The rectangular pulsed plasma thruster (PPT) is an electromagnetic thruster that ablates Teflon propellant to produce thrust in a discharge that lasts 5-20 microseconds. In order to integrate PPTs onto spacecraft, it is necessary to investigate possible thruster plume-spacecraft interactions. The PPT plume consists of neutral and charged particles from the ablation of the Teflon fuel bar as well as electrode materials. In this thesis a novel application of quadruple Langmuir probes is implemented in the PPT plume to obtain electron temperature, electron density, and ion speed ratio measurements (ion speed divided by most probable thermal speed). The pulsed plasma thruster used is a NASA Glenn laboratory model based on the LES 8/9 series of PPTs, and is similar in design to the Earth Observing-1 satellite PPT. At the 20 J discharge energy level, the thruster ablates 26.6 mg of Teflon, creating an impulse bit of 256 mN-s with a specific impulse of 986 s. The quadruple probes were operated in the so-called current mode, eliminating the need to make voltage measurements. The current collection to the parallel to the flow electrodes is based on Laframboise's theory for probe to Debye length ratios between 5 and 100, and on the thin-sheath theory for ratios above 100. The ion current to the perpendicular probe is based on a model by Kanal and is a function of the ion speed ratio, the applied non-dimensional potential and the collection area. A formal error analysis is performed using the complete set of nonlinear current collection equations. The quadruple Langmuir probes were mounted on a computer controlled motion system that allowed movement in the radial direction, and the thruster was mounted on a motion system that allowed angular variation. Measurements were taken at 10, 15 and 20 cm form the Teflon fuel bar face, at angles up to 40 degrees off of the centerline axis at discharge energy levels of 5, 20, and 40 J. All data points are based on an average of four PPT pulses. Data analysis shows the temporal and spatial variation in the plume. Electron temperatures show two peaks during the length of the pulse, a trend most evident during the 20 J and 40 J discharge energies at 10 cm from the surface of the Teflon fuel bar. The electron temperatures after the initial high temperature peak are below 2 eV. Electron densities are highest near the thruster exit plane. At 10 cm from the Teflon surface, maximum electron densities are 1.04e20 ± 2.8e19 m-3, 9.8e20 ± 2.3e20 m-3, and 1.38e21 ± 4.05e20 m-3 for the 5 J, 20 J and 40 J discharge energy, respectively. The electrons densities decrease to 2.8x1019 ± 8.9e18 m-3, 1.2e20 ± 4.2e19 m-3, and 4.5e20 ± 1.2e20 m-3 at 20 cm for the 5 J, 20 J, and 40 J cases, respectively. Electron temperature and density decrease with increasing angle away from the centerline, and with increasing downstream distance. The plume is more symmetric in the parallel plane than in the perpendicular plane. Ion speed ratios are lowest near the thruster exit, increase with increasing downstream distance, but do not show any consistent angular variation. Peak speed ratios at a radial distance of 10 cm are 5.9±3.6, 5.3±0.39, and 4.8±0.41 for the 5 J, 20 J and 40 J discharge energies, respectively. The ratios increase to 6.05±5.9, 7.5±1.6, and 6.09±0.72 at a radial distance of 20 cm. Estimates of ion velocities show peak values between 36 km/s to 40 km/s, 26 km/s to 30 km/s, and 26 km/s to 36 km/s for the % J, 20 J, and 40 J discharge energies, respectively.

La turbulence de Langmuir Forte dans les plasmas a de nombreuses conséquences tant dans les applications à la fusion rapide qu'à l'astrophysique. La déduction des équations couplant le spectre turbulent de Langmuir des cavités en effondrement et la fonction de distribution des particules se trouve exposée en détail dans ce mémoire. Le traitement numérique de ces équations confirme le développement d'une queue de particules suprathermiques prédite théoriquement. Par ailleurs, l'importance du rôle du rayonnement d'ondes sonores est mise en évidence . Il est montré que ce rayonnement se manifeste par une réaction sur la source de la turbulence, lorsque la queue d'électrons chauds s'est étendue, par l'intermédiaire du phénomène de conversion aléatoire. La prise en compte de ce dernier phénomène conduit à une sorte d'intermittence, cette tendance a été confirmée numériquement d'abord par une modélisation à 3 et 4 degrés de liberté puis sur l'ensemble des équations spectrales.

De nombreux plasmas astrophysiques, dont le vent solaire, sont non-collisionels. Les fréquences typiques des processus dynamiques sont grandes devant la fréquence de collision, de sorte que le vent solaire est hors équilibre thermodynamique local. Dans ce contexte, les processus cinétiques et/ou non-linéaires (interactions ondes-particules et ondesondes) permettent de redistribuer l'énergie dans le plasma. Si les processus cinétiques et la théorie non-linéaire des plasmas ont été intensivement étudiés depuis les années 1960, des preuves observationnelles concluantes manquent encore. L'objectif de cette thèse est double : d'une part comprendre les effets cinétiques et/ou nonlinéaires (en particulier dans le cas des couplages electrostatiques ions-electrons) et d'autre part fournir des preuves observationnelles de leur existence dans les plasmas spatiaux. Cette étude se fonde sur des observations in-situ et des simulations numériques. Les mesures de formes d'onde de champ électrique sont fournies par l'instrument radioWAVES embarqué sur les sondes STEREO. Les simulations numériques sont réalisées en utilisant un code cinétique Vlasov-Poisson unidimensionel dans l'approximation électrostatique. Les résultats de cette thèse sont les suivants. (1) Une méthode de mesure et d'étalonnage in-situ des fluctuations de densité haute fréquence (0.1 - 1kHz donc dans un domaine non accessible par les instruments particulaires) a été développée en utilisant les variations quasi-statiques du potentiel flottant des sondes. (2) Des mesures simultanées de champ électrique et de densité sur plus de trois ans de données fournissent la première preuve observationnelle d'effets pondéromoteurs dans le vent solaire, permettant de coupler la densité du plasma aux ondes de Langmuir de grande amplitude. (3) Ce travail fournit également la première preuve observationnelle directe de l'instabilité de décroissance des ondes de Langmuir, un archétype d'interaction onde-onde, associé à un sursaut de type III. Le caractère résonant de l'interaction est validé grâce aux observations de forme d'ondes, en vérifiant la conservation de l'impulsion et de l'énergie (relations de résonances), ainsi que la résonance de phase à travers une analyse de bicohérence. Les simulations fournissent une nouvelle expression du seuil d'instabilité de décroissance des ondes de Langmuir, en accord avec les niveaux d'énergie observés. (4) Enfin, les simulations Vlasov-Poisson montrent que l'évolution de la turbulence faible de Langmuir sur des temps longs tend vers un régime de turbulence forte via la formation de structures cohérentes électrostatiques (cavitons). Cette thèse illustre l'importance d'une approche complémentaire observations-simulations pour l'étude des plasmas spatiaux, ainsi que le rôle fondamental joué par les processus cinétiques.

Ce travail présente une étude des raies de plasma observées à l'aide du radar à diffusion incohérente EISCAT. Le travail est centré sur deux points. Tout d'abord, la conception d'une expérience raies de plasma pour le radar EISCAT, avec une résolution spatiale améliorée. Puis, la comparaison de données raies de plasma acquises avec le radar EISCAT avec une théorie améliorée sur l'intensité et le décalage Doppler en fréquence des raies de plasma. Pour améliorer la résolution spatiale, nous avons conçu la première expérience raies de plasma mettant en oeuvre la technique du code alternatif. Cette expérience a été tournée avec succès avec une résolution spatiale de 3 km au lieu de 40-50 km obtenu avec les techniques conventionnelles. Parce qu'il est très difficile de construire un modèle cohérent de la fonction de distribution des vitesses des électrons satisfaisant tous les intervalles d'énergies pertinents, nous avons construit une représentation adéquate de la distribution des vitesses des électrons en séparant la distribution en deux populations : la thermique et la suprathermique. La population thermique est représentée par la fonction de Spitzer qui tient compte de l'effet d'un champ électrique et/ou d'un gradient de température. La population suprathermique est déduite du flux angulaire d'énergie calculé grâce à un modèle numérique du transport des électrons. Un code numérique a été développé pour calculer la fonction diélectrique et la fonction réduite de distribution des vitesses pour toutes distributions des vitesses à deux dimensions dont nous avons besoin pour modéliser l'intensité et le décalage Doppler en fréquence des raies de plasma. Nous avons pu reproduire les caractéristiques de l'intensité et du décalage Doppler en fréquence des raies de plasma avec des données mesurées avec le radar VHF EISCAT. En particulier, nous avons identifié deux pics étroits dans la distribution des vitesses des suprathermiques comme la signature de la photo-ionisation de N_2 et O. Ces pics ont été observés sur les données. L'effet d'un gradient de température - qui produit une correction importante au décalage Doppler des raies de plasma - a été pris en compte plus précisement que précédemment en calculant numériquement les intégrales singulières, au lieu d'utiliser les premiers termes d'une expansion en séries comme auparavant. C'est important car cela a permis pour la première fois à un modèle de reproduire précisément l'intensité et le décalage Doppler des raies de plasma mesurés par une expérience EISCAT.

Untersuchungen an Monoschichten amphiphiler Lipide auf wässriger Lösung sind in der Grenzflächenforschung von grundlegender Bedeutung. Aufgrund der Anwendbarkeit zahlreicher analytischer Methoden sind schwimmende unlösliche Monoschichten als Modellsysteme sehr geeignet, um Ordnung und Strukturbildung sowie den Transport von Materie in zwei Dimensionen oder die Wechselwirkung von Molekülen an der Grenzfläche mit Teilchen in Lösung (Stichwort &ldquo;molekulare Erkennung&rdquo;) zu studieren. Aus dem Verhalten von Monoschichten lassen sich z. B. Rückschlüsse ziehen auf die Eigenschaften von Lipidschichten auf festen Substraten oder in biologischen Membranen. <br /> Diese Arbeit befasst sich mit spezifischen und fundamentalen Wechselwirkungen in Monoschichten sowohl auf molekularer als auch auf mikroskopischer Ebene und deren Beziehung zu Gitterstruktur, Aussehen und thermodynamischem Verhalten von Monoschichten an der Wasser/Luft Grenzfläche. Als Modellsystem werden hauptsächlich Monoschichten langkettiger Fettsäuren verwendet, da in ihnen die molekularen Wechselwirkungen durch Änderung des Subphasen-pH-Werts über den Dissoziationsgrad gezielt und schrittweise verändert werden können. Ausser über die Subphasenzusammensetzung werden die molekularen Wechselwirkungen auch über die Temperatur und die Monoschichtzusammensetzung systematisch variiert. Mit Hilfe von Isothermen- und Oberflächenpotentialmessungen, Brewsterwinkel-Mikroskopie, Röntgenbeugung unter streifendem Einfall und polarisationsmodulierter Infrarot-Reflexions-Absorptions-Spektroskopie wird die Änderung der Monoschichteigenschaften als Funktion eines äusseren Parametern analysiert. Dabei werden aus den Röntgenbeugungsdaten quantitative Masse für die molekularen Wechselwirkungen und für die Kettenkonformationsordnung in Monoschichten abgeleitet. <br /> Zu den interessantesten Ergebnissen dieser Arbeit zählen die Aufklärung des Ursprungs von regelmässigen polygonalen und dendritischen Domänenformen, die vielfältige Wirkung von Cholesterin auf die Molekülpackung und Gitterordnung langkettiger Amphiphile, sowie die Entdeckung einer abrupten Änderung in den Kopfgruppenbindungswechselwirkungen, der Kettenkonformationsordnung und des Phasenübergangsdrucks zwischen geneigten Monoschichtphasen in Fettsäuremonoschichten nahe pH 9. Zur Deutung des letzten Punkts wird ein Modell für die Kopfgruppenbindungsstruktur von Fettsäuremonoschichten als Funktion des pH-Werts entwickelt. / Research on monolayers of amphiphilic lipids on aqueous solution is of basic importance in surface science. Due to the applicability of a variety of surface sensitive techniques, floating insoluble monolayers are very suitable model systems for the study of order, structure formation and material transport in two dimensions or the interactions of molecules at the interface with ions or molecules in the bulk (headword 'molecular recognition'). From the behavior of monolayers conclusions can be drawn on the properties of lipid layers on solid substrates or in biological membranes.<br /> This work deals with specific and fundamental interactions in monolayers both on the molecular and on the microscopic scale and with their relation to the lattice structure, morphology and thermodynamic behavior of monolayers at the air-water interface. As model system especially monolayers of long chain fatty acids are used, since there the molecular interactions can be gradually adjusted by varying the degree of dissociation by means of the suphase pH value. For manipulating the molecular interactions besides the subphase composition also temperature and monolayer composition are systematically varied. The change in the monolayer properties as a function of an external parameter is analyzed by means of isotherm and surface potential measurements, Brewster-angle microscopy, X-ray diffraction at grazing incidence and polarization modulated infrared reflection absorption spectroscopy. For this a quantitative measure for the molecular interactions and for the chain conformational order is derived from the X-ray data. <br /> The most interesting results of this work are the elucidation of the origin of regular polygonal and dendritic domain shapes, the various effects of cholesterol on molecular packing and lattice order of long chain amphiphiles, as well as the detection of an abrupt change in the head group bonding interactions, the chain conformational order and the phase transition pressure between tilted phases in fatty acid monolayers near pH 9. For the interpretation of the latter point a model of the head group bonding structure in fatty acid monolayers as a function of the pH value is developed.

We present results on the ionospheric structure around Titan observed during numerous deep (&lt;1000 km) flybys by the Cassini spacecraft. Our results are based on measurements by the radio and plasma wave science instrument, in particular the Langmuir probe. In addition, data from the magnetometer and electron spectrometer have contributed. The ionosphere of Titan is created when the atmosphere of the moon becomes ionised. There are several mechanisms that contribute to this, the most important of which are considered to be photoionisation by EUV from the Sun with associated photoelectron ionisation, and particle impact ionisation by electrons and ions from Saturn’s corotating magnetosphere. We investigate the influence of the solar zenith angle on the electron number density at the ionospheric peak. The results show on average four times more plasma on the dayside compared to the nightside, with typical densities of 2500 – 3500 cm-3 and 400 – 1000 cm-3, respectively. In a complementary study, we make a case study of a nightside flyby and show that the altitude structure of the deep ionosphere is reproducible by a simple electron impact ionisation model. Taken together, this leads to the conclusion that solar photons are the main ionisation source of the dayside ionosphere. However, magnetospheric particle precipitation also contributes and can explain the electron densities seen on the nightside. As Titan does not exhibit any large intrinsic magnetic field, the fact that it is embedded in the magnetosphere of Saturn means that the Kronian field drapes around the moon and gives rise to an induced magnetosphere. We show that there are currents of the order of 10 – 100 nA m-2 flowing in the ionosphere of the moon. Associated with the currents are perpendicular electric fields ranging from 0.5 to 3 µV m-1. Finally, we investigate measurements obtained during T70, the deepest Titan flyby performed to date. We show that there is a substantial amount of negative ions present below an altitude of 900 km. This confirms previous result by the electron spectrometer, showing negative ions at higher altitudes in Titan’s ionosphere.

In this thesis the interactions in cellulose systems havebeen studied with emphasis on surface forces and adsorptionphenomenon. The study was limited to surfaces and polymers ofinterest for papermaking. During papermaking both therunability of the paper machine as well as the properties ofthe final paper will depend on the molecular interactionsbetween the components present in the suspension. The objectiveof this work was to gain a better understanding of theseinteraction forces and how they are affected by solutionconditions like pH and electrolyte concentration. The maintechniques employed for this purpose were direct surface forcemeasurements using both the interferometric surface forceapparatus (SFA) and the atomic force microscopy (AFM)colloidal-probe technique. In addition, both electronspectroscopy for chemical analysis (ESCA) and AFM imaging wereused for surface characterisation and to study adsorptionbehaviour. Since a smooth and transparent surface is needed forsurface force studies using SFA, Langmuir-Blodgett films ofcellulose were employed. The interactions between cellulose surfacesand xylansurfaces were studied. Cellulose is the main constituent of thewood fibre. In close association with cellulose in the cellwall are the hemicelluloses, xylan being a commonhemicellulose. Steric forces were found to dominate theinteractions between these substances in aqueous solutions.Still factors like charge density, solution pH and electrolyteconcentration were important. The adhesion between cellulosesurfaces in air depended on the contact area. The effect of acationic polyelectrolyte on the forces between cellulosesurfaces and between cellulose and mineral surfaces wasinvestigated to obtain a better understanding of the effects ofcationic retention and strength additives. In the presence of acationic polyelectrolyte the forces at large distances weredominated by double-layer repulsion. Bridging attraction was insome cases observed, but the presence and magnitude of thisforce was dependent on the properties of the substratesurface. Lignin on the fibre surface affects brightness, swelling andstrength of paper. In addition, dissolved lignin interfereswith added polymers during papermaking. For this reason theadsorption of lignin on cellulose fibre surfaces was explored.The adsorption of lignin was influenced by the concentration oflignin in solution and by the electrolyte composition of thesolution. The retention of lignin was affected by the presenceof a cationic polyelectrolyte and particularly by how thepolyelectrolyte was added. The AFM imaging revealed thestructure of the adsorbed lignin, which varied with the way ofadding the polyelectrolyte, and gave an idea about theadsorption mechanism. The effect of lignin on strengthproperties of paper sheets was also evaluated. Keywords: cellulose, hemicellulose, xylan, lignin, surfaceforces, adsorption, polyelectrolyte, SFA, AFM, ESCA,Langmuir-Blodgett films, chitosan, steric forces,bridging,adhesion

The profile of the poloidal velocity in the edge region of tokamak plasmas has been identified as playing a major role in the confinement of particles and energy. It has been suggested that a strongly sheared poloidal flow can reduce particle and energy losses by the stabilization of unstable modes and decorrelation of turbulence the edge region of the plasma. A Gundestrup probe, a Mach probe array, is used to measure both the parallel and perpendicular flow velocities in the Saskatchewan Torus-Modified (STOR-M) tokamak during several discharge conditions. It is observed that during Ohmic discharges there is no velocity shear and the direction of the parallel flow is independent of the direction of the toroidal magnetic field. During H-mode induced by a turbulent heating current pulse, a region of strong velocity shear develops in the plasma edge and an edge transport barrier develops. This results in a short period of improved particle and energy confinement with reduced fluctuation amplitudes. During electrode biasing experiments, a stainless steel biasing electrode is inserted into the plasma up to r = 82 mm and biased to +500 V relative to the vacuum chamber. It is observed that the particle confinement improves during the biasing phase while the energy confinement is degraded. A region of weak shear in the poloidal flow is observed in the plasma scrapeoff layer (SOL). The results from STOR-M are compared with results from data taken in the Czech Academy of Sciences Torus (CASTOR) tokamak during both Ohmic discharges and discharges with electrode biasing.

The profile of the poloidal velocity in the edge region of tokamak plasmas has been identified as playing a major role in the confinement of particles and energy. It has been suggested that a strongly sheared poloidal flow can reduce particle and energy losses by the stabilization of unstable modes and decorrelation of turbulence the edge region of the plasma. A Gundestrup probe, a Mach probe array, is used to measure both the parallel and perpendicular flow velocities in the Saskatchewan Torus-Modified (STOR-M) tokamak during several discharge conditions. It is observed that during Ohmic discharges there is no velocity shear and the direction of the parallel flow is independent of the direction of the toroidal magnetic field. During H-mode induced by a turbulent heating current pulse, a region of strong velocity shear develops in the plasma edge and an edge transport barrier develops. This results in a short period of improved particle and energy confinement with reduced fluctuation amplitudes. During electrode biasing experiments, a stainless steel biasing electrode is inserted into the plasma up to r = 82 mm and biased to +500 V relative to the vacuum chamber. It is observed that the particle confinement improves during the biasing phase while the energy confinement is degraded. A region of weak shear in the poloidal flow is observed in the plasma scrapeoff layer (SOL). The results from STOR-M are compared with results from data taken in the Czech Academy of Sciences Torus (CASTOR) tokamak during both Ohmic discharges and discharges with electrode biasing.

Effects of a magnetic field on the double-probe technique are studied experimentally by means of symmetric floating computer controlled fast double probes in low and intermediate pressure plasmas. In addition, the effects of the magnetic field on the electron temperature, electron density, and electric field have been investigated. As it is expected, when there is no magnetic field, properties of the discharge plasma are best described by Langmuir theory. Whereas, when there&rsquo / s a magnetic field of sufficient strength Schottky&rsquo / s theory of ambipolar diffusion applies.