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.

<p> The absence of a protecting magnetic field, such as the dipole magnetic field around Earth, makes the interaction of solar wind with unmagnetized objects particularly interesting. Long-term evolution of the object&rsquo;s surface and atmosphere is closely tied to its interaction with the outer space environment. The ionospheric plasma layer around unmagnetized objects acts as an electrically conducting transition layer between lower atmospheric layers and outer space. This study considers two distinct types of unmagnetized objects: Titan and comet 67P/Churyumov-Gerasimenko (67P/CG). For many years, Titan has been a key target of the National Aeronautics and Space Administration (NASA) Cassini mission investigations; and the European Space Agency (ESA) Rosetta spacecraft explored comet 67P/CG for more than two years. </p><p> Ionospheric composition and primary ion production rate profiles for Titan are modeled for various solar activity conditions. Photoionization is the main source of ion production on the dayside; on the nightside, electron-impact ionization is the main ionization source. This dissertation uses model results and in-situ measurements by the Ion and Neutral Mass Spectrometer (INMS) and the Langmuir Probe (LP) onboard the Cassini spacecraft to show that while the solar activity cycle impacts the primary ion species significantly, there is little effect on heavy ion species. Solar cycle modulates the Titan&rsquo;s ionospheric chemistry. The solar cycle effects of on each ion species are quantified n this work. In some cases the solar zenith angle significantly overshadows the solar cycle effects. How each individual ion reacts to changes in solar activity and solar zenith angle is discussed in details. A method to disentangle these effects in ion densities is introduced. </p><p> At comet 67P/CG, the fast-moving solar wind impacts the neutral coma. Two populations of electrons are recognizable in the cometary plasma. These are the hot suprathermal electrons, created by photoionization or electron-impact ionization, and the cold/thermal electrons. Even though photoionization is the dominant source of ion production, electron-impact ionization can be as high as the photoionization for certain solar events. At 3 AU, electron energy spectra from in-situ measurements of the Ion and Electron Sensor (IES) instrument exhibit enhancement of electron fluxes at particular energies. Model-data comparisons show that the flux of electrons is higher than the typical solar wind and pure photoionization fluxes. The probable cause of this enhancement is the ambipolar electric field and/or plasma compression. </p><p> This research also discusses formation of a new boundary layer around the comet near perihelion, similar to the diamagnetic cavity at comet 1P/Halley. At each crossing event to the diamagnetic cavity region, flux of suprathermal electrons with energies between 40 to 250 eV drops. The lower flux of solar wind suprathermal electrons in that energy range can cause this flux drop. </p><p>

<p>The magnetosphere-ionosphere (M-I) transition region is the several thousand--kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa. We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfven waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite. Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvenic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases occur during ~30% of the four-year period studied, but together account for more than 65% of global Alfvenic energy deposition and electron precipitation, and more than 70% of the coincident ion outflow. We compare observed interplanetary magnetic field (IMF) control of inertial Alfven wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvenic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvenic power in the Northern Hemisphere. Observed and predicted prenoon Alfvenic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation reverses under dawnward IMF. Despite clear observational and simulated signatures of dayside Alfvenic power, the generation mechanism remains unclear. Last, we present premidnight FAST observations of accelerated precipitation that is best described by a kappa distribution, signaling a nonthermal source population. We examine the implications for the commonly used Knight Relation.

This paper examines the neutral coma of comet 67P/Churyumov–Gerasimenko by using measurements of charged particles (water ions) and tracing them back to their place of ionisation. The measurements were taken from Rosetta’s Ion Composition Analyser. The simulations made use of an existing program which traces particles forward, which was changed to trace particles backwards, with new conditions for terminating the simulation. Two types of simulations were made. The first type is referred to as ”one-day simulations”. In these, simulations are made using data from a single occasion, with nine occasions studied per selected day. The days were selected so that the spacecraft was in different positions in relation to the comet. The second is referred to as the ”full-hemisphere” simulation. In this simulation, data from all usable days are used to produce an image of the hemisphere facing the Sun. The full-hemisphere simulation suffers from lack of simultaneous measurements, and indeed it is impossible to obtain in-situ measurements at all positions at once. Both simulations could be improved using more precise models, which could not be done within the allotted time of this work.

No description available.

No description available.

Measurements of reflectivity and Hall effect have been made on polycrystalline n-type samples of GaAs and alloys of the systems GaAs xSb1-x and Ga1-xAlxAs to find values of electron effective mass at the bottom of the conduction band m*00/m . The experimental data were obtained with a Baird monochromator which was modified to give double beam operation and extended wavelength range up to 30 mum, so that measurements of the free carrier reflectivity could be made on samples with low carrier concentration. The reflection coefficient R and hence the index of refraction eta were obtained from the experimental measurements. The variation of eta2 was plotted as a function of the square of the wavelength. For each sample, the graphical result (eta 2 vs lambda2) was found to be a straight line and it was extrapolated to zero wavelength to obtain the optical dielectric constant epsilon infinity. The slope of the line also was determined and used to obtain the value of effective mass at the bottom of the conduction band. For the systems GaAsxSb1-x the alloy compositions were determined by the X-ray powder photograph method. For the two alloy systems GaAsxSb1-x and Ga 1-xAlxAs, optical dielectric constant and effective mass values were measured from infrared reflectivity for the first time. The values of the effective masses were determined by the simultaneous solution of the integrals giving the statistical carrier concentration and the slope of the free carrier reflectivity under the condition of the general degeneracy, the lattice contribution to the slope being taken into account. Theoretical values of the effective masses in the (000) conduction band as a function of alloy composition were calculated for the alloy system GaAs xSb1-x using the disorder equation (73W) and Kane equation (57K) for the effective masses. The experimental results were found to be in better agreement with the disorder equation of the effective mass than with the Kane equation. Finally, to complete the outline of the project, it should be mentioned that the values of optical Fermi energy, dielectric constant, optical relaxation time, optical mobility and optical conductivity were calculated for 12 samples of the alloys GaAsxSb1-x and Ga1-xAl xAs.

Abstract not available.

Abstract not available.

A superheterodyne Dicke type radiometer suitable for the measurement of radiation from a high temperature plasma in the 35 GHz range has been developed. The radiometer employs a balanced mixer at the radiometer frequency, a 3.5 GHz parametric amplifier using a varactor diode as the first IF amplifier, a broad-band transistor amplifier at the second IF of 7Q MHz and a commutator detector. The performance of the radiometer has been measured by conducting hot load tests and by using an S-band argon noise source. The minimum detectable temperature change was found from the hot load tests to be 11 deg K for an output bandwidth of 0.32 Hz. However, from argon noise source measurements, a minimum detectable temperature change of 1.4 x 10³ deg K was determined for an output bandwidth of 6.4 KHz and 9.5 x 10³ deg K for an output bandwidth of 160 KHz. The equation for the minimum detectable temperature change for the Dicke radiometer has been deduced following conventional analysis. It has been found that there are two errors in Goldstein's derivation the effects of which cancel out and his final formula is correct. Thus, the change suggested by Ring does not appear to be valid. For the two channel subtraction radiometer it has been found that the expression given by Graham should be multiplied by √2. The d.c. radiometer has also been analysed and it has been found that its minimum detectable signal power is independent of both the radiometer bandwidth and the output bandwidth. The effect of noise at the radiometer input before the modulating switch has been investigated and it is shown that this noise could produce a cutoff condition in the Dicke radiometer and the two channel subtraction radiometer. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate