High repetition frequency nanosecond pulses have been shown to be effective in generating plasma for reconfigurable RF systems. In the present work, the focus is on simulation of nanosecond pulsed discharges in Argon at 3 Torr and inter-electrode spacing of 2 cm with pulse repetition frequency of 30 kHz. The simulations have been carried out using a hybrid model, HPEM code developed by Prof. Mark J. Kushner at University of Michigan. The simulation results were compared to the experiments. Although a mismatch of results has been found, the simulations seem to capture the underlying physical phenomena. The electron temperature in the afterglow of the pulse seems to decay faster compared to the electron number density in the plasma, which is an essential feature in designing low noise plasma antennas.

Dielectric Barrier Discharge (DBD) excimer lamp is a very attractive source for Ultraviolet (UV) radiation. It has a number of advantages compared to the mercury lamp which is the main lamp used in the industry for UV production. Some of these advantages are instant UV radiation (no warm-up period), narrow UV spectrum, longer life times and simple construction. The DBD UV lamp can be used in number of applications like water disinfection, Plasma Display Panels (PDP) and surface treatment in the semiconductor industry. Yet, the full industrial application of this lamp still faces some problems mainly related to finding the optimum electrical driver to maximize the efficiency of such a lamp. This includes the type of the electrical waveform to generate and the power electronic driver to produce it. In this thesis, firstly a physically based circuit model for the DBD lamp using the Finite Volume Method (FVM) is developed. This model provides the electrical and optical characteristics of the lamp. Using this model the sensitivity of the lamp efficiency to the proposed electrical waveform has been determined. Secondly, the order of this FVM model has been reduced to obtain a model which is used in the design procedure of the proposed driver. Since the DBD lamp has a capacitive nature, a current controlled driver is proposed in this thesis as opposed to most of the published drivers which are voltage controlled drivers. The design of this driver is intended to enhance the electrical to optical efficiency of the lamp and therefore enhancing the overall efficiency of the system. The driver topology permits direct control of the peak lamp current and the operating frequency of the supplied current to the DBD lamp. The width of the current pulses is determined by the transformer magnetizing inductance and the lamp capacitance. Experimental results of the proposed driver connected to a XeCl DBD lamp are presented to validate the performance of the driver and to prove the concept of such a current controlled driver. The proposed driver performance is compared to a voltage source driver which was also implemented. The proposed driver produced higher overall system efficiency but at the expense of a reduction in the driver efficiency as compared to the voltage source driver. The complete system, which consists of the developed FVM based model and the equivalent circuit of the proposed driver, was simulated and the results were compared to the experimental results to validate the accuracy of the developed model for the DBD lamp.

<p>Large scale and cost-efficient synthesis of carbon nanostructured materials has garnered tremendous interest over the last decade owing to their plethora of engineering and bio-science applications. One promising method is roll-to-roll radio frequency chemical vapor deposition and this work presents a computational investigation of the capacitively coupled radio frequency plasma in such a system. The system operates at moderate pressures (less than 30 mbar) with an 80 kHz square wave voltage input. The computational model aids the understanding of plasma properties and α-γ transition parameters which strongly influence the nanostructure deposition characteristics in the system. One dimensional argon and hydrogen plasma models are developed to characterize the effects of input voltage, gas pressure, frequency, and waveform on the plasma properties. A hybrid mode which displays the characteristics of both α and γ discharges is found to exist for the low cycle frequency 80 kHz square wave voltage input due to the high frequency harmonics associated with a square waveform. The threshold voltage at which the transition between the different regimes occurs is higher for hydrogen than for argon owing to its diatomic nature. Collision radiative modeling is performed to predict the argon emission intensity in the discharge gap. The results are found to lie within 16% of the optical emission spectroscopy measurements with better agreement at the center of the discharge, where the measurement uncertainty is low and the emission by ions is not significant. A quasi-zero dimensional steady state chemistry model which uses the hydrogen plasma properties as inputs predicts high concentrations of C₂H, C₂H₂, C₂H₃⁺, C₂H₄⁺and C₂H₆⁺during carbon nanostructure deposition.</p> <p> </p> <p>Carbon nanostructures are popularly used as field emitters. Field emission based microplasma actuators generate highly non-neutral surface discharges that can be used to heat, pump, and mix the flow through microchannels and offer an innovative solution to the problems associated with microcombustion. They provide a constant source of heat to counter the large heat loss through the combustor surface, they aid in flow transport at low Reynolds numbers without the use of moving parts, and they provide a constant supply of radicals to promote chain branching reactions. This work presents two actuator concepts for the generation of field emission microplasma, one with offset electrodes and the other with planar electrodes. They operate at input voltages in the 275 to 325 V range at a frequency of 1 GHz which is found to be the most suitable value for flow enhancement. The momentum and energy imparted by the charged particles to the neutrals as modeled by 2D Particle-In-Cell with Monte Carlo Collisions (PIC/MCC) are applied to actuate flow in microchannels using 2D Computational Fluid Dynamics modeling. The planar electrode configuration is found to be more suitable for the purpose of heating, igniting and mixing the flow, as well as improving its residence time through a 10 mm long microcombustor. The combustion of hydrogen and air with the help of 4 such actuators, each with a power consumption of 47.5 mW/cm, generates power with an efficiency of 28.8%. Coating the electrode surface with carbon nanostructures improves the combustion efficiency by a factor of 2.5 and reduces the input voltage by a factor of 6.5. Such microcombustors can be applied to all battery based systems requiring micropower generation with the ultimate goal of “generating power on a chip'”.</p>

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.

Dielectric Barrier Discharge (DBD) excimer lamp is a very attractive source for Ultraviolet (UV) radiation. It has a number of advantages compared to the mercury lamp which is the main lamp used in the industry for UV production. Some of these advantages are instant UV radiation (no warm-up period), narrow UV spectrum, longer life times and simple construction. The DBD UV lamp can be used in number of applications like water disinfection, Plasma Display Panels (PDP) and surface treatment in the semiconductor industry. Yet, the full industrial application of this lamp still faces some problems mainly related to finding the optimum electrical driver to maximize the efficiency of such a lamp. This includes the type of the electrical waveform to generate and the power electronic driver to produce it. In this thesis, firstly a physically based circuit model for the DBD lamp using the Finite Volume Method (FVM) is developed. This model provides the electrical and optical characteristics of the lamp. Using this model the sensitivity of the lamp efficiency to the proposed electrical waveform has been determined. Secondly, the order of this FVM model has been reduced to obtain a model which is used in the design procedure of the proposed driver. Since the DBD lamp has a capacitive nature, a current controlled driver is proposed in this thesis as opposed to most of the published drivers which are voltage controlled drivers. The design of this driver is intended to enhance the electrical to optical efficiency of the lamp and therefore enhancing the overall efficiency of the system. The driver topology permits direct control of the peak lamp current and the operating frequency of the supplied current to the DBD lamp. The width of the current pulses is determined by the transformer magnetizing inductance and the lamp capacitance. Experimental results of the proposed driver connected to a XeCl DBD lamp are presented to validate the performance of the driver and to prove the concept of such a current controlled driver. The proposed driver performance is compared to a voltage source driver which was also implemented. The proposed driver produced higher overall system efficiency but at the expense of a reduction in the driver efficiency as compared to the voltage source driver. The complete system, which consists of the developed FVM based model and the equivalent circuit of the proposed driver, was simulated and the results were compared to the experimental results to validate the accuracy of the developed model for the DBD lamp.

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L'intégration des nouveaux éléments basés sur la physique des plasmas dans le domaine des circuits et des systèmes micro-ondes est l'objectif de ce travail. En profitant des caractéristiques électromagnétiques des plasmas et en jouant sur leur architecture, on développe des micro-commutateurs micro-ondes et d'autres circuits radio et hyperfréquences en technologies microrubans ou en guide d'onde… La simulation de la propagation des ondes électromagnétiques dans un plasma et les études de l'interaction entre un plasma et les ondes électromagnétiques nécessite la connaissance des paramètres fondamentaux du plasma comme la permittivité. C'est pour cela qu'on étudie aussi les mesures plasmas par différents techniques comme la transmission/réflexion des ondes électromagnétiques, la perturbation des cavités résonnantes, ... Un schéma électrique équivalent modélisant un micro-commutateur hyperfréquence en plasma, est obtenu grâce aux mesures des courants de décharge électrique, à la rétro-simulation et aux techniques de modélisation numérique. Un coupleur directif hybride compact est utilisé pour les mesures plasmas en assurant la protection du matériel et de l'équipement de mesure des signaux d'un plasma. / Integration of new plasma-based elements for RF and microwave circuits and systems is the goal of this work. Taking advantage of electromagnetic characteristics of plasmas and playing on their architecture, we develop microwave micro-switches and other RF and microwave circuits by different technologies such as microstrip, waveguide circuits. The simulation of the propagation of electromagnetic waves in plasma and studying the interaction between plasma and electromagnetic waves require a pre-knowledge of its basic intrinsic parameters such as permittivity for that we also study measures and plasma different techniques like transmission/reflection of an electromagnetic waves, cavity perturbation technique... An equivalent electrical circuit modeling the plasma will be used for modeling microwave micro-switches. It is obtained by measurements of electric discharge currents, the reverse CAD simulation and numerical modeling techniques. A compact hybrid directional coupler is used to measure plasma and to protect test equipment from dangerous signals of the electrical discharge.

Cette thèse propose différentes méthodes théoriques et numériques pour simuler à coût réduit le comportement des plasmas ou des faisceaux de particules chargées sous l’action d’un champ magnétique fort. Outre le champ magnétique externe, chaque particule est soumise à champ électromagnétique créé par les particules elles-mêmes. Dans les modèles cinétiques, les particules sont représentées par une fonction de distribution f(x,v,t) qui vérifie l’équation de Vlasov. Afin de déterminer le champ électromagnétique, cette équation est couplée aux équations de Maxwell ou de Poisson. L’aspect champ magnétique fort est alors pris en compte par un dimensionnement adéquat qui fait apparaître un paramètre de perturbation singulière 1/ε. / This thesis is devoted to the study of charged particle beams under the action of strong magnetic fields. In addition to the external magnetic field, each particle is submitted to an electromagnetic field created by the particles themselves. In kinetic models, the particles are represented by a distribution function f(x,v,t) solution of the Vlasov equation. To determine the electromagnetic field, this equation is coupled with the Maxwell equations or with the Poisson equation. The strong magnetic field assumption is translated by a scaling wich introduces a singular perturbation parameter 1/ε.