in a plasma. Several possible experiments with injected particles underline the interdisciplinary character of the plasma environment. To understand the inter particle interactions the particle charge is a crucial parameter. In this thesis several experiments determining the particle charge will be discussed. In this frame the experiments on board of the International Space Station have been performed to measure the residual charge in the particle afterglow. In the last section experiments on particle cluster rotation as observed in an additional confinement will be discussed. It will be shown that the particles tend to form vertical strings due to the wake field that forms downstream of each particle. Finally the insight gained on the possibilities of tuning of the interaction potential by electric fields will be discussed. The results are then compared to the predictions of earlier simulations.

Plasmas seeded with solid particulates of nanometer to micron sizes (complex plasma systems) are a ubiquitous feature of intergalactic, interstellar and planetary environments but also of plasma processing applications or even fusion devices. Their novel aspects compared with ideal multi-component plasmas stem from (i) the large number of elementary charges residing on the grain surface, (ii) the variability of the charge over mass ratio of the dust component, (iii) the inherent openness and dissipative nature of such systems.   Their statistical description presents a major challenge; On one hand by treating dust grains as point particles new phase space variables must be introduced augmenting the classical Hamiltonian phase space, while the microphysics of interaction between the plasma and the grains will introduce additional coupling between the kinetic equations of each species, apart from the usual fine-grained electromagnetic field coupling. On the other hand complex plasma systems do not always exist in a gaseous state but can also condensate, i.e. form liquid, solid or crystalline states.   In this thesis we study gaseous partially ionized complex plasma systems from the perspective of the Klimontovich technique of second quantization in phase space. Initially, in regimes typical of dust dynamics. Starting from the Klimontovich equations for the exact phase space densities, theory deliverables such as the permittivity, the spectral densities of fluctuations and the collision integrals are implemented either for concrete predictions related to low frequency electrostatic waves or for diagnostic purposes related to the enhancement of the ion density and electrostatic potential fluctuation spectra due to the presence of dust grains. Particular emphasis is put to the comparison of the self-consistent kinetic model with multi-component kinetic models (treating dust as an additional massive charged species) as well as to the importance of the nature of the plasma particle source. Finally, a new kinetic model of complex plasmas (for both constant and fluctuating sources) is formulated. It is valid in regimes typical of ion dynamics, where plasma discreteness can no longer be neglected, and, in contrast to earlier models, does not require relatively large dust densities to be valid. / QC 20120316

<p>This licentiate thesis reports analytical results for the electrostatic response to a test charge moving through dusty plasma. Two particular cases for a slowly moving test charge, namely, grain size distribution and grain charging dynamics are considered. Analytical results for the delayed shielding of a test charge due to dynamical grain charging in dusty plasma are also reported. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. This kind of work has relevance both in space and astrophysical plasmas.</p>

I study dusty plasma produced by electrostatically confining melamine formaldehyde microparticles in a radio-frequency glow discharge plasma. Dusty plasma is a mixture of particles of solid matter (dust), electrons, ions, and neutral gas atoms. The dust particles have a very high charge and a mass compared to the electrons and ions in the ambient plasma. As a consequence, a dusty plasma exhibits collective phenomena such as dust acoustic waves, crystallization, and melting. The discrete nature of dust particles gives rise to compressibility. In this thesis I report findings of four tasks that were performed to investigate dust acoustic waves, compressibility, and melting. First, the nonlinear phenomenon of synchronization was characterized experimentally for the dust acoustic wave propagating in a dust cloud with many layers. I find four synchronized states, with frequencies that are multiples of 1, 2, 3, and 1/2 of the driving frequency. Comparing to phenomena that are typical of the van der Pol paradigm, I find that synchronization of the dust acoustic wave exhibits the signature of the suppression mechanism but not that of the phaselocking mechanism. Additionally, I find that the synchronization of the dust acoustic wave exhibits three characteristics that differ from the van der Pol paradigm: a threshold amplitude that can be seen in the Arnold tongue diagram, a branching of the 1:1 harmonic tongue at its lower extremity, and a nonharmonic state. Second, to assess which physical processes are important for a dust acoustic instability, I derived dispersion relations that encompass more physical processes than commonly done. I investigated how various physical processes affect a dust acoustic wave by solving these dispersion relations using parameters from a typical dust acoustic wave experiment. I find that the growth rate diminishes for large ion currents. I also find that the compressibility, a measure of the coupling between the dust particles, have a strong effect on the wave propagation. Comparing the kinetic vs. hydrodynamic descriptions for ions, I find that under typical laboratory conditions the inverse Landau damping and the ion-neutral collisions contribute about equally to the dust acoustic instability. Third, I performed dust acoustic wave experiments to resolve a previously unremarked discrepancy in the literature regarding the sign of the compressibility of a strongly-coupled dust component in a dusty plasma. According to theories compressibility is negative, whereas experiments suggest that it is positive. I find that the compressibility is positive. This conclusion was reached after allowing for a wide range of experimental uncertainties and model dependent systematic errors. Finally, the polygon construction method of Glaser and Clark was used to characterize crystallization and melting in a single-layer dusty plasma. Using particle positions measured in a previous dusty plasma experiment, I identified geometrical defects, which are polygons with four or more sides. These geometrical defects are found to proliferate during melting. I also identify a possibility of latent heat involvement in melting and crystallization processes of a dusty plasma.

This licentiate thesis reports analytical results for the electrostatic response to a test charge moving through dusty plasma. Two particular cases for a slowly moving test charge, namely, grain size distribution and grain charging dynamics are considered. Analytical results for the delayed shielding of a test charge due to dynamical grain charging in dusty plasma are also reported. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. This kind of work has relevance both in space and astrophysical plasmas. / QC 20101220