A dusty plasma is a mixture of electrons, ions, neutral gas atoms, and small particles of solid matter (dust). In a dusty plasma produced in the laboratory, dust particles gain a large electric charge from the other charged species, so that their interparticle interactions can be very strong. Frequently, the average interparticle potential energy is higher than the thermal kinetic energy of the dust particles, and in this case, they constitute a strongly coupled plasma. As with all strongly coupled plasmas, the dust particles can behave like typical solids or liquids. In this thesis, I report the results of dusty plasma experiments that are focused on the behavior of liquids. I use a so-called two-dimensional (2D) dusty plasma that consists of only a single horizontal layer of dust particles. Tracking each particle with video microscopy and image analysis methods allows the calculation of important liquid properties, like the viscosity coefficient. In Chapter 2, I describe an improved laser heating method for producing liquid-like conditions in a 2D dusty plasma. Two laser beams are scanned across the dust layer in a new pattern to increase the kinetic energy of the particles and melt the ground state crystalline lattice. The new scanning pattern improves the randomness of the resulting particle motion so that it more closely resembles that of a liquid in a thermal equilibrium. In Chapter 3, I report a viscosity measurement in a dusty plasma that is unaffected by the complicating effects of temperature nonuniformities and shear thinning. This measurement is enabled by an addition to my experimental apparatus that I also detail here. I find the viscosity to be significantly higher than in previous measurements, which I attribute to the avoidance of shear thinning. In Chapter 4, I present measurements of viscosity using the Green-Kubo method, and compare the results to those of my previous measurement. I find that the two methods yield viscosity values that differ by about 60%, over the entire temperature range attained in the experiment. Possible sources of this difference are evaluated. Finally, in Chapter 5, I report the first experimental confirmation of a theoretical expression describing the decay of time autocorrelation functions. This theoretical expression fits experimentally calculated autocorrelation functions within error bars, especially at short times when a simple exponential decay fails. I also propose an intuitive description wherein an observed transition in the autocorrelation function is due to the onset of collisional scattering.

A strongly-coupled plasma is a collection of free charged particles that interact with a Coulomb repulsion that is so strong that nearby particles do not easily move past one another. Unlike weakly-coupled plasmas, strongly-coupled plasmas exhibit a self-organization of particles into an arrangement like a solid crystalline lattice or a liquid. Dusty plasmas consist of micron-size particles of solid matter that are immersed in a plasma of electrons and ions. The dust particles gain a large electric charge and become strongly coupled. The motion of discrete particles can be tracked using a video microscopy diagnostic. Dusty plasma experiments allow a study of strongly-coupled plasma physics and an experimental simulation of condensed matter physics. Experiments are reported using a single layer of particles in the plasma to study two-dimensional (2D) physics. It is demonstrated experimentally that in addition to the solid and liquid states, a strongly-coupled dusty plasma can exist in an exotic state called a superheated solid. A 2D dusty plasma, initially self-organized in a crystalline lattice, is heated rapidly by rastered laser beams. The suspension remains in a solid lattice at a temperature well above the melting point. Shear-induced melting is studied in a 2D dusty plasma by applying shear to a crystalline lattice using a pair of oppositely-directed laser beams. Unexpectedly, coherent longitudinal waves are also excited in the resulting shear flow. In the first experiment of its kind, a suddenly-applied shear is found to produce a melting front that spreads at the transverse sound speed. The viscoelasticity of strongly-coupled plasmas in a liquid state is quantified. In the first experiment for any kind of physical system, the wavenumber-dependent viscosity, η(k), is computed from measurements of the random motion of particles. It is found that η(k) diminishes with increasing k, indicating that viscous behavior is gradually replaced by elastic behavior as the scale length is reduced. As a tool for studying transport at a microscopic level, the self-intermediate scattering function (self-ISF) is used in numerical simulations of 2D dusty plasmas. Two physical processes are studied using the self-ISF: relaxation of random motion, and melting. The wavenumber-dependence of the relaxation time in a liquid-phase strongly-coupled plasma is shown to be useful for distinguishing normal and anomalous diffusion. The self-ISF is also demonstrated to be a sensitive indicator of the melting transition. An improved image-analysis method is developed for calculating particle positions with minimal measurement errors. This development also provides an understanding of sources of error and the dependence on parameters that the experimenter can control.

L'étude des plasmas poussiéreux est maintenant un domaine scientifique en plein développement qui attire l'attention d’une large communauté de scientifiques. Rappelons que le plasma poussiéreux est un plasma classique avec des particules injectées ou qui s’y sont formées dont les tailles peuvent atteindre quelques micromètres. Ces particules (poussières) peuvent acquérir de très grandes charges jusqu'à 103 à 105 charges élémentaires. Dans la littérature, il est également appelé plasma à phase condensée dispersée, plasma aérosol et aussi plasma complexe. Les plasmas poussiéreux sont d’un grand intérêt à la fois sur le plan pratique afin de trouver des solutions à des problèmes industriels et sur le plan scientifique fondamental afin d’élargir nos connaissances sur les phénomènes fondamentaux de la nature ainsi que les propriétés et la structure de la matière. En raison du fait que les particules de poussière macroscopique sont visuellement distinguables, le plasma poussiéreux est un objet d’étude unique pour l'étude de certaines propriétés physiques de la matière condensée, telles que les transitions de phase, la propagation d’ondes, les phénomènes de dislocation, les processus de transport, etc…On a constaté que dans de nombreuses technologies modernes mettant en oeuvre un plasma, en raison de l'interaction du plasma avec la surface des matériaux, des particules macroscopiques sont éjectées de celles-ci dans le plasma (dont les tailles peuvent être de quelques nanomètres jusqu'à quelques dizaines de micromètres). Il en résulte ainsi la formation d’un plasma complexe. Le nom le plus commun de ce plasma est un plasma poussiéreux. Un des aspects les plus intéressants est la formation dans certaines conditions de structures ordonnées (« cristaux ou liquide coulombiens »). Toutes ces structures plasmapoussière, se formant de façon naturelle, sont une contamination indésirable qui affecte négativement les propriétés physiques et mécaniques (micro dureté, résistance à la corrosion, etc.) des matériaux et dispositifs manufacturés.L'un des problèmes scientifiques et technologiques les plus importants, à l’heure actuelle, est la réalisation de la fusion thermonucléaire contrôlée. Dans ces conditions extrêmes se forment aussi au voisinage des parois des Tokamaks des poussières qui jouent un rôle fondamental : les données expérimentales récentes montrent que la présence de poussières dans le plasma peut affecter le temps global de confinement du plasma. L'utilisation du plasma poussiéreux dans la production de matériaux composites, à haute valeur ajoutée, est un nouveau champ d'applications. On peut citer à titre d’exemples, le traitement de surface de petites particules sphériques avec des revêtements, d’épaisseur nanométrique, déposés par plasma. Afin d'étudier les mécanismes de formation de particules homogènes ayant des propriétés désirées et une production stable, il est nécessaire de trouver les conditions optimales de production. Ainsi, l'étude des propriétés des plasmas poussiéreux et leurs diagnostics sont des tâches très importantes, à la fois pour les connaissances scientifiques fondamentales et que pour les aspects appliqués. / The study of the dusty plasma is now a developing scientific field, attracting the attention of scientists. Recall that the dusty plasma is conventional plasma with inserted or formed therein particles of condensed matter of microns sizes, the size of these particulates (dusts) can acquire very large charges up to 3 5 10 ¸10 of the elementary charges. In the literature, it is also named as plasma with a condensed dispersed phase, aerosol plasma. Dusty plasma is of interest both for the solution of the applied problems, and to expand our knowledge of the fundamental phenomena in nature, properties and structure of matter. Due to the fact that the macroscopic dust are visually distinguishable the dispersed plasma is unique comfort object for the study of some physical properties of condensed matter, such as phase transitions, transport processes, etc.It was found that in many modern plasma technologies, due to the interaction of the plasma with the material surfaces macroscopic particles from the material fall into the plasma (sizes are from micron fractions up to a few hundred microns). As result complex plasma is formed. The most common name of this plasma is dusty plasma. An interesting fact is that the dusty plasma forms under certain conditions the ordered structures ("plasma crystal", clouds, droplets). All of these plasma- dust structures are naturally occurring undesirable contamination and negatively affect on the physical and mechanical properties (microhardness, corrosion resistance, etc.) of the constructional materials.One of the most important scientific and technological problems is the realization of the controlled thermonuclear fusion. Formed in the wall region of the Tokamak dusty plasma can play a big role: recent experimental data show that the presence of dust in the plasma can affect the global energy confinement time. The use of the dusty plasma in the production of high composite materials is new field of application, for example, small spherical particles with nanocoating deposited in the plasma. In order to study formation of a homogeneous powder of the dust particles with desired properties and stability of its production, it is necessary to find the optimal conditions and time of production. Thus, the study of dusty plasma properties, their diagnostics are very important tasks, both from the scientific and applied aspects.

Title: Dust - UV interaction Author: Libor Nouzak Department: Department of Surface and Plasma Science Supervisor: RNDr. Jiri Pavlu, Ph.D. Supervisor's e-mail address: jiri.pavlu@mff.cuni.cz Abstract: Micrometer objects (dust grains) are an integral part of the universe. As other objects in the plasma, these dust grains charge to potencial close to the potencial of the plasmas (in this case, interplanetary plasma). In the universe, the photoelectric charging dust grain dominantes all other charging processes. In general, the resulting charge of dust grain is given by a balance of all processes, which haven't been mostly jet theoretically described. In our laboratory, we are simulating space conditions and measure resulting charge and his changes on a single separated dust grain. This work is partly focused to UV source application and to finishing its electronics, and partly on test measurements and model calculations, connected with newly built experiment (e.g., to estimate effects of backgound currents, surfaces, and the geometry of the dust trap electrodes). The work is finished by the first measurements of glass grain charge under electron bombardment with provisional detection optics. Obtained results are compared with previous measurements on the same type of dust grains. Key words: dust, dusty plasma,...

The study of waves and instabilities in quantum plasmas is of fundamental importance for understanding collective interactions in superdense astrophysical objects, in high intense laser-plasma/solid-matter interactions, in microelectronic devices and metallic nanostructures. In dense quantum plasmas, there are new pressure laws associated with the Fermi-Dirac distribution functions and new quantum forces associated with the quantum Bohm potential and the Bohr magnetization involving electron ½ spin. These forces significantly alter the collective behavior of dense quantum plasmas. This thesis contains six papers, considering several novel collective modes and instabilities at quantum scales. In Paper I, we have used the quantum hydrodynamical (QHD) model for studying the one-dimensional dust-acoustic (DA) waves incorporating the Fermi pressure law and the quantum Bohm potential. The latter modifies the DA wave dispersion relation in a collisional plasma. In Paper II, we have calculated the electrostatic potential of a test charge in an unmagnetized electron-ion quantum plasma. It is found that the Debye-Hückel and oscillatory wake potentials strongly depend upon the Fermi energy at quantum scales. The results can be of interest for explaining the charged particle attraction and repulsion in degenerate quantum plasmas, such as those in semiconductor and microelectronic devices. Paper III presents the parametric study of nonlinear electrostatic waves in two-dimensional collisionless quantum dusty plasmas. A reductive perturbation method has been employed to the QHD equations together with the Poisson equation, obtaining the cylindrical Kadomtsev-Petviashvili (CKP) equations and their stationary localized solutions. We have numerically examined the quantum mechanical and geometrical effects on the profiles of nonplanar quantum dust-ion-acoustic (DIA) and DA solitary waves. The role of static as well as mobile (negatively or positively charged) dust particles on the low-frequency electrostatic waves has also been highlighted for metallic nanostructures. Paper IV introduces the nonlinear properties of the ion-sound waves in a dense electron-ion Fermi magnetoplasma. The computational analysis of the nonlinear system reveals that the Sagdeev-like potential and the ion-sound density excitations are significantly affected by the wave direction cosine and the Mach number at quantum scales. Paper V considers the nonlinear interactions of electrostatic upper-hybrid (UH), ion-cyclotron (IC), lower-hybrid (LH), and Alfvén waves in a quantum magnetoplasma. The nonlinear dispersion relations have been analyzed analytically to obtain the growth rates for both the decay and modulational instabilities involving the dispersive IC, LH, and Alfvén waves. In Paper VI, we have identified a new drift-like dissipative instability in a collisional quantum plasma. The modified unstable drift-like mode can cause cross-field anomalous ion-diffusion at quantum scales.

Titan, the largest moon of Saturn, is the only known moon with a fully developed nitrogen-rich atmosphere, its ionosphere is detectable as high as 2200 km above its surface and hosts complex organic chemistry. Titan’s atmosphere and ionosphere has striking similarities to current theories of these regions around Earth 3.5 billion years ago. The Cassini spacecraft has been in orbit around Saturn since 2004 and carries a wide range of instruments for investigating Titan’s ionosphere, among them the Langmuir probe, a “space weather station”, manufactured and operated by the Swedish Institute of Space Physics, Uppsala. This thesis presents studies of positive ions, negative ions and negatively charged dust grains (also called aerosols) in Titan’s ionosphere using the in-situ measurements by the Cassini Langmuir probe, supplemented by the data from particle mass spectrometers. One of the main results is the detection of significant (up to about 4000 cm-3) charge densities of heavy (up to about 13800 amu/charge) negative ions and dust grains in Titan’s ionosphere below 1400 km altitude. The dust is found to be the main negative charge carrier below about 1100 km on the nightside/terminator ionosphere, forming a dusty plasma (also called “ion-ion” plasma). A new analysis method is developed using a combination of simultaneous observations by multiple instruments for a case study of four flybys of Titan’s ionosphere, further constraining the ionospheric plasma charge densities. This allows to predict a dusty plasma in the dayside ionosphere below 900 km altitude (thus declaring it a global phenomenon), as well as to empirically estimate the average charge of the negative ions and dust grains to between -2.5 and -1.5 elementary charges. The complete Cassini dataset spans just above 13 years, allowing to study effects of the solar activity on Titan’s ionosphere. From solar minimum to maximum, the increase in the solar EUV flux increases the densities by a factor of ~2 in the dayside ionosphere and, surprisingly, decreases by a factor of ~3-4 in the nightside ionosphere. The latter is proposed to be an effect of the ionospheric photochemistry modified by higher solar EUV flux. Modelling photoionization also reveals an EUV trend (as well as solar zenith angle and corotational plasma ram dependencies) in the loss rate coefficient.

This work focuses on the analysis of plasma irregularities generated during two active space experiments: the injection of an artificial dust layer, and high-power radio waves. The objective of the "first experiment is to examine the effects of artificially created dust layers on the scatter of radars from plasma irregularities embedded in dusty plasma in space. This is an alternate approach for understanding the mechanisms of enhanced radar scatter from plasma irregularities embedded in Noctilucent Clouds and Polar Mesospheric Summer Echoes. The second experiment involves a transmission of high power electromagnetic waves into the ionospheric plasma from the ground, which can excite stimulated electromagnetic emissions offset from the transmitter frequency. These stimulated electromagnetic emissions provide diagnostic information of the ionosphere and thus can be used to investigate fundamental physical principles which govern the earth\'s ionosphere, so that present and future transmission technologies may take into account the complexities of the ionosphere. The interaction altitude of the artificial dust layer and high power radio waves is approximately 250 km and 160 km respectively, thus dealing with uniquely different regions of the ionosphere. Each experiment is discussed separately using theoretical, observational and advanced computational methodologies. The study first investigates plasma turbulence associated with the creation of an artificial dust layer in the earth's ionosphere. Two scenarios are considered for plasma irregularity generation as dust is injected at an oblique angle across the geomagnetic field. The first is a shear-driven plasma instability due to inhomogeneities in the boundary layer between the injected charged dust layer and the background plasma. This begins to appear at very early times once the dust is released into the space plasma, which is of the order or less than the dust charging time period. The second mechanism is free streaming of the charged dust relative to the background plasma. This produces irregularities at times much longer than the dust charging period and also longer than the dust plasma period. Although both mechanisms are shown to produce turbulence in the lower hybrid frequency range, the resulting irregularities have important differences in their physical characteristics. A comparison between the processes is made to determine the consequences for upcoming observations. Both processes are shown to have the possibility of generating turbulence after the release of dust for the regimes of upcoming space experiments over a range of timescales. This work also presents the first observations of unique narrowband emissions ordered near the Hydrogen ion (H+) gyro-frequency (fcH) in the Stimulated Electromagnetic Emission (SEE) spectrum when the transmitter is tuned near the second electron gyro-harmonic frequency (2fce), during ionospheric modification experiments. The frequency structuring of these newly discovered emission lines is quite unexpected since H+ is known to be a minor constituent in the interaction region which is near 160 km altitude. The spectral lines are typically shifted from the pump wave frequency by harmonics of a frequency about 10% less than fcH (" 800 Hz) and have a bandwidth of less than 50 Hz which is near the O+ gyro-frequency fcO. A theory is proposed to explain these emissions in terms of a Parametric Decay Instability (PDI) in a multi-ion species plasma due to possible proton precipitation associated with the disturbed conditions during the heating experiment. The observations can be explained by including several percent H+ ions into the background plasma. The implications are new possibilities for characterizing proton precipitation events during ionospheric heating experiments. / Ph. D.

Depuis la fin des années 80, les plasmas poussiéreux sont l’objet d’un grand nombre d’études. Plusieurs domaines de la physique des plasmas sont confrontés à la présence de ces particules: en astrophysique, dans les procédés de dépôt ou de gravure, dans les plasmas de fusion thermonucléaire contrôlée. Les plasmas poussiéreux ont très peu été étudiés dans des décharges micro-onde basse pression. Il y a une quinzaine d’années encore, il était admis que les probabilités de recombinaisons d’espèces réactives en volume étaient négligeables à cause de la faible densité du gaz. Au LAPLACE, des poussières incandescentes sont observées en plasma RCER d’acétylène. La présente étude a pour objectif d’apporter des éléments de réponses sur les mécanismes liés à la formation, au transport et au chauffage de ces poussières. Ce document présente les résultats obtenus durant ces 4 années de thèse. Le chapitre 1 introduit brièvement l’émergence de la thématique des plasmas poussiéreux, ainsi que certains aspects théoriques importants des décharges multipolaires. Le chapitre 2 détaille le dispositif expérimental ainsi que les différents diagnostiques utilisés durant cette étude: sonde de Langmuir, sonde de Mach, sonde de flux aux parois et imagerie rapide. Le chapitre 3 présente en détail les mécanismes de chargement et de chauffage des poussières. Dans cette partie, des mesures expérimentales ainsi qu’un modèle sont couplés afin d’expliquer l’incandescence et d’estimer la charge des particules. Le chapitre 4 décrit la caractérisation du transport des poussières dans une plasma d’acétylène par imagerie rapide. Dans ce chapitre, nous discutons des forces pouvant être responsables de ce transport. Enfin, le chapitre 5 passe en revue les résultats obtenus sur l’interaction plasma surface, à l’aide d’analyses ex-situ ainsi que des mesures de sondes de flux aux parois. / Since the late 1980s, dusty plasmas have been the subject of a large number of studies. Several fields of plasma physics are confronted with the presence of these particles: astrophysics, deposition or etching processes, or controlled thermonuclear fusion plasmas. However, few dusty plasma studies have been reported in low pressure microwave discharges. Fifteen years ago, it was accepted that dust particles cannot be formed in the plasma volume, due to the low probability of recombining reactive species, because of the low density of the gas. At LAPLACE, incandescent dusts are observed in RECR acetylene plasma. The present study aims to provide some answers on the mechanisms related to the formation, transportation and heating of dust particles. This document presents the results obtained during these four years of theses. Chapter 1 briefly introduces the emergence of the topic of dusty plasmas, as well as some important theoretical aspects of multipolar discharges. Chapter 2 details the experimental setup and the different diagnostics used during this study: Langmuir probe, Mach probe, wall probe current and rapid imaging. Chapter 3 details the mechanisms for charging and heating dust. In this part, experimental measurements and a model are coupled to explain the incandescence and to estimate the particles charges. Chapter 4 describes the characterisation of dust transport in acetylene plasma by rapid imaging. In this chapter, we discuss the forces that can be responsible for this transport. Finally, Chapter 5 reviews the results obtained on the plasma-surface interaction, using ex-situ analyzes as well as measurements of wall probe currents.

Ce travail de thèse de doctorat propose et évalue différentes solutions pour caractériser, avec des outils optiques et électromagnétiques non intrusifs, les nanoparticules et agrégats observés dans différents systèmes physiques : suspensions colloïdales, aérosols et plasma poussiéreux. Deux types de modèles sont utilisés pour décrire la morphologie d'agrégats fractals (p. ex. : suies issues de la combustion) et agrégats compacts (qualifiés de « Buckyballs » et observés dans des aérosols produits par séchage de nano suspensions). Nous utilisons différentes théories et modèles électromagnétiques (T-Matrice et approximations du type dipôles discrets) pour calculer les diagrammes de diffusion (ou facteur de structure optique) de ces agrégats, de même que leurs spectres d'extinction sur une large gamme spectrale. Ceci, dans le but d'inverser différentes données expérimentales. Différents outils numériques originaux ont également été mis au point pour parvenir à une analyse morphologique quantitative de clichés obtenus par microscopie électronique. La validation expérimentale des outils théoriques et numériques développés au cours de ce travail est focalisée sur la spectrométrie d'extinction appliquée à des nano agrégats de silice, tungstène et silicium. / This Ph.D. work provides and evaluates various solutions to characterize, with optical/electromagnetic methods nanoparticles and aggregates of nanoparticles found in suspensions, aerosols and dusty plasmas. Two main models are introduced to describe the morphology of particle aggregates with fractal-like (for particles in plasmas and combustion systems) and Buckyballs-like (aerosols, suspensions) shapes. In addition, the author proposes various solutions and methods (T-Matrix, Rayleigh type approximations) to calculate the scattering diagrams (optical structure factors) of fractal aggregates as well as algorithms to inverse extinction spectra. As a reference case for the performed analysis, several tools to describe the morphology of fractal aggregates from electron microscopy images have been also developed. The experimental validation carried out with the Light Extinction Spectrometry (LES) technique (for nano silica beads, tungsten, dusty plasma and silicon aggregates) clearly proves the validity of the algorithms developed as well as the potential of the LES technique.

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