Physical vapour deposition technologies have been on the fast track of development for the last two decades due to their ability to meet demands for special materials and performance tools. The ever increasing complexity of the required coating microstructure and chemical composition can be achieved only by the development of PVD technology and in particular plasma sources for vapour generation that can provide the necessary tools. This thesis describes plasma diagnostic studies of plasma discharges, developments of plasma sources and deposition of CrN coatings. Initially the project investigated vacuum arc plasma discharges used in the Hauzer HTC1000/ABS industrially sized coater. The attention was concentrated to the plasma pretreatment by low energy (1200 - 3600 eV) Cr ion implantation into substrates, which contributed to an enhanced adhesion of subsequently deposited TiAIN coatings. Optical emission spectroscopy (OES), electrostatic probes, and time-of-flight (TOF) spectroscopy were used to study the interactions of the arc plasma with the gas atmosphere in the chamber. It was shown that increasing the pressure of Ar gas had a strong effect on the composition of the generated metal ion flux as the density of highly charged metal species reduced significantly to the benefit of gas ionisation. The mechanisms behind these observations are discussed and supported by further experiments. Based on the plasma diagnostic results, a novel two-stage pretreatment method was developed which allowed an enhanced adhesion due to faster sputter cleaning of the substrate surface and more efficient metal ion incorporation in the substrate material. In the final stages of the project a novel high power pulsed magnetron sputtering (HIPIMS) process utilising peak power densities of 3000 Wcm[-2] was investigated. OES studies showed the first evidence of doubly charged Cr and Ti ions generated by the HIPIMS discharge. Peak plasma densities of 10[13] cm[-3] were measured and, in the case of Cr, metal ions were found to constitute 30% of the total deposition flux to substrates. The influence of power on the plasma density, plasma composition and time evolution of the plasma was studied in detail using OES and electrostatic probes. The conditions for glow-to-arc transition were investigated. CrN coatings (thickness 2 mum) were deposited for the first time using HIPIMS of Cr in a nitrogen atmosphere. The microstructure observed in transmission electron microscopy cross sections was highly dense and droplet free and contributed to an excellent corrosion and wear resistance superior to 20 mum thick electroplated hard Cr, and CrN coatings deposited by arc and unbalanced magnetron sputtering. The HIPIMS discharge was used also for pretreatment of substrates with metal ions analogous to the one performed previously with arc discharge. High adhesion was achieved as indicated by the scratch test critical load value Lc = 85 N.Finally, at an intermediate stage of the PhD project, an alternative source providing metal ionisation was studied. It was based on a radio frequency (RF) powered coil that was inductively coupled to a magnetron sputtering discharge. Energy resolved mass spectroscopy and OES in a laboratory-sized version of the plasma source revealed elevated metal ion densities and high ion energies of the order of 60 eV. This source was upscaled, installed, and tested successfully in the industrially sized Hauzer coater. The ion-to-neutral ratio at the substrate position could be increased 5-fold for a similar increase in RF power.

Les interactions entre décharges Nanosecondes Répétitives Pulsées et des écoulements de gaz laminaires sont étudiées. L’influence d’écoulements d’air stationnaires et instationnaires sur les régimes de décharges NRP est étudiée et les résultats interprétés au moyen de nombres adimensionnels afin de mettre en évidence l’effet synergétique du nombre d’impulsions appliquées, ainsi que de la puissance des pulses, sur le régime de décharge NRP observé. Une étude de l’effet de flammes méthane-air laminaires prémélangées sur des décharges NRP est ensuite présentée. Dans les deux configurations expérimentales utilisées, un effet de la flamme sur les décharges NRP en régime couronne est démontré. De plus, l’influence du mélange de gaz entre les électrodes sur la forme des décharges plasma est démontrée. Enfin, l’effet de décharges NRP en régime couronne sur des flammes plates laminaires prémélangées est étudié. Les décharges NRP entraînent un déplacement de la flamme vers l’amont. Des simulations numériques de flammes axisymétriques sont ensuite réalisées.Cette étude met en évidence l’effet des décharges NRP sur une flamme et donne des indications sur le phénomène à l’origine de cet effet, à savoir l’augmentation de la vitesse de flamme laminaire par le biais de la génération de chaleur et d’ozone par les décharges plasma. De plus, l’étude démontre l’effet opposé de mélanges réactifs sur les décharges NRP. Les décharges NRP sont modifiées par le phénomène de convection du gaz entre les électrodes ainsi que par la constitution de ce gaz. / The interactions between Nanosecond Repetitively Pulsed plasma discharges and laminar reactive flows are investigated.The influence of steady and unsteady air flows on the regimes of NRP discharges is investigated. The results are interpreted with the use of characteristic dimensionless numbers; this analysis allows to highlight a synergetic effect between the high-voltage pulses as well as the power of the pulses on the NRP discharge regime observed. Then, an investigation of the effect of laminar premixed methane-air flames on NRP discharges is presented. An effect of the flame on the NRP corona discharges is displayed; this effect is a function of the proximity of the flame to the discharges. the influence of the inter-electrode gas mixture on the shape of the plasma discharges is also visually assessed. Finally, the effect of NRP corona discharges on laminar premixed flat flames is investigated. The NRP discharges induce a displacement of the flame in the upstream direction which is verified with numerical simulations.This study displays the effect of NRP discharges on a flame and gives insights as to the phenomenon underlying this effect. Moreover, the study highlights the opposite effect of reactive mixtures on the NRP discharges. The visual modification of the NRP discharges is a function of the transport of the inter-electrode flow and of the nature of the gas itself.

The effect of temperature on fuel-air ignition and combustion (thermal effects) have been widely studied and well understood. However, a comprehensive understanding of nonequilibrium plasma effects (in situ generation of reactive species and radicals combined with gas heating) on the combustion process is still lacking. Over the past decade, research efforts have advanced our knowledge of electron impact kinetics and low temperature chain branching in fuel-air mixtures considerably. In contrast to numerous experimental investigations, research on modeling and simulation of plasma assisted combustion has received less attention. There is a dire need for development of self-consistent numerical models for construction and validation of plasma chemistry mechanisms. High-fidelity numerical models can be invaluable in exploring the plasma effects on ignition and combustion in turbulent and high-speed flow environments, owing to the difficulty in performing spatially resolved quantitative measurements. In this work, we establish a multi-scale modeling framework to simulate the physical and chemical effects of nonequilibrium, nanosecond plasma discharges on reacting flows. The model is capable of resolving electric field transients and electron impact dynamics in sub-ns timescales, as well as calculating the cumulative effects of multiple discharge pulses over ms timescales. Detailed chemistry mechanisms are incorporated to provide deep insight into the plasma kinetic pathways. The modeling framework is utilized to study ignition of H₂-air mixtures subjected to pulsed, nanosecond dielectric barrier discharges in a plane-to-plane geometry. The key kinetic pathways responsible for radicals such as O, H and OH generation from nanosecond discharges over multiple voltage pulses (ns-ms timescales) are quantified. The relative contributions of plasma thermal and kinetic effects in the ignition process are presented. The plasma generated radicals trigger partial fuel oxidation and heat release when the temperature rises above 700 K, after which the process becomes self-sustaining leading to igntion. The ignition kernel growth is primarily due to local plasma chemistry effects rather than flame propagation, and heat transport does not play a significant role. The nanosecond pulse discharge plasma excitation resulted in nearly simultaneous ignition over a large volume, in sharp contrast to hot-spot igniters. Next, the effect of nanosecond pulsed plasma discharges on the ignition characteristics of nC₇H₁₆ and air in a plane-to-plane geometry is studied at a reduced pressure of 20.3 kPa. The plasma generated radicals initiate and significantly accelerate the H abstraction reaction from fuel molecules and trigger a “self-accelerating” feedback loop via low-temperature kinetic pathways. Application of only a few discharge pulses at the beginning reduces the initiation time of the first-stage temperature rise by a factor of 10. The plasma effect after the first stage is shown to be predominantly thermal. A novel plasma-flame modeling framework is developed to study the direct coupling of steady, laminar, low-pressure, premixed flames to highly non-equilibrium, nanosecond-pulsed plasma discharges. The simulations are performed with and without a burst of 200 nanosecond discharge pulses to quantify the effect of non-equilibrium plasma on a pre-existing lean premixed H₂/O₂/N₂ (ϕ = 0.5) flame at 25 torr. Simulation results showed a significant increase in O and H densities due to plasma chemistry, with peak values increasing by a factor of 6 and a factor of 4, respectively. It is demonstrated that Joule heating alone cannot move the temperature and species profiles as far upstream (i.e. closer to the burner surface) as the pulsed plasma source of the same total power. LES (large eddy simulation) of ignition and combustion of H₂ jets injected into a supersonic O₂ crossflow is performed. Nanosecond plasma discharges are studied for their potential to produce radicals and impact on the flame-holding process. The plasma has a significant effect on the O atom distribution near the discharge domain as well as in the leeward side of the second jet. The other species distributions, however, remained unchanged with or without plasma. We believe the reason for this behavior was the high jet momentum ratios considered in the present study. The plasma generated radicals were unable to have an effect on the flame development downstream because of the strong penetration of the cold fuel jet.

La miniaturisation d’antenne est un défi important, en particulier en bande VHF où les longueurs d’onde sont grandes. Parmi les différentes techniques rencontrées dans la littérature, une approche théorique originale repose sur l’utilisation de la résonance électrostatique de sphères sub-longueur d’onde de permittivité négative (ENG pour Epsilon NeGative). L’implémentation pratique de cette solution en considérant une décharge plasma comme milieu ENG est étudiée dans ces travaux de thèse. Le plasma laisse entrevoir des potentialités intéressantes pour ce type d’antennes miniatures comme la furtivité et la reconfigurabilité en fréquence. Dans un premier temps, différents modèles analytiques sont développés afin étudier le comportement électromagnétique de petites sphères réalistes de plasma. Ces modèles permettent par ailleurs la construction de schémas numériques précis et adaptés aux simulateurs électromagnétiques commerciaux. Dans un second temps, un prototype fonctionnel est méthodiquement conçu. La solution proposée permet l’intégration du système d’excitation de la décharge plasma au sein de l’antenne sans en perturber son fonctionnement nominal. Ce prototype permet la caractérisation des paramètres plasma de la décharge et du comportement électromagnétique du résonateur sphérique à plasma. Enfin, un travail annexe d’intégration de décharges plasma dans des circuits planaires en technologie micro-ruban est présenté. Les conceptions, modélisations et caractérisations expérimentales de ces résonateurs planaires permettent de mettre en évidence les capacités du plasma pour leur accordabilité en fréquence. / Antenna miniaturisation is a major issue, especially in the VHF band whose wavelengths are significant. Amongst the solution in the litterature, a recent theoretical technique relies upon the electrostatic resonance of negative permittivity (ENG) subwavelength spheres. In this work, the use of a plasma discharge as ENG medium is under consideration. Plasma indeed suggests new potentialities for this kind of small antennas, such as stealth and frequency agility. Firstly, several analytical models are developed to study the electromagnetic response of subwavelength realistic plasma spheres. These models further allow to derive accurate numerical representations that fit commercial electromagnetic solvers. A working prototype that comprises a plasma ignition system within the antenna structure without altering its operation is then designed. It is used to both characterize the plasma discharge and the electromagnetic behavior of the plasma spherical resonator. Finally, this work is extended to the case of planar circuits by integrating a plasma discharge inside microstrip resonators. The design, the modeling and the experimental studies of these resonators highlight the ability of the plasma to tune the resonant frequency.

Dans un propulseur à courant de Hall, la création des ions et leur accélération sont régis par le même phénomène physique. L'idée du propulseur de Hall double étage (DSHT) est de découpler l'ionisation du gaz (poussée) et l'accélération des ions (ISP), de sorte à rendre le système davantage versatile. Les travaux menés durant cette thèse visent à démontrer, grâce à des essais expérimentaux, la pertinence et la faisabilité d'un tel concept. Dans un premier temps, un prototype de DSHT, baptisé ID-HALL, a été conçu et assemblé. Il est constitué d'une source inductive magnétisée insérée dans un tube en céramique et d'un étage d'accélération identique à une barrière magnétique de propulseur simple étage. La source inductive a été optimisée de sorte à réduire le couplage capacitif et à maximiser l'efficacité du transfert de puissance par ajout de pièces en ferrite et diminution de la fréquence RF d'excitation. Dans un deuxième temps, la source inductive du propulseur a été caractérisée indépendamment du propulseur en argon et xénon pour différentes pressions. Le dispositif expérimental a permis notamment de tracer une cartographie 2D de la densité et de la température. Enfin, le propulseur a été monté dans son caisson et des mesures préliminaires (caractéristiques courant-tension, mesures par sonde RPA) ont été menées. En parallèle, des simulations utilisant un modèle hybride 2D ont été effectuées en mode simple et double étage. Elles mettent en évidence un fonctionnement versatile du moteur pour des tensions inférieures à 150 V. A terme, on visera à démontrer que la densité de courant et l'énergie des ions peuvent être, dans certaines conditions, significativement découplées. / In Hall thrusters, the same physical phenomenon is used both to generate the plasma and to accelerate ions. Furthermore, only a single operating point is experimentally observed. The double stage Hall thruster (DSHT) design could allow a separate control of ionization (thrust) and ions acceleration (ISP) to make the system more versatile. The work carried out during this PhD aims to experimentally demonstrate the relevance and the feasibility of this concept. Firstly, a new design of DSHT, called ID-HALL, was proposed and a new prototype was built. It combines the concentric cylinder configuration of a single stage Hall thruster with a magnetized inductively coupled RF plasma source (ICP) whose coil is placed inside the inner cylinder. The ICP source was improved in terms of power coupling efficiency by adding ferrite parts and by decreasing the heating RF frequency. The ICP source used in the ID-HALL thruster was then characterized independently of the thruster using argon and xenon and varying pressure. The experimental setup has allowed to measure the spatial variations of the electron density and temperature. Finally, the thruster was mounted in its vacuum chamber and preliminary measures (voltage-current characteristics, RPA measurements) were led. At the same time, simulations using a two-dimensional hybrid model were performed in single and double stage. A versatile operation for voltages lower than 150 V was highlighted. An emphasis will be given to demonstrate that the current density (given by the ion flux probe) and the ions energy (given by the RPA) might be significantly decoupled.

The aim of this thesis was to elaborate the issue of the decomposition of volatile organic compounds in the Gliding Arc plasma discharge at atmospheric pressure. Technologies based on nonthermal plasma could offer a good alternative to conventional techniques for the decomposition of volatile organic compounds, such as thermal and catalytic oxidation. Gliding Arc discharge (GidArc) is a widely exploited nonthermal plasma source used for many industrial applications, such as air-pollution control. The energy efficiency, reaction selectivity or production of specific species may be achieved in this kind of plasma, and thus for various chemical processes it can be much more effective then in conventional techniques. Presented experiments are linked to the previous results published in diploma thesis, which gave us the basics for construction of new reactor and optical emission spectroscopy measurements have been done to characterize the plasma. Toluene (aromatic, unsaturated), cyclohexane (aromatic, saturated) and hexane (aliphatic, saturated) were used as the model compounds for these experiments in the concentration range from hundreds to thousands ppm. Results focused on the electrical parameters of the reactor were carried out, with the aim to operate the system at a lower energy cost. In order to get the time-resolved diagnostics of the moving plasma channel, the evolution of the plasma channel was recorded continuously by using a high-speed video camera. In next part of the work, some results concerning generation of low molecular products like nitric oxide, nitrogen dioxide, hydrogen and carbon monoxide on the discharge conditions are presented. In combustion process, undesirable mixture of toxic highmolecular by-products can be formed. Samples were therefore analysed in gas chromatograph linked to mass spectrometer, to characterize the chemical transformation pathway of VOC in plasma.

Interactions between flames and thermal phenomena are the guiding thread of this work. Flamesproduce heat indeed, but can also be affected by it. Large Eddy Simulations (LES) are used hereto investigate these interactions, with a focus on two main topics: wall heat transfer andcombustion control. In a first part, wall heat transfer in a rocket engine sub-scale CH4/O2 burner isstudied. In the context of launchers re-usability and cost reduction, which are major challenges,new propellant combinations are considered and wall heat fluxes have to be precisely predicted.The aim of this work is to evaluate LES needs and performances to simulate this kind ofconfiguration and provide a computational methodology permitting to simulate variousconfigurations. Numerical results are compared to experimental data provided by the TechnischeUniversität München (Germany). In a second part, combustion control by means of NanosecondRepetitively Pulsed (NRP) plasma discharges is studied. Modern gas turbine systems use indeedlean combustion with the aim of reducing fuel consumption and pollutant emissions. Lean flamesare however known to be prone to instabilities and combustion control can play a major role in thisdomain. A phenomenological model which considers the plasma discharges as a heat source isdeveloped and applied to a swirl-stabilized CH4/Air premixed lean burner. LES are performed inorder to evaluate the effects of the NRP discharges on the flame. Numerical results are comparedwith experimental observations made at the King Abdulla University of Science and Technology(Saudi Arabia).

<p>A small plasma generation system was first developed using a ring-pin electrode configuration with the goal of producing a plasma disk at the burner outlet. Two distinct plasma regimes were identified: diffused and filamentary. Diffuse discharges were generated at low frequencies while filamentary discharges were generated at moderate to high frequencies. The induced flow fields generated by both diffuse and filamentary plasma discharges were investigated using high-speed schlieren visualization and particle image velocimetry. The rise in gas temperature was measured using optical emission spectroscopy. Lastly, the electrical properties for both types of plasma discharges was measured. The measurements provided a set of pulse parameters for the investigation of the plasma-flame interaction on the atmospheric pressure burner. </p> An atmospheric pressure plasma-assisted burner with a ring-pin electrode geometry was designed and fabricated to investigate the effect of nanosecond repetitively pulsed discharges on methane-air flames. The burner can produce both Bunsen-type and swirl-stabilized flames (helical vane swirlers, swirl number of 0.62) with a modular design to allow for a removable block swirler component. Flame chemiluminescence and direct imaging of flame structure and dynamics was done to understand the burner’s operating limits. The burner can operate 6 – 13 kW flames, with flames stabilizing at approximately 2 inches above the burner exit. The effect of air flow rate on plasma formation was investigated and it was found that the high velocity of the incoming gas changes the plasma regime and electrical properties. Finally, the plasma discharge was applied on lifted, swirled flames and used for plasma-assisted ignition. For lifted swirled flames, we found that a minimum of 100 pulses is required to generate a filamentary discharge in the air stream. Higher number of pulses at high frequencies appeared to extinguish the primary flame. A minimum of 6000 was used for ignition. The plasma-assisted burner will allow for future studies to investigate the plasma flame coupling for various conditions using a wide variety of diagnostics. <br>

Les interactions entre les flammes et les phénomènes thermiques sont le fil conducteur de ce travail. En effet, les flammes produisent de la chaleur, mais peuvent aussi être affectées par des transferts ou des sources de chaleur. La Simulation aux Grandes Echelles (SGE) est utilisée ici pour étudier ces interactions, en mettant l’accent sur deux sujets principaux: le transfert de chaleur aux parois et le contrôle de la combustion. Dans un premier temps, on étudie le transfert de chaleur aux parois dans un modèle de brûleur CH4/O2 de moteur-fusée. Dans un contexte deréutilisabilité et de réduction des coûts des lanceurs, qui constituent des enjeux majeurs, de nouveaux couples de propergols sont envisagés et les flux thermiques à la paroi doivent êtreprécisément prédits. Le but de ce travail est d’évaluer les besoins et les performances des SGEpour simuler ce type de configuration et de proposer une méthodologie de calcul permettant desimuler différentes configurations. Les résultats numériques sont comparés aux donnéesexpérimentales fournies par la Technische Universität München (Allemagne). Dans un deuxième temps, le contrôle de la combustion au moyen de décharges de plasma de type NRP (en anglaisNanosecond Repetitively Pulsed) est étudié. Les systèmes de turbines à gaz modernes utilisent en effet une combustion pauvre dans le but de réduire la consommation de carburant et les émissions de polluants. Les flammes pauvres sont connues pour être sujettes à des instabilités et le contrôle de la combustion peut jouer un rôle majeur dans ce domaine. Un modèle phénoménologique qui considère les décharges de plasma comme une source de chaleur est développé et appliqué à un brûleur pauvre avec prémélange CH4/Air stabilisé par un swirler. LesSGE sont réalisées afin d’évaluer les effets des décharges NRP sur la flamme. Les résultats numériques sont comparés aux observations expérimentales faites à la King Abdulla University ofScience and Technology (Arabie Saoudite) / Interactions between flames and thermal phenomena are the guiding thread of this work. Flamesproduce heat indeed, but can also be affected by it. Large Eddy Simulations (LES) are used hereto investigate these interactions, with a focus on two main topics: wall heat transfer andcombustion control. In a first part, wall heat transfer in a rocket engine sub-scale CH4/O2 burner isstudied. In the context of launchers re-usability and cost reduction, which are major challenges,new propellant combinations are considered and wall heat fluxes have to be precisely predicted.The aim of this work is to evaluate LES needs and performances to simulate this kind ofconfiguration and provide a computational methodology permitting to simulate variousconfigurations. Numerical results are compared to experimental data provided by the TechnischeUniversität München (Germany). In a second part, combustion control by means of NanosecondRepetitively Pulsed (NRP) plasma discharges is studied. Modern gas turbine systems use indeedlean combustion with the aim of reducing fuel consumption and pollutant emissions. Lean flamesare however known to be prone to instabilities and combustion control can play a major role in thisdomain. A phenomenological model which considers the plasma discharges as a heat source isdeveloped and applied to a swirl-stabilized CH4/Air premixed lean burner. LES are performed inorder to evaluate the effects of the NRP discharges on the flame. Numerical results are comparedwith experimental observations made at the King Abdulla University of Science and Technology(Saudi Arabia).