Dissertationen zum Thema „Plasmas (gaz ionisés) – Confinement – Modèles mathématiques“
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Isoardi, Livia. „Modelisation du transport dans le plasma de bord d'un tokamak“. Aix-Marseille 3, 2010. http://www.theses.fr/2010AIX30066.
Der volle Inhalt der QuelleMage, Lucile. „Caractérisation d'un réacteur plasma de type résonance cyclotronique électronique à antenne longue : évaluation du réacteur pour un processus de dépôt“. Toulouse 3, 1997. http://www.theses.fr/1997TOU30174.
Der volle Inhalt der QuelleSama, Juvert Njeck. „The effect of beta on the nonlinear generation of zonal structures in experimentally relevant tokamak plasmas“. Electronic Thesis or Diss., Université de Lorraine, 2024. https://docnum.univ-lorraine.fr/ulprive/DDOC_T_2024_0111_SAMA.pdf.
Der volle Inhalt der QuelleSpatial gradients in temperature and density in tokamak plasmas excite micro-instabilities, which interact non-linearly to form turbulence. Turbulence increases heat and particle transport, reducing the energy confinement time. Understanding turbulence dynamics is important to achieving the conditions for self-sustained combustion in a fusion reactor. Zonal structures (ZS), i.e., the axisymmetric perturbations of a tokamak plasma, are generated by turbulence and play an important role in its self-consistent saturation. Two types of ZS exist: zero-frequency zonal flows (ZFZF) and geodesic acoustic modes (GAM). Recent electrostatic nonlinear studies of turbulence-excited GAMs in Asdex upgrade (AUG) have shown that radially extended GAM structures can be excited by turbulence. The dynamics of GAMs have recently been shown to change when going from low confinement mode (L-mode) to intermediate confinement mode (I-mode) and from I-mode to high confinement mode (H mode). In particular, GAMs are observed experimentally in L-mode and I-mode and are more rarely observed in H-mode. A first linear model explaining this behavior was constructed using the combination of their Landau and continuum damping, which affects GAMs more strongly in H mode. Zonal structures generated by the GAM modes can interact and couple with the zonal structures generated by the turbulence induced by the instabilities, such as the so-called ITG (Ion Temperature Gradient) type modes. Kinetic and particle trapping effects can oppose Landau damping and dominate the zonal flow dynamics generated by ITGs. It is particularly important to understand the dynamics of zonal flows, their excitation mechanism, and their interaction with different plasma instabilities and turbulence. In this thesis, the dynamics of GAMs and ZFZF are studied in different configurations. In Chapter Two, we study the linear dynamics of geodesic acoustic modes in anisotropic plasma. We studied the effects of ion temperature anisotropy that can be introduced by various plasma heating mechanisms, such as neutral beam injection (NBI), ion cyclotron resonance heating (ICRH), and electron cyclotron resonance heating (ECRH). We show that ion temperature anisotropy can significantly modify the damping rate of the geodesic acoustic mode. In the third chapter of this thesis, we developed a global linear theory to study the linear dynamics of plasma waves in tokamak geometry for arbitrary particle distribution functions. We report a generalized expression of the GAM frequency in terms of the distribution function of the ion species and the mode. The generalized mode structure equation of the Alfven/ITG mode structure equation is in the large poloidal mode number unit. In chapter four, the numerical simulation code ORB5 is discussed in detail, pointing out all assumptions and domains of applicability. In chapter five. Our main focus was investigating the impact of zonal flows forced-driven by Alfven modes on linear ITG instabilities. We isolated this effect from self-consistent nonlinear electromagnetic simulations and tested it independently using a set of numerical tools that will be discussed later. We show that zonal flows forced-driven by Alfven modes can significantly mitigate ITG instabilities in an experimentally relevant scenario magnetic geometry. In chapter six, we review the "particle mode" model. We show that the synchronization of particle modes leads to the amplification of the zonal flows, which occurs even when the ions and electrons admit to the same temperature
Militello, Fulvio. „Linear theory and saturation of tearing modes in plasmas“. Aix-Marseille 1, 2006. http://www.theses.fr/2006AIX11027.
Der volle Inhalt der QuelleIn this work, the linear theory and the saturation of the Tearing Mode in plasmas are investigated. This instability is associated to magnetic reconnection, and has been proved a valid model to explain several plasma processes, such as the solar flares, the behavior of Earth's magnetosphere and the physics of the experimental devices used in nuclear fusion research (Tokamak). Specific attention is devoted to the influence of the asymmetries of the equilibrium current density. It is shown that an asymmetric equilibrium can affect significantly both the linear dispersion relation of the mode and the overall saturation level. A rigorous mathematical procedure, which employs perturbative techniques, is developed to solve the nonlinear saturation problem. This procedure allows reliable predictions of the final width of the magnetic island associated with the instability. Three relevant physical regimes of plasma are investigated, depending on the model for the evolution of the resistivity, which may be affected by the growth of the mode. In the final section of the work, part of the analytical results obtained is employed in the understanding of the Tearing Mode in a physical framework relevant for fusion plasmas. In particular, the mathematical model is extended to include effects related to the so-called Neoclassical description of the Tokamak. The complexity of the nonlinear problem does not allow a straightforward analytical approach, and has to be handled with numerical tools. A systematic numerical investigation of the saturation of the Neoclassical Tearing Mode is presented, the results of which are interpreted with a simplified theoretical model
Coulette, David. „Simulation numérique de modèles cinétiques réduits pour l'étude de la dynamique des plasmas de fusion par confinement magnétique“. Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0159/document.
Der volle Inhalt der QuelleThe research exposed therein is developed in the context of the study of turbulent energy and particle transport phenomena occuring in magnetically confined fusion plasmas. A study of the ion temperature gradient instability, one of the main sources of such turbulent transport, is carried out using a gyrokinetic model. The main originality of this work lies in the use of a reduced model, the so-called Multi-Water-Bag model, which allows to reduce the problem dimension while preserving kinetic effects. The model is developed in two types of confinement field geometries. In cylindrical geometry, the growth of the instability is analysed by the mean of three dynamical models : linear, quasi-linear and non-linear. Starting from a given unstable stationary state, linear stability analysis allows one to obtain spectral and geometrical characteristics of the instability. In a second phase, comparing results of numerical simulations implementing the three dynamical models, the growth of turbulence is analysed as well as the first stages of non-linear saturation of the instability. In toroidal geometry, a linear stability analysis is performed. Two different methods, time-based and spectral, were implemented in order to obtain the spectral and geometrical characteristics of the most unstable modes. In both field geometries encompassed by this research, the numerical methods used to obtain the results are described and their performances analyzed. Throughout the work, particular care is given to the balance between the benefits and costs of the Multi-Water-Bag reduction
Tamain, Patrick. „Etude des flux de matière dans le plasma de bord des tokamaks : alimentation, transport et turbulence“. Aix-Marseille 1, 2007. http://www.theses.fr/2007AIX11060.
Der volle Inhalt der QuelleParticle transport in the edge of tokamaks plays a decisive role both in the center on plasma performances, since it governs the building of density profiles from external particle fuelling, and in the edge on the lifetime of plasma facing components, since it determines particle and energy fluxes reaching the wall. However, this subject has been little explored due to the complexity of modelling the interaction, in the same volume, of the plasma with strong particle, momentum and energy sources and sinks. In the perspective of ITER, the capability of gas puffing systems to reach required density levels without degrading the confinement, as well as the properties of density profiles and flows near the pedestal and in the SOL, remain open questions. This thesis contributes to the effort aiming at giving a better understanding of the mechanisms governing particle fluxes in the edge plasma and their impact on these questions. In a first phase of our work, we present an original approach for the modelling of fuelling by gas puffing, focusing on the thermal impact of the injection on the plasma. On the basis of analytical and numerical models with a reduced number of dimensions, we demonstrate the existence of thermal bifurcations trigerred by the injection and their importance in the dynamics of the neutral penetration and of the plasma relaxation. In the case of Tore Supra, we show that the local cooling linked to a strong injection allows a deeper penetration of particles (r/a = 1. 1 to r/a = 0. 9), but can also lead to a thermal instability of the whole plasma below a given ratio heating power / particle source. The extrapolation of this study for ITER remains pessimistic on the penetration depth of neutrals. However, the sensitivity of the results of these simplified models to the interaction between the parallel and perpendicular directions show that the developpement of numerical tools modelling coherently particle transport in both directions is necessary to progress on these questions. This led to the design of a 3D code presented in the second part of this work. This new tool is a full-torus code, including curvature effects. It solves electrostatic fluid drift equations without scale separation hypothesis, which allows to address with the same tool issues linked to large scale transport as well as micro-turbulence. Two versions of the code have been developped and validated : one treats exclusively closed field lines ; the other, more demanding from the numerical point of view, includes both the Scrape Off Layer (SOL) and the external part of the confined plasma. In a last part, the code is used to address the issue of poloidal asymmetries of parallel flows in the SOL which are observed experimentally but whose origin is not fully clear yet. Simulations reproduce the order of magnitude of measured amplitudes and evidence two different mechanisms which are likely to play a role in this phenomenon, the first at large scales, the other linked to turbulence. The former leans on a coupling between large scale drifts and curvature effects in the SOL while the latter is linked to the ballooning of the radial turbulent flux on the low field side. Finally, the importance of the plasma parallel resistivity on the characteristics of the turbulent transport is analysed as well as the impact of a localized particle injection on the local properties of turbulence
Métral, Jérôme. „Modélisation et simulation numérique de l'écoulement d'un plasma atmosphérique pour l'étude de l'activité électrique des plasmas sur avion“. Châtenay-Malabry, Ecole centrale de Paris, 2002. http://www.theses.fr/2002ECAP0868.
Der volle Inhalt der QuelleA ionized gas (or plasma) has the ability of absorbing or reflecting electromagnetic (radar) waves if its ionization rate is high enough. This is particularly interesting for aeronautics. This study aims at predicting the electric and energetic characteristics of a weakly ionized air plasma in an atmospheric pressure flow. The plasma is described by a two-temperature model, coming from the non-equilibrium description of plasmas. Plasma flow is then described by a two-temperature hydrodynamic system coupled with a collisional model (energy exchanges rates) and a kinetic model (chemical reactions). An algorithm was built to simulate plasma flow in axisymetric geometry. The algorithm is a 2D Lagrange + Projection scheme. The projection step was adapted to multi-components advection, using a second order, non oscillating, and bidimensionnal scheme. This algorithm allows the simulation of experiments concerning atmospheric pressure plasma and then the validation of the model parameters. In a second part, we study the Perfectly Matched Layer (PML) which is a boundary condition to simulate wave propagation in open domains. This method is particularly efficient for electromagnetic problems, and we want to enlarge this approach to aeroacoutics problems (linearized Euler equations). We propose two solutions: a practical approach to avoid numerical oscillations of the solution and a more general approach which consists in a new absorbing layer formulation which leads to well-posed problems
Leray, Gary. „PEGASES: Plasma Propulsion with Electronegative Gases“. Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005935.
Der volle Inhalt der QuelleLabit, Benoît. „Transport de chaleur électronique dans un tokamak par simulation numérique directe d'une turbulence de petite échelle“. Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11052.
Der volle Inhalt der QuelleBen, Abdallah Naoufel. „Etude de modèles asymptotiques de transport de particules chargées : asymptotique de Child-Langmuir“. Palaiseau, Ecole polytechnique, 1994. http://www.theses.fr/1994EPXX0003.
Der volle Inhalt der QuelleBian, Nicolas. „Turbulence convective et transport intermittent dans un plasma magnétisé“. Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11012.
Der volle Inhalt der QuelleMekkaoui, Mohamed. „Transport des atomes et des molécules dans les plasmas fluctuants de bord des machines de fusion“. Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4784/document.
Der volle Inhalt der QuelleEdge plasma of tokamaks manifests high level of fluctuations amplitude (>50%). It has been demonstrated that such a fluctuations affect significantly the transport of neutral particles, and in particular the slow particles as molecules and sputtered impurities. That is their penetration depth in the plasma is enhanced in the average. Then turbulent fluctuations are now implemented in the monte carlo transport code EIRENE used for the design of ITER
Salanne, Jean-Philippe. „Contrôle du point de fonctionnement des décharges électriques par l'intermédiaire de leur alimentation“. Toulouse, INPT, 2005. http://ethesis.inp-toulouse.fr/archive/00000167/.
Der volle Inhalt der QuelleThe aims of this study is to control the operating point of electrical discharges. These points, resulting from the coupling between the power supply and its load, may be unstable because of the dynamic behaviour of the discharge or any change of its length. To optimize the design and the electronic control of the power supply, the couplings between the later and the discharge are prospected. Numerical and analytical models of the system are presented. These models can simulate the couplings between the power supply and a discharge and are used to achieve the design of the power supply and its control. This approach is completed by experimental investigations considering discharge between 2 points, glidarc and DBD
Bonnement, Audrey. „Modélisation numérique par approximation fluide du plasma de bord des tokamaks (projet ITER)“. Nice, 2012. http://www.theses.fr/2012NICE4088.
Der volle Inhalt der QuelleMagnetic confinement fusion allows to favour fusion reactions and energy production with toric devices, called tokamaks, using an electro-magnetic field in order to confine the plasma. To study the edge plasma of tokamak, we use a fluid model, obtained from the Vlasov-Maxwell kinetic model and the Braginskii closure. A finite volume/element method is chosen to approach the model. The system is similar to the Euler or anisotropic Navier-Stokes systems, with additional terms to model the plasma confinement. We propose some methods to approach these terms and to model Bohm boundary conditions, characteristic of tokamak. Moreover, a finite volume method in cylindrical coordinates is proposed in order to preserve the conservative form of the equations. Thus, we consider as elementary volume, the cell which is given by rotation around the tokamak axis of the 2D cell. Several numerical results are given, e. G. For an anisotropic diffusion problem with radiation and also for simulations of pellet injections (matter ice cubes) to refuel the tokamak
Dejarnac, Renaud. „Etude du plasma de bord du tokamak Tore Supra en vue de l'optimisation du pompage des particules et de l'injection supersonique de matière“. Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11055.
Der volle Inhalt der QuelleSavatier, François. „Dynamique du modèle des sacs : application à la transition de phase de déconfinement“. Montpellier 2, 1988. http://www.theses.fr/1988MON20205.
Der volle Inhalt der QuelleCrispel, Pierre. „Modélisation mathématique et simulation de la transition d'une décharge électrostatique primaire vers un arc électrique secondaire entretenu par la puissance photovoltaïque d'un générateur solaire de satellite“. Toulouse, ENSAE, 2005. http://www.theses.fr/2005ESAE0021.
Der volle Inhalt der QuelleYang, Chang. „Analyse et mise en oeuvre des schémas numériques pour la physique des plasmas ionosphériques et de tokamaks“. Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10183/document.
Der volle Inhalt der QuelleThis thesis focuses on modeling and numerical simulation of ionospheric and Tokamak plasmas.The first part of this work concerns the modeling and simulation of ionospheric perturbations effects for earth-satellite communications. The starting point of this part is an asymptotic analysis of Euler-Maxwell model leading to Dynamo model, which results into a 3D coupling problem between an elliptic equation for the electric potential and a mass conservation equation for the plasma density. Because of the strong anisotropy of the diffusion matrix associated with the elliptic equation, we developed an asymptotic preserving numerical scheme thus allowing the well conditioned linear system. The simulation of the mass conservation equation is made by using high order conservation laws scheme. The validation of this model Dynamo is obtained by a comparison with the 2D Striation model. In the second part, we are interested in tokamak plasma. We extract from TOKAM3D model, a 2D nonlinear energy balance equation containing all the numerical difficulties. Standard numerical methods are very CPU consuming, thus we develop an implicit-explicit scheme shown efficient and stable for this type of problem. Finally, this scheme is combined with dimensional splitting method for the discretization and numerical experiments are then presented
Lesur, Maxime. „The Berk-Breizman Model as a Paradigm for Energetic Particle-driven Alfvén Eigenmodes“. Phd thesis, Ecole Polytechnique X, 2010. http://tel.archives-ouvertes.fr/tel-00563110.
Der volle Inhalt der QuelleMadaule, Éric. „Schémas numériques adaptatifs pour les équations de Vlasov-Poisson“. Electronic Thesis or Diss., Université de Lorraine, 2016. http://www.theses.fr/2016LORR0112.
Der volle Inhalt der QuelleMany numerical experiments are performed on the Vlasov-Poisson problem since it is a well known system from plasma physics and a major issue for future simulation of large scale plasmas. Our goal is to develop adaptive numerical schemes using discontinuous Galerkin discretisation combined with semi-Lagrangian description whose mesh refinement based on multi-wavelets. The discontinuous Galerkin formulation enables high-order accuracy with local data for computation. It has recently been widely studied by Ayuso de Dioset al., Rossmanith et Seal, etc. in an Eularian framework, while Guo, Nair and Qiu or Qiu and Shu or Bokanowski and Simarta performed semi-Lagrangian time resolution. We use multi-wavelets framework for the adaptive part. Those have been heavily studied by Alpert et al. during the nineties and the two thousands. Some works merging multi-scale resolution and discontinuous Galerkin methods have been described by Müller and his colleagues in 2014 for non-linear hyperbolic conservation laws in the finite volume framework. In the framework of relativistic Vlasov equation, Besse, Latu, Ghizzo, Sonnendrücker and Bertrand presented the advantage of using adaptive meshes. While they used wavelet decomposition, which requires large data stencil, multi-wavelet decomposition coupled to discontinuous Galerkin discretisation only requires local stencil. This favours the parallelisation but, at the moment, semi-Lagrangian remains an obstacle to highly efficient distributed memory parallelisation. Although most of our work is done in a 1d × 1v phase space, we were able to obtain a few results in a 2d × 2v phase space
Chable, Stéphane. „Modélisation numérique d'un propulseur à plasma stationnaire“. Toulouse, ENSAE, 2003. http://www.theses.fr/2003ESAE0007.
Der volle Inhalt der QuelleGélix, Franck. „Modélisation des phénomènes de transport au sein d'un four à plasma“. Bordeaux 1, 1999. http://www.theses.fr/1999BOR10665.
Der volle Inhalt der QuelleGraille, Benjamin. „Modélisation de mélanges gazeux réactifs ionisés dissipatifs“. Phd thesis, Ecole Polytechnique X, 2004. http://tel.archives-ouvertes.fr/tel-00007444.
Der volle Inhalt der Quelletransport à partir d'un modèle de type Boltzmann par un développement de Enskog. Nous étudions alors les propriétés de symétrie apportées par l'entropie de ces équations couplées avec celles de Maxwell pour obtenir un théorème d'existence locale en temps d'une solution bornée et régulière pour le problème de Cauchy. Nous étudions ensuite un modèle de plasma ambipolaire en considérant la masse de l'électron comme un paramètre. Nous démontrons que la solution globale dépend continument de la masse de l'électron lorsque celle-ci s'annule. Nous calculons enfin des flammes ionisées planes et étirées d'un mélange hydrogène-air et obtenons des structures de flammes typiques avec un faible impact de l'ionisation.
Bezanahary, Tahinaharinjaka. „Modélisation du comportement de la colonne positive d'un plasma de décharge dans les gaz rares purs“. Toulouse 3, 2003. http://www.theses.fr/2003TOU30239.
Der volle Inhalt der QuelleCesses, Yannick. „Modélisation bidimentionnelle d'une décharge à barrière diélectrique : mise en évidence de l'importance des phénomènes aux électrodes“. Toulouse 3, 2004. http://www.theses.fr/2004TOU30036.
Der volle Inhalt der QuelleGélix, Franck. „Modélisation des phénomènes de transport au sein d'un four à plasma“. Bordeaux 1, 1999. http://www.theses.fr/1999BOR12150.
Der volle Inhalt der QuelleGauthier, Gaëtan. „Étude de structures électroniques non-linéaires dans la magnétosphère et le vent-solaire : théorie et simulations“. Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS676.
Der volle Inhalt der QuelleIn the course of this thesis, we carried out a study in two distinct parts, with one thing in common : beam-plasma (bump-on-tail) instability. Firstly, we studied electromagnetic wave emissions at the plasma frequency and its first harmonic in the heliospheric context. Our study was essentially numerical, based on massively-parallel 2D3V Particle-In-Cell (PIC) simulations (Smilei) generating electrostatic and then electromagnetic waves by relaxation of an electron beam at the origin of type III radio bursts propagating in the solar wind plasma. By generalizing previous studies, the physical and numerical characteristics of our simulations have enabled us to study the principal modes of the waves associated with these emissions generated by non-linear coupling. Through a choice of parameters, we showed that the numerical noise (inherent in PIC codes) could be reduced sufficiently to allow us to model the density fluctuations observed in the solar wind. This is a prerequisite for showing that these fluctuations, although very small, can modify the emission characteristics. We then turned our attention to the non-linear kinetic structures known as electron holes in phase space (or EH for short) observed in many regions of the magnetosphere. Our study has been carried out using two approaches : (i) A theoretical study based on the BGK (Bernstein-Greene-Kruskal) integral method to determine the distributions of particles (electrons and ions) associated with these EHs, as well as their conditions of existence. We have thus developed a 3D model of revolution symmetry around the ambient magnetic field, which takes into account both electron polarization drift and a more realistic des- cription of plasma boundary conditions with the introduction of the EH’s velocity relative to the ambient plasma. This model has enabled us to characterize the relationship between parallel and perpendicular scales of EHs in different regions of the magnetosphere, as well as some restrictions on their conditions of existence. (ii) The second approach is a numerical PIC study, which allows us to generate these EHs with realistic initial conditions and to compare them with in situ spatial observations. Thanks to a pa- rametric study, we have shown that environmental conditions (ambient magnetic field, beam density) have an impact on their generation and nature (quasi-electrostatic or with an internal magnetic field component). This qualitative and quantitative numerical study has made it possible to specify certain parameters, such as beam density, which is still not easily accessible to space mission measurements, as well as other fundamental characteristics of EHs, such as their propagation speed or even the conservation and conversion of energy within them
Parisot, Martin. „Modélisation intermédiaire entre équations cinétiques et limites hydrodynamiques : dérivation, analyse et simulations“. Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10052/document.
Der volle Inhalt der QuelleThis work is devoted to the study of a problem resulting from plasma physics: heat transfer of electrons in a plasma close to Maxwellian equilibrium. Firstly, the asymptotic regime of Spitzer-Harm is studied. A model proposed by Schurtz and Nicolai is analyzed and located in the context of hydrodynamic limits outside of the strictly asymptotic. The link to non-local models of Luciani and Mora is established, as well as the mathematical properties such as the principle of maximum and entropy dissipation. Then, a formal derivation from the Vlasov equations is proposed. A hierarchy of intermediate models between the kinetic equations and the hydrodynamic limit is described. In particular, a new system hydrodynamics, integro-differential by nature, is proposed. The system Schurtz and Nicolai appears as a simplification of the system resulting from the diversion. The existence and uniqueness of the solution of the nonstationary system are established in a simplified framework.The last part is devoted to the implementation of a specific numerical scheme for solving these models. We propose a finite volume approach can be effective on unstructured grids. The accuracy of this scheme to capture specific effects such as kinetic, which may not be reproduced by the asymptotic Spitzer-Harm model. The consistency of this pattern with that of the Spitzer-Harm equation is highlighted, paving the way for a strategy of coupling between the two models
Bianchetti, Morales Rennan. „Density profile reconstruction methods for extraordinary mode reflectometry“. Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0031/document.
Der volle Inhalt der QuelleThe goal of this PhD is to improve the data analysis techniques of frequency swept reflectometry for determination of the density profile of fusion plasmas. There has been significant improvements in the last two decades on the hardware design and signal extraction techniques, but the data analysis is lagging behind and require further improvements to meet the required standards for continuous operation in future reactors. The improvements obtained in this thesis on the reconstruction of density profiles provide a better accuracy in a shorter time, even in the presence of a density hole, also enabling sufficiently precise measurements of the properties of turbulence used to validate numerical models, and allowing real-time monitoring of the shape and position of the plasma
Zahri, Abdellatif. „Développement du modèle PIC-MCC 2D : application aux décharges radiofréquence“. Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1344/.
Der volle Inhalt der QuelleThe particle-in-cell method combined with the Monte Carlo techniques is a well established method for plasma modelling, and is widely used to simulate low pressure radiofrequency discharges. This technique is a simple and effective method for solving a wide variety of complex problems involving a large number of particles moving under the action of internal forces and external forces (electromagnetic fields. . . ) The purpose of our model is to understand and characterize the behaviour of low pressure plasmas in a two-dimensional geometry. We want to understand what is happening in the sheath and in particular the behaviour of the ions. In this work, we describe the PIC-MCC models and techniques needed to build such models. We chose this technique by its ability to describe correctly the plasma physics at low pressure. Indeed, this technique provides more details without any assumption on the distribution function of electrons or ions, which is far from being the case for other models including fluid models. We show some distribution functions (density and energy of charged particles, EEDF) ; the electrical characteristics of the discharge are presented. This work is part of the European project EMDPA : New Elemental and Molecular Depth Analysis of advanced materials by modulated radio frequency glow discharge time of flight mass spectrometry. This project is funded by the European Commission through the research program for technological development
Liard, Laurent. „Transport non linéaire dans un réacteur Hélicon“. Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005954.
Der volle Inhalt der QuelleMadaule, Éric. „Schémas numériques adaptatifs pour les équations de Vlasov-Poisson“. Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0112/document.
Der volle Inhalt der QuelleMany numerical experiments are performed on the Vlasov-Poisson problem since it is a well known system from plasma physics and a major issue for future simulation of large scale plasmas. Our goal is to develop adaptive numerical schemes using discontinuous Galerkin discretisation combined with semi-Lagrangian description whose mesh refinement based on multi-wavelets. The discontinuous Galerkin formulation enables high-order accuracy with local data for computation. It has recently been widely studied by Ayuso de Dioset al., Rossmanith et Seal, etc. in an Eularian framework, while Guo, Nair and Qiu or Qiu and Shu or Bokanowski and Simarta performed semi-Lagrangian time resolution. We use multi-wavelets framework for the adaptive part. Those have been heavily studied by Alpert et al. during the nineties and the two thousands. Some works merging multi-scale resolution and discontinuous Galerkin methods have been described by Müller and his colleagues in 2014 for non-linear hyperbolic conservation laws in the finite volume framework. In the framework of relativistic Vlasov equation, Besse, Latu, Ghizzo, Sonnendrücker and Bertrand presented the advantage of using adaptive meshes. While they used wavelet decomposition, which requires large data stencil, multi-wavelet decomposition coupled to discontinuous Galerkin discretisation only requires local stencil. This favours the parallelisation but, at the moment, semi-Lagrangian remains an obstacle to highly efficient distributed memory parallelisation. Although most of our work is done in a 1d × 1v phase space, we were able to obtain a few results in a 2d × 2v phase space
Latocha, Vladimir. „Deux problèmes en transport des particules chargées intervenant dans la modélisation d'un propulseur ionique“. Toulouse, INSA, 2001. https://tel.archives-ouvertes.fr/tel-00002194.
Der volle Inhalt der QuelleThe modelling of the ionic thruster belonging to the SPT class raises many problems of plasma physics. We studied two of them, namely the electron transport and the computation of the electric potential. The electron transport is subject to the influence of the fields (magnetic and electric) set in the channel of the thruster on the one hand, and to the collisions of electrons with heavy species and at the walls on the oher hand. We participated to the development of a SHE model, wich is derived by performing an asymptotic analysis of the Boltzmann equation with a condition that models the reflection at the walls. This model allow to approximate the Electron Energy Distribution Function by solving a diffusion equation in the {position, energy} space, whose scales are macroscopic. More precisely, we extended an existing approach to the case where scattering against atoms are taken into account, as well as inelastic collisions at the walls. Then we compared the implementation of this model tot the results of a Monte Carlo simulation. We obtain similar results at a very reduced computational cost. This work lead to three publications, which are incorporated to the thesis. In a second stage, we studied the computation of the electric field in two dimensions. Due to the presence of a magnetic field, this problem gives rise to an anisotropic elliptic problem. Furthermore, the conductivities along the magnetic field and across the magnetic field lines can differ by several orders of magnitude. We implemented a finite volume scheme and we showed the numerical difficulties raised by such anisotropies. Hence, we improved this method by relating the solution of a highly anisotropic problem to a sequence of isotropic problems. This method proved to behabe well and we should be able to treat realistic cases shortly
Martin, Marie. „Modélisations fluides pour les plasmas de fusion : approximation par éléments finis C1 de Bell“. Phd thesis, Université Nice Sophia Antipolis, 2013. http://tel.archives-ouvertes.fr/tel-00845922.
Der volle Inhalt der QuelleBorghol, Saja. „Modélisation mathématique de la charge de surface des satellites en orbite basse“. Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10040/document.
Der volle Inhalt der QuelleIn this work we are concerned with a mathematical study of the spacecraft charging phenomena of Low Earth Orbit (LEO).After recalling the physical context, we derive a two-fluid type model for the plasma around the spacecraft. Indeed in LEO, the plasma can be considered highly colisional compared with the case for example of Polar Earth Orbit (PEO). The model used here consist in the Euler equations for the conservation of mass, momentum and energy plus a Poisson equation for the electrostatic potentiel and is derived in the three dimensionnal case.For the mathematical study of the model, we concentrate our attention on the one dimensionnal case to point out the main difficulties.We first consider the stationnary Euler equations coupled to the Poisson equation. The charging dynamics is then embodied into the boundary conditions where the time derivative of the potentiel appears. We present rigourous existence and unicity results together with numerical simulations. Here we only use some Dirichlet boundary conditions for the macroscopic quantities. They can be far from the ones of physical interest wich we only know at a kinetic level.That's why we next propose a numerical solution to incorporate in the simulation of the evolutive Euler equations boundary condition that come from a microscopic modeling in the small mean free path regime. THe boundary condition relies on the analysis of boundary layers formation that accounts from the fact that the incoming kinetic flux might be far from the equilibrium
Tavant, Antoine. „Study of the plasma/wall interaction and erosion on a plasma thruster of low power“. Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX085.
Der volle Inhalt der QuelleElectric propulsion systems that accelerate plasma ions are important for the success of spatial missions (GPS, weather forecast, communication, etc.).The Hall effect thruster is one of the most used and efficient technology.However, its conception and optimization is slow and costly, as key processes are still poorly understood, in particular the electron transport and the plasma-wall interaction.In order to study both phenomena, we use a bi-dimensional kinetic simulation.We showed with 2D PIC simulation results that electrons are non-local, as they are absorbed more quickly at the wall compared to the collision frequency.Consequently, we derived a non-isothermal sheath model using a polytropic state law for the electrons that describes more accurately the plasma-wall interaction.The model can be used with and without secondary electron emission.With electron emission, the sheath model can present up to three solutions, explaining the oscillations observed in the simulations.The azimuthal instability observed, responsible for the electron transport, is compared to the dispersion relation of the ion acoustic wave and the electron cyclotron drift instability.We show that, while the first linear stage of the instability is well understood, the saturated quasi-steady-state is affected by particle-wave interactions and non-linear mechanisms that are not included in the dispersion relation
Crestetto, Anaïs. „Optimisation de méthodes numériques pour la physique des plasmas : application aux faisceaux de particules chargées“. Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00735569.
Der volle Inhalt der QuelleEnache, Ionut. „Etude expérimentale et modélisation du transfert de matière dans des décharges de Townsend à pression atmosphérique en mélange HMDSO-N2O-N2 et SiH4-N2O-N2“. Toulouse 3, 2007. http://thesesups.ups-tlse.fr/97/.
Der volle Inhalt der QuelleThe aim of this work is to better understand the primary deposition mechanisms in atmospheric pressure plasma-enhanced thin film deposition in order to optimize the processes which lead to a silicon oxide film in HMDSO-N2O-N2 or SiH4-N2O-N2 mixtures. First, the chemical and structural layer properties were determined for various experimental conditions. The process is then simulated using FLUENT(c) taking into account fluid dynamics, mass-transfer and chemical reactions. Once validated based on experimental results, this simulation provides a better understanding of the mechanisms which govern the growth process. For HMDSO-containing mixtures, our results highlight that the HMDSO dissociation into silicon-containing radicals is the process rate-limiting step. The relative importance of convection and diffusion in the transport of radicals is quantified. The model also shows that HMDSO quenches nitrogen metastable species which are responsible for the dissociation of the precursor. For SiH4-containing mixtures powders appear to form at rates which are much higher than those allowed by the gas-kinetic theory. Besides, the influence of the gas recirculations on the discharge stability and on the film homogeneity is established. Based on our results, an optimization study of the cell discharge is achieved
Tresset, Guillaume. „Caractérisation, Modélisation et Contrôle des Scénarios Avancés dans le Tokamak Européen JET“. Phd thesis, Université de Provence - Aix-Marseille I, 2002. http://tel.archives-ouvertes.fr/tel-00001803.
Der volle Inhalt der QuelleGuisset, Sébastien. „Modélisation et méthodes numériques pour l'étude du transport de particules dans un plasma chaud“. Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0117/document.
Der volle Inhalt der QuelleAngular moments models represent alternative descriptions situated in between the kinetic and the fluid models. In this work, angular moments models based on an entropy minimisation principle are considered for plasma physics applications. This manuscript is organised in three parts. The first one is a contribution to plasma physics modelling within the formalism of angular moments models. The validity domain of angular moments models in collisionless regimes is studied. It is also shown that the collisional operators proposed for the M1 angular moments model enable to recover accurate plasma transport coefficients. The second part of this document deals with the derivation of numerical methods for the long timescales particle transport. Appropriate asymptotic-preserving numerical schemes are designed for the M1 angular moments model and numerical validations are performed. The third part represents a first important step toward multi-species modelling. The M1 angular moments model in a moving frame is introduced and applied to rarefied gas dynamics. The model properties are highlighted, a numerical scheme is proposed and a numerical validation is carried out
Zakari, Mustapha. „Modélisation Volumes-Finis en maillages non-structurés de décharges électriques à la pression atmosphérique“. Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2013. http://tel.archives-ouvertes.fr/tel-00940096.
Der volle Inhalt der QuelleAhmad, Ahmad. „Etude de la production d'ions négatifs sur des surfaces de carbone dans un plasma d'hydrogène sans Cs à basse pression“. Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4702/document.
Der volle Inhalt der QuelleThis thesis deals with negative ions (INs) surface production for applications in controlled fusion. Negative ions (NIs) formed at the sample surface from positive ions bombardment in hydrogen plasma are collected and analyzed with energy mass spectrometer (MS). The NI energy distribution functions (NIDF) measured by the MS are different from those emitted from surface f(E, Θ) due to modifications trajectories and energies which result when NI cross plasma and MS. In order to determine the NIDF emitted by the surface f(E,Θ) using the NIDF measured by MS f''(E), we developed a model that calculates the ion trajectories between the surface and MS detector. Then from a test function f(E,Θ) it is possible to calculate f''(E) and compare it to the experimental one. The critical issue is this method is the choice of f(E, Θ). The approach used in this thesis is the neutral backscattered and sputtered distribution function calculated by SRIM software during a surface bombardment similar to the experimental conditions. The model resulting show a good agreement between experimental and calculated NIDF, and validate our calculations and the choice of SRIM.In order to compare production mechanisms and NIs yields, a comparative study on different carbons materials was performed. Measured NIDFs show the same shape at room temperature. This indicates that the mechanisms involved in the NI production and the contribution of these mechanisms in the NIDF are the same for all materials. The best NI yield at low temperature is observed on DLC surface. The highest NI yield for all temperatures is observed on Boron doped diamond (BDD) surface at 400°C
Quezada, Maxwell Josias. „Hydrogénation catalytique de CO₂ en méthanol en lit fixe sous chauffage conventionnel et sous plasma à DBD ZSM-5 surface modification by plasma for catalytic activity improvement in the gas phase methanol-to-dimethylether reaction“. Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR12.
Der volle Inhalt der QuelleThe objective of this thesis is to contribute to the optimisation of the production of methanol by hydrogenation of CO₂ by synthesising new catalysts in the form of extrudates for industrial use. In this regard, six Cu-ZnO based catalysts supported on alumina and ZSM-5 were prepared and tested. At 36 bar and under conventional heating, the CuZnO/Al₂O₃ showed the best methanol yield. An industrial process based on this catalyst has been proposed and optimised. The influence of extracting water and methanol from the reaction medium using two reactors in series instead of one was investigated and it was found to increase methanol yield considerably. Tests at atmospheric pressure and under DBD plasma showed that the Cu/Al₂O₃ gives better CO₂ conversions, while the CuZnO/ZSM-5 showed better methanol yields. This was attributed to the ionic conductivity and the dielectric constant of the catalysts