Thèses : « Plasmi in tokamak »

1

CASIRAGHI, IRENE. « First principle based integrated modelling in support of the Divertor Tokamak Test facility design ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2023. https://hdl.handle.net/10281/402360.

Texte intégral

Résumé :

Nel programma di ricerca europeo per la fusione termonucleare controllata sono stati definiti otto differenti obiettivi a lungo termine. Una di queste sfide cruciali riguarda lo smaltimento (exhaust) di particelle ed energia provenienti da un reattore a fusione. Per sviluppare e testare delle strategie alternative atte a risolvere il problema dell'exhaust, una nuova macchina sperimentale è attualmente in costruzione in Italia a Frascati presso il centro di ricerca ENEA: il Divertor Tokamak Test facility (DTT). Per progettare un nuovo tokamak sono richiesti sforzi congiunti di fisici ed ingegneri. Al fine di ridurre i costi e minimizzare i rischi, uno strumento essenziale è la modellizzazione integrata il più completa possibile basata su principi primi. Il presente progetto di dottorato è incentrato sullo sviluppo di simulazioni multi-canale basate sulla fisica dei principali scenari operazionali di riferimento di DTT. Modelli all'avanguardia di trasporto, riscaldamento, fuelling ed equilibrio magnetico vengono integrati in queste simulazioni per predire in modo auto-consistente profili di plasma e parametri di scenario. Vengono anche calcolate tutte le interazioni non lineari tra sistemi di riscaldamento e plasma e tra i diversi canali di trasporto. Durante questo lavoro, le simulazioni di DTT sono state progressivamente migliorate perfezionandone le impostazioni e includendo un crescente numero di aspetti grazie all'aggiunta di codici appositi. Inoltre sono stati inclusi man mano aggiornamenti dei sistemi di riscaldamento, dell'equilibrio magnetico e della configurazione della macchina per seguire l'evoluzione del progetto. Il confronto tra simulazioni analoghe con differenti modelli quasi-lineari di trasporto ci rende fiduciosi dell'affidabilità dei profili di plasma predetti e ci permette di identificare i punti deboli dei modelli nei vari regimi in cui opera DTT. Questi modelli quasi-lineari sono stati inoltre validati mediante simulazioni girocinetiche nel range di parametri di DTT. L'accuratezza delle predizioni è state migliorata in modo ricorsivo accordando le condizioni al contorno delle simulazioni di core e delle simulazioni del SOL, garantendo così una consistenza core-edge-SOL. Abbiamo studiato lo scenario a massime performance per guidare la progettazione della macchina e il primo plasma e gli scenari intermedi per assistere le fasi iniziali. Le performance dello scenario a piena potenza è stato testato con nove differenti opzioni di riscaldamento allo scopo di selezionare la distribuzione di potenza ottimale tra i tre sistemi di riscaldamento ausiliario. È stata poi verificata la compatibilità dello scenario a piena potenza con le capacità del sistema di bobine elettromagnetiche. Inoltre per la prima volta sono stati stimati, nello scenario a massima potenza, i denti di sega e gli ELMs di DTT. Un'analisi delle prestazioni richieste ai sistemi di fuelling per sostenere gli alti profili di densità ha dimostrato che sarebbe insufficiente utilizzare solamente un sistema di gas puffing e che sono necessari pellet di deuterio per alimentare DTT. Sono stati stimati i tassi di emissione neutronica, risultando compatibili con il progetto attuale delle schermature neutroniche. Questo progetto di dottorato ha portato all'ottimizzazione delle dimensioni della macchina e alla definizione delle potenze di riferimento dei sistemi di riscaldamento e ha fornito i profili di riferimento per la progettazione delle diagnostiche, la stima delle rese neutroniche, il calcolo delle perdite di particelle veloci, i requisiti del gas puffing e/o dei pellet per il fuelling, valutazioni MHD e altri lavori.
The European research roadmap towards thermonuclear fusion energy defined eight different missions to guide the long–term programme. One of these crucial challenges is the controlled power and particle exhaust from a fusion reactor. To develop and test alternative strategies to solve the exhaust problem, in Italy a new experimental device is now under construction at the ENEA Research Center in Frascati: the Divertor Tokamak Test facility (DTT). Designing a new tokamak requires concerted efforts of physicists and engineers. To reduce costs and minimise risks, a first–principle based integrated modelling as comprehensive as possible of plasma discharges is an essential tool. The focus of this PhD project was to perform the first physics–based multi–channel simulations of the main baseline operational scenarios of DTT. In these simulations state–of–art modules for transport, heating, fuelling, and magnetic equilibrium are integrated to achieve self–consistent predictions of plasma profiles and scenario parameters. All non–linear interactions between heating and plasma and between the different transport channels are also calculated. During this work, the DTT simulations have been progressively enhanced adding codes to include a growing number of aspects and refining run settings. Moreover, updates of the heating systems, magnetic equilibria, and device configuration have been included to comply with the evolving machine design. The comparison among analogous simulations with different quasi–linear transport models made us confident in the reliability of the predicted plasma profiles and allowed us to identify the weak points of the models in the various DTT operational regimes. A validation of these quasi–linear models against the gyrokinetic simulations in the specific DTT range of parameters was also performed. The prediction accuracy has been improved recursively by matching the core and SOL simulation boundary conditions to guarantee the core–edge–SOL consistency. We investigated the full performance scenario to guide the machine design, and the first plasma and intermediate scenarios to assist the commissioning phases. The full performance scenario was tested with nine different heating mix options to select the optimal power distribution amongst the three auxiliary heating systems. The compatibility of the full power scenario with the electromagnetic coil system capabilities was then verified. In addition, the DTT sawteeth and ELMs during the full power scenario were estimated for the first time. An analysis of the required fuelling system performance to sustain the high density profiles proved that only the gas puffing system would be insufficient and that deuterium pellets are needed for the DTT fuelling. Neutron rates were evaluated and found compatible with the present design of the neutron shields. This PhD modelling work led to the optimisation of the device size and of the reference heating mix, and provided reference profiles for diagnostic system design, estimates of neutron yields, calculations of fast particle losses, gas puffing and/or pellet requirements for fuelling, MHD evaluations, and other tasks.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Severo, José Helder Facundo. « Estudo da rotação de plasma no tokamak TCABR ». Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06092012-125249/.

Texte intégral

Résumé :

Este trabalho, que pode ser dividido em duas partes, teórica e experimental, trata da rotação residual de plasma no TCABR. No que se refere à parte teórica, foi obtida uma expressão geral para a velocidade poloidal e o fluxo de calor, para tokamaks com seção transversal arbitrária, em um plasma que está sujeito a um fluxo subsônico toroidal. Foram estudadas em detalhe as dependências da velocidade poloidal com o número de Mach sigma e o fluxo de calor iônico e foi verificado que a velocidade poloidal troca de sentido para um certo valor sigma=sigma IND.0. Também foi verificado que existe um valor sigma=sigma IND.K, a velocidade poloidal começa a diminuir. Quanto ao fluxo de calor, foi observado que ele é fortemente afetado pela geometria e é proporcional a q POT.2, onde q é o fator de segurança. Para q=1, o fluxo de calor tem um máximo para um fator de elongação k=1, correspondente a uma seção transversal circular, diminui com o aumento de k e apresenta um mínimo em k=2. No que se refere à parte experimental,foram obtidos pela primeira vez, no tokamak TCABR, os perfis radiais das velocidade de rotação poloidal e toroidal para um regime colisional, usando o deslocamento Doppler das linhas espectrais das impurezas de CIII (646,74nm) e CVI (529,02nm), medidas com um espectrômetro TH1000 de distância focal 1000mm e dispersão linear de 8 A/mm. Os resultados experimentais mostram que a velocidade poloidal tem um máximo de (4,5 + OU -1,0).10 POT.5cm/s, cujo sentido de deriva diamagnética dos elétrons. Estes resultados mostram uma boa concordância com a teoria neoclássica para a região da coluna r=5-14 cm, enquanto que para r>14 cm os resultados experimentais estão de desacordo com a teoria. No que diz respeito à velocidade de rotação toroidal, ela é oposta à corrente de plasma e tem um valor máximo de (20 + OU -1).10 POT.5cm/s, o que está em razoável concordância com o modelo proposto por ) Kim e Diamond. Foi observado que a velocidade de rotação toroidal troca de sentido em r>16 cm, indicando haver um forte cisalhamento da rotação na borda da coluna de plasma. A partir dos resultados das velocidades poloidal e toroidal e do gradiente de temperatura iônica, foi calculada a componente radial do campo elétrico que resultou negativo em toda a coluna de plasma. Finalmente, estes resultados estão em boa concordância com os resultados obtidos em tokamaks semelhantes ao TCABR. Os resultados experimentais para a velocidade poloidal podem ser bem descritos pela teoria neoclássica de rotação em tokamaks, exceto nas regiões próximas ao limitador. No entanto, ainda não existe uma teoria geral satisfatória para explicar os resultados da rotação toroidal do plasma em tokamaks. Existem teorias interessantes, porém não são aplicáveis ao tokamak TCABR
In the present work we investigated theorically and experimentally the plasma residual rotation in the tokamak TCABR. Using the neoelassical theory, general expressions for the poloidal velocity and heat flux were obtained for tokamaks with arbitrary plasma cross-sections, and subsonic toroidal flows. The dependency of the poloidal velocity and the heat flow with Mach number a were analyzed. It was found that the poloidal velocity changes sign for a ccrtain valuc alpfa = alpha 0, a critical value ak of a exists corresponding to a maximum value of ion poloidal velocity, and that for alpha > alpha k the poloidal velocity is a decreasing function of alpha.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Bae, Cheonho. « Extension of neoclassical rotation theory for tokamaks to account for geometric expansion/compression of magnetic flux surfaces ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45839.

Texte intégral

Résumé :

An extended neoclassical rotation theory (poloidal and toroidal) is developed from the fluid moment equations, using the Braginskii decomposition of the viscosity tensor extended to generalized curvilinear geometry and a neoclassical calculation of the parallel viscosity coefficient interpolated over collision regimes. Important poloidal dependences of density and velocity are calculated using the Miller equilibrium flux surface geometry representation, which takes into account elongation, triangularity, flux surface compression/expansion and the Shafranov shift. The resulting set of eight (for a two-ion-species plasma model) coupled nonlinear equations for the flux surface averaged poloidal and toroidal rotation velocities and for the up-down and in-out density asymmetries for both ion species are solved numerically. The numerical solution methodology, a combination of nonlinear Successive Over-Relaxation(SOR) and Simulated Annealing(SA), is also discussed. Comparison of prediction with measured carbon poloidal and toroidal rotation velocities in a co-injected and a counter-injected H-mode discharges in DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] indicates agreement to within <10% except in the very edge in the co-injected discharge.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Hornung, Grégoire. « Etude de la turbulence plasma par réflectrométrie à balayage ultra-rapide dans le tokamak Tore Supra ». Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4741/document.

Texte intégral

Résumé :

La turbulence plasma engendre un transport anormal de la chaleur et des particules qui dégrade l’efficacité d’un réacteur de fusion. La mesure de la turbulence plasma dans un tokamak est donc essentielle à la compréhension et au contrôle de ce phénomène. Parmi les instruments de mesure à disposition, le réflectomètre à balayage installé sur le tokamak Tore Supra a accès à la densité du plasma et ses fluctuations depuis le bord jusqu’au centre des décharges, avec une excellente résolution spatiale (mm) et temporelle (µs), de l’ordre des échelles de la turbulence. Cette thèse est dédiée à la caractérisation de la turbulence plasma dans Tore Supra à partir de mesures de réflectométrie à balayage ultrarapide. Des analyses de corrélations ont permis d’évaluer les échelles spatiales et temporelles de la turbulence ainsi que sa vitesse radiale. Dans la première partie, la caractérisation des propriétés de la turbulence à partir des profils de densité reconstruits est discutée, notamment au travers d’une comparaison avec les données des sondes de Langmuir. Ensuite une étude paramétrique est présentée mettant en relief l’effet de la collisionalité sur la turbulence, dont une interprétation est proposée en termes de stabilisation d’une turbulence électronique due aux électrons piégés. Finalement, on illustre comment le chauffage additionnel produit une modification locale de la turbulence dans le plasma proche des parois, se traduisant par une augmentation de la vitesse des structures et une diminution de leur temps de corrélation. L’effet supposé des potentiels rectifiés générés par l’antenne est étudié à l’aide de simulations
The performance of a fusion reactor is closely related to the turbulence present in the plasma. The latter is responsible for anomalous transport of heat and particles that degrades the confinement. The measure and characterization of turbulence in tokamak plasma is therefore essential to the understanding and control of this phenomenon. Among the available diagnostics, the sweeping reflectometer installed on Tore Supra allows to access the plasma density fluctuations from the edge to the centre of the plasma discharge with a fine spatial (mm) and temporal resolution (µs ) , that is of the order of the characteristic turbulence scales.This thesis consisted in the characterization of plasma turbulence in Tore Supra by ultrafast sweeping reflectometry measurements. Correlation analyses are used to quantify the spatial and temporal scales of turbulence as well as their radial velocity. In the first part, the characterization of turbulence properties from the reconstructed plasma density profiles is discussed, in particular through a comparative study with Langmuir probe data. Then, a parametric study is presented, highlighting the effect of collisionality on turbulence, an interpretation of which is proposed in terms of the stabilization of trapped electron turbulence in the confined plasma. Finally, it is shown how additional heating at ion cyclotron frequency produces a significant though local modification of the turbulence in the plasma near the walls, resulting in a strong increase of the structure velocity and a decrease of the correlation time. The supposed effect of rectified potentials generated by the antenna is investigated via numerical simulations

Styles APA, Harvard, Vancouver, ISO, etc.

5

Song, Shaodong. « Etude du transport de la chaleur et des particules dans les tokamaks Tore Supra et HL-2A ». Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10142/document.

Texte intégral

Résumé :

Le transport de la chaleur et des particules est un des sujets de recherche fondamentaux de la physique des plasmas chauds confinés par des champs magnétiques, systèmes physiques qui sont étudiés dans le cadre des recherches sur la fusion thermonucléaire contrôlée. Ces phénomènes de transport sont essentiellement liés à la turbulence électromagnétique et ils sont donc extrêmement difficiles à modéliser par la théorie. Des expériences spécifiques sont alors réalisées sur des machines expérimentales, telles que les tokamaks ou les stellarators, afin d'améliorer la connaissance de ces phénomènes. Cette thèse décrit des études expérimentales de ce type réalisées sur deux tokamaks de grande dimension: Tore Supra (machine basée au CEA/Cadarache) et HL-2A (basée au South-Western Institute of Physics, Chengdu, Chine). La technique utilisée consiste à injecter, de façon modulée dans le temps, des ondes de forte puissance afin de perturber la température électronique du plasma, et des faisceaux supersoniques de particules pour en perturber la densité. La température est mesurée par l'Emission Cyclotronique Electronique et la densité par Réflectométrie micro-onde. Ces expériences on mis en évidence une convection de la chaleur vers l'intérieur du plasma (un phénomène dont l'existence est toujours controversée), et des effets dus aux termes non-diagonaux de la matrice de transport. Ces résultats ont été comparés aux modèles de transport existants
Heat and particle transport is one of the fundamental subjects of research in the physics of hot plasmas confined by magnetic fields, a class of physical systems that are studied in the framework of research on controlled thermonuclear fusion. These transport phenomena are mainly related to electromagnetic turbulence and are therefore extremely difficult to model at a first-principle level. Specific experiments in this area, on plasma devices such as tokamaks or stellarators, are widely used to improve understanding of these phenomena. This thesis reports on experimental studies performed on two large tokamaks : Tore Supra (based at CEA/Cadarache, France) and HL-2A (based at the South-Western Institute of Physics, Chengdu, China). The technique used consists in modulated injection of wave power to perturb the electron temperature and/or of Supersonic Molecular Beams to perturb the plasma density. Temperature is then measured by Electron Cyclotron Emission and density by Reflectometry, and Fourier analysis is used to determine the transport properties. Evidence has been found of inward heat convection (a phenomenon whose existence is still controversial) as well as of peculiar effects due to the non-diagonal terms of the transport matrix. Comparison with transport models has been carried out

Styles APA, Harvard, Vancouver, ISO, etc.

6

Mercadier, Laurent. « Spectrocopie de plasma induit par laser pour l'analyse des composants face au plasma de tokamaks : étude paramétrique et mesures autocalibrées ». Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22071/document.

Texte intégral

Résumé :

Lors du fonctionnement d'un réacteur de fusion nucléaire par confinement magnétique comme ITER, une fraction de tritium est piégée par les composants face au plasma et doit être mesurée pour des raisons de sureté nucléaire. La spectroscopie de plasma induit par laser est proposée pour effectuer cette mesure. Le plasma laser produit sur des tuiles de Tore Supra en composite à fibre de carbone est analysé à l'aide d'une étude paramétrique : il doit avoir une température supérieure à 10000 K et une densité électronique supérieure à 10^17 cm^-3 pour optimiser l'application. Une méthode "autocalibrée" prenant en compte l'auto-absorption des raies est utilisée pour déterminer la concentration relative d'hydrogène à partir des spectres expérimentaux. La caractérisation spatio-temporelle du panache d'ablation révèle la présence d'un gradient de température dirigé du centre vers la périphérie du plasma. La prise en compte de ce gradient permet de déduire le rapport des concentrations H/C. L'incertitude de la mesure est évaluée et discutée. La mesure du rapport isotopique D/H sous pression réduite d'argon met en évidence un effet de ségrégation qui doit être pris en compte afin d'éviter des erreurs de mesure de l'ordre de 50%. Les matériaux à base de tungstène sont analysés et les difficultés associées aux données spectroscopiques sont abordées. Enfin, la faisabilité de l'analyse LIBS résolue en profondeur est validée pour des échantillons métalliques multicouches préalablement étalonnés
During the operation of a nuclear fusion device like the future reactor ITER, a fraction of tritium is trapped in the plasma facing components and has to be measured in order to fulfill nuclear safety requirements. Laser-induced breakdown spectroscopy is proposed to achieve this measurement. The laser plasma produced on carbon fibre composite tiles from the Tore Supra reactor is analyzed via a parametric study : it has to have a temperature over 10000 K and an electron density over 10^17 cm^-3 to optimize the application. A calibration-free procedure that takes into account self-absorption is proposed to determine the relative concentration of hydrogen from the experimental spectra. The time- and space-resolved spectral emission of the plasma plume is investigated and reveals the presence of a temperature gradient from the core towards the periphery. This gradient is taken into account and the H/C concentration ratio is deduced. The accuracy of the results is evaluated and discussed. The study of the D/H isotopic ratio under low pressure argon reveals the presence of plume segregation that leads to an error of about 50%, error that can partially be reduced. Tungsten materials are investigated and difficulties related to spectroscopic databases are discussed. Finally, the feasibility of LIBS analysis with depth resolution is validated for multilayered metallic samples

Styles APA, Harvard, Vancouver, ISO, etc.

7

Breton, Sarah. « Tungsten transport in a tokamak : a first-principle based integrated modeling approach ». Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0007.

Texte intégral

Résumé :

La fusion par confinement magnétique est actuellement la voie la plus avancée pour produire de l’énergie grâce à la réaction de fusion. L’un des défis à relever concerne la contamination du plasma par le Tungstène (W), un matériau capable de résister aux hauts flux de chaleur. A cause de son grand nombre atomique, le W rayonne dans les plasmas de tokamak. S’il s’accumule au cœur du tokamak, il refroidit le plasma. Il est donc crucial de comprendre les mécanismes du transport du W et d’identifier les paramètres favorisant son accumulation. Le W interagit de façon non-linéaire avec les différents paramètres du plasma. La simulation intégrée est le seul outil permettant à tous ces paramètres d’être simulés de façon auto-consistante durant plusieurs temps de confinement. Pour la première fois, l’outil de simulation intégrée est couplé à des codes de transport premiers principes modélisant de façon auto-consistante les transports turbulent et collisionnel du W, les profils de densité, température, rotation, radiation, et l’évolution du chauffage. Pour des raisons numériques, certains phénomènes ne sont pas modélisés et l'interaction plasma/paroi interne est simplifiée. A chaque pas de temps, cette simulation reproduit avec succès les signaux expérimentaux et le comportement du W. De plus, des acteurs responsables de l’accumulation du W (la rotation et la source centrale de particules) sont identifiés. Enfin, la simulation intégrée a permis de mettre en lumière l’effet stabilisant du W sur la turbulence. Le travail accompli montre que la simulation intégrée premiers principes permet désormais d'optimiser à l'avance les scénarios de plasma afin d'y limiter l'accumulation de W
Magnetic confinement fusion is currently the most advanced way to produce energy thanks to Deuterium/Tritium reaction. One of the challenges is the limitation of the reaction contamination because of Tungsten (W), a material capable of resisting high heat fluxes. W large atomic number causes W to radiate inside tokamak plasmas. If W accumulates in the central part, it cools down the plasma. It is therefore crucial to understand the mechanisms of W transport and identify the actuators of the accumulation process. W transport is involved in complex interplays with the plasma parameters (density, temperature, rotation). Therefore the use of integrated modeling is mandatory in order to evolve self-consistently all those parameters for several confinement times. For the first time, an integrated modeling tool is coupled to first-principle transport codes to self-consistently simulate the time evolution of the W behavior, as well as the evolution of density, temperature, rotation profiles, radiation and external heating. For numerical reasons, several phenomena are not modeled, and the physics of the interaction with the inner wall is simplified. At each time step, this simulation successfully reproduces experimental profiles and the W central accumulation. Moreover, actuators of the central W accumulation (rotation and central particle fueling) were identified. Finally, integrated modeling simulation allowed bringing out a very interesting non-linear mechanism: the stabilizing effect of W on turbulence. This work demonstrates that first-principles integrated modeling now allows to design and optimize in advance plasma scenarios with limited W central accumulation

Styles APA, Harvard, Vancouver, ISO, etc.

8

Lerche, Ernesto Augusto. « Aquecimento do plasma por ondas de Alfvén no tokamak TCABR ». Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-17072012-141903/.

Texte intégral

Résumé :

Os resultados de uma extensa campanha experimental, realizada no tokamak TCABR, para se investigar a física das ondas de Alfvén e suas aplicações para o aquecimento de plasmas em tokamaks são apresentados. Ao longo das investigações, foram testados dois tipos de antena, tendo sido observado aquecimento considerável do plasma com ambas, mesmo com valor moderado da potência RF injetada no plasma. Diversas configurações de excitação e diversas condições do plasma foram investigadas, e foi verificado que a escolha correta da helicidade da onda excitada PE crucial para se reduzir o acoplamento parasítico com o plasma periférico. Também foi verificada a importância de uma limpeza periódica da superfície das antenas, realizada durante as descargas de limpeza do tokamak, para melhorar o desempenho dos experimentos com aquecimento por ondas de Alfvén. Com a antena original, que produz um espectro poloidal bastante selecionado, a tensão de polarização dinâmica induzida nas antenas observada durante os experimentos era alta, aumentando a taxa de sputtering em seus elementos e podendo, inclusive, levar à disruptura do plasma em potêncis RF mais elevadas. Com o novo tipo de antena, projetado com dimensões poloidais reduzidas, a tensão de polarização induzida caiu pela metade. No entanto, o acoplamento parasítico com a borda do plasma aumentou, como foi indicado por maiores perturbações observadas nos potenciais do SOL, nesse caso. Ademais, a taxa de injeção/ionização de impurezas parece ser maior do que a observada com a antena original em condições semelhantes, como foi indicado pór um aumento maior no sinal do bolômetro durante o pulso RF e por medidas de espectroscopia. Esses fatos sugerem que o espectro excitado pela antena nova é menos seletivo quanto à componente poloidal M, e os modos eletrostáticos devem estar sendo excitados com amplitude considerável. As modificações causadas pela absorção das ondas de Alfvén no perfil radial da temperatura eletrônica do plasma puderam ser estudadas com um radiômetro heteródino de varredura ECE. Esses estudos nos permitiram determinar experimentalmente os perfis radiais de deposição de potência RF no plasma, que estão em surpreendente concordância com os perfis de deposição de potência RF no plasma, que estão surpreendente concordância com os perfis de deposição teóricos, calculados com um código cinético-toroidal para as condições típicas do TCABR. Esses resultados são inéditos em pesquisas com ondas de Alfvén, e reforçam a sua utilização para aquecimento localizado de plasmas e controle de fluxos cizalhados em tokamaks.
The results of na extensive experimental campaign performed in the TCABR tokamak to investigate the Physics of the Alfvén wave and its application to tokamak plasma heating are presented. In the course of the experiments, Téo types of Alfvén Wave antennae were studied, and considerable plasma heating was observed in both cases, even with rather small amount of RF Power injected in the plasma. Many antennae configurations and plasma conditions were tried out, and it was verified that the correct choice of the helicity of the excited wave is crucial to reduce the parasitic coupling with the edge plasma. It was also noticed that periodic conditioning of the antenna surface, performed together with the daily tokamak cleaning discharges, also contributes to improve the performance of the heating experiments. With the first antenna type, which produced a rather well defined poloidal spectrum, the dynamic polarication voltage induced in the antennae during the RF experiments was high, causing increased sputtering of its elements and, for higher RF powr input, even plasma disruptions. With the new antenna type, designed with smaller poloidal dimensions, the dynamic polarization voltage of the antenna was reduced twice. However the parasitic coupling with the plasma hás increased, as indicated by stronger perturbations of the electrostatic potentials in the scrape-off layer observed in this case. In addition, the impurity injection/ionization rate also seems to have increased with respect to the previous antenna type in approximately the same conditions, as indicated by a stronger rise in the bolometer signal observed during the RF pulse, and by spectroscopic measurements. These facts suggest that, with the new antenna type, the excited wave spectrum is rather broad with respect to the poloidal wave number M, and electrostatic modes must be excited with quite high amplitude. The change in the radial profiles of the electron temperature due to the Alfvén wave absorption could be studied with a heterodyne sweping ECE radiometer. These sutidies allowed us to determine experimentally the RF Power deposition profiles inside the plasma, which were in surprisingly good agreement with the theoretical deposition profiles, calculated with a kinetic-toroidal code for the TCABR plasma conditions. These results are unprecedented in experimental Alfvén wave research, and strengthen the use of these waves for localized plasma heating and shear flow control in tokamaks.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Marx, Alain. « Deux étapes majeures pour le développement du code XTOR : parallélisation poussée et géométrie à frontière libre ». Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX095/document.

Texte intégral

Résumé :

Le code XTOR-2F simule la dynamique 3D des instabilités MHD bi-fluides de plasmas de tokamaks.La première partie de la thèse a été consacrée à la parallélisation du code XTOR-2F. Le code a été parallélisé significativement malgré la représentation pseudo-spectrale pour les deux directions angulaires, la raideur des équations résolues et l’utilisation d’une décomposition LU exacte afin d’inverser le préconditionneur physique. Le temps d’exécution de la version parallèle est un ordre de grandeur plus petit que la version séquentielle sur un maillage basse résolution. L’accélération croît ensuite avec la taille du maillage. La parallélisation permet également de réaliser des simulations avec des maillages plus grands, autrefois non réalisables par la limitation du stockage en RAM.La seconde partie de la thèse a été consacrée au développement d’une version du code permettant de réaliser des simulations en géométrie à frontière libre, s’approchant de la géométrie des tokamaks expérimentaux de grandes tailles. Les conditions initiales sont fournies par le code d’équilibre CHEASE à l’intérieur du plasma. A l’extérieur du plasma, la solution a été étendue en ajustant le potentiel magnétique avec un ensemble de bobines magnétiques poloïdales externes. Les conditions de bord utilisent des fonctions de Green afin de calculer une matrice de transfert permettant de relier les composantes tangentes et normales du champ magnétique externe à la coque avec la solution interne. Ceci permet de modéliser une coque résistive fine. Cette nouvelle version élargie le domaine d’investigation de XTOR-2F, autrefois restreint aux instabilités internes, aux instabilités externes. Le comportement linéaire du code est validé sur deux familles d’instabilités, les modes axisymétriques n = 0 et les kinks externes n = 1 / m = 2. Afin de valider le comportement non linéaire, des simulations en MHD résistive de modes tearing à bêta nul évoluant vers un état stationnaire ont été réalisées
The XTOR-2F code simulates the 3D dynamics of full bi-fluid MHD instabilities in tokamak plasmas.The first part of the thesis was dedicated to the parallelisation of XTOR-2F code. The code has been parallelised significantly despite the numerical profile of the problem solved, i.e. a discretisation with pseudo-spectral representations in all angular directions, the stiffness of the two-fluid stability problem in tokamaks, and the use of a direct LU decomposition to invert the physical pre-conditioner. The execution time of the parallelised version is an order of magnitude smaller than the sequential one for low-resolution cases, with an increasing speedup when the discretisation mesh is refined. Moreover, it allows to perform simulations with higher resolutions, previously forbidden because of memory limitations.The second part of the thesis was dedicated to the development of free boundary condition. The original fixed boundary computational domain of the code was generalised to a free-boundary one, thus approaching closely the geometry of today’s and future large experimental devices. The initial conditions are given by the CHEASE equilibrium code inside the plasma. Outside the plasma, fitting the magnetic potential at the CHEASE computation domain boundary with a set of external poloidal magnetic coils extends the solution. The boundary conditions use Green functions to construct a response matrix matching the normal and tangential components of the outside magnetic field with the inside solution. A thin resistive wall can be added to the computational domain. This new numerical setup generalises the investigation field from internal MHD instabilities towards external instabilities. The code linear behaviour is validated with two families of instabilities, n = 0 axisymmetric modes and n = 1/m = 2 external kinks. In order to validate the nonlinear behaviour, nonlinear resistive MHD simulations of tearing modes at zero beta evolving to a stationary state have been performed

Styles APA, Harvard, Vancouver, ISO, etc.

10

Morel, Pierre. « Le modèle "water bag" appliqué aux équation cinétiques des plasmas de Tokamak ». Phd thesis, Université Henri Poincaré - Nancy I, 2008. http://tel.archives-ouvertes.fr/tel-00453088.

Texte intégral

Résumé :

Ce travail a porté sur l'étude des instabilités de gradient de température ioniques (ITG) en géométrie cylindrique, le champ magnétique étant supposé constant et dirigé selon l'axe du cylindre. Une fonction de distribution discrète en forme de marche d'escalier est utilisée pour décrire la direction de vitesse parallèle au champ magnétique. L'équation de Vlasov se résume à un système de type multi fluides couplés par l'équation de quasi neutralité. Chaque fluide est décrit par un système fermé d'équations (continuité, Euler et fermeture adiabatique), caractéristiques d'un fluide incompressible, d'ou la dénomination de sac d'eau ou “water bag”. Le recours à cette description water bag est particulièrement intéressant dans le cas de problèmes à une seule dimension en vitesse. Ainsi, dans le cas des plasmas fortement magnétisés, un modèle water bag peut se combiner avantageusement aux modèles dits girocinétiques. Les paramètres associés a la représentation water bag ont pu être identifiés et reliés aux grandeurs macroscopiques par le biais d'une méthode originale d'équivalence au sens des moments. L'analyse water bag des ITG a permis de valider le modèle et les méthodes choisies. Ce travail a également permis de montrer que le concept de water bag peut sans problème prendre en compte des effets variés comme ceux liés a l'introduction d'un rayon de Larmor fini, tout comme à la description d'un plasma composé de plusieurs espèces d'ions.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Poye, Alexandre. « Dynamique des ilots magnétiques en présence de feuille de courant et en milieu turbulent ». Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4793/document.

Texte intégral

Résumé :

La stabilité des plasmas de fusion est un enjeu crucial dans le cadre du développement de nouvelles sources d'énergie. L'interaction entre le plasma et le champ magnétique peut en effet amener à la destruction du confinement : c'est une disruption. Le sujet de cette thèse porte sur les îlots magnétiques, une des causes des disruptions. Ces îlots magnétiques sont observés expérimentalement et analytiquement. Les théories peuvent prévoir la croissance d'un îlot magnétique et sa taille, mais les restrictions sur le domaine de validité de la théorie sont fortes et elles dé-corrèlent largement les domaines de validité théoriques et expérimentaux. Dans une première partie, nous montrons que, génériquement, les méthodes de contrôle dynamiques d'évolution des îlots magnétiques, basées notamment sur une relation entre la taille de l'îlot et la perturbation de flux magnétique à la résonance, devraient prendre en compte la modification du flux magnétique moyenné le long de la ligne de champ. Nous donnons aussi des limites quand au cadre de notre assertion (coalescence des îlots, effondrement du point X, ...). la seconde partie de la thèse aborde un nouvel effet dû au courant de part et d'autre de l'îlot magnétique. Il change la dynamique de l'îlot et la perception que l'on en a. Jusqu'à présent la dynamique de l'îlot était étudiée principalement au travers de mécanisme actifs au niveau de la résonance. Nous démontrons que la présence de courant aux abords de l'îlot peuvent jouer un rôle très important sur sa croissance et sur sa taille finale. La troisième partie détaille comment la turbulence aux abords d'un îlot magnétique peut affecter sa croissance
The fusion plasma stability is a critical point for the developpement of newenergy source. The interaction between the plasma and the magnetic field can drive to the confinement descrution : it is a disruption. The topic of this thesis is the magnetic island, one of disruption causes. Those magnetic islands are observed theoretically and numerically. The theory can predict the growth and the final size of magnetic islands, but restrictions of its validity range are strong and they decorrelate the experimental and theoritical validity domain. In the first part, we show that the dynamic method of magnetic island control, based on the link between the island size and the perturbed magnetic flux at the resonance, should take in account the modification of the magnetic flux averaged along the field line. We show aswell the limitation of our assertion (magnetic island coalescence, X point collapse ...). The second part of the thesis address a new effet du to the current on sides of the magnetic island. This effect changes the magnetic island dynamics and the perception we got on it. Until now, the magnetic island dynamics have been studied through active mechanisms at the resonance. We show that the presence of current on sides can play an important role on the growth and saturation of the magnetic island. The last part of thesis details how the turbulence on the outskirts of a magnetic island can affect the island growth. We show that a turbulence generate by an interchange instability can penetrate into a stable zone concerning tearing mode and induce by a 3D mechanisme the growth of an magnetic island

Styles APA, Harvard, Vancouver, ISO, etc.

12

Kelly, Frederick Alan. « Tokamak density limits ». Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16628.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

13

Taborda, David Ciro. « Magnetic field modeling for non-axisymmetric tokamak discharges ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-04012017-142757/.

Texte intégral

Résumé :

In this work we study the magnetic field modeling of realistic non-axisymmetric plasma equilibrium configurations and the heat flux patterns on the plasma facing components of tokamak divertor discharges. We start by establishing the relation between generic magnetic configurations and Hamiltonian dynamical systems. We apply the concept of magnetic helicity, used to establish topological bounds for the magnetic field lines in ideal plasmas, and to understand the self-consistency of reconnected magnetic surfaces in non-axisymmetric configurations. After this theoretical discussion, we present some results on magnetohydrodynamic equilibrium and the use of analytical solutions to the Grad-Shafranov equation for describing real tokamak discharges based on the experimental diagnostics and realistic boundary conditions. We also compare the equilibrium reconstruction of a DIII-D discharge obtained with a numerical reconstruction routine, developed as part of this research, and the EFIT code used by several tokamak laboratories around the world. The magnetic topology and plasma profiles obtained with our method are in considerable agreement with the numerical reconstruction performed with the other code. Then, we introduce a simplified description of the generic non-axisymmetric magnetic field created by known sources and implement it numerically for describing the magnetic field due to external coils in tokamak devices. After that, we use this routines to develop a numerical procedure to adjust a suitable set of non-linear parameters of internal filamentary currents, which are intended to model the plasma response based on the magnetic field measurements outside the plasma. Finally, these methods are used to model the magnetic field created by a slowly rotating plasma instability in a real DIII-D discharge. The plasma response modeling is based on the magnetic probe measurements and allow us to calculate the magnetic field in arbitrary locations near the plasma edge. Using this information we determine the non-axisymmetric plasma edge through the magnetic invariant manifolds routine developed during this work. The intersection of the calculated invariant manifold with the tokamak chamber agrees considerably well with the heat flux measurements for the same discharge at the divertor plates, indicating the development of a rotating manifold due to the internal asymmetric plasma currents, giving quantitative support to our simplified description of the magnetic field and the plasma edge definition through the invariant manifolds.
Neste trabalho estuda-se a modelagem do campo magnético em configurações realistas de plasmas em equilíbrio não-axissimétrico e o fluxo de calor nos componentes em contato com o plasma em descargas de tokamaks com desviadores poloidais. Começa-se estabelecendo a relação entre configurações magnéticas arbitrárias e sistemas dinâmicos Hamiltonianos. Então aplicamos o conceito de helicidade magnética, que é usado para estabelecer limitações topológicas sobre as linhas de campo magnético em plasmas ideais, assim como para compreender a auto-consistência das superfícies magnéticas reconectadas em configurações não-axissimétricas. Após esta discussão teórica, apresentam-se alguns resultados sobre o equilíbrio magnetohidrodinâmico e o uso de soluções analíticas à equação de Grad-Shafranov para descrever descargas reais em tokamaks, com base em diagnósticos experimentais e condições de contorno realistas. Também realiza-se uma comparação entre a reconstrução do equilíbrio de uma descarga do DIII-D, obtida mediante uma rotina numérica desenvolvida para esta pesquisa, com a obtida mediante o código EFIT, usado amplamente em diversos tokamaks. Após isso, apresenta-se uma descrição simplificada do campo magnético não-axissimétrico, criado por fontes determinadas, e a sua implementação para descrever o campo magnético devido às correntes externas em tokamaks. Então, usam-se estas rotinas para desenvolver um procedimento numérico que ajusta um conjunto adequado de parâmetros não-lineares de correntes filamentares internas, com as quais pretende-se modelar a resposta do plasma com base nas medidas de campo magnético fora do plasma. Finalmente, estes métodos são utilizados para modelar o campo magnético criado por uma instabilidade com rotação lenta numa descarga do DIII-D. Com base nas medidas das sondas magnéticas é possível modelar os campos criados em regiões arbitrárias próximas da borda do plasma. Usando esta informação é possível determinar a borda não-axissimétrica do plasma mediante as invariantes magnéticas calculadas com a utilização de uma rotina desenvolvida durante este trabalho. A intersecção da superfície invariante com a câmara do tokamak coincide satisfatoriamente com as medidas de fluxo de calor nas placas do divertor para a mesma descarga, indicando o desenvolvimento de uma variedade giratória criada pelas correntes de plasma não-axissimétricas, e sustentando quantitativamente a nossa descrição simplificada do campo magnético, assim como a definição da borda do plasma mediante as invariantes magnéticas.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Oliveira, Alexandre Machado de. « Emissivity Profiles at TCABR Tokamak ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-05092017-154738/.

Texte intégral

Résumé :

The determination of plasma equilibrium profiles is necessary to evaluate the properties of the confinement and to investigate perturbation effects. Optical diagnostics can be used to determine some of these profiles. However, these diagnostics measure all emitted radiation at a solid angle that illuminate each diagnostic channel through a slit. Therefore, the real measured quantity is the emissivity integrated along the line-of-sight and some unfolding procedure, like Abels inversion, is commonly used to recover the emissivity profile. In TCABR tokamak, at the Physics Institute of the University of São Paulo, a 24-channel bolometer and a 20-channel soft X-ray optical diagnostics are used to measure the plasma emissivity in wavelength range from 1.0 to 1000 nm, depending on the used filters. In this work, a numerical simulation is used to compute the signal measured by the diagnostics for a given emissivity profile, allowing direct comparison with the experimental data and avoiding the use of the Abel\'s inversion directly and the numerical difficulties associated with unfolding procedures. By considering TCABR tokamak geometry, spatial coordinates can be related to the normalized linear coordinates of the plasma by imposing a plasma emissivity model that depends on some free parameters, allowing the emissivity resulting in each point can be calculated. Thus, the luminosity of each channel is calculated by the integral of the emissivity modeled in each line-of-sight (Radon Transformation). Emissivity model free parameters are determined by fitting calculated luminosity to measured one. We considered three types of emissivity profiles: a parabolic model in law of power, a Gaussian model and a model based on Bessel functions. We observed that the parabolic profile fits well the bolometer data, while the Gaussian profile is adequate to describe the data obtained with the soft X-ray detector.
A determinação dos perfis de equilíbrio do plasma é necessária para avaliar as propriedades do confinamento e para investigar os efeitos de perturbações. Diagnósticos ópticos podem ser usados para determinar alguns desses perfis. No entanto, esses diagnósticos medem toda a radiação luminosa emitida em um ângulo sólido que ilumina cada canal do detector através de uma fenda. Assim, a verdadeira grandeza física medida é a emissividade integrada ao longo da linha de visada. Com isso, algum procedimento de deconvolução, como a inversão de Abel, se faz necessário para obter o perfil de emissividade. No tokamak TCABR do Instituto de Física da USP, um bolômetro de 24 canais e um detector de raios-X moles de 20 canais são utilizados para medir a emissividade do plasma no intervalo de comprimento de onda de 1 a 1.000 nm, dependendo dos filtros utilizados. Neste trabalho, uma simulação numérica é usada para calcular o sinal medido pelos diagnósticos para um dado perfil de emissividade, possibilitando a comparação direta com os dados experimentais, evitando a realização da inversão de Abel e os problemas numéricos associados aos procedimentos de deconvolução. Pela consideração da geometria do tokamak TCABR, as coordenadas espaciais podem ser relacionadas com as coordenadas lineares normalizadas do plasma por meio da imposição de um modelo de emissividade para o plasma que dependa de alguns parâmetros livres, permitindo que a emissividade resultante em cada ponto possa ser calculada. Assim, a luminosidade de cada canal é calculada pela integral da emissividade modelada em cada linha de visada (Transformada de Radon). Os parâmetros livres dos perfis de emissividade são determinados ajustando-se as luminosidades calculadas em termos das luminosidades medidas. Nós consideramos três modelos de perfis de emissividade: um modelo parabólico em lei de potência, um modelo gaussiano e um modelo baseado em funções de Bessel. Observamos que o perfil parabólico ajusta-se bem aos dados do bolômetro, ao passo que o perfil gaussiano é adequado para descrever os dados obtidos com o detector de raios-X moles.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Weening, Richard Henry. « Completely bootstrapped tokamak ». W&M ScholarWorks, 1991. https://scholarworks.wm.edu/etd/1539623812.

Texte intégral

Résumé :

A fundamental requirement for the successful operation of a tokamak is the maintenance of a toroidal electric current within the tokamak plasma itself. Maintaining this internal plasma current can be a very difficult technological problem. In this work, a well-known but non-standard method for maintaining the tokamak current called the bootstrap effect is discussed. The bootstrap effect occurs when a fusion plasma is near thermonuclear conditions, and allows the tokamak to greatly amplify its electric current.;Because the bootstrap effect amplifies but does not create a plasma current, it has long been argued that a completely bootstrapped tokamak is not possible. That is, it has been argued that some fraction of the tokamak current must be created externally and injected into the plasma for a bootstrap amplification to occur. This injection of current is not desirable, however, since current-drive schemes are difficult to implement and are only marginally efficient.;An important but largely unexplored implification of the bootstrap effect is that the effect, by itself, creates hollow (outwardly peaked) tokamak current profiles. Hollow tokamak current profiles are known to lead to tearing modes, which are resistive (non-ideal) magnetohydrodynamic (MHD) plasma instabilities. Although usually characterized as harmful for plasma confinement, it turns out that tearing modes may actually be beneficial for the tokamak bootstrap effect.;In this work, a new theoretical approach based on a helicity conserving mean-field Ohm's law is used to examine the interaction between the bootstrap effect and tearing modes. Magnetic helicity is a topological quantity which is conserved even in turbulent plasma. Computer simulation results of the mean-field Ohm's law are presented which suggest that a completely bootstrapped tokamak may indeed be possible. In a completely bootstrapped tokamak, the tokamak self-maintains its electric current by amplifying an intrinsic internal plasma current due to the tearing modes.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Abiteboul, Jérémie. « Transport turbulent et néoclassique de quantité de mouvement toroïdale dans les plasmas de tokamak ». Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4062/document.

Texte intégral

Résumé :

L'objectif de la fusion par confinement magnétique, et notamment du tokamak, est de produire de l'énergie à partir des réactions de fusion nucléaire, dans un plasma à faible densité et haute température. Expérimentalement, une amélioration de la performance des tokamaks a été observée en présence de rotation toroïdale. Or, les sources extérieurs de quantité de mouvement seront très limitées dans les futurs tokamaks, et notamment ITER. Une compréhension de la physique de la génération intrinsèque de rotation toroïdale permettrait donc de prédire les profils de rotation dans les expériences futures. Parmi les mécanismes envisagés, on s'intéresse ici à la génération de rotation par la turbulence, qui domine le transport de la chaleur dans les tokamaks. Les plasmas de fusion étant faiblement collisionnels, la modélisation de cette turbulence suppose un modèle cinétique décrivant la fonction de distribution des particules dans l'espace des phases à six dimensions (position et vitesse). Cependant, ce modèle peut être réduit à cinq dimensions pour des fréquences inférieures à la fréquence cyclotronique des particules. Le modèle gyrocinétique qui découle de cette approximation est alors accessible avec les ressources numériques actuelles. Les travaux présentés portent sur l'étude du transport de quantité de mouvement toroïdale dans les plasmas de tokamak, dans le cadre du modèle gyrocinétique. Dans un premier temps, nous montrons que ce modèle réduit permet une description précise du transport de quantité de mouvement en dérivant une équation locale de conservation. Cette équation est vérifiée numériquement à l'aide du code gyrocinétique GYSELA
The goal of magnetic conﬁnement devices such as tokamaks is to produce energy from nuclear fusion reactions in plasmas at low densities and high temperatures. Experimentally, toroidal ﬂows have been found to signiﬁcantly improve the energy conﬁnement, and therefore the performance of the machine. As extrinsic momentum sources will be limited in future fusion devices such as ITER, an understanding of the physics of toroidal momentum transport and the generation of intrinsic toroidal rotation in tokamaks would be an important step in order to predict the rotation proﬁle in experiments. Among the mechanisms expected to contribute to the generation of toroidal rotation is the transport of momentum by electrostatic turbulence, which governs heat transport in tokamaks. Due to the low collisionality of the plasma, kinetic modeling is mandatory for the study of tokamak turbulence. In principle, this implies the modeling of a six-dimensional distribution function representing the density of particles in position and velocity phase-space, which can be reduced to ﬁve dimensions when considering only frequencies below the particle cyclotron frequency. This approximation, relevant for the study of turbulence in tokamaks, leads to the so-called gyrokinetic model and brings the computational cost of the model within the presently available numerical resources. In this work, we study the transport of toroidal momentum in tokamaks in the framework of the gyrokinetic model

Styles APA, Harvard, Vancouver, ISO, etc.

17

Nace, Nicolas. « Dynamics of driven and spontaneous transport barriers in the edge plasma of tokamaks ». Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0101/document.

Texte intégral

Résumé :

Les réacteurs à fusion thermonucléaire sont une des solutions à moyen - long terme pour transiter vers un monde dominé par des énergies décarbonées. Les réactions de fusion requièrent des températures si extrêmes que le plasma d'isotopes d'hydrogène doit être confiné magnétiquement dans une forme torique. Le maintien d'un tel niveau élevé de confinement des particules et de l'énergie reste un problème clé. Les réacteurs devraient opérer dans un régime de confinement avancé, le mode H, dans lequel le transport turbulent est réduit par la présence d'une barrière de transport dans le plasma de bord. Ce régime est observé dans toutes les machines actuelles mais demeure en partie incompris. Dans cette thèse, plusieurs mécanismes impliqués dans la transition vers le mode H sont étudiés. Pour cela, plusieurs outils de simulation numériques sont utilisés avec une complexité croissante. Des mécanismes de base, supposés jouer un rôle dans le développement des barrières de transport et impacter la turbulence, sont détaillés et analysés avec des modèles simples. En allant vers des modèles plus complexes, la pertinence de cette physique pour le mode H est discutée au regard des observations expérimentales. La géométrie magnétique et notamment le cisaillement magnétique sont en particulier désignés comme étant des acteurs clés
Thermonuclear fusion reactors are one of the mid to long term solutions to transit towards a world dominated by carbon-free energy. Extreme temperatures are required for fusion reactions and the plasma of hydrogen isotopes must be magnetically confined in a torus shape. Sustaining such high level of particle and energy confinements is a key issue. Reactors are expected to operate in a high confinement regime - the H-mode - in which turbulent transport is reduced by the presence of a transport barrier in the edge plasma. This regime is observed in all current devices but remains largely miss-understood. In this thesis, we investigate several mechanisms involved in the transition towards H-mode. For that purpose, we use a range of numerical simulation tools of increasing complexity. Using simple models, we first highlight and analyze basic mechanisms likely to play a role in the on-set of transport barriers and in their impact on turbulence. Moving progressively to more complex models, we discuss the relevance of these physics in explaining experimental observations. The magnetic geometry and especially the magnetic shear are pointed out as key players

Styles APA, Harvard, Vancouver, ISO, etc.

18

Honda, Mitsuru. « Transport simulation of tokamak plasmas including plasma rotation and radial electric field ». 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136227.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

19

Mavkov, Bojan. « Control of coupled transport in Tokamak plasmas ». Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT004/document.

Texte intégral

Résumé :

L'objectif de cette thèse est le développement de nouvelles méthodes d'analyse et de commande pour une classe d'équations aux dérivées partielles couplées permettant de modéliser le transport combiné du flux magnétique et de la pression (produit de la densité et de la température) dans les plasmas tokamak. Le système couplé est représenté par deux équations 1D de diffusion résistive. Dans cette thèse, on a obtenu deux types de modèles: le premier repose sur des principes physiques et le second exploite les données obtenues en utilisant des techniques d'identification des systèmes. La conception de commande est basée sur l'etude en dimension infinie en utilisant l'analyse de Lyapunov. Le contrôle composite est synthétisé en utilisant la théorie des perturbations singulières pour isoler la composante rapide de la composante lente. Tout le travail théorique est implémenté et testé dans des simulations basées sur la physique avancée en utilisant le simulateur de plasma pour les tokamaks DIII-D, ITER et TCV
The objective of this thesis is to propose new methods for analysis and control of partial differential equations that describe the coupling between the transport models of the electron pressure (density multiplied by the temperature) and the magnetic flux in the tokamak plasma. The coupled system is presented by two1D resistive diffusion equations. In this thesis two kinds of control models are obtained. The first is a first-principle driven model and the second one is the data-driven model obtained using system identification techniques. The control design is based on an infinite dimensional setting using Lyapunov analysis. Composite control is designed using singular perturbation theory to divide the fast from the slow component. All the theoretical work is implemented and benchmarked in advanced physics based on simulations using plasma simulator dor DIII-D, ITER and TCV tokamaks

Styles APA, Harvard, Vancouver, ISO, etc.

20

Moradi, Sara. « Transport analysis in tokamak plasmas ». Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210097.

Texte intégral

Résumé :

In this thesis we mainly focus on the study of the turbulent transport of impurity particles in the plasma due to the electrostatic drift wave microinstabilities. In a fusion reactor, the helium produced as a result of the fusion process is an internal source of impurity. Moreover, impurities are released from the material surfaces surrounding the plasma by a variety of processes: by radiation from plasma, or as a result of sputtering, arcing and evaporation. Impurities in tokamak plasmas introduce a variety of problems. The most immediate effect is the radiated power loss (radiative cooling). Another effect is that the impurity ions produce many electrons and in view of the operating limits on density and pressure, this has the effect of replacing fuel ions. For example, at a given electron density, $n_{e}$, each fully ionized carbon ion (used in the wall materials in the form of graphite) replaces six fuel ions, so that a 7\\% concentration of fully ionized carbon in the plasma core, would reduce the fusion power to one half of the value in a pure plasma. Therefore, for all tokamaks it become an immediate and continuing task to reduce impurities to acceptably low concentrations. However, the presence of impurities, with control, can be beneficial for the plasma performance and reduction of strong plasma heat loads on the plasma facing walls. The radiative cooling effect which was mentioned above can be used at the edge of the plasma in order to distribute the plasma heat more evenly on the whole surface of the vessel walls and therefore, reduce significantly plasma heat bursts on the small regions on the divertor or limiter tiles. The experiments at TEXTOR show that the presence of the impurities at the plasma edge can also improve the performance and reduce the turbulent transport across the magnetic field lines. The observed behavior was explained trough the proposed mechanism of suppression of the most important plasma drift wave microinstability in this region, namely, the Ion Temperature Gradient mode (ITG mode) by the impurities. The impurity's positive impact on the plasma performance offered a possibility to better harness the fusion power, however, it is vital for a fusion reactor to have feedback controls in order to keep impurities at the plasma edge and limit their accumulation in the plasma core where the fusion reactions are happening. In order to have control over the impurity transport we first need to understand different mechanisms responsible for its transport.

One of the least understood areas of the impurity transport and indeed any plasma particle or heat transport in general, is the turbulent transport. Extensive efforts of the fusion plasma community are focused on the subject of turbulent transport. Motivated by the fact that impurity transport is an important issue for the whole community and it is an area which needs fundamental research, we focused our attention on the development of turbulent transport models for impurities and their examination against experiments. In a collaboration effort together with colleagues (theoreticians as well as experimentalist) from different research institutes, we tried to find, through our models, physical mechanisms responsible for experimental observations. Although our main focus in this thesis has been on the impurity transport, we also tried a fresh challenge, and started looking at the problem of drift wave turbulent transport in a different framework all together. Experimental observation of the edge turbulence in the fusion devices show that in the Scrape of Layer (SOL: the layer between last closed magnetic surface and machine walls) plasma is characterized with non-Gaussian statistics and non-Maxwellian Probability Distribution Function (PDF). It has been recognized that the nature of cross-field transport trough the SOL is dominated by turbulence with a significant ballistic or non-local component and it is not simply a diffusive process. There are studies of the SOL turbulent transport using the 2-D fluid descriptions or based on probabilistic models using the Levy statistics (fractional derivatives in space). However, these models are base on the fluid assumptions which is in contradiction with the non-Maxwellian plasmas observed. Therefore, we tried to make a more fundamental study by looking at the effect of the non-Maxwellian plasma on the turbulent transport using a gyro-kinetic formalism. We considered the application of fractional kinetics to plasma physics. This approach, classical indeed, is new in its application. Our aim was to study the effects of a non-Gaussian statistics on the characteristic of the drift waves in fusion plasmas.

Ce travail de thèse porte sur le transport turbulent d'impuretés dans les plasmas de fusion

par confinement magnétique. C'est une question de la plus haute importance pour le développement

de la fusion comme source d'énergie. En effet, une accumulation d'impuretés au coeur

du plasma impliquerait des pertes d'énergie par radiation, conduisant par refroidissement à

l'extinction des réactions de fusion. Il est par contre prévu d'injecter des impuretés dans le

bord du plasma, afin d'extraire la chaleur par rayonnement sans endommager les éléments de

la première paroi. Ces contraintes contradictoires nécessitent un contrôle précis du transport

d'impuretés, afin de minimiser la concentration d'impuretés au coeur du plasma tout en la

maximisant au bord. Une très bonne connaissance de la physique sous-jacente au transport

est donc indispensable. L'effet de la turbulence, principal mécanisme de transport, sur les impuretés

est alors une question centrale. Dans cette thèse, un code numérique, AFC-FL, a été développé sur la base d'une approche ``fluide' linéaire pour la turbulence d'ondes de dérive. Il calcule les taux de croissance qui caractérisent la rapidité de l'amorçage des instabilités. L'analyse de stabilité est complétée par l'évaluation des taux de croissance en présence d'un gradient de densité, un cisaillement magnétique ou un nombre arbitraire de différentes espèces d'impureté. Les formules complètes du flux turbulent d'impuretés pour ces taux de croissance calculés des instabilités des ondes de dérive ont été dérivées. Un modèle de transport anormal qui nous permet d'étudier la dépendence du transport en fonction de la charge d'impureté a été développé. Ce modèle prend en compte les effets collisionnels entre les ions, l'impureté et les particules principales de plasma. Une telle dépendence du transport anormal en fonction de la charge de l'impureté est observée dans les expériences et il a été montré que les résultats obtenus sont en bon accord avec les observations expérimentales. Nous avons également étudié l'effet des impuretés sur le confinement de l'énergie dans les plasmas du tokamak JET. La modélisation de transport a été exécutée pour des plasmas avec injection de néon dans la périphérie du tokamak. Cette technique est utilisée afin d'extraire la chaleur par rayonnement sans endommager la paroi et pour réduire certaines instabilités (ELM). Des simulations du code RITM ont été comparées à des mesures effectuées lors d'expériences au JET. Il a été montré que l'injection de néon mène toujours à une dégradation du confinement par rapport aux décharges sans néon. Cependant, l'augmentation de la charge effective, en raison du presence du néon peut diminuer le taux de croissance d'autres instabilité (ITG) et amèliorer le confinement du coeur du plasma. Ce confinement amélioré du coeur peut alors compenser la dégradation au bord et le confinement global du plasma peut s'améliorer.

Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished

Styles APA, Harvard, Vancouver, ISO, etc.

21

Klein, Rudy. « Le modèle gyro-water-bag appliqué à l'étude des instabilités dans les plasmas magnétisés ». Thesis, Nancy 1, 2009. http://www.theses.fr/2009NAN10134/document.

Texte intégral

Résumé :

Les modèles fluides décrivant les plasmas chauds sont aujourd'hui bien développés. L'étude des micro-instabilités présentes dans ces plasmas nécessite cependant une description cinétique basée sur l'équation de Vlasov. Les modèles cinétiques étant très gourmands en ressources informatiques, une idée alternative est l'utilisation systématique des propriétés d'invariance des systèmes étudiés telles que la propriété d'invariance de la fonction de distribution le long des trajectoires dans l'espace des phases ou l'invariance adiabatique du moment magnétique dans les plasmas magnétisés. C'est dans ce cadre que nous appliquons un modèle water-bag à plusieurs types de problèmes : les ondes de dérive collisionnelles dans les colonnes de plasma magnétisé, les instabilités d'interchange, ITG, et Rayleigh-Taylor dans les cœurs de tokamaks. Ces études visent à permettre une meilleure compréhension de la turbulence et ainsi participer à la maîtrise du transport anormal qui dégrade le confinement dans les cœurs de tokamak
The study of microinstabilities that arises in these plasmas demands a kinetic description based on the Vlasov equation. Kinetic models being very demanding in computer ressources, an alternative approach lies in a systematic use of invariances properties in the studied systems, such as the invariance of the distribution function along the particle trajectories or the first magnetic moment invariance. In this framework, we make use of the water-bag model on a few problems: collisional drif-waves in magnetized plasma column, interchange instability, ion temperature gradient (ITG), and Rayleigh-Taylor instabilities in the core of tokamaks. The goal of these studies is to allow a better understanding of plasma turbulence and therefore contribute to the control of anomalous transport which degrades the confinment in the core of tokamaks

Styles APA, Harvard, Vancouver, ISO, etc.

22

Fernandes, Tiago. « Instabilidades MHD no Tokamak TCABR ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-03062016-155509/.

Texte intégral

Résumé :

Este trabalho descreve o estudo das instabilidades magneto-hidro-dinâmicas (MHD) comumente observadas nas descargas elétricas de plasma no tokamak TCABR, do Instituto de Física da USP. Dois diagnósticos principais foram empregados para observar essas instabilidades: um conjunto poloidal de 24 bobinas magnéticas (bobinas de Mirnov) colocadas próximas à borda do plasma e um medidor de emissões na faixa do Ultra Violeta e de raios X moles com 20 canais (sistema SXR), cujo circuito de condicionamento de sinais foi aprimorado como parte deste trabalho. Esses diagnósticos foram escolhidos porque fornecem informações complementares, uma vez que o sistema SXR observa a parte central da coluna de plasma, enquanto as bobinas de Mirnov detectam as instabilidades MHD na região mais externa da coluna. As informações coletadas por esses diagnósticos foram submetidas à análise espectral com resolução temporal e espacial, possibilitando determinar a evolução das características espectrais e espaciais das instabilidades MHD observadas. Essas análises revelaram que durante a etapa inicial da formação do plasma (quando a corrente de plasma ainda está aumentando) ilhas magnéticas com números de onda decrescente, identificadas como sendo modos kink de borda, são detectadas nas bobinas de Mirnov. Após a formação do plasma, quando os parâmetros de equilíbrio estão relativamente estáveis (platô), oscilações são detectadas tanto nas bobinas de Mirnov quanto no sistema de SXR, indicando a presença de instabilidades MHD em toda a coluna de plasma. Em geral as oscilações medidas nas bobinas de Mirnov tem baixa amplitude e correspondem a pequenas ilhas magnéticas que foram identificadas como sendo modos de ruptura (modos tearing). Por outro lado, as instabilidades na região central foram identificadas como dentes de serra, que correspondem a relaxações periódicas da região interna à superfície magnética com fator de segurança q=1 e que são acompanhadas de oscilações precursoras, cuja amplitude depende da fase do ciclo de relaxação. Devido à essa modulação de amplitude, aparecem picos de frequência satélite nos espectrogramas dos sinais do SXR. Além disso, devido ao fato dos ciclos de relaxação não serem sinusoidais, os harmônicos da frequência de relaxação também aparecem nesses espectrogramas. No entanto, em muitas descargas do TCABR, a intensidade das oscilações medidas nas bobinas de Mirnov aumentam significativamente durante o platô, com efeitos sobre a frequência de todas as instabilidades MHD, até mesmo sobre os dentes de serra localizados na região central da coluna. Em todos os casos, observou-se que durante o platô a frequência das ilhas magnéticas coincide com a frequência das oscilações precursoras do dente de serra, apesar de serem duas instabilidades distintas, localizadas em posições radiais muito diferentes. Essa coincidência de frequências possibilitou descrever a evolução em frequência de todas as oscilações detectadas em diversos diagnósticos com base em apenas duas frequências básicas: a dos ciclos de relaxação dente de serra e a das ilhas magnéticas.
This work describes the study of magneto-hydro-dynamic instabilities (MHD) commonly observed in plasma discharges in tokamak TCABR (at Instituto de Física da USP). Two main diagnostics were employed to observe these instabilities: a poloidal set of 24 magnetic coils (Mirnov coils) placed near the plasma border and a detector of emissions in the Ultra Violet and soft X-ray range with 20 channels (SXR system) which improvement of the signal conditioning circuit was done as part of this work. These diagnostics were chosen because they provide complementary information, since the SXR system measures the central part of the plasma column, while the Mirnov coils detect the MHD instabilities in the outer part of the column. The information collected by these diagnoses was submitted to spectral analysis with temporal and spatial resolution, making it possible to determine the evolution of the spectral and spatial characteristics of the observed MHD instabilities. These analyzes revealed that during the initial stage of the plasma formation (when the plasma current is still increasing) magnetic islands with decreasing wave numbers, identified as edge kink modes, are detected in the Mirnov coils. After the plasma formation, when the equilibrium parameters are relatively flat (plateau), oscillations are detected in both Mirnov coils and SXR system, indicating the presence of MHD instability in the whole plasma column. In general, the fluctuations measured by the Mirnov coils have low amplitude corresponding to small magnetic islands, which were identified as tearing modes. On the other hand, the instabilities at the central region were identified as sawteeth oscillations that correspond to periodic relaxations in the internal region of the magnetic surface with safety factor q = 1 and that are accompanied by precursor oscillations which amplitude depends on the phase of the relaxation cycles. Due to this amplitude modulation, frequency satellite peaks appear in the spectrograms of the SXR signals. Furthermore, due to the fact that relaxation cycles are not sinusoidal, harmonics of the relaxation frequency also appear in the spectrograms. However, in many TCABR discharges, the intensity of the oscillations measured by the Mirnov coils increase significantly during the plateau, with affects the frequency of all MHD instabilities, even over the sawteeth in the central region of the column. In all cases, it was observed that during the plateau the frequency of the magnetic islands coincides with the frequency of the sawtooth precursors, although they are two different instabilities located in separated radial positions. This coincidence of frequencies allowed describing the frequency evolution of all measured oscillations by considering only two basic frequencies: the cycles of sawtooth relaxation and the magnetic islands.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Mazzi, Samuele. « Impact of fast ions on microturbulence in fusion plasmas ». Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0470.

Texte intégral

Résumé :

L'exploitation des plasmas de fusion magnétiquement confinés en tant que source d'énergie durable et propre est limitée par le transport turbulent radial vers l'extérieur. Ce transport est principalement induit par les micro-instabilités. Les future réacteurs seront principalement chauffés par les particules alpha produites par les réactions de fusion nucléaire. Les particules alpha doivent être bien confinées afin de transférer leur énergie aux ions thermiques. Cependant, on a aujourd'hui très peu de connaissances sur l'interaction entre les particules alpha et la microturbulence. Ainsi, des régimes de turbulence et de transport inattendus peuvent avoir des effets néfastes sur les performances des futurs réacteurs chauffés par les particules alpha. L'étude d'un scénario de tokamak qui peut imiter les conditions expérimentales attendues dans les futurs réacteurs est donc cruciale. Des études numériques sur l'impact des ions rapides hautement énergétiques, imitant la dynamique des particules alpha, sur le transport turbulent provoqué par le gradient de température des ions et les instabilités du mode des électrons piégés ont été réalisées. Il est démontré qu'une suppression du transport turbulent à l'échelle ionique peut être obtenue en présence de tels ions hautement énergétiques. Les modes d'Alfvén (AEs), déstabilisés par les ions hautement énergétiques à travers une interaction onde-particule, jouent un rôle essentiel dans le mécanisme multi-échelle menant à la suppression de la turbulence. Des analyses approfondies soulignent en outre la possibilité de reconnaître les caractéristiques de la réduction du transport à l'échelle des ions
The exploitation of magnetically confined fusion plasmas as a sustainable and clean energy source is limited by the radially outward turbulent transport. Such transport is mainly induced by microinstabilities. Next-generation fusion devices will be mainly heated by the alpha particles born from the nuclear fusion reactions. Alpha particles must be well confined in order to transfer their energy to the bulk ions. However, very little knowledge is available regarding the interaction between alpha particles and microturbulence. Thus, unexpected turbulence and transport regimes may lead to further detrimental effects on the performance of future alpha-heated devices. The study of a tokamak scenario which can mimic the experimental conditions expected in future devices is hence crucial. Numerical investigations on the impact of highly energetic fast ions, mimicking the alpha particle dynamics, on the turbulent transport driven by Ion Temperature Gradient and Trapped Electron Mode instabilities have been carried out in a validated framework. It is shown that a suppression of the ion-scale turbulent transport may be achieved in the presence of such highly energetic ions. Alfvén Eigenmodes (AEs), destabilized by the highly energetic ions through a wave-particle interaction, play an essential role in the multi-scale mechanism leading to the turbulence suppression. Deep analyses further highlight the possibility to recognize hallmarks of the ion-scale transport reduction, regardless the dominant turbulent regime

Styles APA, Harvard, Vancouver, ISO, etc.

24

Duthoit, François-Xavier. « Physique néoclassique pour la génération de courant dans les plasmas de tokamaks ». Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00708795.

Texte intégral

Résumé :

Le formalisme de la transformation de Lie est appliqué à la dynamique des particules chargées dans la topologie magnétique d'un tokamak, afin de construire un opérateur de type Fokker-Planck pour les collisions coulombiennes utilisable pour la génération de courant. Cette approche permet de réduire le problème à trois dimensions (deux dans l'espace des vitesses, une dans l'espace des configurations) tout en gardant la richesse des effets croisés entre les es- paces résultant de la conservation du moment canonique toroïdal (axisymétrie). Cette approche cinétique permet de d'écrire des phénomènes physiques liés à la présence de forts gradients de pression dans des plasmas de forme quelconque, comme le courant " bootstrap " dont le rôle sera primordial pour le futur réacteur ITER. Le choix des coordonnées et la méthode utilisée sont particulièrement adaptés à la résolution numérique de l'équation de dérive cinétique permettant de calculer la distribution des particules, celle-ci pouvant présenter un fort écart à la maxwellienne sous l'effet d'un champ électrique (statique ou produit par une onde radio- fréquence). Les travaux dédiés principalement à la physique des plasmas de tokamak ont été étendus à ceux des plasmas de l'espace relevant d'une configuration magnétique dipolaire.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Kloe, Joost de. « Pellet-plasma interaction in a tokamak / ». [S.l. : s.n], 2000. http://catalogue.bnf.fr/ark:/12148/cb37725261x.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

26

Thomsen, Henning. « A Dynamics investigation into edge plasma turbulence ». [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=96493230X.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

27

Dachicourt, Remi. « Contrôle du rayonnement dans les plasmas de fusion par confinement magnétique ». Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4097.

Texte intégral

Résumé :

La résolution d'un certain nombre de problèmes physiques est nécessaire au développement de réacteurs électrogènes utilisant la fusion thermonucléaire contrôlée. Le travail présenté ici traite du contrôle du rayonnement dans le cadre général de la tenue des matériaux aux flux de chaleur, ainsi que de l'opération d'un tokamak à forte densité. Ces deux points concernent plus particulièrement le futur réacteur de démonstration, appelé DEMO, pas intermédiaire entre ITER et un réacteur commercial. L'opération de DEMO sera contrainte par la nécessité de rayonner dans un large volume afin de limiter le dépôt de puissance localisé sur les plaques du divertor. Une grande fraction de rayonnement (80 à 90% de la puissance extraite) devra être obtenue tout en conservant un excellent confinement et une pollution réduite au cúur du plasma. Les études actuelles montrent que cette fraction de rayonnement est atteignable tout en limitant la contamination du plasma, mais l'amélioration des modèles de rayonnement est indispensable, tout comme les études concernant la compatibilité entre un bord fortement rayonnant et l'existence d'une barrière de transport permettant l'accès à un régime de confinement amélioré, le mode H. En parallèle, une forte densité (fraction de Greenwald supérieure à l'unité) est aussi indispensable pour atteindre la fraction de rayonnement désirée. De plus, la puissance fusion, et donc le bilan économique d'un réacteur est directement liée à la densité dans la zone de réaction, au centre du plasma
The route presently envisaged towards the development of a commercial fusion power plant includes that a few remaining physics issues are solved. The present work addresses two of them: plasma radiation control, as a part of the more general power handling issue, and high density tokamak operation. These two issues will be most critical in the demonstration reactor, called DEMO, intermediate step between ITER and a future commercial reactor. For DEMO, the need to radiate a large fraction of the power so as to limit the peak power load on the divertor will be a key constraint. High confinement will have to be combined with high radiated power fraction, and the required level of plasma purity. A fractional radiated power, including bremsstrahlung radiation, of 80-90% of the total power loss will be required. Present studies suggest that this level of radiation could be achieved with acceptable levels of plasma contamination, but improvements are required in models of plasma radiation, and compatibility with the edge transport barrier of the H-mode has to be further assessed. Correlatively, high plasma density (typically with a Greenwald fraction above unity) is required, both because it allows efficient radiation of exhaust power to the reactor walls, and because the final cost of electricity is directly influenced by the achieved Greenwald value

Styles APA, Harvard, Vancouver, ISO, etc.

28

Najera, Omar Cipriano Usuriaga. « Tomografia de emissão H-alfa no tokamak TCABR ». Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27022008-133846/.

Texte intégral

Résumé :

Neste trabalho foi feito um estudo do perfil tomográfico da emissão da linha do átomo de hidrogênio, H-alfa (?=656,28 nm) no plasma do TCABR, um tokamak de porte médio em operação no Laboratório de Física de Plasmas do Instituto de Física da Universidade de São Paulo. Nosso trabalho centrou-se no estudo dos efeitos da introdução de um eletrodo polarizado na borda do plasma no tokamak TCABR. O eletrodo pode ser introduzido até 1,5 cm para dentro da coluna do plasma, sem causar disrupturas para polarização positiva de 0 até +350V, e situado no plano equatorial do tokamak. Perfis tomográficos de H-alfa com e sem polarização foram medidos. A comparação dos perfis mostra um aumento da densidade de linha na posição central, quando a emissividade H-alfa diminui. A análise dos perfis tomográficos de H-alfa, tempo de confinamento das partículas e também do estudo de reciclagem das partículas neutras, indica que o plasma entra no regime de alto confinamento (modo-H). Cálculos de turbulência e de transporte na borda do plasma (SOL), feitos medindo o potencial flutuante e a corrente de saturação de íons, mostram uma diminuição forte no espectro de potência e de transporte. Também foram feitos estudos do novo regime de descargas com elétrons fugitivos (\"runaway electron\"), descoberto no tokamak TCABR. As características distintivas deste regime são um plasma de baixa temperatura fracamente ionizado, destacado do limitador devido a processos de recombinação, e instabilidade de relaxação com fortes picos de emissão H-alfa correlacionados com instabilidade dente de serra da densidade eletrônica de linha. No presente trabalho fazemos a descrição das condições experimentais para a geração destas descargas. A produção dos elétrons fugitivos é analisada; mostrando que a geração de elétrons fugitivos somente pode ser explicada pelo mecanismo de avalanche. A confirmação de baixa temperatura do plasma é obtida de uma análise do perfil tomográfico da emissão H-alfa. Esta emissão não pode ser explicada por excitação de elétrons no plasma. A recombinação, de outro lado, dá uma explicação plausível para a dependência temporal da emissão, em particular para alta densidade de partículas neutras.
A study of the tomography profile of the emission of the line of Hydrogen, atomic H-alpha line (?=656.28 nm), was carried out in TCABR, a medium-size tokamak in operation at the Laboratory of Plasma Physics of the Institute of Physics of the University of São Paulo. Our work focuses on the study of the effects of due to the introduction of a biased electrode in the plasma edge of the TCABR tokamak. The electrode could be introduced up to 1.5 cm inside the plasma, without plasma disruptions for positive voltages from 0 to +350V, and was located on the equatorial plane of the plasma column. Tomography profiles of H-alpha with and without bias were measured. Comparison of the profiles shows an increase of the central line-averaged density, while the emissivity of the line H-alpha decreases. The analysis of the tomography profiles of H-alpha, time of confinement of particles and also the study of recycling of the neutral particles, indicate that the confined plasma enters the H-mode regime. Calculations of turbulence and transport at the Scrape-Off-Layer, using measured floating potentials and ion saturation currents, show a strong decrease in the power spectra and transport. The H-alpha tomography was also employed to study the new regime of runaway discharges that has been discovered in the TCABR tokamak. The distinctive features of this regime are weakly ionized low-temperature plasma detached from the limiter due to the recombination process, and a relaxation instability with strong spikes of H-alpha emission correlated with sawtooth relaxation of the line density. In the present thesis we report experimental data on conditions for generation of these discharges. The runaway electron production is analyzed; show that generation of runaway electrons can only be explained by the runaway avalanche mechanism. The confirmation of low plasma temperature is a obtained from an analysis of the tomography profile of H-alpha emission. This emission cannot be explained by excitation by plasma electrons. Recombination, on the other hand, gives a rather plausible explanation for the time dependency of the emission, in particular at high neutral densities.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Bourdelle, Clarisse. « Analyse de stabilité de plasmas de Tokamak ». Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10101.

Texte intégral

Résumé :

Dans un plasma de tokamak, le transport de l'energie est principalement de nature turbulente. Afin d'augmenter le nombre de reactions de fusion, il est necessaire d'ameliorer le confinement de l'energie. L'objet de cette these est d'identifier les parametres permettant l'obtention de plasmas dont l'energie est mieux confinee afin de guider les experiences a venir. Pour ce faire, un code numerique a ete developpe. Il calcule les taux de croissance qui caracterisent la rapidite de l'amorcage des instabilites. L'analyse de stabilite est completee par l'evaluation du taux de cisaillement de la vitesse de rotation due au champ electrique radial. Lorsque ce taux est superieur au taux de croissance local maximal, la turbulence ionique est stabilisee. Le taux de cisaillement de rotation et le taux de croissance sont determines a partir des profils radiaux de densite, de temperature et du facteur de securite d'un plasma donne. En particulier, trois familles de plasmas sont analysees. Dans les plasmas radiatifs de textor (modes ri), l'injection d'ions de nombre de charge eleve entraine la diminution des taux de croissance. Dans les plasmas a forte densite de tore supra, un fort cisaillement magnetique et/ou un chauffage des ions plus efficace associe a une bifurcation de la direction de rotation toroidale (par ailleurs non-expliquee) declenchent l'amelioration du confinement. Dans tore supra, des gradients de pression electronique localement tres raides (appeles barrieres internes de transport) sont obtenus suite a une inversion du cisaillement magnetique. Ce cisaillement magnetique localement negatif a un effet stabilisant. Dans ces trois types de plasmas, les taux de croissance diminuent, le confinement s'ameliore, les profils de densite et de temperature se piquent. Ces piquages entrainent une augmentation du taux de cisaillement de rotation qui permet de maintenir la qualite du confinement.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Sharma, Atul Stefan. « Tokamak modelling & ; control ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270120.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

31

Duarte, Vinícius Njaim. « Quasilinear and nonlinear dynamics of energetic-ion-driven Alfvénic eigenmodes ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-01082017-195849/.

Texte intégral

Résumé :

The destabilization of plasma waves upon their interaction with fast ions is studied using a kinetic framework. The work consists of two parts: (I) a study of the applicability of quasilinear theory using a pertubative, early-time nonlinear evolution of a mode and its prediction with respect to chirping oscillations, and (II) the resonance-broadened quasilinear formulation of the evolution of unstable modes. In part I, we have developed predictive capabilities for the type of fast-ion-induced transport by means of a criterion for the likelihood of a mode to oscillate at a constant frequency or to evolve to a bifurcation consisting of nonlinear chirping oscillations. The proposed criterion is derived and evaluated using the linear codes NOVA and NOVA-K. The criterion was shown to be in agreement with experimentally observed modes in the tokamaks DIII-D and NSTX. The analysis reveals that micro-turbulence is a key mediator for suppressing chirping and therefore allowing quasilinear theory to be applicable. In part II, a system of resonance-broadened quasilinear equations (RBQ) was derived using action and angle variables, which takes advantage of system symmetries by using the invariants of the unperturbed motion as variables when accounting for the effects of perturbations due to modes. The equations capture information on mode structures and on resonances that are spread over phase space. We then expressed them in terms of NOVA code notation. The RBQ model is presented, along with the finite-difference scheme used for numerical integration. Numerical results and future developments are also described.
A desestabilização de ondas em plasmas quando de sua interação com íons rápidos é estudada utilizando a abordagem cinética. Este trabalho consiste em duas partes: (I) um estudo sobre a aplicabilidade da teoria quase-linear, utilizando a evolução não linear perturbada em seu estágio inicial de um modo e sua previsão com respeito às oscilações do tipo gorjeio (chirping), e (II) a formulação quase-linear de ressonâncias alargadas da evolução de modos instáveis. Na parte I, desenvolvemos capacidades preditivas em relação ao tipo de transporte in- duzido por íons rápidos por meio de um critério a respeito da probabilidade de um modo oscilar com uma frequência constante ou evoluir para uma bifurcação que consista de os- cilações de gorjeio não lineares. O critério proposto é derivado e calculado utilizando os códigos lineares NOVA e NOVA-K. Mostramos que o critério obtido concorda com modos observados experimentalmente nos tokamaks DIII-D e NSTX. A análise revela que a mi- croturbulência é um mediador-chave na supressão dos gorjeios e que, portanto, permite que a teoria quase-linear seja aplicável. Na parte II, um sistema de equações quase-lineares com ressonâncias alargadas (RBQ) foi derivado utilizando variáveis de ângulo e ação, tirando-se proveito das simetrias do sistema ao se tomar como variáveis os invariantes do movimento não perturbado quando consideramos os efeitos das perturbações aos modos. As equações capturam as informações sobre a estrutura dos modos e sobre as ressonâncias que se espalham sobre o espaço de fase. Expressamo-las, então, em termos da notação do código NOVA. O modelo RBQ é apresentado, juntamente com um esquema de diferenças finitas, utilizado para a integração numérica. Resultados numéricos e desenvolvimentos futuros também são descritos.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Baquero, Wilson Andres Hernandez. « Flutuações turbulentas de temperatura no Tokamak TCABR ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-30012018-100934/.

Texte intégral

Résumé :

A contribuição dos eventos extremos, chamados \\emph{bursts}, relacionados com estruturas coerentes que se propagam na turbulência, parece ser parte da explicação para o transporte anômalo que acontece em plasmas confinados. Porém, ainda não existe um modelo adequado no quadro da teoria neoclássica de transporte, para explicar adequadamente a contribuição destes eventos extremos. Assim, a caracterização do transporte de partículas e energia, devido a esses eventos extremos, e a sua estrutura interna, são questões relevantes no estudo do plasma de fusão. Para isso, medições locais da temperatura dos elétrons são necessárias, pois o transporte de partículas e energia sofre correções devido à temperatura. Por terem boa resolução espacial e serem relativamente fáceis de construir, as sondas eletrostáticas são comumente utilizadas em tokamaks para medir a temperatura local na região da borda de plasmas confinados magneticamente. Os métodos de varredura de tensão e a configuração de sonda tripla estão dentre os métodos mais usados para medir a temperatura local na borda do plasma com sondas eletrostáticas. Neste trabalho, é apresentada uma comparação entre as medições de temperatura usando esses dois métodos no tokamak TCABR. Para esse fim, foram utilizadas descargas de plasma em condições padrão, onde a corrente de plasma e a densidade são mantidas praticamente estáveis e há baixa atividade MHD, isto é, a fase estacionária da descarga, com os parâmetros macroscópicos de equilíbrio aproximadamente constantes. As medições da temperatura pelos dois métodos têm boa correspondência na região da sombra do limitador, mas existem discrepâncias quando as medidas são feitas dentro da coluna de plasma. Verificou-se que esta discrepância se deve ao efeito de expansão da região de transição entre o plasma e a superfície da sonda, conhecida como bainha de plasma. Portanto, foram modificadas as equações do método da sonda tripla a fim de considerar, de maneira adequada, este efeito. Esta modificação conduz a medições de temperatura compatíveis entre os dois métodos. Também se estudou as estruturas coerentes que se propagam na turbulência da borda (bursts), que são detectados como picos no sinal de corrente de saturação iônica. Para esse fim, foi usada a técnica da análise condicional. Os resultados obtidos parecem ser compatíveis com estruturas que apresentam uma inclinação no plano radial-poloidal. Esta inclinação implica que o método comumente usado para medir a velocidade de propagação das estruturas, baseado no atraso entre a detecção do pico entre dois pinos próximos, pode levar a resultados completamente errados. Os resultados para a evolução média da temperatura durante os bursts são incompatíveis entre os dois métodos. De fato, os resultados fornecidos pelo método de sonda tripla aparentam estar fisicamente errados, uma vez que indicam um alto gradiente de temperatura dentro dos bursts. Constatou-se que este problema é devido aos altos gradientes de potencial dentro dos bursts que inviabilizam a hipótese de potencial uniforme na região entre os pinos da sonda tripla.
The contribution of the extreme events related to propagating structures in the turbulence, the so-called bursts, seems to be part of the explanation to anomalous transport in confined plasma. But, up to now, there is not an adequate model in the frame of neoclassical transport theory to properly account the contribution of these extreme events. Therefore, the characterization of the particle and energy transport due to the extreme events and the burst internal structure are an important issue in fusion plasma research. However, local electron temperature measurements are necessary to investigate those topics, because particles and energy transport have temperature corrections. Due to their good spatial resolution and relatively easy construction, electrostatic probes are often used to measure temperature in the plasma edge of tokamak. The triple probe configuration and voltage sweep technique are among the most common techniques used with electrostatic probes to measure local temperature in the plasma edge. We present a comparison between the temperature measurement using these two techniques in the tokamak TCABR. For this purpose, it was used stationary standard plasma discharges (it is, discharges with almost stable plasma current and density and with low MHD activity). For temperature measurement, the two methods have good correlation in the Scrape-Off-Layer region but there are discrepancies between their values inside the plasma column. We found that this discrepancy is due to the sheath expansion effect. Therefore, the triple probe equations were modified to properly consider this effect. The modification leads to compatible average temperature measurements between the two methods. We also studied coherent structures propagating in the edge turbulence (detected as bursts in the saturation current) by using the conditional analysis technique. The results seem to be compatibles with structures tilted in the radial-poloidal plane. This tilt implies that the common method to measure the propagation velocity using the delay time of detection between two probes, could produce wrong values. The results for the average temporal behavior of temperature during the bursts are inconsistent between the two methods. Indeed, the triple probe results seems to be physically wrong, once it indicates a strong temperature gradient inside the bursts. We found that this problem is due to the strong potential gradients inside the burst, breaking the assumption that the pins used in the triple probe configuration are in a homogeneous plasma.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Theodoro, Victor Cominato. « Estudo espectral das instabilidades MHD no tokamak TCABR ». Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-18112014-153714/.

Texte intégral

Résumé :

Neste trabalho foram estudadas instabilidades magnetohidrodinâmicas (MHD) utilizando um novo sistema bolométrico que foi instalado no tokamak TCABR para medidas da evolução temporal da potência irradiada. Este novo sistema conta com 24 cordas verticais, capazes de mapear toda uma secção poloidal da coluna de plasma com resolução espacial de aproximadamente 2 cm e uma resolução temporal de 20 µs. Como se sabe, as instabilidades MHD degradam o connamento do plasma e modicam a topologia das superfícies magnéticas, causando a perda da energia do plasma. Por conta disso, compreender essas instabilidades é fundamental para o sucesso dos futuros reatores de fusão nuclear. As perturbações (oscilações) causadas pelas instabilidades MHD modulam diversos parâmetros macroscópicos do plasma como a densidade, a temperatura e a potência irradiada. Então, utilizando o diagnóstico bolométrico, é possível medir as oscilações no perl de potência irradiada e, a partir deles, extrair informações importantes para determinar a origem e as características de tais instabilidades. No tokamak TCABR, as instabilidades foram caracterizadas através da análise espectral dos 24 sinais provenientes do novo sistema bolométrico. Para auxiliar a caracterização das instabilidades, um programa foi desenvolvido em Matlab para simular as medidas das perturbações no perl de potência irradiada. Através do mesmo procedimento de análise espectral, os resultados simulados foram comparados aos experimentais de forma que os parâmetros simulados, como largura e posição das ilhas magnéticas, fossem ajustados aos experimentais. Através dessa metodologia de análise, que combina simulação e experimento, foi possível caracterizar diversas instabilidades como o precursor dos dentes de serra e ilhas magnéticas de modos m = 2 e m = 3.
In this dissertation, magnetohydrodynamic (MHD) instabilities were investigated using a new bolometric system that was installed in the TCABR tokamak for radiation power measurements. This diagnostic is composed by 24 vertical chords that provide a full view of the poloidal cross section of the plasma column and provides spatial and temporal proles with approximately 2 cm space and 20 µs time resolution. As it is well known, the MHD instabilities degrade the plasma connement and modify the magnetic topology, leading to energy loss from the plasma. Therefore, the understanding of these instabilities is essential for the success of the controlled thermonuclear fusion reactors. The MHD instabilities also cause perturbations (oscillations) in various macroscopic parameters, such as plasma density, temperature, and radiated power. Therefore, the oscillations in the radiated power prole measured by the bolometric diagnostic system provide a possibility to investigate the origin and features of the instabilities. In the TCABR tokamak, the instabilities were characterized by spectral analysis of the 24 vertical chords of the bolometric signals. In addition, a Matlab program was developed to simulate the integral characteristic of the oscillations in the radiated power measured by the bolometric system. The spectral analysis of the simulated signals is then compared with the spectral analysis of the bolometric signals. The simulated parameters, island width and radial position, were then adjusted to t the experimental spectrum results. Using this method of analysis, which combines experiment and simulation, it was possible to characterize various instabilities, such as sawtooth precursor and m = 2 and m = 3 magnetic islands.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Pierre, Ralf. « Lokale Einschlusszeiten eines Tokamak-Plasmas ». [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=966424131.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

35

Lima, Gustavo Zampier dos Santos. « Análise espectral por wavelet da turbulência no tokamak TCABR ». Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-08082014-151615/.

Texte intégral

Résumé :

Desenvolvemos uma aplicação das análises espectrais por Fourier e wavelet para o estudo de flutuações intermitentes e não estacionárias. Para isso, elaboramos algoritmos adequados, que revelam os modos principais presentes nas flutuações analisadas e as suas evoluções. Baseados nesses algoritmos, apresentamos um método para a seleção de \"bursts\" (irrupções) em meio ao background da série intermitente analisada. Inicialmente, aplicamos essa análise às flutuações intermitentes obtidas integrando numericamente as equações de Lorenz. Dessa forma, obtivemos a evolução do espectro das frequências dessas flutuações e selecionamos os seus bursts. Similarmente, obtivemos a evolução dos espectros de frequência de flutuações elétricas turbulentas medidas no tokamak TCABR. Confirmamos que a análise por wavelet é adequada para observar a modulação da turbulência pelas oscilações magnéticas. Para essas flutuações, selecionamos os bursts intermitentes presentes nas flutuações turbulentas e obtivemos as distribuições dos intervalos de tempo entre bursts sucessivos. Obtivemos, ainda, as distribuições das medidas da flutuação da turbulência no TCABR. Com a modulação mencionada, a distribuição obtida pode ser reproduzida como a convolução entre as distribuições senoidais (associadas às flutuações magnéticas) e uma distribuição (associada às flutuações turbulentas) como a observada sem a modulação (como as observadas no plasma não perturbado).
We apply the Fourier and wavelet spectral analyses to study nonstationary intermittent fluctuations. For that we introduce algorithms that show the dominant frequency modes and their evolution. Moreover, applying these algorithms, we present a method to discriminate the burst from the background in the intermittent fluctuations. Initially, we apply this analysis to the intermittent fluctuations obtained integrating numerically the Lorenz equations. Thus, we obtain the frequency spectra evolution of these fluctuations as well as the selected bursts sequence. Similarly, we obtain the frequency spectra evolution for the electric plasma edge turbulence in the TCABR tokamak. We confirm that the wavelet analysis describes well the turbulence modulation by the magnetic fluctuations. For this turbulence, we selected the intermittent bursts and present the histograms of the time interval between two successive bursts. Furthermore, we also present the PDFs of the total turbulent fluctuations. When the turbulence is modulated by the magnetic fluctuation, the observed PDF is interpreted as the convolution between sine distributions (due to the magnetic fluctuations influence) and the distribution (due to the turbulence) observed without modulation.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Caschera, Elisabetta. « Global confinement properties in global, flux-driven, gyrokinetic simulations ». Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0509.

Texte intégral

Résumé :

La compréhension du confinement du plasma dans les réacteurs à fusion est l’une des étapes manquantes pour la disponibilité de l’énergie de fusion. La conception de futurs réacteurs tels que ITER sont bases sur l'extrapolation de lois d'échelle empiriques. Dans ce travail de thèse nous étudions les propriétés globales du confinement du plasma dans un Tokamak avec l'une des simulations numériques les plus complétés. Les recherches portent sur deux sujets principaux: les propriétés d’échelle du confinement et l’effet de la limite du plasma sur le transport turbulent. Un résultat important est obtenu lors de la reproduction de la loi d’échelle globale du temps de confinement de l’énergie avec les simulations numériques. La condition aux limites du code a été modifié pour imiter cela au bord du plasma dans les expériences. Une physique supplémentaires est accessibles aux simulations, telles que l'instabilité de type Kelvin-Helmeholtz au niveau de la separatrice et la turbulence sous-critique de bord
Understanding and predicting the performance of a fusion reactor in terms of confinement is one of the missing milestones for the availability of fusion energy. The predictions for the design of future reactors such as ITER are based on the extrapolation of empiricalscaling laws. We investigate global confinement properties of turbulent heat transport in a Tokamak with first principle simulations. The research is carried on two main topics: the scaling properties of plasma confinement and the effect of the plasma boundary on the turbulent transport. An important result is obtained when reproducing the global scaling for the energy confinement time with numerical simulations. However the scaling properties are found to brake at the local level. The boundary condition of the code has been modified to mimic the experimental Scrape-Off Layer at the plasma edge. Additional physics is now accessible, such as Kelvin-Helmholtz-like instability at separatrix and edge subcritical turbulence

Styles APA, Harvard, Vancouver, ISO, etc.

37

Asp, Elina. « Drift-Type Waves in Rotating Tokamak Plasma ». Doctoral thesis, Uppsala University, Department of Astronomy and Space Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3400.

Texte intégral

Résumé :

The concept of energy production through the fusion of two light nuclei has been studied since the 1950’s. One of the major problems that fusion scientists have encountered is the confinement of the hot ionised gas, i.e. the plasma, in which the fusion process takes place. The most common way to contain the plasma is by using at magnetic field configuration, in which the plasma takes a doughnut-like shape. Experimental devices of this kind are referred to as tokamaks. For the fusion process to proceed at an adequate rate, the temperature of the plasma must exceed 100,000,000C. Such a high temperature forces the plasma out of thermodynamical equilibrium which plasma tries to regain by exciting a number of turbulent processes. After successfully quenching the lager scale magnetohydrodynamic turbulence that may instantly disrupt the plasma, a smaller scale turbulence revealed itself. As this smaller scale turbulence behaved contrary to the common theory at the time, it was referred to as anomalous. This kind of turbulence does not directly threaten existents of the plasma, but it allows for a leakage of heat and particles which inhibits the fusion reactions. It is thus essential to understand the origin of anomalous turbulence, the transport it generates and most importantly, how to reduce it. Today it is believed that anomalous transport is due to drift-type waves driven by temperature and density inhomogeneities and the theoretical treatment of these waves is the topic of this thesis.

The first part of the thesis contains a rigorous analytical two-fluid treatment of drift waves driven solely by density inhomogeneities. Effects of the toroidal magnetic field configuration, the Landau resonance, a peaked diamagnetic frequency and a sheared rotation of the plasma have been taken into account. These effects either stabilise or destabilise the drift waves and to determine the net result on the drift waves requires careful analysis. To this end, dispersion relations have been obtained in various limits to determine when to expect the different effects to be dominant. The main result of this part is that with a large enough rotational shear, the drift waves will be quenched.

In the second part we focus on temperature effects and thus treat reactive drift waves, specifically ion temperature gradient and trapped electron modes. In fusion plasmas the α-particles, created as a by-product of the fusion process, transfer the better part of their energy to the electrons and hence the electron temperature is expected to exceed the ion temperature. In most experiments until today, the ion temperature is greater than the electron temperature and this have been proven to improve the plasma confinement. To predict the performance of future fusion plasmas, where the fusion process is ongoing, a comprehensive study of hot-electron plasmas and external heating effects have been carried out. Especially the stiffness (heat flux vs. inverse temperature length scale) of the plasma has been examined. This work was performed by simulations done with the JETTO code utilising the Weiland model. The outcome of these simulations shows that the plasma response to strong heating is very stiff and that the plasma energy confinement time seems to vary little in the hot-electron mode.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Ford, Oliver P. « Tokamak Plasma Analysis through Bayesian Diagnostic Modelling ». Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526369.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

39

Grandgirard, Virginie. « Modelisation de l'equilibre d'un plasma de tokamak ». Besançon, 1999. http://www.theses.fr/1999BESA2039.

Texte intégral

Résumé :

Cette these traite de la modelisation, de la simulation numerique et du controle optimal de l'equilibre du plasma dans un tokamak. Dans le premier chapitre, les equations aux derivees partielles, regissant l'equilibre d'un plasma axisymetrique, sont presentees. Il s'agit d'un probleme elliptique, non-lineaire, a frontiere libre, avec conditions limites a l'infini. Le probleme faible associe est linearise par un algorithme de newton et resolu par elements finis sur un domaine suffisamment grand pour y appliquer une condition de dirichlet sur la frontiere. Dans le second chapitre, un traitement rigoureux des conditions a l'infini est presente. Le domaine est divise en une partie interieure, comprenant toutes les non-linearites et en la partie exterieure complementaire. En choisissant une frontiere semi-circulaire entre ces deux domaines, les problemes interieurs et exterieurs sont decouples. Dans le troisieme chapitre, deux methodes iteratives (gmres et bigradient conjugue preconditionnes) sont comparees a une methode directe (woodbury associe a une decomposition de cholesky) en termes de taille memoire et temps de calcul. Le probleme inverse est formule, dans le quatrieme chapitre, en terme de controle optimal. Le lagrangien associe et le systeme d'optimalite de premier ordre sont alors definis. Une methode d'optimisation quadratique, utilisant l'algorithme du gradient conjugue, est introduite. Des exemples d'applications pour les projets de tokamaks futurs, sont presentes. Enfin, dans le dernier chapitre, est decrite une methode iterative d'approximations successives, associee a une application de point fixe croissante-decroissante. Il est demontre que cette methode permet, a partir d'un couple de sur et sous-solutions, de construire des suites monotones convergeant vers un encadrement de la solution.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Bodi, Vasudeva Raghavendra Kowsik. « Anomalous radial transport in tokamak edge plasma ». Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3390465.

Texte intégral

Résumé :

Thesis (Ph. D.)--University of California, San Diego, 2010.
Title from first page of PDF file (viewed February 18, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 67-72).

Styles APA, Harvard, Vancouver, ISO, etc.

41

Merle, Antoine. « Stability and properties of electron-driven fi shbones in tokamaks ». Palaiseau, Ecole polytechnique, 2012. https://pastel.hal.science/docs/00/77/31/03/PDF/Merle_PhD.pdf.

Texte intégral

Résumé :

In tokamaks, the stability of magneto-hydrodynamic modes can be modified by populations of energetic particles. In ITER-type fusion reactors, such populations can be generated by fusion reactions or auxiliary heating. The electron-driven fishbone mode belongs to this category of instabilities. It results from the resonant interaction of the internal kink mode with the slow toroidal precessional motion of energetic electrons and is frequently observed in present-day tokamaks with Electron Cyclotron Resonance Heating or Lower Hybrid Current Drive. These modes provide a good test bed for the linear theory of fast-particle driven instabilities as they exhibit a very high sensitivity to the details of both the equilibrium and the electronic distribution function. In Tore Supra, electron-driven fishbones are observed during LHCD-powered discharges in which a high-energy tail of the electronic distribution function is created. Although the destabilization of those modes is related to the existence of a fast particle population, the modes are observed at a frequency that is lower than expected. Indeed, the corresponding energy assuming resonance with the toroidal precession frequency of barely trapped electrons falls in the thermal range. The linear stability analysis of electron-driven fishbone modes is the main focus of this thesis. The fishbone dispersion relation is derived in a form that accounts for the contribution of the parallel motion of passing particles to the resonance condition. The MIKE code is developed to compute and solve the dispersion relation of electron-driven fishbones. The code is successfully benchmarked against theory using simple analytical distributions. When coupled to the relativistic Fokker-Planck code LUKE and to the integrated modeling platform CRONOS, it is used to compute the stability of electron-driven fishbones using reconstructed data from tokamak experiments. Using the code MIKE with parametric distributions and equilibria, we show that both barely trapped and barely passing electrons resonate with the mode and can drive it unstable. More deeply trapped and passing electrons have a non-resonant effect on the mode that is, respectively, stabilizing and destabilizing. MIKE simulations using complete ECRH-like distribution functions show that energetic barely passing electrons can contribute to drive a mode unstable at a relatively low frequency. This observation could provide some insight to the understanding of Tore Supra experiments
La stabilité des modes magnéto-hydrodynamiques dans les plasmas de tokamaks est modifiée par la présence de particules rapides. Dans un tokamak tel qu'ITER ces particules rapides peuvent être soit les particules alpha créées par les réactions de fusion, soit les ions et électrons accélérés par les dispositifs de chauffage additionnel et de génération de courant. Les modes appelés fishbones électroniques correspondent à la déstabilisation du mode de kink interne due à la résonance avec le lent mouvement de précession toroidale des électrons rapides. Ces modes sont fréquemment observés dans les plasmas des tokamaks actuels en présence de chauffage par onde cyclotronique électronique (ECRH) ou de génération de courant par onde hybride basse (LHCD). La stabilité de ces modes est particulièrement sensible aux détails de la fonction de distribution électronique et du facteur de sécurité, ce qui fait des fishbones électroniques un excellent candidat pour tester la théorie linéaire des instabilités liées aux particules rapides. Dans le tokamak Tore Supra, des fishbones électroniques sont couramment observés lors de décharges où l'utilisation de l'onde hybride basse crée une importante queue de particules rapides dans la fonction de distribution électronique. Bien que ces modes soit clairement liés à la présence de particules rapides, la fréquence observée de ces modes est plus basse que celle prévue par la théorie. En effet, si on estime l'énergie des électrons résonants en faisant correspondre la fréquence du mode avec la fréquence de précession toroidale des électrons faiblement piégés, on obtient une valeur comparable à celle des électrons thermiques. L'objet principal de cette thèse est l'analyse linéaire de la stabilité des fishbones électroniques. La relation de dispersion de ces modes est dérivée et la forme obtenue prend en compte, dans la condition de résonance, la contribution du mouvement parallèle des particules passantes. Cette relation de dispersion est implémentée dans le code MIKE qui est ensuite testé avec succès en utilisant des fonctions de distributions analytiques. En le couplant au code Fokker-Planck relativiste LUKE et à la plate-forme de simulation intégrée CRONOS, MIKE peut estimer la stabilité des fishbones électroniques en utilisant les données reconstruites de l'expérience. En utilisant des fonctions de distributions et des équilibres analytiques dans le code MIKE nous montrons que les électrons faiblement piégés ou faiblement passants peuvent déstabiliser le mode de kink interne en résonant avec lui. Si l'on s'éloigne de la frontière entre électrons passants et piégés, les effets résonants s'affaiblissent. Cependant les électrons passants conservent une influence déstabilisante alors que les électrons piégées tendent à stabiliser le mode. D'autres simulations avec MIKE, utilisant cette fois des distributions complètes similaires à celles obtenues en présence de chauffage de type ECRH, montrent que l'interaction avec les électrons faiblement passants peut entraîner une déstabilisation du mode à une fréquence relativement basse ce qui pourrait permettre d'expliquer les observations sur le tokamak Tore Supra

Styles APA, Harvard, Vancouver, ISO, etc.

42

Sugita, Satoru. « Etude par simulation numérique du transport radial dans le plasma de bord du tokamak ». Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10010/document.

Texte intégral

Résumé :

Il est maintenant accepté expérimentalement que les filaments de plasma alignés sur le champ magnétique, appelés “blobs”, jouent un rôle important dans le transport dans le plasma de bord. Dans cette thèse, les phénomènes fondamentaux du transport dans le plasma de bord sont étudiés en mettant l'accent sur le phénomène de filaments plasma. Dans un premier temps, les mécanismes de propagation de blobs uniques sont envisagés. Puis la génération de blobs par la turbulence de bord est étudiée, et le transport turbulent est discuté entant que phénomène collectif. Des particularités du transport turbulent, incluant les blobs auto-organisés, sont reliées à un transport de type Bohm (c'est à dire des perturbations avec des corrélations radiales longues, et un coefficient de transport effectif quisuit la dépendance Bohm). De plus, en prolongement de ce travail, un effort initial vers une transposition du transport non-local au plasmade bord est décrite
Recently, it has been accepted that magnetic field aligned plasma filaments, referred to as "blobs" play important roles in the transport of Scrape-off Layer (SoL) plasmas. In this thesis, putting an emphasis on the plasma blob phenomenon, we study fundamental processes of SoL transport using numerical simulation. At first, weinvestigate the propagation mechanisms of single and isolated blobs.Next, we study the generation of blobs from edge turbulence, and discuss the SoL turbulent transport as a collective phenomenon. Features of turbulent transport, which includes the self-organized blobs in SoL, are identified as Bohm-like transport (i.e., the perturbation with long radial correlations and the effective transport coefficient that follows the dependence of Bohm-like transport). Additionally, as an advancement of study, we describe an initial effort to extend the view of non local transport to edge plasmas

Styles APA, Harvard, Vancouver, ISO, etc.

43

Hodille, Etienne. « Etude de l'implantation du deutérium dans les composés face au au plasma constituants du tokamak ITER ». Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4065.

Texte intégral

Résumé :

Lors de l’opération d’ITER, des flux importants d’isotopes d’hydrogène (HI) constituant le fuel interagissent avec les composants face au plasma (CFP) de la machine. Dans le cas du Tungstène (W) composant le divertor qui est la zone la plus exposée aux interactions plasma paroi, le flux incident est implanté et diffuse ensuite dans le corps du matériau entrainant un piégeage du fuel. Pour des raisons de sureté, l’inventaire de Tritium retenu dans les parois d’ITER est limité. De plus, le dégazage du fuel depuis les parois vers le plasma, lors des opérations plasma peut avoir un impact sur le contrôle global du plasma. Le but de cette thèse est d’abord de déterminer les paramètres de piégeages du fuel dans le W (énergies/températures de dépiégeage, concentrations de pièges) grâce à la modélisation de résultats expérimentaux. Ces simulations de résultats expérimentaux montrent que l’implantation d’HIs dans le W peut induire, sous certaines conditions, la formation de lacunes contenant des impuretés. En plus de ce piège induit par l’implantation d’ions, 2 pièges intrinsèques sont présents dans le W. Ces 3 pièges retiennent les HIs jusqu’à 700 K. Enfin, il est montré que le W endommagé par des ions lourds ou des neutrons contient des dislocations, des boucles de dislocations et des cavités retenant les HIs jusqu’à 1000 K.Après avoir déterminé ces paramètres de piégeages des HIs dans le W, la rétention des HIs durant l’opération d’ITER est estimée. Lors de cette opération, la température des CFP W atteint environ 1000 K. Les simulations montrent donc que la rétention dans les CFPs non endommagé est bien plus faible que dans le cas d’un CFP endommagé
During ITER operation, important flux of Hydrogen Isotopes (HIs) constituting the fuel interact with the plasma facing components (PFC) of the machine. In the case of tungsten (W) making the divertor which is the most exposed area to the plasma wall interaction, the incident flux can be implanted and diffuse inside the bulk material inducing a trapping of the fuel. To safety issue, the tritium inventory retained in ITER’s PFC is limited. In addition, the outgassing of the fuel during plasma operation can impact the edge plasma control.The aim of this PhD project is first to determined relevant trapping parameters of the fuel in W (detrapping energies/temperatures and trap concentrations) by modelling experimental results. The simulations of experimental results shows that under specific condition, the HI implantation can induce the formation of mono-vacancies containing impurities. In addition to this induced trap, 2 intrinsic traps are present in W. This 3 traps retain HIs up to 700 K. Finally, it has been shown that the damaged W by heavy ions or neutrons contains dislocations, dislocation loops and cavities that can trap HIs up to 1000 K.After determining the fuel retention properties of W, the HIs retention during ITER operation is estimated. During this operation, the PFC temperature reaches around 1000 K so the simulations show that the damaged W retains much more HIs than the undamaged W

Styles APA, Harvard, Vancouver, ISO, etc.

44

Sa, Wanderley Pires de. « Reconstrução do equilíbrio no tokamak TCA/BR ». Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-12122013-162240/.

Texte intégral

Résumé :

A determinação precisa e rápida das configurações de equilíbrio Magnetohidrodinâmico (MHD) em tokamaks é de fundamental importância para o confinamento magnético do plasma. Através do conhecimento dos parâmetros que caracterizam este equilíbrio MHD é possível controlar o plasma durante a sua formação por processos de realimentação. Uma análise mais detalhada destes parâmetros é necessária, também, entre um disparo e outro, para a estruturação do experimento. Neste trabalho é investigada a reconstrução das configurações de equilíbrio MHD no tokamak TCA/BR a partir de medidas magnéticas externas, utilizando um método que permite uma rápida determinação dos parâmetros principais da descarga. A tese divide-se em duas partes. Na primeira, é apresentada a construção de um código de equilíbrio que resolve a equação de Grad-Shafranov para a configuração geométrica que caracteriza o tokamak TCA/BR. Na segunda, é descrito o processo de reconstrução do equilíbrio MHD através de medidas de campos e fluxos magnéticos externos ao plasma no TCA/BR, e utilizando o método de Função de Parametrização FP. Este método baseia-se no tratamento estatístico de um banco de dados simulados de configurações de equilíbrio, com o objetivo de obter uma expressão simples relacionando os parâmetros que caracterizam o equilíbrio e as medidas realizadas. Os resultados obtidos através da FP são comparados com os obtidos através de outros métodos convencionais.
The accurate and rapid determination of the Magnetohydrodynamic (MHD) equilibrium configuration in tokamaks is a fundamental subject for the magnetic confinement of the plasma. With the knowledge of characteristic plasma MHD equilibrium parameters it is possible to control the plasma position during its formation using feed-back techniques. It is also necessary an on-line analysis between successive discharges to program external parameters for the subsequent discharges. In this work it is investigated the MHD equilibrium configuration reconstruction of the TCA/BR tokamak from external magnetic measurements, using a method that is able to determine fastly the main parameters of discharge. The thesis has two parts. Firstly it is presented the development of an equilibrium co de that solves de Grad-Shafranov equation for the TCA/BR tokamak geometry. Secondly it is presented the MHD equilibrium reconstruction process from external magnetic field and flux measurements using the Function Parametrization FP method. This method is based on the statistical analysis of a database of simulated equilibrium configurations, with the goal of obtaining a simple relationship between the parameters that characterize the equilibrium and the measurements. The results from FP are compared with conventional methods.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Fil, Alexandre. « Modeling of massive gas injection triggered disruptions in tokamak plasmas ». Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4040/document.

Texte intégral

Résumé :

Les disruptions du plasma sont des phénomènes se produisant dans les tokamaks et qui entraînent une perte totale du confinement du plasma et la fin de la décharge. Ces disruptions sont des phénomènes rapides et violents et peuvent endommager les murs du tokamak ainsi que sa structure si elles ne sont pas contrôlées. Un système de mitigation des disruptions est donc indispensable pour ITER afin de réduire les forces électromagnétiques, mitiger les charges thermiques et éviter les électrons runaways générés par les disruptions du plasma. Remplir tous ces objectifs fait du design de ce système une tâche difficile, pour laquelle un apport conséquent de l’expérience et de la modélisation est nécessaire. Nous présentons dans cette thèse des résultats de modélisation sur l’amortissement des disruptions par injection massive de gaz, qui est une des méthodes principales envisagées sur ITER pour le système de mitigation. Premièrement, un modèle issu des premiers principes pour décrire le transport des neutres dans un plasma est donné et est appliqué à l’étude de l’interaction entre l’injection massive de gaz et le plasma. Les principaux mécanismes en jeu sont décrits et étudiés. L’échange de charge entre les neutres et les ions du plasma est isolée comme jouant un rôle majeur dans cette dynamique. Ensuite, le code 3D de Magnétohydrodynamique non linéaire JOREK est appliqué à l’étude des disruptions déclenchées par injection massive de gaz. Un intérêt particulier est porté sur la phase de quench thermique et les phénomènes MHD qui le déclenchent. Les résultats obtenus avec ce code sont comparés avec les expériences effectuées sur le tokamak JET
Plasma disruptions are events occuring in tokamaks which result in the total loss of the plasma confinement and the end of the discharge. These disruptions are rapid and violent events and they can damage the tokamak walls and its structure if they are not controlled. A Disruption Mitigation System (DMS) is thus mandatory in ITER in order to reduce electromagnetic forces, mitigate heat loads and avoid Runaway Electrons (RE) generated by plasma disruptions. These combined objectives make the design of the DMS a complex and challenging task, for which substantial input from both experiments and modeling is needed. We present here modeling results on disruption mitigation by Massive Gas Injection (MGI), which is one of the main methods considered for the DMS of ITER. First, a model which stems from first principles is given for the tranport of neutrals in a plasma and applied to the study of the interaction of the MGI with the plasma. Main mechanisms responsible for the penetration of the neutral gas are described and studied. Charge-exchange processes between the neutrals and the ions of the plasma is found to play a major role. Then, the 3D non linear MHD code JOREK is applied to the study of MGI-triggered disruptions with a particular focus on the thermal quench phase and the MHD events which are responsible for it. The simulation results are compared to experiments done on the JET tokamak

Styles APA, Harvard, Vancouver, ISO, etc.

46

Fonseca, António Manuel Marques. « "Emissão Eletrociclotrônica no Tokamak TCABR : Um Estudo Experimental" ». Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-29092005-132047/.

Texte intégral

Résumé :

Descreve-se neste trabalho um estudo experimental da Emissão Eletrociclotrônica (EEC) no tokamak TCABR. Um radiômetro de EEC foi instalado, calibrado e utilizado para o estudo do plasma em descargas térmicas. O radiômetro é do tipo heteródino de varredura operando na faixa de 50-85 GHz, no modo extraordinário e na segunda harmônica. Determinou-se a temperatura de ruído do radiômetro e também sua estabilidade em amplitude e freqüência. Foi medida a largura de banda em freqüência do radiômetro (resolução espacial horizontal). A antena utilizada é do tipo gaussiana sendo que o raio da cintura do feixe gaussiano e a posição do foco foram experimentalmente determinados (W0 ~ 1 cm e d ~ 37 cm, respectivamente). A posição da cintura da antena foi posicionada próxima do centro geométrico do vaso. Foi feita a calibração absoluta do equipamento considerando-se os efeitos das janelas de diagnóstico (reflexão e absorção). O sistema pode operar em modo varredura, para a obtenção de perfis radiais de Te ou modo freqüência única onde se tem alta resolução temporal. As medidas da radiação EC foram feitas, na sua maioria, em descargas com densidade eletrônica média entre 1.10+19 m-3 e 1,5.1019 m-3 de forma a se ter acessibilidade da radiação EC e também minimizar-se a presença de elétrons fugitivos. Para ne > 1,5.1019 m-3 (com B0 = 1,14 T) verifica-se o corte parcial da radiação EC. Nesta condição, o corte na EEC foi utilizado na determinação do perfil radial da densidade eletrônica e aplicado em três diferentes situações: descargas com injeção adicional de gás, com a aplicação do eletrodo de polarização e em descargas com injeção de ondas de radiofreqüência na região das ondas de Alfvén para o TCABR. Usando um perfil parabólico típico para a densidade eletrônica, observou-se que, para descargas com injeção adicional de gás ou em descargas com a aplicação de ondas de radiofreqüência tem-se 0,85 < alfa < 1, e para descargas com aplicação do eletrodo de polarização obteve-se alfa ~ 0,6. Foram feitas observações simultâneas da temperatura eletrônica, a partir do sinal da EEC, e das oscilações de Mirnov (freqüência ~ 11,7 kHz) em descargas térmicas com q(r=0) > 1. Os resultados indicam a presença de um modo de ruptura dominante em rs ~ 9,5 cm com a largura da ilha magnética de W ~ 2,0-2,5 cm. Estes resultados experimentais obtidos estão em acordo com os resultados indicados por teorias de transporte na região das ilhas magnéticas. Observou-se também que a localização da ilha magnética coincide com uma região onde o perfil radial da temperatura de plasma é aproximadamente plano. Num outro cenário, com q(r=0) < 1, observaram-se oscilações dente de serra com período de ~ 0,44 ms, tempo de queda de ~ 0,12 ms, e raio de inversão em r ~ 4 cm. Neste tipo de descargas observou-se que, no perfil radial da amplitude das oscilações da Te, |DeltaTe|, devido à propagação dos pulsos dente de serra, apresentavam posições de mínimos e que estes coincidiam com as posições onde ocorrem patamares no perfil radial da temperatura eletrônica. Partindo destes resultados, juntamente com o perfil de q(r), dão-nos os modos racionais (m/n), posições (r) e larguras(W) para as ilhas magnéticas, presentes nestas descargas, a saber: m/n = 4/3 (r ~ 9 cm, W4/3 ~ 0,9 cm), m/n = 3/2 (r ~ 11,8 cm, W3/2 ~ 0,9 cm) e m/n = 2/1 (r ~ 13,7 cm, W2/1 ~ 1,4 cm). Este novo método, aqui proposto, permite a determinação direta da posição e da largura das ilhas magnéticas, em descargas onde a instabilidade dente de serra encontra-se presente.¶
In this work, an experimental study of the Electron Cyclotron Emission (ECE) in the TCABR Tokamak, is described. An ECE sweeping heterodyne radiometer, operating in the 50-85 GHz frequency range, was installed, calibrated and used to detect ECE radiation in the second harmonic extraordinary mode from thermal plasma discharges. The noise temperature, amplitude and frequency stability of the radiometer were determined. The frequency bandwidth (horizontal space resolution) was measured. A Gaussian Antenna is used and the gaussian beam waist radius (W0 ~ 1 cm) and the focus position (d ~ 37 cm) were experimentally determined. The focus of the antenna was positioned close to the center of the vacuum vessel. The absolute calibration of the equipment was done and the effect of the diagnostic window was considered (reflections and absorptions). The system can operate in sweeping mode, in order to obtain the radial electron temperature profiles, and also in the single frequency mode to obtain temporal electron temperature profiles with high time resolution. Due to the TCABR accessibility conditions and also to avoid runaway electrons, most of the ECE measurements were obtained in discharges with line electron density between 1.0x10+19 m-3 and 1.5x1019 m-3. For ne > 1.5x1019 m-3 (with B0 = 1.14 T) the cutoff in the ECE radiation was observed. The ECE cutoff was used to determine the radial profile of the electron density and applied to three different situations: discharges with additional gas puffing, with the application of a biasing electrode and in discharges with radio-frequency wave injection. Using a parabolic profile it was observed that, 0.85 < alfa < 1.0 for discharges with additional gas injection or with RF injection, and alfa ~ 0.6 for the electrode biasing experiments. The electron temperature profiles and Mirnov oscillations (f ~ 11.7 kHz) were simultaneously measured in discharges with q (r=0) > 1. The position and the width of the magnetic island were therefore calculated. The results indicate the presence of a dominant tearing mode in rs ~ 9.5 cm and the magnetic island width W ~ 2.0-2.5 cm. These experimental results are in agreement with the theoretical results foreseen by models of heat transport in the presence of magnetic islands. It was also observed that, the position of the magnetic island coincided with the region where the temperature radial profile is approximately flat. In another plasma scenario, with q(r=0) < 1, sawteeth oscillations with a period ~ 0.44 ms, crash time ~ 0.12 ms, inversion radius r ~ 4 cm, were measured. Peculiarities in the Te radial profile associated with the amplitude of Te oscillations, |DeltaTe|, due to the sawtooth instability, were observed. It was verified that the minimum values of the |DeltaTe| profile coincided with the region where the temperature radial profile was approximately flat. These results together with the q(r) profile yielded the following mode numbers (m/n), positions (r) and widths (W) of the magnetic islands: m/n = 4/3 (r ~ 9 cm, W4/3 ~ 0.9 cm), m/n = 3/2 (r ~ 11.8 cm, W3/2 ~ 0.9 cm) and m/n = 2/1 (r ~ 13.7 cm, W2/1; ~ 1.4 cm). A novel method to determine the position and width of the magnetic islands, in discharges with the presence of sawtooth instability, is presented here.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Henneberg, Sophia I. A. « Filamentary plasma eruptions in tokamaks ». Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/15376/.

Texte intégral

Résumé :

The nonlinear MHD ballooning model is exploited for two distinct studies: firstly, the interaction of multiple filamentary eruptions in magnetised plasmas in a slab geometry is investigated and secondly, this model is examined quantitatively against experimental observations of ELMs in MAST and JET-like geometries. The model consists of two differential equations which characterise the spatial and temporal evolution of the displacement: the first differential equation describes the displacement along the field line, the second differential equation is a two-dimensional nonlinear ballooning-like equation which is often second order in time, but can involve a fractional derivative in a tokamak geometry. Filaments always evolve independently in the linear regime and equally sized filaments evolve independently in the nonlinear regime. However, we find that filaments with varying heights interact with each other in the nonlinear regime: Smaller filaments are slowed down and eventually are completely suppressed by the larger filaments which grow faster due to the interaction. This mechanism is explained by the down-draft caused by the nonlinear drive of the larger filaments which pushes the smaller filaments downwards. To employ the second differential equation for a specific geometry one has to evaluate the coefficients of the equation which is non-trivial in a tokamak geometry as it involves field line averaging of slowly converging functions. The coefficients of a Type I ELMy equilibrium from MAST and a Type II ELMy JET-like equilibrium have been determined. In both cases the two coefficients of the nonlinear terms are negative which would imply imploding rather than exploding filaments. By changing the equilibrium the signs of these coefficients can be inverted. This suggests that either the nonlinear Ballooning model does not capture the behaviour of Type I and Type II ELMs, or that the calculation of the coefficients are too sensitive to a given equilibrium.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Kubic, Martin. « Étude expérimentale d'interactions entre antennes HF et plasma périphérique d'un Tokamak ». Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0220/document.

Texte intégral

Résumé :

Les antennes en opération dans la gamme de fréquence cyclotron ionique représentent un moyen utile pour chauffer du plasma dans les tokamaks et autres plasmas de fusion. Ces systèmes de chauffage sont amenés à jouer un rôle important dans le projet ITER. Conjointement avec le chauffage souhaité, les interactions parasites avec le bord du plasma et de la limite des matériaux apparaissent. Plusieurs de ces effets délétères sont causés par la formation de la radio-fréquence des gaines. L'objectif de cette thèse est d'étudier, principalement de façon expérimentale, les modifications du plasma de bord «scrape-off layer» causées par les effets non-linéaires des gaines RF. Cela se fait en utilisant les sondes électrostatiques (de Langmuir, Retarded Field Analyser, tunnel) pour différentes configurations du plasma et des antennes: avec des études paramétriques en fonction du déséquilibre entre les émetteurs de l'antenne, de la puissance injectée et de la densité SOL. De plus, l'influence des gaines RF sur les mesures du potentiel de la gaine avec le RFA sont analysées. Cette étude s'effectue à l'aide d'un code 1D basé sur le modèle cinétique «particle-in-cell». Ces simulations ont montré que la RFA est capable de mesurer de manière fiable le potentiel gaine, toutefois cela reste limité pour les fréquences de plasma ionique wpi proche de la fréquence injectée wrf. Par contre, pour des conditions réelles du SOL (wpi>wrf), quand RFA est magnétiquement connectée à la structure de l'antenne RF, il est fortement sous-estimé. Enfin, les mesures de RFA dans Tore Supra indiquent que les potentiels RF se propagent au moins jusqu'à de 12m de l'antenne le long de lignes de champ magnétiques
Antennas operating in the ion cyclotron range of frequency (ICRF) provide a useful tool for plasma heating in many tokamaks and are foreseen to play an important role in ITER. However, in addition to the desired heating in the core plasma, spurious interactions with the plasma edge and material boundary are known to occur. Many of these deleterious effects are caused by the formation of radio-frequency (RF) sheaths. The aim of this thesis is to study, mainly experimentally, scrape-off layer (SOL) modifications caused by RF sheaths effects by means of Langmuir probes that are magnetically connected to a powered ICRH antenna. Effects of the two types of Faraday screens' operation on RF-induced SOL modifications are studied for different plasma and antenna configurations - scans of strap power ratio imbalance, injected power and SOL density. In addition to experimental work, the influence of RF sheaths on retarding field analyzer (RFA) measurements of sheath potential is investigated with one-dimensional particle-in-cell code. One-dimensional particle-in-cell simulations show that the RFA is able to measure reliably the sheath potential only for ion plasma frequencies wpi similar to RF cyclotron frequency wrf, while for the real SOL conditions (wpi > wrf), when the RFA is magnetically connected to RF region, it is strongly underestimated. An alternative method to investigate RF sheaths effects is proposed by using broadening of the ion distribution function as an evidence of the RF electric fields in the sheath. RFA measurements in Tore Supra indicate that RF potentials do indeed propagate from the antenna 12m along magnetic field lines

Styles APA, Harvard, Vancouver, ISO, etc.

49

Caron, Xavier. « Propositions de diagnostic d'un courant toroïdal localisé dans un plasma de tokamak à l'aide de la résonance cyclotron électronique : aspects théorique et numérique ». Nancy 1, 1992. http://www.theses.fr/1992NAN10005.

Texte intégral

Résumé :

Dans une machine de type tokamak, il faut chauffer le plasma jusqu'à une température limite à partir de laquelle pourront se déclencher un nombre suffisant de réactions de fusion. De plus, pour avoir un réacteur, il faut fonctionner en régime continu. Pour résoudre en partie ces problèmes, on envoie des ondes à la fréquence hybride inferieure qui, transférant leur énergie aux particules du plasma, créent un courant toroïdal. Des mesures expérimentales de la localisation spatiale et du profil de ce courant semblent en contradiction avec les prévisions théoriques. Nous proposons deux méthodes de diagnostic de ce courant par l'envoi d'ondes vérifiant la relation de résonance cyclotron électronique. Le principe est de mesurer l'atténuation de ces ondes de façon à reconstituer le profil de densité de courant. La première des deux méthodes concerne le cas des plasmas peu denses. Elle consiste en l'envoi d'ondes le long de cordes verticales dans le plan poloïdal. Le profil de densité de courant est obtenu après une inversion d'Abel. Dans la seconde méthode, adaptée à des plasmas plus denses, l'envoi d'ondes dans le plan équatorial entraine une réfraction. Dans ce cas, l'inversion d'Abel n'est pas utilisable et une nouvelle méthode d'inversion numérique a été mise au point. Ces deux diagnostics ont été simulés numériquement en modélisant le mieux possible un plasma de tokamak et le comportement des ondes vérifiant la résonance cyclotron électronique. Nous montrons que l'accord entre les profils de densité de courant initiaux et les profils reconstitués est très satisfaisant

Styles APA, Harvard, Vancouver, ISO, etc.

50

Vignichouk, Ladislas Tancrède Raymond. « Dynamics of metallic dust particles in tokamak edge plasmas ». Thesis, KTH, Rymd- och plasmafysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118454.

Texte intégral

Résumé :

The study of dust dynamics in tokamaks has been carried out by means of the DDFTU numericalcode solving the coupled equations of motion, charging and heat balance for a dust grainimmersed in plasmas with given profiles. The code has been updated to include (i) a non-steadystate heat balance model and phase transitions, (ii) geometrical properties of the vessel suchas gaps, (iii) realistic boundary conditions for dust-wall collisions. The models for secondaryelectron emission (SEE), thermionic emission and black body radiation have also been refined,and sensitivity of the results to the SEE strength is demonstrated. The DDFTU code has been used for the first time to explore a large range of initial conditions(position, velocity and radius) for dust grains of various tokamak-relevant materials. This studyconfirmed the impact of the drag force as one of the main factors in dust dynamics and allowedto estimate average lifetimes, to locate preferred sites for dust deposition and to judge thesensitivity to initial conditions. This is a first step towards the use of the code as a predictivetool for devices of importance, such as JET and ITER. Preliminary simulations of scenarios relevant for dust injection experiments in TEXTOR haveyielded results in remarkable agreement with experimental data. These preliminary studies allowed to identify the most crucial issues affecting dust dynamics,lifetime, deposition rate and contribution to impurities, which are to be pursued in futurestudies.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Plasmi in tokamak »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres