Dissertations / Theses on the topic 'Particle-in-cell simulation'
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Przebinda, Viktor. "Vertical optimization of particle in cell simulation." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p1425790.
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Fox, Justin M. 1981. "Parallelization of particle-in-cell simulation modeling Hall-effect thrusters." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/28905.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.Includes bibliographical references (p. 136-139).
MIT's fully kinetic particle-in-cell Hall thruster simulation is adapted for use on parallel clusters of computers. Significant computational savings are thus realized with a predicted linear speed up efficiency for certain large-scale simulations. The MIT PIC code is further enhanced and updated with the accuracy of the potential solver, in particular, investigated in detail. With parallelization complete, the simulation is used for two novel investigations. The first examines the effect of the Hall parameter profile on simulation results. It is concluded that a constant Hall parameter throughout the entire simulation region does not fully capture the correct physics. In fact, it is found empirically that a Hall parameter structure which is instead peaked in the region of the acceleration chamber obtains much better agreement with experiment. These changes are incorporated into the evolving MIT PIC simulation. The second investigation involves the simulation of a high power, central-cathode thruster currently under development. This thruster presents a unique opportunity to study the efficiency of parallelization on a large scale, high power thruster. Through use of this thruster, we also gain the ability to explicitly simulate the cathode since the thruster was designed with an axial cathode configuration.
by Justin M. Fox.
S.M.
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Van, der Straaten Trudy. "A particle-in-cell simulation of a DC magnetron discharge." Thesis, The University of Sydney, 1996. https://hdl.handle.net/2123/27510.
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Magnetron discharges have applications in the materials processing industry for the fabrication of thin films via sputter deposition. Despite their wide use, the underlying physics of the discharge is not well understood. In particular, the transport mechanisms that enable the electrons to migrate across magnetic field lines at low pressures have not
been conclusively established. The research reported in this thesis is directed toward understanding this problem further.
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Beidler, Penh Koetwongjun 1974. "Two dimensional particle-in-cell simulation model for Hall type thrusters." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9726.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.Includes bibliographical references (p. 79-80).
In this master's thesis, a two-dimensional model of a Hall type thruster, was developed, to include secondary electron emission at the wall, ion recombination at the wall, diffuse reflection for neutrals bouncing off of the wall, wall potential calculation based on the collected wall charge and a steady state non-uniform magnetic field found in Hall thruster configurations. The model used a non-collisional, two dimensional in regular space and three dimensional in phase space, particle-in-cell (PIC) formulation for simulation of the plasma, while a separate model accounted for particle collisions, using Argon-electron elastic, excitation and ionization cross-sections. The collision model used an electron-neutral collision frequency on the same order as the electron plasma frequency, which made the neutral density to be on the order of 1025m- 3 Such a large neutral density implied that ion-neutral interactions, typically neglected in Hall thrusters, must also be taken into account. However, in this simulation they were neglected. Proceeding forward, the simulation size was 50x20 Debye lengths. Cell size was half of the plasma Debye length, in both dimensions. Time step was based on the condition that the electron gyroradius be ten times the Debye length, for a given electron temperature of 10 eV and maximum magnetic field of 0.8 Tesla, which made the electron density to be on the order of 10-2 0m - 3 . Neutral particle injection rate assumed a particle temperature of 1000K. Electron injection rate from the cathode equaled the electron collection rate at the anode. Ion and neutral mass were set to 1000 times that of the electron mass, in an attempt to accelerate plasma phenomena. Simulation of the model proceeded for 50000 iterations or 7.11 x 10- 9 seconds, which was equivalent to three ion passes through the simulation. Results analysis consisted of studying simulation output at different points in time. It was concluded that the simulation here does not simulate an actual Hall thruster, but introduces some computer models for it.
by Penh Koetwongjun Beidler.
S.M.
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Chae, Gyoo-Soo. "Numerical Simulation of Ion Waves in Dusty Plasmas." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29165.
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There has been a great deal of interest in investigating numerous unique types of electrostatic and electromagnetic waves and instabilities in dusty plasmas. Dusty plasmas are characterized by the presence of micrometer or submicrometer size dust grains immersed in a partially or fully ionized plasma. In this study, a two-dimensional numerical model is presented to study waves and instabilities in dusty plasmas. Fundamental differences exist between dusty plasmas and electron-ion plasmas because of dust charging processes. Therefore, a primary goal of this study is to consider the unique effects of dust charging on collective effects in dusty plasmas.
The background plasma electrons and ions here are treated as two interpenerating fluids whose densities vary by dust charging. The dust is treated with a Particle-In-Cell PIC model in which the dust charge varies with time according to the standard dust charging model. Fourier spectral methods with a predictor-corrector time advance are used to temporally evolve the background plasma electron and ion equations. The dust charge fluctuation mode and the damping of lower hybrid oscillations due to dust charging, as well as plasma instabilities associated with dust expansion into a magnetized background plasma are investigated using our numerical model. Also, an ion acoustic streaming instability in unmagnetized dusty plasmas due to dust charging is investigated. The numerical simulation results show good agreement with theoretical
predictions and provide further insight into dust charging effects on wave modes and instabilities in dusty plasmas.Ph. D.
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Pierru, Julien. "Development of a Parallel Electrostatic PIC Code for Modeling Electric Propulsion." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/34597.
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This thesis presents the parallel version of Coliseum, the Air Force Research Laboratory plasma simulation framework. The parallel code was designed to run large simulations on the world fastest supercomputers as well as home mode clusters. Plasma simulations are extremely computationally intensive as they require tracking millions of particles and solving field equations over large domains. This new parallel version will allow Coliseum to run simulations of spacecraft-plasma interactions in domain large enough to reproduce space conditions. The parallel code ran on two of the world fastest supercomputers, the NASA JPL Cosmos supercomputer ranked 37th on the TOP500 list and Virginia Tech's System X, ranked 7th. DRACO, the Virginia Tech PIC module to Coliseum, was modified with parallel algorithms to create a full parallel PIC code. A parallel solver was added to DRACO. It uses a Gauss-Seidel method with SOR acceleration on a Red-Black checkerboard scheme. Timing results were obtained on JPL Cosmos supercomputer to determine the efficiency of the parallel code. Although the communication overhead limits the code's parallel efficiency, the speed up obtained greatly decreases the time required to run the simulations. A speed up of 51 was reached on 128 processors. The parallel code was also used to simulate the plume expansion of an ion thruster array composed of three NSTAR thrusters. Results showed that the multiple beams merge to form a single plume similar to the plume created by a single ion thruster.Master of Science
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Vanderburgh, Richard N. "One-Dimensional Kinetic Particle-In-Cell Simulations of Various Plasma Distributions." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1610313011646245.
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Tran, Binh Phuoc. "Modeling of Ion Thruster Discharge Chamber Using 3D Particle-In-Cell Monte-Carlo-Collision Method." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33510.
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This thesis is aimed toward developing a method to simulate ion thruster discharge chambers in a full three dimensional environment and to study the effect of discharge chamber size on ion thruster performance. The study focuses solely on ring-cusped thrusters that make use of Xenon for propellant and discharge cathode assembly for mean of propellant ionization. Commercial software is used in both the setup and analysis phases. Numerical simulation is handled by 3D Particle-In-Cell Monte-Carlo-Collision method. Simulation results are analyzed and compared with other works. It is concluded that the simulation methodology is validated and can be used to simulate different cases. Therefore, different simulation cases of varying chamber sizes are done and the results are used to develop a performance curve. This plot suggests that the most efficient case is the 30 cm thruster. The result further validates the simulation process since the operating parameters used for all of the cases are taken from a 30 cm thruster experiment. One of the obvious applications for such a simulation process is to determine a set of the most efficient operating parameters for a certain size thruster before actual fabrication and laboratory testing.Master of Science
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Jin, Hanbing. "Particle-in-Cell Simulation of Electromagnetic Pulse Generated by High-power Laser-target Interaction." Thesis, KTH, Fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231339.
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Tatomirescu, Emilian-Dragos. "Accélération laser-plasma à ultra haute intensité - modélisation numérique." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0013/document.
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Avec les dernières augmentations de l'intensité maximale de laser réalisable grâce à de courtes impulsions à haute puissance (gamme femtoseconde) un intérêt a surgi dans les sources de plasma laser potentiels. Les lasers sont utilisés en radiographie proton, allumage rapide, hadronthérapie, la production de radioisotopes et de laboratoire astrophysique. Au cours de l'interaction laser-cible, les ions sont accélérés par des processus physiques différents, en fonction de la zone de la cible. Tous ces mécanismes ont un point commun: les ions sont accélérés par des champs électriques intenses, qui se produisent en raison de la séparation de forte charge induite par l'interaction de l'impulsion laser avec la cible, directement ou indirectement. Deux principales sources distinctes pour le déplacement de charge peuvent être mis en évidence. Le premier est le gradient de charge provoquée par l'action directe de la force ponderomotive de laser sur les électrons dans la surface avant de la cible, qui est la prémisse pour le processus d'accélération des radiations de pression (RPA). Une deuxième source peut être identifiée comme provenant du rayonnement laser qui est transformée en énergie cinétique d'une population d'électrons relativistes chaud (~ quelques MeV). Les électrons chauds se déplacent et font recirculer à travers la cible et forment un nuage d'électrons relativistes à la sortie de la cible dans le vide. Ce nuage, qui se prolonge pour plusieurs longueurs de Debye, crée un champ électrique extrêmement intense longitudinal, la plupart du temps dirigé le long de la surface normale, ce qui, par conséquent, est la cause de l'accélération d'ions efficace, qui conduit à l'accélération cible normale gaine (TNSA) processus . Le mécanisme TNSA permet d'utiliser des géométries différentes cibles afin de parvenir à une meilleure focalisation des faisceaux de particules de l'ordre de plusieurs dizaines de microns, avec des densités d'énergie élevées. Les électrons chauds sont produits par l'irradiation d'une feuille solide avec une impulsion laser intense; ces électrons sont transportés à travers la cible, la formation d'un champ électrostatique fort, normal à la surface cible. Protons et les ions chargés positivement de la surface arrière de la cible sont accélérés par ce domaine jusqu'à ce que la charge de l'électron est compensée. La densité d'électrons chauds et la température dans le vide arrière dépendent des propriétés géométriques et de composition cibles tels que la courbure de la cible, les structures de mise au point d'impulsion et de microstructure pour l'accélération de protons améliorée. Au cours de ma première année, j'ai étudié les effets de la géométrie de la cible sur le proton et l'ion énergie et la distribution angulaire afin d'optimiser les faisceaux de particules laser accéléré au moyen de deux dimensions (2D) particule-in-cell (PIC) simulations de l'interaction de l'ultra-court impulsions laser avec plusieurs cibles microstructurées. Également au cours de cette année, je l'ai étudié la théorie derrière les modèles utilisésWith the latest increases in maximum laser intensity achievable through short pulses at high power (femtosecond range) an interest has arisen in potential laser plasma sources. Lasers are used in proton radiography, rapid ignition, hadrontherapy, production of radioisotopes and astrophysical laboratory. During the laser-target interaction, the ions are accelerated by different physical processes, depending on the area of the target. All these mechanisms have one thing in common: the ions are accelerated by intense electric fields, which occur due to the separation of high charge induced by the interaction of the laser pulse with the target, directly or indirectly. Two main distinct sources for charge displacement can be identified. The first is the charge gradient caused by the direct action of the laser ponderomotive force on the electrons in the front surface of the target, which is the premise for the pressure ramping acceleration (RPA) process. A second source can be identified as coming from the laser radiation which is transformed into kinetic energy of a hot relativistic electron population (~ a few MeV). The hot electrons move and recirculate through the target and form a cloud of relativistic electrons at the exit of the target in a vacuum. This cloud, which extends for several lengths of Debye, creates an extremely intense longitudinal electric field, mostly directed along the normal surface, which is therefore the cause of effective ion acceleration, which leads to the normal target sheath acceleration (TNSA) process. The TNSA mechanism makes it possible to use different target geometries in order to obtain a better focusing of the beams of particles on the order of several tens of microns, with high energy densities. Hot electrons are produced by irradiating a solid sheet with an intense laser pulse; these electrons are transported through the target, forming a strong electrostatic field, normal to the target surface. Protons and positively charged ions from the back surface of the target are accelerated by this domain until the charge of the electron is compensated. The density of hot electrons and the temperature in the back vacuum depend on the target geometric and compositional properties such as target curvature, pulse and microstructure tuning structures for enhanced proton acceleration. In my first year I studied the effects of target geometry on the proton and energy ion and angular distribution in order to optimize the accelerated laser particle beams by means of two-dimensional (2D) particle -in-cell (PIC) simulations of the interaction of ultra-short laser pulses with several microstructured targets. Also during this year, I studied the theory behind the models used
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Bramer, Elinor C. "Development of a particle in cell code for the simulation of dual stage ion thrusters." Thesis, University of Sussex, 2014. http://sro.sussex.ac.uk/id/eprint/48913/.
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This thesis focuses on the design, development and testing of a two dimensional particle in cell (PIC) code (PICSIE) written in Matlab. The code is applied to the specific problem of modelling the performance of dual stage ion thrusters. The code simulates one full aperture within dual stage ion thruster systems, focusing on the flow of ions through the aperture. Only the ions have been included in the simulation in order to minimize running time. The results produced by the simulation code are compared with results obtained from the vacuum chamber testing of the DS4G prototype, along with results from other simulation codes and research papers in order to verify the performance of the simulation code. The Dual-Stage 4-Grid (DS4G) and Dual-Stage 3-Grid (DS3G) thrusters are both sim- ulated in order to compare the performance of the two thrusters and assess the benefits and disadvantages of including the fourth grid in a dual stage thruster system. Different grid configurations are simulated in order to find the most efficient configuration of the ion optics and accelerating voltages for each thruster, with the aim being to find the con- figurations that produce the maximum particle momentum, thrust and specific impulse while minimizing the rate of erosion of the ion optics and maximising the efficiency of the thruster. These simulations are applied to the problem of deciding if the advantages provided in using a 4th grid outweigh the disadvantages compared to the 3 grid design. The results show that if erosion due to backstreaming ions is disregarded, including the fourth grid in the thruster design results in no apparent advantages in terms of the perfor- mance parameters studied in this work. The only noticeable difference between the three and four grid cases is a significant increase in the change in ion momentum observed when the fourth grid is not included in the design. The conclusion of the work is that the fourth grid should not be included in the dual stage design unless a very long lifetime is required and it is thought that erosion due to backstreaming will prevent the three grid thruster from fulfilling this criteria. The concept of propagating waves through the plasma within the ion thruster discharge chamber is investigated, with the aim of discovering any benefits and improvements in performance that may arise and forming a conclusion on whether further study on the topic of waves within the discharge chamber may be beneficial. No improvements in per- formance parameters were observed in this work, although further study in the area may show benefits to introducing waves into the plasma.
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Hammel, Jeffrey Robert. "Development of an unstructured 3-D direct simulation Monte Carlo/particle-in-cell code and the simulation of microthruster flows." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0510102-153614.
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Sewell, Stephen. "Efficient particle-in-cell simulation of auroral plasma phenomena using a CUDA enabled graphics processing unit." Thesis, The University of Alabama in Huntsville, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1559557.
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This thesis introduces a software framework that effectively utilizes low-cost commercially available Graphic Processing Units (GPUs) to simulate complex scientific plasma phenomena that are modeled using the Particle-In-Cell (PIC) paradigm. The software framework that was developed conforms to the Compute Unified Device Architecture (CUDA), a standard for general purpose graphic processing that was introduced by NVIDIA Corporation. This framework has been verified for correctness and applied to advance the state of understanding of the electromagnetic aspects of the development of the Aurora Borealis and Aurora Australis.
For each phase of the PIC methodology, this research has identified one or more methods to exploit the problem's natural parallelism and effectively map it for execution on the graphic processing unit and its host processor. The sources of overhead that can reduce the effectiveness of parallelization for each of these methods have also been identified. One of the novel aspects of this research was the utilization of particle sorting during the grid interpolation phase. The final representation resulted in simulations that executed about 38 times faster than simulations that were run on a single-core general-purpose processing system. The scalability of this framework to larger problem sizes and future generation systems has also been investigated.
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Pfeiffer, Marcel [Verfasser]. "Simulation elektromagnetischer Wechselwirkungen in Plasmaströmungen großer Skalengradienten unter Verwendung eines gekoppelten Particle-In-Cell und Direct Simulation Monte Carlo-Verfahrens / Marcel Pfeiffer." München : Verlag Dr. Hut, 2015. http://d-nb.info/1079769005/34.
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Hägg, Martin. "Theoretical analysis and simulation of microwave-generation from a coaxial vircator." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316595.
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High-power microwave, HPM, systems can be used as non-lethal weapons with the ability to destroy or disturb electronics, by damaging internal circuits and inducing high currents. Today microwave sources are being developed with peak powers exceeding 1 GW, one of these devices is the vircator, a narrowband source which is unique to the HPM community. In order to understand and develop microwave sources like the vircator it is necessary to have computer models, as simulations gives an invaluable understanding of the mechanisms involved during operation, saving time and development costs. This thesis presents the results from a theoretical analysis and a simulation study using a well known electromagnetic particle-in-cell code, Computer Simulation Technology Particle Studio. The results are then compared to measured data from a HPM system, the Bofors HPM Blackout. The results show that CST PS can be used to design and study the coaxial vircator with good results.
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Zemzemi, Imene. "High-performance computing and numerical simulation for laser wakefield acceleration with realistic laser profiles." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX111.
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Le développement des lasers ultra-courts à de hautes intensités a permis l’émergence de nouveaux domaines de recherche en relation avec l’interaction laser-plasma. En particulier, les lasers petawatt femtoseconde ont ouvert la voie vers la possibilité de concevoir une nouvelle génération d’accélérateurs de particules. La modélisation numérique a largement contribué à l’essor de ce domaine d’accélération des électrons par sillage laser. Dans ce contexte, les codes Particle-In-Cell sont les plus répandus dans la communauté. Ils permettent une description fiable de l’interaction laser plasma et surtout de l’accélération par sillage laser.Cependant, une modélisation précise de la physique en jeu nécessite de recourir à des simulations 3D particulièrement coûteuses. Une manière pour accélérer efficacement ce type de simulations est l’utilisation de modèles réduits qui, tout en assurant un gain en temps de calcul très important, garantissent une modélisation fiable du problème. Parmi ces modèles, la décomposition des champs en modes de Fourier dans la direction azimutale est particulièrement adaptée à l’accélération laser plasma.Dans le cadre de ma thèse, j’ai implémenté ce modèle dans le code open-source SMILEI, dans un premier temps, avec un schéma différences finies (FDTD) pour discrétiser les équations de Maxwell. Néanmoins, ce type de solveur peut induire un effet de Cherenkov numérique qui corrompt les résultats de la simulation. Pour mitiger cet artéfact, j’ai également implémenté une version pseudo-spectrale du solveur de Maxwell qui présente de nombreux avantages en termes de précision numérique.Cette méthode est ensuite mise en oeuvre pour étudier l’impact de profils de lasers réalistes sur la qualité du faisceau d’électrons en exploitant des mesures réalisées sur le laser Apollon. Sa capacité à modéliser correctement les processus physiques présents est analysée en déterminant le nombre de modes nécessaires et en comparant les résultats avec ceux issus des simulations 3D en géométrie Cartésienne. Cette étude montre qu’inclure les défauts du laser mène à des différences dans les résultats et que ces derniers dégradent la performance des accélérateurs-laser plasma notamment en termes de quantité de charge injectée. Ces simulations, instructives pour les futures expériences d’accélération d’électrons par le laser Apollon, mettent en avant la nécessité d’inclure les mesures expérimentales dans la simulation et particulièrement celle du front de phase, pour aboutir à des résultats précisThe advent of ultra-short high-intensity lasers has paved the way to new and promising, yet challenging, areas of research in laser-plasma interaction physics. The success of building petawatt femtosecond lasers offers a promising path for designing future particle accelerators and light sources.Achieving this goal intrinsically relies on the combination of experiments and numerical modeling. So far, Particle-In-Cell (PIC) codes have been the ultimate tool to accurately describe the laser-plasma interaction especially in the field of Laser WakeField Acceleration (LWFA). Nevertheless, the numerical modeling of laser-plasma accelerators in 3D can be a very challenging task due to their high computational cost.A useful approach to speed up such simulations consists of employing reduced numerical modes which simplify the problem while retaining a high fidelity.Among these models, Fourier field decomposition in azimuthal modes for the cylindrical geometry is particularly well suited for physical problems with close to cylindrical symmetry, which is the case in LWFA.During my Ph.D., I first implemented this method in the open-source code SMILEI in the Finite Difference Time Domain (FDTD) discretization scheme for the Maxwell solver. However, this kind of solvers may suffer from numerical Cherenkov radiation (NCR). To mitigate this artifact, I also implemented Maxwell’s solver in the Pseudo Spectral Analytical Domain (PSATD) scheme which offers better accuracy of the results.This method is then employed to study the impact of realistic laser profiles from the Apollon facility on the quality of the accelerated electron beam. Its ability to correctly model the involved physical processes is investigated by determining the optimal number of modes and benchmarking its results with full 3D Cartesian simulations. It is shown that the imperfections in the laser pulse lead to differences in the results compared to theoretical profiles. They degrade the performance of laser-plasma accelerators especially in terms of the quantity of injected charge. These simulations, insightful for the future experiments of LWFA that will be held soon with the Apollon laser, put forward the importance of including realistic lasers in the simulation to obtain reliable results
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Mitchell, Robert Andrew III. "Understanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440411512.
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Dieckmann, Mark Eric. "A survey of elementary plasma instabilities and ECH wave noise properties relevant to plasma sounding by means of particle in cell simulations." Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327557.
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Hurtig, Tomas. "Plasma cloud penetration across magnetic boundaries." Doctoral thesis, KTH, Alfvén Laboratory, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3804.
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Drouin, Mathieu. "Vers la simulation particulaire réaliste de l'interaction laser-plasma surcritique : conception d'un schéma implicite avec amortissement ajustable et fonctions de forme d'ordre élevé." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2009. http://tel.archives-ouvertes.fr/tel-00442715.
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Le caractère éminemment cinétique et hors équilibre de l'interaction laser-plasma et du transport électronique nécessite de résoudre le système complet des équations de Vlasov-Maxwell. Cette thèse se concentre sur les méthodes PIC (‘‘Particle-In-Cell''), et vise à en accroître le régime de fonctionnement. Tout d'abord, nous présentons l'analyse de stabilité linéaire d'un algorithme PIC explicite incluant l'effet de la discrétisation spatio-temporelle. Cette analyse met en exergue l'instabilité d'aliasing, que nous relions au problème, plus général, du chauffage numérique dans les codes PIC en régime surcritique. Nous montrons l'influence bénéfique de la montée en ordre du facteur de forme pour réduire ce chauffage, permettant ainsi d'atteindre des régimes de densité jusque là inaccessibles. Les codes PIC implicites ne sont pas soumis aux mêmes contraintes de stabilité que leurs équivalents explicites. En particulier nous ne sommes plus tenus de résoudre les modes haute fréquence électroniques. Une telle propriété est particulièrement précieuse lorsqu'on modélise l'interaction entre un laser à ultra-haute intensité et un plasma fortement sur-critique. Nous présentons ici l'extension relativiste de la méthode implicite dite directe, en y incluant un paramètre d'amortissement ajustable et des facteurs de forme d'ordre élevé. Ce formalisme a été implémenté dans le code ELIXIRS, 2D en espace et 3D en vitesse. Ce code est validé sur de nombreux problèmes de physique des plasmas, allant de l'expansion d'un plasma à une ou deux températures électroniques, à l'interaction laser-plasma à haut-flux, en passant par les instabilités ‘‘deux faisceaux'' et de filamentation en régime relativiste. Nous montrons notamment la capacité du code à capturer les principales caractéristiques de l'interaction laser-plasma, malgré une discrétisation spatio-temporelle dégradée, autorisant ainsi des gains substantiels en temps de calcul.
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Pachler, Klaus, Thomas Frank, and Klaus Bernert. "Simulation of Unsteady Gas-Particle Flows including Two-way and Four-way Coupling on a MIMD Computer Architectur." Universitätsbibliothek Chemnitz, 2002. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200200352.
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The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction.
Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account.
For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma.
Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low.
Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.
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Spirkin, Anton M. "A three-dimensional particle-in-cell methodology on unstructured Voronoi grids with applications to plasma microdevices." Link to electronic dissertation, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050506-145257/.
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Stock, Andreas [Verfasser]. "A High-Order Particle-in-Cell Method for Low Density Plasma Flow and the Simulation of Gyrotron Resonator Devices / Andreas Stock." München : Verlag Dr. Hut, 2013. http://d-nb.info/1037287029/34.
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Penkal, Bryan James. "Steps in the Development of a Full Particle-in-Cell, Monte Carlo Simulation of the Plasma in the Discharge Chamber of an Ion Engine." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1367586856.
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Hoshi, Kento. "Study on Active Spacecraft Charging Model and its Application to Space Propulsion Systeｍ." Kyoto University, 2018. http://hdl.handle.net/2433/232002.
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Revel, Adrien. "Modélisation des plasmas magnétisés. Application à l'injection de neutres pour ITER et au magnétron en régime impulsionnel haute puissance." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112083/document.
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Un plasma est défini comme un gaz partiellement ou totalement ionisé. Bien que très présent dans l'univers visible, les plasmas naturels sont rares sur Terre. Cependant, ils représentent un intérêt majeur pour les industries et les instituts de recherche (traitement de surface, propulsion spatiale). Toutefois, la compréhension du comportement d'un plasma est complexe et fait appel à de nombreux domaines de la physique. De plus, ces plasmas peuvent être magnétisé i.e. lorsqu'un champ magnétique extérieur ou induit influence significativement la trajectoire des particules : r/L<1 où r est le rayon de Larmor et L la longueur caractéristique du système. Ce travail de thèse s'intéresse à la modélisation du comportement du plasma présent dans deux dispositifs : l'accélérateur de l'Injecteur de Neutres (IdN) rapides d'ITER et le magnétron en régime DC ou HiPIMS. La réalisation de la fusion nucléaire sur Terre fait actuellement l'objet de nombreuses recherche dans le monde. Du fait de l'énergie nécessaire au franchissement de la barrière de répulsion coulombienne, le plasma doit être confiné. Dans le cas d'ITER, le confinement est réalisé par de puissant champ magnétique. Cependant, pour atteindre les conditions nécessaires aux réactions de fusion, notamment en température, un injecteur de particules neutres à haute énergie (1MeV) est nécessaire. L'accélération de ces particules est une phase critique dans la création du faisceau de neutres et elle représente un défi technologique qui fait l'objet d'une étude dans ce travail de thèse. Le magnétron est un procédé industriel permettant la réalisation de couches minces par pulvérisation cathodique. Les ions créés par un plasma de décharge arrachent les atomes de la cathode qui se déposent sur l'anode. Le champ magnétique créé par des aimants permanents piège les électrons à proximité de la cathode augmentant l'efficacité du dispositif. Le comportement du plasma magnétron est ainsi étudié en régime continu ou pulsé ainsi que l'apparition de structures auto-organisées en rotation autour de l'axe du magnétron dans certaines conditions. Afin d'étudier ces dispositifs, plusieurs programmes de simulation numérique ont été développés. La méthode Paticle-In-Cell a été choisie car elle permet de prendre en compte la charge d'espace des particules de manière auto-cohérente. Diverses techniques (technique de collision nulle, Monte Carlo Collision, a posteriori Monte Carlo) et améliorations (maillage non uniforme, projections de charges au troisième ordre) ont été développées et implémentées. De plus, une méthode originale, Pseudo 3D, permettant un traitement à trois dimension du magnétron a été utilisées avec succès. Enfin, ces programmes ont été parallélisés afin de réduire le temps de calculA plasma is defined as a partially or completely ionized gas. Even though, they are very present in the visible universe, natural plasmas are rare on Earth. However, they are a major interest for industries and research institutes (surface treatment, spatial propulsion). Nevertheless, the understanding of plasma behavior is complicated because of the numerous physical fields involved. Moreover, theses plasmas can be magnetized, i.e., a magnetic field, external or induced, affects significantly the particle trajectories: r/L<1 where r is the Larmor radius and L the typical length of the system. This thesis is focused on the plasma modeling in two device: the accelerator of the ITER's neutral beam injector (NBI) and the magnetron in DC or HiPIMS regime. The feasibility of nuclear fusion on Earth is subject of numerous research around the world. Because of the energy necessary to get over the Coulomb barrier, the plasma must be confined. For ITER, the confinement is achieved by intense magnetic fields. However, to reach the required conditions of nuclear fusion reactions, especially in temperature, a high energy (1MeV) neutral beam injector is needed. The particle acceleration is a critical part in the creation of the neutral beam and it represents a technical challenge which is studied in this thesis work. The magnetron is an industrial process for creating thin film by physical sputtering. The ions created by a plasma discharge tear the atoms out of the cathode which are then deposited on the anode. The magnetic field created by permanent magnets trap the electrons near the cathode improving the process efficiency. The plasma behavior inside the magnetron is studied in direct and pulsed current as well as the appearance of self-organized structures in rotation around the magnetron axis. To study these devices, several program of numerical simulation have been developed. The Particle-In-Cell methode has been chosen because it takes into account, self-consistently, the space charge of the particules. Several techniques (null collision technique, Monte Carlo Collision, a posteriori Monte Carlo) and improvement (Non uniform mesh, third order charge projection) have been developed and implemented. Moreover, an original method, Pseudo 3D, allowing a three dimensional study of the magnetron, has been used with success. Finally, these programs have been parallelized to reduce the computation time
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Meige, Albert, and albert@meige net. "Numerical modeling of low-pressure plasmas: applications to electric double layers." The Australian National University. Research School of Physical Sciences and Engineering, 2006. http://thesis.anu.edu.au./public/adt-ANU20070111.002333.
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Inductive plasmas are simulated by using a one-dimensional particle-in-cell simulation including Monte Carlo collision techniques (pic/mcc). To model inductive heating, a non-uniform radio-frequency (rf) electric field, perpendicular to the electron motion is included into the classical particle-in-cell scheme. The inductive plasma pic simulation is used to confirm recent experimental results that electric double layers can form in current-free plasmas. These results differ from previous experimental or simulation systems where the double layers are driven by a current or by imposed potential differences. The formation of a super-sonic ion beam, resulting from the ions accelerated through the potential drop of the double layer and predicted by the pic simulation is confirmed with nonperturbative laser-induced fluorescence measurements of ion flow. It is shown that at low pressure, where the electron mean free path is of the order of, or greater than the system length, the electron energy distribution function (eedf) is close to Maxwellian, except for its tail which is depleted at energies higher than the plasma potential. Evidence supporting that this depletion is mostly due to the high-energy electrons escaping to the walls is given.
¶
A new hybrid simulation scheme (particle ions and Boltzmann/particle electrons), accounting for non-Maxwellian eedf and self-consistently simulating low-pressure high-density plasmas at low computational cost is proposed. Results obtained with the improved hybrid model are in much better agreement with the full pic simulation than the classical non self-consistent hybrid model. This model is used to simulate electronegative plasmas and to provide evidence supporting the fact that propagating double layers may spontaneously form in electronegative plasmas. It is shown that critical parameters of the simulation were very much aligned with critical parameters of the experiment.
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Mitma, Pillaca Elver Juan de Dios. "Estudo do processo de implantação iônica por imersão em plasma com campo magnético externo usando técnicas numéricas e experimentais." Guaratinguetá : [s.n.], 2011. http://hdl.handle.net/11449/102487.
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Orientador: Konstantin Georgiev KostovCo orientador: Mario Ueda
Banca: Milton Eiji Kayama
Banca: Rogério Pinto Mota
Banca: Munemasa Machida
Banca: Joaquim José Barroso de Castro
Resumo: Implantação iônica por imersão em plasma com campo magnético (3IPCM) foi investigada usando técnicas numéricas e experimentais. O campo magnético considerado é essencialmente não uniforme e é produzido por duas bobinas magnéticas posicionadas ao redor da câmara de vácuo. O estudo é centrado na análise do efeito de dois dos parâmetros mais importantes: tensão e pressão no processo 3IPCM. Outro tema importante como a dinâmica dos elétrons secundários foi também abordado neste trabalho. Neste contexto, o processo 3IPCM foi pesquisado inicialmente usando o código computacional KARAT. Os resultados numéricos mostraram um incremento da densidade do plasma ao redor do alvo durante a variação dos parâmetros de tensão, pressão e campo magnético considerados. Como consequência deste aumento, um incremento da densidade de corrente iônica sobre o alvo foi observado. Os resultados numéricos mostraram que o sistema de campos cruzados E×B intensifica o processo 3IPCM. Posteriormente, 3IPCM foi realizado experimentalmente. Resultados experimentais mostraram que a densidade de corrente foi incrementada em aproximadamente 100 % em relação ao caso sem campo magnético quando os parâmetros externos foram variados. Todos estes resultados numéricos e experimentais são explicados através do mecanismo de ionização do gás por colisão com os elétrons magnetizados realizando movimento de deriva em campos E×B. Finalmente, para analisar os efeitos do processo 3IPCM no tratamento de materiais foram realizados implantações em amostras de silício. Os resultados mostraram que o processo 3IPCM promove mudanças nas propriedades superficiais das amostras, tornando-as hidrofóbicas. Esta técnica mostra ser atrativa posto que foi possível incrementar a dose e a profundidade de implantação em alta tensão.
Abstract: Plasma immersion ion implantation (PIII) with magnetic field has been investigated using numerical and experimental methods. The magnetic field in consideration is essentially non-uniform and is generated by two magnetic coils installed outside the PIII vacuum chamber. The study is focused on analysis of the effect of two of the most important process parameters: voltage and gas pressure on the PIII with magnetic field. Another important subject such as the dynamics of secondary electrons has also been considered in this work. In this context, the PIII process with magnetic field has been initially analyzed numerically using the 2.5D computer code KARAT. The numeric results have shown an increase of the plasma density around of the target in the range of the considered parameters, voltage, pressure and magnetic field. As consequence of this an enhancement of the ion current density on the target was observed. The simulation results have demonstrated that the system of crossed E×B fields intensifies the PIII process with magnetic field. Later, the PIII process with magnetic field has been carried out experimentally. Experimental results have shown an increase of the current density in about 100 % in relation to the case without magnetic field when the external parameters have been varied. The numerical and experimental results are explained through the mechanism of gas ionization by collision with electrons drifting in crossed E×B field. Finally, to analyze the effect of the PIII process with magnetic field in material treatment implantation in Silicon samples has been carried out. The results indicate that the PIII process with magnetic field promotes changes of the samples surface properties, turning them hydrophobic. This PIII technique is attractive since it can increase the dose and the depth of implantation at high voltage.
Doutor
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Xi, Hong. "Theoretical and Numerical Studies of Frequency Up-shifted Ionospheric Stimulated Radiation." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29279.
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Stimulated electromagnetic emission (SEE) produced by interactions of high-power radio waves with the Earth's ionosphere is currently a topic of significant interest in ionospheric modification physics. SEE is believed to be produced by nonlinear wave-wave interactions involving the electromagnetic and electrostatic plasma waves in the altitude region where the pump wave frequency is near the upper hybrid resonance frequency. The most prominent upshifted feature in the SEE spectrum is the broad upshifted maximum (BUM). In this study, the instability processes thought to be responsible to the BUM spectra in the SEE experiments are discussed and analyzed using theoretical and electrostatic particle-in-cell (PIC) models.
From characteristics of this feature, a four-wave parametric decay process has been studied as a viable mechanism for its production. The object is to (1) investigate the early time nonlinear development of the four-wave decay instability by using theoretical and numerical simulation models, (2) study the variation of the four-wave decay instability spectral features for a wide range of plasma and pump wave parameters, and (3) access its possible role in the production of the BUM spectral feature. Results of this investigation show that there is good agreement between predictions of the proposed theoretical model and the numerical simulation experiments. The simulation electric field power spectrum exhibits many of the important features of the experimental observations. The numerical simulation results show that consideration of the full nonlinear development of the four-wave parametric instability is crucial in providing insight into the asymmetric nature of the wave frequency spectrum observed during the experiments.
The velocity-space ring-plasma instability, another generation mechanism for the BUM spectra, is studied using a theoretical model. The theoretical calculations show that the growth rate is larger in the region of the upper hybrid wave than that of the electron Bernstein wave. In addition, the effects of various plasma parameters are analyzed and it is predicted that the BUM should be more prominent with a hotter ring, at the direction perpendicular to the magnetic field, or in a closer region of cyclotron harmonic. A detailed comparison of the velocity space ring-plasma instability and the four-wave parametric process is presented where both the differences and the possible relations are discussed.Ph. D.
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Mitma, Pillaca Elver Juan de Dios [UNESP]. "Estudo do processo de implantação iônica por imersão em plasma com campo magnético externo usando técnicas numéricas e experimentais." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/102487.
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Implantação iônica por imersão em plasma com campo magnético (3IPCM) foi investigada usando técnicas numéricas e experimentais. O campo magnético considerado é essencialmente não uniforme e é produzido por duas bobinas magnéticas posicionadas ao redor da câmara de vácuo. O estudo é centrado na análise do efeito de dois dos parâmetros mais importantes: tensão e pressão no processo 3IPCM. Outro tema importante como a dinâmica dos elétrons secundários foi também abordado neste trabalho. Neste contexto, o processo 3IPCM foi pesquisado inicialmente usando o código computacional KARAT. Os resultados numéricos mostraram um incremento da densidade do plasma ao redor do alvo durante a variação dos parâmetros de tensão, pressão e campo magnético considerados. Como consequência deste aumento, um incremento da densidade de corrente iônica sobre o alvo foi observado. Os resultados numéricos mostraram que o sistema de campos cruzados E×B intensifica o processo 3IPCM. Posteriormente, 3IPCM foi realizado experimentalmente. Resultados experimentais mostraram que a densidade de corrente foi incrementada em aproximadamente 100 % em relação ao caso sem campo magnético quando os parâmetros externos foram variados. Todos estes resultados numéricos e experimentais são explicados através do mecanismo de ionização do gás por colisão com os elétrons magnetizados realizando movimento de deriva em campos E×B. Finalmente, para analisar os efeitos do processo 3IPCM no tratamento de materiais foram realizados implantações em amostras de silício. Os resultados mostraram que o processo 3IPCM promove mudanças nas propriedades superficiais das amostras, tornando-as hidrofóbicas. Esta técnica mostra ser atrativa posto que foi possível incrementar a dose e a profundidade de implantação em alta tensão.
Plasma immersion ion implantation (PIII) with magnetic field has been investigated using numerical and experimental methods. The magnetic field in consideration is essentially non-uniform and is generated by two magnetic coils installed outside the PIII vacuum chamber. The study is focused on analysis of the effect of two of the most important process parameters: voltage and gas pressure on the PIII with magnetic field. Another important subject such as the dynamics of secondary electrons has also been considered in this work. In this context, the PIII process with magnetic field has been initially analyzed numerically using the 2.5D computer code KARAT. The numeric results have shown an increase of the plasma density around of the target in the range of the considered parameters, voltage, pressure and magnetic field. As consequence of this an enhancement of the ion current density on the target was observed. The simulation results have demonstrated that the system of crossed E×B fields intensifies the PIII process with magnetic field. Later, the PIII process with magnetic field has been carried out experimentally. Experimental results have shown an increase of the current density in about 100 % in relation to the case without magnetic field when the external parameters have been varied. The numerical and experimental results are explained through the mechanism of gas ionization by collision with electrons drifting in crossed E×B field. Finally, to analyze the effect of the PIII process with magnetic field in material treatment implantation in Silicon samples has been carried out. The results indicate that the PIII process with magnetic field promotes changes of the samples surface properties, turning them hydrophobic. This PIII technique is attractive since it can increase the dose and the depth of implantation at high voltage.
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Stock, Andreas [Verfasser], and Claus-Dieter [Akademischer Betreuer] Munz. "A high-order particle-in-cell method for low density plasma flow and the simulation of gyrotron resonator devices / Andreas Stock. Betreuer: Claus-Dieter Munz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2013. http://d-nb.info/1036874745/34.
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Matsui, Ryutaro. "Study of nonlinear structures and dynamics in collisionless plasmas created by the interaction between high power laser and cluster medium." Kyoto University, 2019. http://hdl.handle.net/2433/242326.
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Buron, Franck. "Etude d'une nouvelle approche de la méthode Particle-In-Cell pour le calcul d'écoulements instationnaires incompressibles tridimensionnels de fluide parfait ; application au cas de la plaque plane en incidence." Poitiers, 2000. http://www.theses.fr/2000POIT2255.
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Ce memoire a pour objet le developpement d'une methode particle-in-cell tridimensionnelle et son application au calcul d'ecoulements instationnaires incompressibles de fluide parfait autour d'une plaque plane en incidence. La plaque plane est discretisee par une repartition de singularites de type doublets normaux surfaciques. Une description lagrangienne des zones tourbillonnaires permet de traiter l'evolution du sillage. La nappe tourbillonnaire est alors constituee de particules, chacune portant un vecteur tourbillon, que l'on suit dans leur mouvement. L'application du schema pic au calcul, a chaque pas de temps, du nouveau champ des vitesses, s'effectue en trois phases. Dans un premier temps, une loi de ponderation volumique est proposee pour distribuer la vorticite de chaque particule sur les sommets d'une cellule a base triangulaire superposee au domaine de calcul. Ensuite, contrairement aux schemas classiques qui utilisent une resolvante de poisson, nous conservons une interaction directe (biot-savart) entre les nuds du maillage pour y obtenir les vitesses et les gradients de vitesses induits. Enfin, une interpolation permet un transfert des valeurs de la grille vers les positions lagrangiennes des tourbillons. Cette technique associee a un maillage genere a partir de la discretisation du profil mince permet a la fois de minimiser la diffusion numerique, d'attenuer le temps de calcul et d'assurer une repartition plus homogene de la condition de glissement sur la paroi de la plaque et une non-penetration de cette derniere. Cette nouvelle approche est appliquee a l'ecoulement autour de la plaque plane pour diverses incidences et divers allongements. Les resultats sont confrontes a des donnees experimentales.
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Pebernet, Laura. "Etude d'un modèle Particle-In-Cell dans une approximation Galerkin discontinue pour les équations de Maxwell-Vlasov : recherche d'une solution hybride non conforme efficace." Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1080/.
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Cette thèse présente l'étude et le développement d'un outil de simulation numérique efficace pour la modélisation de l'interaction plasma/micro-ondes, à partir d'un solveur électromagnétique basé sur une approximation Galerkin Discontinue (GD). Le travail est organisé en deux parties principales. Tout d'abord, nous développons un modèle Particle-In-Cell (PIC) approprié au schéma GD. Pour cela, d'une part, nous proposons un modèle de correction hyperbolique pour la prise en compte de la loi de conservation de la charge et, d'autre part, nous intégrons des modèles physiques propres au plasma tels que les sources micro-ondes de forte puissance, les surfaces d'émission de particules et les faisceaux d'électrons. Ensuite, nous nous orientons vers la recherche de performances optimales pour le couplage Maxwell-Vlasov afin d'augmenter l'efficacité et la taille des applications à traiter. Cette recherche conduit à l'étude d'une hybridation non conforme de méthodes pour résoudre le problème Maxwell-Vlasov. Dans un premier temps, nous travaillons sur une méthode hybride entre différents schémas numériques pour la résolution d'un problème Maxwell 1D sur des maillages non conformes. Dans un second temps, nous nous intéressons au cas d'un problème 2D en mode TE, dans l'optique d'introduire un modèle PIC. Finalement, nous réalisons une hybridation FDTD/FDTD sur deux maillages non coïncidents pour les équations Maxwell-Vlasov 2DThis thesis presents the study and the development of an efficient numerical simulation's tool for the modeling of plasma/microwave interaction in an electromagnetic software based upon a Discontinuous Galerkin (DG) scheme. This work is organized following two main steps. First, we develop a Particle-In-Cell (PIC) model appropriate for DG scheme. For this, on the one hand, we propose a hyperbolic corrector method to take into account the charge conservation law and, on the other hand, we integrate physical plasma models such as high power microwave sources, emission particles surfaces and electrons beams. Then, we propose also optimal performances for the coupling of Maxwell-Vlasov equations in order to increase the efficiency and the size of the applications to treat. This leads to study a non conformal hybridization of methods to solve the Maxwell-Vlasov problem. In the first time, we work on a hybrid method between different numerical schemes to solve a 1D Maxwell problem on non conformal meshes. In the second time, we interest in a 2D TE Maxwell problem, in order to introduce a PIC model. Finally, we realise a FDTD/FDTD hybridization on two non coincident meshes for the 2D Maxwell-Vlasov system
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Bordikar, Maitrayee Ranade. "Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23206.
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This work focuses on the analysis of plasma irregularities generated during two active space experiments: the injection of an artificial dust layer, and high-power radio waves. The objective of the "first experiment is to examine the effects of artificially created dust layers on the scatter of radars from plasma irregularities embedded in dusty plasma in space. This is an alternate approach for understanding the mechanisms of enhanced radar scatter from plasma irregularities embedded in Noctilucent Clouds and Polar Mesospheric Summer Echoes. The second experiment involves a transmission of high power electromagnetic waves into the ionospheric plasma from the ground, which can excite stimulated electromagnetic emissions offset from the transmitter frequency. These stimulated electromagnetic emissions provide diagnostic information of the ionosphere and thus can be used to investigate fundamental physical principles which govern the earth\'s ionosphere, so that present and future transmission technologies may take into account the complexities of the ionosphere. The interaction altitude of the artificial dust layer and high power radio waves is approximately 250 km and 160 km respectively, thus dealing with uniquely different regions of the ionosphere. Each experiment is discussed separately using theoretical, observational and advanced computational methodologies.
The study first investigates plasma turbulence associated with the creation of an artificial dust layer in the earth's ionosphere. Two scenarios are considered for plasma irregularity generation as dust is injected at an oblique angle across the geomagnetic field. The first is a shear-driven plasma instability due to inhomogeneities in the boundary layer between the injected charged dust layer and the background plasma. This begins to appear at very early times once the dust is released into the space plasma, which is of the order or less than the dust charging time period. The second mechanism is free streaming of the charged dust relative to the background plasma. This produces irregularities at times much longer than the dust charging period and also longer than the dust plasma period. Although both mechanisms are shown to produce turbulence in the lower hybrid frequency range, the resulting irregularities have important differences in their physical characteristics. A comparison between the processes is made to determine the consequences for upcoming observations. Both processes are shown to have the possibility of generating turbulence after the release of dust for the regimes of upcoming space experiments over a range of timescales.
This work also presents the first observations of unique narrowband emissions ordered near the Hydrogen ion (H+) gyro-frequency (fcH) in the Stimulated Electromagnetic Emission (SEE) spectrum when the transmitter is tuned near the second electron gyro-harmonic frequency (2fce), during ionospheric modification experiments. The frequency structuring of these newly discovered emission lines is quite unexpected since H+ is known to be a minor constituent in the interaction region which is near 160 km altitude. The spectral lines are typically shifted from the pump wave frequency by harmonics of a frequency about 10% less than fcH (" 800 Hz) and have a bandwidth of less than 50 Hz which is near the O+ gyro-frequency fcO. A theory is proposed to explain these emissions in terms of a Parametric Decay Instability (PDI) in a multi-ion species plasma due to possible proton precipitation associated with the disturbed conditions during the heating experiment. The observations can be explained by including several percent H+ ions into the background plasma. The implications are new possibilities for characterizing proton precipitation events during ionospheric heating experiments.Ph. D.
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Psikal, Jan. "Ion acceleration in small-size targets by ultra-intense short laser pulses (simulation and theory)." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13941/document.
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Cette thèse a pour but l'étude de l’interaction des impulsions laser brèves et ultra-intenses avec des cibles de petite taille. Nous nous intéressons surtout des phénomènes liés à l’accélération des ions aux granges énergies. L'outil principal de cette étude est notre code Particle-in-Cell (PIC) bidimensionnel, qui est capable d'effectuer le calcul du mouvement des particules et de l'évolution des champs en régime relativiste et sans collisions. Ce mémoire présente la théorie de l’accélération d’ions par laser, les simulations numériques des différents régimes d'accélération, ainsi que les algorithmes mis en œuvre dans notre code. Les nouveaux résultats obtenus dans le cadre de cette thèse concernent trois cas principaux: 1) l’interaction des impulsions laser intenses avec des cibles de la masse limitée; 2) l’accélération des protons par laser dans des gouttelettes fines d’eau vaporisé; 3) le transport latéral des électrons chauds dans une feuille mince et son effet sur l’accélération d’ions. Nos études théoriques et les simulations numériques sont appliquées pour l'interprétation des résultats des deux expériences récentes réalisées par les équipes de recherche en Allemagne et en France. Ces expériences montrent une accélération efficace d’ions dans les conditions prévues dans nos travaux théoriques. Le spectre énergétique et le nombre des protons accélérés dans les feuilles minces de la surface limitée et dans les gouttelettes d’eau se comportent conformément aux nos prévisions. Le modèle théorique développé dans cette thèse considère l'accélération des ions en deux étapes. Le champ du laser n'interagit pas directement avec les ions du plasma du à sa masse très élevée. Par contre, les électrons chauds, générés pendant l’interaction de l'impulsion laser avec une cible, produisent les champs électrostatiques importants qui accélèrent les ions aux hautes énergies. Ces champs peuvent être amplifiés si la masse de la cible est suffisamment petite. Nous considérons que la cible a une masse limitée, si toutes ses dimensions sont comparables avec la taille du faisceau laser dans la zone d'interaction. Ces cibles permettent de réduire la dispersion des électrons chauds, et donc d'améliorer la transformation de l'énergie cinétique d'électrons dans l’´energie des ions. Nos simulations numériques indiquent que la taille de cible transverse optimale est égale au diamètre du faisceau laser. Les expériences récentes avec des feuilles minces de la surface limitée ont confirmé que la transformation de l’énergie laser `a l’énergie des ions est plus efficace, l’énergie des ions est plus élevée, et la divergence du faisceau d’ions diminue avec la diminution de la surface de feuille. La physique de l’interaction d'un faisceau laser avec les gouttelettes d’eau est plus complexe, car il faut prendre en compte plusieurs facteurs tels que l'ionisation inhomogène des atomes de la gouttelette et la recombinaison, sa position dans le focus de laser, les collisions des électrons etc. Nous avons modélisé l’interaction de l’impulsion laser avec une gouttelette de diamètre de 100 nm. Dans un petit agrégat des atomes irradié par laser, les électrons sont expulsés par la force pondéromotrice et, pas conséquent, les ions sont accélérés par la force de Coulomb. Nous avons réussi d'expliquer la formation d'un pic dans la fonction de distribution des protons en énergie par l'effet de la répulsion mutuelle entre deux espèces des ions. Finalement, nous avons étudié le transport latéral des électrons dans le cas de l'incidence rasante du faisceau laser sur la cible mince plaine. Avec une série des simulations nous avons démontré qui le transport des électrons accélérés est réalisé par deux mécanismes complémentaires: par le guidage des électrons chauds sur la surface d’avant de la feuille par les champs quasi statiques électrique et magnétique et par la recirculation des électrons entre les faces l'arrière et l'avant de la cibleThe presented thesis is based on a theoretical study of the interaction of femtosecond laser pulses with small-size targets and related phenomena, mainly acceleration of ions. We have employed our relativistic collisionless two-dimensional particle-in-cell code to describe the interaction and subsequent ion acceleration. The theory of ion acceleration and related physics (for example, electron heating mechanisms) have been reviewed as well as computational algorithms used in our simulation code. In the thesis, our obtained results are organized into three main parts: 1) interaction of an intense laser pulse with mass-limited targets; 2) laser proton acceleration in a water spray target; 3) lateral hot electron transport and ion acceleration in thin foils. Our theoretical and numerical studies are accompanied with recent experimental results obtained by cooperating research groups on enhanced ion acceleration in thin foils of reduced surface and on proton acceleration in a cloud of water microdroplets. Since the field of nowadays operating lasers is not sufficient to accelerate directly ions to high energies due to their at least 1000 times larger mass-to-charge ratio compared with electrons, the ion acceleration is mediated by hot electrons creating strong electrostatic fields (a population of electrons heated by the laser wave) in targets of sizes higher or comparable with the laser wavelength or by Coulomb force between ions after electron expulsion in small clusters. Due to reduced target dimensions, the mass-limited targets, defined as the targets having all dimensions comparable with the laser spot size, limit the spread of hot electrons and, thus, the electron kinetic energy is transferred to ions more efficiently. We found via 2D PIC simulations that the optimum transverse target size is about the laser beam diameter. The enhancement of proton energy, laser-to-proton conversion efficiency, and narrower ion angular spread have been observed in recent experiments with thin foil sections and have confirmed our previous theoretical studies. The physics of the laser pulse interaction with water spray is rather complex and includes many phenomena (microdroplet ablation by laser prepulse, inhomogeneous droplet ionization, laser focal spot position in the spray, recombination and collisional effects in the surrounding target material, etc.). We have carried out numerical simulations of the laser pulse interaction with a water microdroplet of diameter of 100 nm, which gives an insight into the physics of ion acceleration in the spray. One can observe a pronounced peak in the proton energy spectra at the cutoff energy, which was explained by mutual interaction between protons and oxygen ions. Finally, we have studied two mechanisms of lateral electron transport in a thin foil - the first is due to hot electron guiding along the foil front surface by generated quasi-static electric and magnetic fields, and the second is caused by the hot electron recirculation (reversing of the normal component of electron velocity when the electron propagating through the foil starts to escape into vacuum, while the transverse velocity is largely unaltered). We found that only a small number of electrons can be guided along the foil surface for large incidence angles (60° and more) of the laser beam on the foil surface, whereas the majority of electrons is laterally transported towards foil edges due to the recirculation through the thin foil. However, electrons guided along the surface can be accelerated to several times higher energy than the recirculating electrons, which enhances the energy of accelerated ions from foil edges
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Plewa, Jérémie-Marie. "Etude de l'influence des plasmas dans les diodes à électrons pour la radiographie éclair." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30156/document.
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La radiographie éclair par faisceau X intense est spécifique en ce sens qu'elle doit permettre de photographier la matière soumise à des conditions extrêmes de densification, de température et de vitesse de déplacement. Le succès de ce type de radiographie repose sur la qualité de la source X qui doit nécessairement être pénétrante (quelques MeV), intense (plusieurs rads), brève (quelques dizaines de ns) et de petite dimension (quelques mm). L'impulsion X est ainsi générée à partir du rayonnement de freinage émis lors de l'interaction avec une cible en métal d'un faisceau focalisé d'électrons de haute énergie (MeV) et de haute intensité (kA). Ce procédé lie très fortement les propriétés du faisceau d'électrons à ceux du faisceau X et donc à la qualité de la radiographie. Dans ce contexte, la thèse porte sur la compréhension de la dynamique du faisceau dans la diode à l'électron (c'est-à-dire juste avant son entrée dans la ligne accélératrice) ainsi que sur la caractérisation du plasma de velours dont sont issus les électrons qui composent le faisceau. Dans un premier temps, la dynamique du faisceau intense d'électrons a été étudiée à l'aide du code LSP reposant sur la méthode " Particle-In-Cell ". Les simulations réalisées ont été comparées avec des mesures effectuées sur l'injecteur d'un accélérateur linéaire à induction, implanté au CEA Valduc sur l'installation Epure. Grâce au modèle de simulation développé, une nouvelle diode à électrons mono-impulsion a été conçue, dimensionnée et réalisée pendant ce travail de thèse afin d'augmenter l'intensité du faisceau d'électrons de 2,0 kA à 2,6 kA permettant ainsi d'améliorer les performances radiographiques de l'installation. Dans un second temps, un modèle permettant d'étudier les mécanismes mis en jeu dans la production du faisceau d'électrons au niveau de plasma de cathode a été développé. Ce dernier est un modèle collisionnel-radiatif (MCR) 0D qui permet de décrire l'évolution de la densité des espèces d'un plasma dont la composition est directement liée aux molécules et atomes désorbés par la cathode de velours. Trois différents mélanges ont été étudiés impliquant de l'hydrogène, de l'oxygène et du carbone dont les proportions ont été estimées par des mesures LIBS (spectroscopie de plasma induit par laser).[...]Intense X-ray flash radiography is used to take a stop-action picture of a material under extreme conditions like high densification, high temperature and high movement speed. The success of this kind of radiography is based on the quality of the X-ray source which must necessarily be penetrating (some MeV), intense (several rads), short (a few tens of ns) and small (a few mm). The X-ray pulse is generated from the bremsstrahlung radiation emitted during the interaction with a metal target of a focused electron beam of high energy (MeV) and high intensity (kA). This process strongly links the properties of the electron beam to those of the X-ray beam and thus to the quality of the radiography picture. In this context, the thesis is about the electron beam dynamics in the electron diode (i.e. just before electrons move towards the accelerator) as well as about the characterization of the velvet plasma from which electrons are extracted to form the beam. Firstly, the dynamics of the intense electron beam was studied using the LSP code based on the "Particle-In-Cell" method. The simulations were compared to measurements made on the injector of a linear induction accelerator, at the CEA Valduc center on the Epure facility. Based on the developed simulation model, a new single-pulse electron diode was designed, sized and realized during this thesis to increase the intensity of the electron beam from 2.0 kA to 2.6 kA, thus improving the radiographic performances of the facility. In a second step, a model allowing to study the mechanisms involved in the production of the electron beam from the cathode plasma was developed. This latter is a collisional-radiative model (CRM) 0D describing the evolution of the plasma species density of a plasma whose composition is directly related to the molecules and atoms desorbed by the velvet cathode. [...]
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Ljung, Patric. "Visualization of Particle In Cell Simulations." Thesis, Linköping University, Department of Science and Technology, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2340.
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A numerical simulation case involving space plasma and the evolution of instabilities that generates very fast electrons, i.e. approximately at half of the speed of light, is used as a test bed for scientific visualisation techniques. A visualisation system was developed to provide interactive real-time animation and visualisation of the simulation results. The work focuses on two themes and the integration of them. The first theme is the storage and management of the large data sets produced. The second theme deals with how the Visualisation System and Visual Objects are tailored to efficiently visualise the data at hand.
The integration of the themes has resulted in an interactive real-time animation and visualisation system which constitutes a very powerful tool for analysis and understanding of the plasma physics processes. The visualisations contained in this work have spawned many new possible research projects and provided insight into previously not fully understood plasma physics phenomena.
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Nakata, Michael Takeshi. "Simulating the FTICR-MS Signal of a Decaying Beryllium-7 Ion Plasma in a 2D Electrostatic PIC Code." Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3370.pdf.
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Birch, Paul C. "Particle-in-cell simulations of the lunar wake." Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392768.
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Blaclard, Guillaume. "Ultra-High Intense Laser on Dense Plasmas : from Periodic to Chaotic Dynamics." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS133.
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L'émergence des lasers ultra-brefs et ultra-intenses a permis le développement d'une nouvelle branche de la physique encore largement inexplorée : la physique UHI (pour Ultra-High Intensity). Lors de la réflexion d'un tel laser sur une cible solide, l'intensité au foyer I₀ peut atteindre des valeurs aussi importantes que 10¹⁸⁻²⁰ W.cm⁻², suffisamment pour ioniser complétement la matière. Le plasma ainsi formé se détend sur une longueur caractéristique Lg, nommée longueur de gradient. Quand Lg <<λ₀ (longueur d'onde du laser), le plasma dense se comporte comme un miroir de qualité optique capable de réfléchir spéculairement la lumière incidente : c'est un miroir plasma. Ce système physique remarquable peut être utilisé dans de multiples applications principalement comme source compacte de faisceaux de particules à hautes charges et hautes énergies ou de lumière intense, principalement ultraviolet ou X, grâce à un phénomène de génération d'harmoniques d'ordres élevés. Le bon contrôle de ces sources nécessite de clairement identifier les différents mécanismes de couplage entre lumière et matière en jeu lors de l'interaction. Dans ce manuscrit, cela est rendu possible grâce à de précises simulations de type Particle-In-Cell (PIC) réalisées avec le code WARP+PXR. Ce nouveau code emploie un solveur pseudo-spectral pour résoudre les équations de Maxwell. Celui-ci améliore grandement la précision des simulations et notamment des émissions harmoniques et électroniques, que les solveurs plus standards ne parviennent à décrire, même à hautes résolutions. Grâce à des simulations WARP+PXR, nous avons étudié l'influence de Lg sur les observables expérimentales que sont les émissions de lumière et de particules, quand un laser de puissance (I₀ = 10¹⁹ W.cm⁻²) se réfléchit sur un plasma dense. Notre étude révèle une claire transition entre un mécanisme périodique en temps et un processus chaotique quand l'interface devient plus lisse. Nous nous sommes principalement concentrés sur le deuxième mécanisme, appelé chauffage stochastique pour lequel des études en profondeur vont être menées en fonction de différents paramètres d'interaction. Dans ce régime, les électrons de la partie sous-dense du plasma subissent une dynamique chaotique dans l'onde stationnaire formée par la superposition des ondes incidente et réfléchie, ce qui leur permet d'absorber une importante part de l'énergie laser. La nature fondamentale de la dynamique en jeu est révélée grâce aux équations du mouvement au sein des deux ondes que l'on peut réduire en équations de pendules forcés (comme celui de Kapitza), systèmes bien connus comme chaotiques. Cette correspondance apporte une intuition physique profonde sur le comportement des électrons pour différentes configurations laser. Ceci nous permet in fine de prédire les principaux aspects du chauffage stochastiqueThe advent of high power femtosecond lasers has paved the way to a promising and still largely unexplored branch of physics called Ultra-High Intensity physics (UHI). Once such a laser is focused on a solid target, the laser intensity I₀ can reach values as large as 10¹⁸⁻²⁰ W.cm⁻², for which matter is fully ionized. The plasma thus formed expands towards vacuum on a spatial scale characterized by a quantity Lg called the density gradient scale length. When Lg << λ₀ (laser wavelength), the dense plasma therefore acts as an optical mirror that specularly reflects the incident light: it is a plasma mirror. This remarkable physical system can be used in many scientific applications as compact source of high-energy and high-charge particle beams (electrons, ions) or bright source of radiations ranging from extreme ultraviolet-rays to X-rays through high harmonic generation processes. In order to finely control these sources, it is required to properly identify the different coupling mechanisms between light and matter at play during the interaction. In this manuscript, this has been made possible by performing accurate Particle-In-Cell (PIC) simulations with the WARP+PXR code. This recently developed code advances Maxwell’s equations in Fourier space, which proves to correctly model harmonic/electron emissions that standard codes fail to accurate describe even at high resolution. Based on WARP+PXR PIC simulations, we investigate the influence of Lg on the experimentally observed emission of light and particles, when a high-power laser pulse (I₀ = 10¹⁹ W.cm⁻²) reflects off a dense plasma. Our study reveals an unambiguous transition from a temporally periodic mechanism to a chaotic process as the interface becomes smoother. In particular, the latter mechanism, named stochastic heating, is fully characterized as well as its domain of validity in terms of laser-plasma parameters. In this regime, electrons in the underdense part of the gradient are exposed to the standing wave formed in front of the overcritical part of the plasma by superposition of incidence and reflected beams. While evolving in the two waves, electrons behave chaotically and absorb an important fraction of the laser energy. The nature of the interaction is revealed by reducing the equations of motion of particles in two waves to physical systems, such Kapitza’s pendulum, well-known to exhibit chaos. That correspondence gives deep physical intuitions on how electrons behave in different laser configurations, which allows us to predict major features of stochastic heating
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Popoola, O. M. "A reconfigurable computer for particle-in-cell plasma simulations." Thesis, University of Sussex, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418534.
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Gasparin, Pedraza Laia. "Particle in Cell Simulations of Electrostatic Waves in Saturn's Magnetosphere." Thesis, KTH, Rymd- och plasmafysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103415.
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The characteristics of electrostatic waves are investigated using PIC simulations of a four component plasma: cool and hot electrons, cool ions and an electron beam. The velocities are de ned by Maxwellian distributions. The system is one dimensional and simulates a collisionless, unmagnetized plasma. Langmuir waves, electron acoustic waves, beam-driven waves and ion acoustic waves are excited in the simulations. The results are analysed using the dispersion relation and compared with previous investigations and analytical results.
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Jeong, Hyunju. "Kinetic Simulations of Spacecraft Charging and Plasma Interactions in the Solar Wind." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/30237.
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Analytical and numerical studies are carried out to investigate spacecraft charging and plasma interactions in the solar wind. The physics of spacecraft charging in solar wind is determined by the mesothermal flow and the photoelectron sheath. In order to properly resolve both plasma flow and the photoelectron sheath, a 3-D full particle PIC model is applied. In this model, all plasma species (ambient ions and electrons, and photoelectrons) are modeled as macro-particles so the detailed dynamics of each species can be resolved around a charged spacecraft. In order to correctly resolve the mesothermal velocity ratio, PIC simulations are carried out using the real ion to electron mass ratio. A charging model based on the capacitance matrix method is integrated into the PIC model so the floating potential can be calculated self-consistently with the PIC code from charges deposited on the surface.
We first investigate the photoelectron sheath in the solar wind. Previous analytical studies of monotonic and non-monotonic sheath profiles in stationary electrons have suggested that there can exist two solutions of the sheath profiles when photoelectron emissions are significant. We extend the previous analytical approach to include the effects of drifting electrons. Full particle PIC simulations suggest that the non-monotonic sheath profile is the stable solution under solar wind conditions. We found that the current balance calculation is not an accurate method to predict the floating potential when photoelectron emissions are significant.
We next apply the simulation model to study spacecraft charging under various solar wind conditions. Due to photoelectron emissions, spacecraft charging is typically not a serious problem. The floating potential is ~2.5V under the mean solar wind condition. We also investigate the plasma interactions of a multi-body system consisting of a large platform and a small free flyer in the absence of photoelectron emissions where we set a free flyer at 2*Debye length behind the platform in the wake. For the particular system studied in this dissertation, the simulation shows that wake charging is not severe under both the mean solar wind condition and severe magnetosheath charging condition.Ph. D.
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Sáez, Pous Xavier. "Particle-in-cell algorithms for plasma simulations on heterogeneous architectures." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/381258.
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During the last two decades, High-Performance Computing (HPC) has grown rapidly in performance by improving single-core processors at the cost of a similar growth in power consumption. The single-core processor improvement has led many scientists to exploit mainly the process level parallelism in their codes. However, the performance of HPC systems is becoming increasingly limited by power consumption and power density, which have become a primary concern for the design of new computer systems. As a result, new supercomputers are designed based on the power efficiency provided by new homogeneous and heterogeneous architectures.
The growth in computational power has introduced a new approach to science, Computational Physics. Its impact on the study of nuclear fusion and plasma physics has been very significant. This is because the experiments are difficult and expensive to perform whereas computer simulations of plasma are an efficient way to progress. Particle-In-Cell (PIC) is one of the most used methods to simulate plasma. The improvement in the processing power has enabled an increase in the size and complexity of the PIC simulations. Most PIC codes have been designed with a strong emphasis on the physics and have traditionally included only process level parallelism. This approach has not taken advantage of multiprocessor platforms. Therefore, these codes exploit inefficiently the new computing platforms and, as a consequence, they are still limited to using simplified models.
The aim of this thesis is to incorporate in a PIC code the latest technologies available in computer science in order to take advantage of the upcoming multiprocessor supercomputers. This will enable an improvement in the simulations, either by introducing more physics in the code or by incorporating more detail to the simulations.
This thesis analyses a PIC code named EUTERPE on different computing platforms. EUTERPE is a production code used to simulate fusion plasma instabilities in fusion reactors. It has been implemented for traditional HPC clusters and it has been parallelized prior to this work using only Message Passing Interface (MPI). Our study of its scalability has reached up to tens of thousands of processors, which is several orders of magnitude higher than the scalability achieved when this thesis was initiated.
This thesis also describes the strategies adopted for porting a PIC code to a multi-core architecture, such as introducing thread level parallelism, distributing the work among different computing devices, and developing a new thread-safe solver. These strategies have been evaluated by applying them to the EUTERPE code. With respect to heterogeneous architectures, it has been possible to port this kind of plasma physics codes by rewriting part of the code or by using a programming model called OmpSs. This programming model is specially designed to make this computing power easily available to scientists without requiring expert knowledge on computing.
Last but not least, this thesis should not be seen as the end of a way, but rather as the beginning of a work to extend the physics simulated in fusion codes through exploiting available HPC resources.Durant les darreres dues dècades, la Computació d'Alt Rendiment (HPC) ha crescut ràpidament en el rendiment mitjançant la millora dels processadors d'un sol nucli a costa d'un creixement similar en el consum d'energia. La millora en els processadors d'un sol nucli ha portat a molts científics a explotar tot el paral·lelisme a nivell de procés en els seus codis. No obstant això, el rendiment dels sistemes HPC està cada cop més limitat pel consum d'energia i la densitat de potència, que s'han convertit en una de les principals preocupacions en el disseny dels nous sistemes informàtics. Com a resultat, els nous supercomputadors estan dissenyats sobre la base de l'eficiència energètica proporcionada per les noves arquitectures homogènies i heterogènies. El creixement de la potència de càlcul ha introduït un nou enfocament a la ciència, la Física Computacional. El seu impacte en l'estudi de la fusió nuclear i la física del plasma ha estat molt significatiu. Això és perquè els experiments són difícils i costosos de realitzar mentre que les simulacions del plasma amb computadors són una manera eficaç de progressar. Particle-In-Cell (PIC) és un dels mètodes més utilitzats per simular el plasma. La millora en la potència de processament ha permès un augment en la grandària i la complexitat de les simulacions PIC. La majoria dels codis PIC s'han dissenyat amb un fort èmfasi en la física i tradicionalment han inclòs només paral·lelisme a nivell de procés. Aquest enfocament no ha aprofitat les plataformes multiprocessador. Per tant, aquests codis exploten ineficientment les noves plataformes de computació i, com a conseqüència, encara estan limitats a tractar amb models simplificats. L'objectiu d'aquesta tesi és incorporar en un codi PIC les últimes tecnologies disponibles en informàtica per tal d'aprofitar els propers supercomputadors multiprocessador. Això permetrà una millora en les simulacions, ja sigui mitjançant la introducció de més física en el codi o mitjançant la incorporació de més detall en les simulacions. Aquesta tesi analitza un codi PIC anomenat EUTERPE en diferents plataformes de computació. EUTERPE és un codi de producció utilitzat per simular les inestabilitats del plasma en els reactors de fusió. S'ha implementat per clústers HPC tradicionals i s'ha paral·lelitzat prèviament a aquest treball usant només la Interfície de Pas de Missatges (MPI). El nostre estudi de la seva escalabilitat ha arribat fins a desenes de milers de processadors, que és diversos ordres de magnitud més gran que l'escalabilitat que s'havia assolit quan es va iniciar aquesta tesi. Aquesta tesi també descriu les estratègies adoptades per portar un codi PIC a una arquitectura multi-nucli, com ara la introducció de paral·lelisme a nivell de thread, la distribució de la feina entre diferents dispositius de computació i el desenvolupament d'un nou solver thread-safe. Aquestes estratègies han estat avaluades amb la seva aplicació al codi EUTERPE. Pel que fa a les arquitectures heterogènies, ha estat possible portar aquest tipus de codis de la física del plasma reescrivint part del codi o mitjançant l'ús d'un model de programació anomenat OmpSs. Aquest model de programació està especialment dissenyat per posar aquesta potència de càlcul a l'abast dels científics sense necessitat de coneixements d'experts en computació. Finalment, però no menys important, aquesta tesi no ha de ser vista com el final d'un camí, sinó més aviat com l'inici d'un treball per estendre la física simulada en els codis de fusió nuclear mitjançant l'explotació dels recursos disponibles de HPC.
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Dowds, Brendan J. P. "Particle-in-cell simulations of streamer initiation and plasma generation." Thesis, University of Glasgow, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398637.
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Kafafy, Raed. "Immersed Finite Element Particle-In-Cell Simulations of Ion Propulsion." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29057.
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A new particle-in-cell algorithm was developed for plasma simulations involving complex
boundary conditions. The new algorithm is based on the three-dimensional
immersed finite element method which is developed in this thesis, and a modified
legacy particle-in-cell code. The model also applies a new meshing technique that
separates the field solution mesh from the particle pushing mesh in order to increase
the computational eciency of the model.
The new simulation model is used in two applications of great importance to the
development of ion propulsion technology: the ion optics performance and the interaction
between spacecraft and the ion thruster. The first application is ion optics
simulations. Simulations are performed to investigate ion optics plasma flow for a
whole subscale NEXT ion optics. The operating conditions modeled cover the entire
cross-over to perveance limit range. The results of the ion optics simulations
demonstrated good agreement with the available experimental data. The second
application is ion thruster plume simulations. Simulations are performed to investigate
ion thruster plume - spacecraft interactions for the Dawn spacecraft. Plume
induced contaminations on the solar array are studied for a variety of ion thruster
configurations including multiple thruster firings.Ph. D.
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Ould, Salihi Mohamed Lemine. "Couplage de méthodes numériques en simulation directe d'écoulements incompressibles." Phd thesis, Université Joseph Fourier (Grenoble), 1998. http://tel.archives-ouvertes.fr/tel-00004901.
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Ce travail est consacré au développement des méthodes lagrangiennes comme alternatives ou compléments aux méthodes euleriennes conventionnelles pour la simulation d'écoulements incompressibles en présence d'obstacles. On s'intéresse en particulier à des techniques ou des solveurs eulériens et lagrangiens cohabitent dans le même domaine de calcul mais traitent différents termes des équations de Navier-Stokes, ainsi qu'à des techniques de décomposition de domaines ou différents solveurs sont utilisés dans chaques sous-domaines. Lorsque les méthodes euleriennes et lagrangiennes cohabitent dans le même domaine de calcul (méthode V.I.C.), les formules de passage particules-grilles permettent de représenter la vorticité avec la même précision sur une grille fixe et sur la grille lagrangienne. Les méthodes V.I.C. ainsi obtenues combinent stabilité et précision et fournissent une alternative avantageuse aux méthodes différences-finies pour des écoulements confinés. Lorsque le domaine de calcul est décomposé en sous-domaines distincts traités par méthodes lagrangiennes et par méthodes euleriennes, l'interpolation d'ordre élevé permet de réaliser des conditions d'interface consistantes entre les différents sous-domaines. On dispose alors de méthodes de calcul avec décomposition en sous-domaines, de type Euler/Lagrange ou Lagrange/Lagrange, et résolution en formulation (vitesse-tourbillon)/(vitesse-tourbillon) ou (vitesse-pression)/(vitesse-tourbillon). Les différentes méthodes développées ici sont testées sur plusieurs types d'écoulements (cavité entrainée, rebond de dipôles de vorticité, écoulements dans une conduite et sur une marche, écoulements autour d'obstacles) et comparées à des méthodes de différences-finies d'ordre élevé.
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Melzani, Mickaël. "Reconnexion magnétique non-collisionelle dans les plasmas relativistes et simulations particle-in-cell." Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0946/document.
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L'objectif de cette thèse est l'étude de la reconnexion magnétique dans les plasmas non-collisionels et relativistes. De tels plasmas sont présents dans divers objets astrophysiques (MQs, AGNs, GRBs...), où la reconnexion pourrait expliquer la production de particules et de radiation de haute énergie, un chauffage, ou des jets. Une compréhension fondamentale de la reconnexion n'est cependant toujours pas acquise, en particulier dans les plasmas relativistes ion-électron. Nous présentons d'abord les bases de la reconnexion magnétique. Nous démontrons des résultats particuliers à la physique des plasmas relativistes, concernant par exemple la distribution de Maxwell-Jüttner. Ensuite, nous réalisons une étude détaillée de l'outil numérique utilisé : les simulations particle-in-cell (PIC). Le fait que le plasma réel contienne beaucoup plus de particules que le plasma PIC a des conséquences importantes (collisionalité, relaxation, bruit) que nous décrivons. Enfin, nous étudions la reconnexion magnétique dans les plasmas ion-électron et relativistes à l'aide de simulations PIC. Nous soulignons des points spécifiques : loi d'Ohm (l'inertie de bulk dominante), zone de diffusion, taux de reconnexion (et sa normalisation relativiste). Les ions et les électrons produisent des lois de puissance, avec un index qui dépend de la vitesse d'Alfvén et de la magnétisation, et qui peut être plus dur que dans le cas des chocs non-collisionels. De plus, les ions peuvent avoir plus ou moins d'énergie que les électrons selon la valeur du champ guide. Ces résultats fournissent une base solide à des modèles d'objets astrophysiques qui, jusque là, supposaient a priori ces résultatsThe purpose of this thesis is to study magnetic reconnection in collisionless and relativistic plasmas. Such plasmas can be encountered in various astrophysical objects (microquasars, AGNs, GRBs...), where reconnection could explain high-energy particle and photon production, plasma heating, or transient large-scale outflows. However, a first principle understanding of reconnection is still lacking, especially in relativistic ion-electron plasmas. We first present the basis of reconnection physics. We derive results relevant to relativistic plasma physics, including properties of the Maxwell-Jüttner distribution. Then, we provide a detailed study of our numerical tool, particle-in-cell simulations (PIC). The fact that the real plasma contains far less particles than the PIC plasma has important consequences concerning relaxation times or noise, that we describe. Finally, we study relativistic reconnection in ion-electron plasmas with PIC simulations. We stress outstanding properties: Ohm's law (dominated by bulk inertia), structure of the diffusion zone, energy content of the outflows (thermally dominated), reconnection rate (and its relativistic normalization). Ions and electrons produce power law distributions, with indexes that depend on the inflow Alfvén speed and on the magnetization of the corresponding species. They can be harder than those produced by collisionless shocks. Also, ions can get more or less energy than the electrons, depending on the guide field strength. These results provide a solid ground for astrophysical models that, up to now, assumed with no prior justification the existence of such distributions or of such ion/electron energy repartition
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Ngirmang, Gregory Kodeb. "Particle-in-Cell Simulations of the Acceleration of Electrons from the Interaction of a Relativistic Laser Reflecting from Solid Density Targets." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1514985418694386.
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