Download or read book Etude Du Transport Turbulent Des Impuret s Dans Les Plasmas de Tokamak written by Shimpei Futatani and published by . This book was released on 2009 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this thesis is to understand impurity transport dynamics in the magnetically confined fusion plasmas. This includes the influence of the turbulent field which induces an anomalous transport in the plasma. Furthermore, this work demonstrates remarkable aspects for impurity transport in two different instabilities: ``ion temperature gradient (ITG) and trapped electron mode (TEM)''. It is shown that in presence of an internal transport barrier (ITB) created by a reversed magnetic shear configuration, one can obtain the reversal of impurity pinch velocity which can change from inward direction to outward direction. This scenario is favourable for expelling impurities from the central region and decontaminating the core plasma. The mechanism of pinch reversal is attributed to a change of direction of the curvature pinch and to a modification of the dominant underlying instability caused by a change of the gradient of the ion temperature which is a consequence of the ITB formation.

Download or read book Transport turbulent et n oclassique de quantit de mouvement toro dale dans les plasmas tokamak written by Jérémie Abiteboul and published by . This book was released on 2012 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Lecture Series on Turbulent Transport in Tokamaks written by Ronald E. Waltz and published by . This book was released on 1987 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Impurity Transport in Tokamak Plasmas written by Peter Donnel and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Impurity transport is an issue of utmost importance for tokamaks. Indeed high-Z materials are only partially ionized in the plasma core, so that they can lead to prohibitive radiative losses even at low concentrations, and impact dramatically plasma performance and stability. On-axis accumulation of tungsten has been widely observed in tokamaks.While the very core impurity peaking is generally attributed to neoclassical effects, turbulent transport could well dominate in the gradient region at ITER relevant collisionality. Up to recently, first principles simulations of corresponding fluxes were performed with different dedicated codes, implicitly assuming that both transport channels are separable and therefore additive. The validity of this assumption is questionned. Simulations obtained with the gyrokinetic code GYSELA have shown clear evidences of a neoclassical-turbulence synergy for impurity transport and allowed the identification of a mechanism that underly this synergy.An analytical work allows to compute the level and the structure of the axisymmetric part of the electric potential knowing the turbulence intensity. Two mechanisms are found for the generation of poloidal asymmetries of the electric potential: flow compressibility and the ballooning of the turbulence. A new prediction for the neoclassical impurity flux in presence of large poloidal asymmetries and pressure anisotropies has been derived. A fair agreement has been found between the new theoretical prediction for neoclassical impurity flux and the results of a GYSELA simulation displaying large poloidal asymmetries and pressure anisotropies induced by the presence of turbulence.

Download or read book Transport Analysis in Tokamak Plasmas written by Sara Moradi and published by LAP Lambert Academic Publishing. This book was released on 2010-08 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the least understood areas of the plasma particle or heat transport is the turbulent transport. In this work the main focus is on the development and data analysis of anomalous transport characteristics (transport coefficients and fluxes) under fusion conditions in large tokamaks. Fluid and gyro-kinetic models are used and obtained results are compared. A model based on fractional kinetics for the study of the SOL turbulent transport characteristics, where non-Gaussian PDFs are observed, is developed.

Download or read book Washington Journal written by and published by . This book was released on with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: Journal of a trip to a GAR encampment in Washington, DC. Very detailed description of his trip to the White House. Includes description of a day spent sight seeing in Cleveland, OH on the return trip to Michigan.

Download or read book Modeling the Turbulent Momentum Transport in Tokamak Plasmas written by Pierre Cottier and published by LAP Lambert Academic Publishing. This book was released on 2014-04-01 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The magnetic confinement in tokamaks is for now the most advanced way towards energy production by nuclear fusion. Both theoretical and experimental studies showed that rotation generation can increase its performance by reducing the turbulent transport in tokamak plasmas. The rotation influence on the heat and particle fluxes is studied along with the angular momentum transport with the quasi-linear gyro-kinetic eigenvalue code QuaLiKiz. For this purpose, the QuaLiKiz code is modified in order to take the plasma rotation into account and compute the angular momentum flux. It is shown that QuaLiKiz framework is able to correctly predict the angular momentum flux including the ExB shear induced residual stress as well as the influence of rotation on the heat and particle fluxes. The different contributions to the turbulent momentum flux are studied and successfully compared against both non-linear gyro-kinetic simulations and experimental data.

Download or read book Turbulence transport et confinement written by Antoine Strugarek and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book ETUDE DU TRANSPORT DES IMPURETES DANS LES PLASMAS TOKAMAK written by Antoine Compant La Fontaine and published by . This book was released on 1984 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: LES MESURES D'EMISSIVITE DE RAIES (10 A 2000A) DES IMPURETES SONT UTILISEES DANS UN CODE DE TRANSPORT CALCULANT LES PROCESSUS ATOMIQUES ET LA DIFFUSION DES IMPURETES. LA DIFFUSION COLLISIONNELLE EST TROP FAIBLE POUR EXPLIQUER LE TRANSPORT OBSERVE. LE COEFFICIENT DE DIFFUSION ANORMAL DES IONS IMPURETES EST INVERSEMENT PROPORTIONNEL A LA MASSE DES IONS DE BASE (H**(+), D**(+), HE**(2+)). METHODE D'EXTRACTION D'UNE IMPURETE DONNEE DU PLASMA LORSQU'ON APPLIQUE UN CHAUFFAGE HF, DANS DES CONDITIONS DETERMINEES. ON ATTRIBUE LE TRANSPORT ANORMAL DES IMPURETES A L'INTERIEUR DE LA SURFACE Q=1 A UNE TURBULENCE Y APPARAISSANT PENDANT LES DISRUPTIONS INTERNES. A L'EXTERIEUR DE LA SURFACE Q=1, ON L'ATTRIBUE A LA MICROTURBULENCE. EN EXPRIMANT LA FONCTION DE LAGRANGE DU SYSTEME DE PARTICULES DANS UN CHAMP ELECTRIQUE TURBULENT, ON VERIFIE LA LOI D'ECHELLE EXPERIMENTALE D::(A)ALPHA MB**(-1)

Download or read book Turbulent Transport in Rotating Tokamak Plasmas written by Francis James Casson and published by . This book was released on 2011 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Finite Beta Effects on Turbulent Transport in Tokamak Plasmas written by Tobias Hein and published by . This book was released on 2011 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulent Transport Modeling in the Edge Plasma of Tokamaks written by Clothilde Colin and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The possibility to produce power by using magnetically confined fusion is a scientific and technological challenge. The perspective of ITER conveys strong signals to intensify modeling effort on magnetized fusion plasmas. The success of the fusion operation is conditioned by the quality of plasma confinement in the core of the reactor and by the control of plasma exhaust on the wall. Both phenomena are related to turbulent cross-field transport that is at the heart of the notion of magnetic confinement studies, particle and heat losses. The study of edge phenomena is therefore complicated by a particularly complex magnetic geometry.This calls for an improvement of our capacity to develop numerical tools able to reproduce turbulent transport properties reliable to predict particle and energy fluxes on the plasma facing components. This thesis introduces the TOKAM3X fluid model to simulate edge plasma turbulence. A special focus is made on the code Verification and the Validation. It is a necessary step before using a code as a predictive tool. Then new insights on physical properties of the edge plasma turbulence are explored. In particular, the poloidal asymmetries induced by turbulence and observed experimentally in the Low-Field-Side of the devices are investigated in details. Great care is dedicated to the reproduction of the MISTRAL base case which consists in changing the magnetic configuration and observing the impact on parallel flows in the poloidal plane. The simulations recover experimental measurements and provide new insights on the effect of the plasma-wall contact position location on the turbulent features, which were not accessible in experiments.

Download or read book Transport in Gyrokinetic Tokamaks written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive study of transport in full-volume gyrokinetic (gk) simulations of ion temperature gradient driven turbulence in core tokamak plasmas is presented. Though this ''gyrokinetic tokamak'' is much simpler than experimental tokamaks, such simplicity is an asset, because a dependable nonlinear transport theory for such systems should be more attainable. Toward this end, we pursue two related lines of inquiry. (1) We study the scalings of gk tokamaks with respect to important system parameters. In contrast to real machines, the scalings of larger gk systems (a/[rho][sub s] [approx-gt] 64) with minor radius, with current, and with a/[rho][sub s] are roughly consistent with the approximate theoretical expectations for electrostatic turbulent transport which exist as yet. Smaller systems manifest quite different scalings, which aids in interpreting differing mass-scaling results in other work. (2) With the goal of developing a first-principles theory of gk transport, we use the gk data to infer the underlying transport physics. The data indicate that, of the many modes k present in the simulation, only a modest number (N[sub k] [approximately] 10) of k dominate the transport, and for each, only a handful (N[sub p] [approximately] 5) of couplings to other modes p appear to be significant, implying that the essential transport physics may be described by a far simpler system than would have been expected on the basis of earlier nonlinear theory alone. Part of this analysis is the inference of the coupling coefficients M[sub kpq] governing the nonlinear mode interactions, whose measurement from tokamak simulation data is presented here for the first time.

Download or read book Fluctuations and Transport in Fusion Plasmas Final Report written by and published by . This book was released on 1995 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: The energy confinement in tokamaks in thought to be limited by transport caused by plasma turbulence. Three dimensional plasma particle-in-cell (PIC) codes are used to model the turbulent transport in tokamaks to attempt to understand this phenomena so that tokamaks can be made more efficient. Presently, hundreds of hours of Cray time are used to model these experiments and much bigger and longer runs are desired, to model a large tokamak with realistic parameters is beyond the capability of existing sequential supercomputers. Parallel supercomputers might be a cost effect tool for performing such large scale 3D tokamak simulations. The goal of the work was to develop algorithms for performing PIC codes on coarse-grained message passing parallel computers and to evaluate the performance of such parallel computers on PIC codes. This algorithm would be used in a large scale PIC production code such as the UCLA 3D gyrokinetic code.

Download or read book Gyrokinetic Simulations of Turbulent Impurity Transport in Tokamaks written by Pierre Manas and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding impurity transport in the core of tokamak plasmas is central to achieving controlled fusion. Indeed impurities are ubiquitous in these devices and their presence in the core are detrimental to plasma confinement (fuel dilution, Bremsstrahlung). Recently, specific attention was given to the convective mechanism related to the gradient of the toroidal rotation to explain experimental flat/hollow impurity profiles in the plasma core. In this thesis, up-to-date modelling tools (NEO for neoclassical transport and GKW for turbulent transport) including the impact of toroidal rotation are used to study both the neoclassical and turbulent contributions to impurity fluxes. A comparison of the experimental and modelled carbon density peaking factor (R/LnC) is performed for a large number of baseline and hybrid H-mode plasmas (increased confinement regimes) with modest to high toroidal rotation from the European tokamak JET. Confrontation of experimental and modelled carbon peaking factor yields two main results. First roto-diffusion is found to have a nonnegligible impact on the carbon peaking factor at high values of the toroidal rotation frequency gradient. Second, there is a tendency to overpredict the experimental R/LnC in the core inner region where the carbon density profiles are hollow. This disagreement between experimental and modelled R/LnC, closely related to the collisionality, is also observed for the momentum transport channel which hints at a common parallel symmetry breaking mechanism lacking in the simulations.

Download or read book tude du transport turbulent dans les plasmas du tokamak Tore Supra written by Alexandre Storelli and published by . This book was released on 2015 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Les tokamaks, machines toroïdales à confinement magnétique conçues pour porter un plasma aux conditions nécessaires à l'obtention de réactions de fusion, ont des performances limitées par le transport turbulent, dont les mécanismes ne sont pas tous élucidés. Les fluctuations turbulentes alimentent des écoulements macroscopiques, dits flots zonaux, dont le cisaillement réduit en retour le niveau de fluctuation. Des dispositifs de rétrodiffusion Doppler ont été installés sur Tore Supra (CEA Cadarache) et permettent de mesurer la vitesse perpendiculaire des fluctuations. Premièrement, il est montré que la vitesse moyenne est près de deux fois supérieure du côté externe du plasma que dans sa partie supérieure, au-delà des prédictions conventionnelles. Ces asymétries sont mises en perspective avec certains aspects de l'équilibre magnétique et des caractéristiques des fluctuations. Puis, les oscillations de la vitesse, attribuées à la branche des flots zonaux dite mode géodésique acoustique (GAM), ont été caractérisées dans des expériences où la collisionalité varie. Elles sont comparées aux prédictions théoriques et aux résultats d'une simulation avec le code gyrocinétique GYSELA, utilisant les profils expérimentaux d'équilibre. La fréquence du GAM dans l'expérience est plus faible que prédit, en particulier aux plus basses collisionalités. Les variations de son intensité, détectées avec la transformée de Hilbert-Huang, montrent des bouffées d'oscillations de distributions analogues entre expérience et simulation, et dont la durée pourrait être liée à son interaction non-linéaire avec la turbulence ainsi qu'au phénomène d'amortissement de continuum observé dans la simulation.

Download or read book Etude des flux de mati re dans le plasma de bord des tokamaks written by Patrick Tamain and published by . This book was released on 2007 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Le transport de la matière dans la zone de bord des tokamaks joue un rôle déterminant à la fois au centre sur les performances du plasma, puisqu’il gouverne l’établissement des profils de densité à partir de l’alimentation externe en particules, et en périphérie sur la durée de vie des composants face au plasma, puisqu’il fixe les flux de particules et d’énergie tombant sur les parois. Ce sujet reste cependant relativement peu exploré car l’interaction du plasma avec d’importants puits et sources de matière, quantité de mouvement et énergie rend la modélisation complexe. Dans la perspective d’ITER, des interrogations subsistent en particulier sur la capacité des systèmes d’alimentation par injection de gaz à atteindre les niveaux de densité élevés souhaités sans dégrader le confinement du plasma, ainsi que sur la forme des profils de densité obtenus et l’intensité des écoulements de matière au bord. Cette thèse s’inscrit dans un effort visant à mieux cerner les mécanismes régissant les flux de matière dans le plasma de bord et leur impact sur ces questions. Dans une première phase de notre travail, nous proposons une approche originale pour la modélisation de l’alimentation par injection de gaz en nous focalisant sur l’impact thermique de l’injection sur le plasma. En nous appuyant sur des modèles analytiques et numériques à nombre réduit de dimensions, nous démontrons en particulier l’existence de bifurcations thermiques déclenchées par l’injection et leur importance dans la dynamique du dépôt de matière. On montre ainsi que dans le cas de Tore Supra, le refroidissement local lié à une forte injection peut permettre une pénétration accrue de la matière (r/a = 1.1 à r/a = 0.9 en rayon normalisé), mais peut également mener à un déséquilibre thermique de l’ensemble du plasma en deçà d’un certain ratio puissance de chauffage / source de particules. L’extrapolation de cette étude pour ITER reste pessimiste quant à la profondeur de pénétration des neutres injectés. Toutefois, la sensibilité des résultats de ces modèles simplifiés à l’interaction entre les directions parallèle et perpendiculaire au champ magnétique montre la nécessité de développer des outils numériques modélisant de façon cohérente le transport de la matière dans les deux directions. Ceci a mené au développement d’un nouveau code 3D, présenté dans la seconde partie de ce travail. Il s’agit d’un code global en géométrie torique, prenant en compte les effets de courbure. Il résout les équations de dérive fluide électrostatique sans hypothèse de séparation d’échelle, ce qui permet de traiter avec le même outil les problématiques de transport à grande échelle comme les phénomènes de turbulence à petite échelle. Deux versions du code ont été développées et validées : l’une se place dans les lignes de champ fermées ; l’autre, plus lourde numériquement, inclut à la fois la Scrape Off Layer (SOL) et la partie externe du plasma confiné. Dans une dernière partie, le code est appliqué à la problématique des asymétries poloïdales sur les écoulements de matière dans la SOL, observées expérimentalement mais dont l’origine reste difficile à expliquer. Les simulations reproduisent l’ordre de grandeur des amplitudes mesurées et mettent à jour deux mécanismes distincts susceptibles de jouer un rôle dans ce phénomène, l’un à grande échelle, l’autre au niveau de la turbulence. Le premier vient d’un couplage entre les dérives à grande échelle et les effets de courbure dans la SOL, le second est lié à un ballonnement du flux radial turbulent côté faible champ. Enfin, l’importance de la résistivité parallèle du plasma sur les caractéristiques du transport turbulent est analysée et nous revenons sur l’impact d’une injection localisée de matière sur les propriétés de la turbulence.