Measurements of neutron emission from a fusion plasma can provide a wealth of information on the underlying temporal, spatial and energy distributions of reacting ions and how they are affected by a wide range of magneto-hydro-dynamic (MHD) instabilities. This thesis focuses on the interpretation of the experimental measurements recorded by neutron flux monitors with and without spectroscopic capabilities installed on the Mega Ampere Spherical Tokamak (MAST). In particular, the temporally and spatially resolved measurements of the neutron rate measured by the neutron camera, which also possesses spectroscopic capabilities, are combined with the temporally resolved measurements of the total neutron rate provided by the absolutely calibrated fission chamber in order to study the properties of the fast ion distributions in different plasma scenarios. The first part of the thesis describes in detail the two forward modelling methods, which employ the set of interconnected codes developed to interpret experimental observations such as neutron count rate profiles and recoil proton pulse height spectra provided by the neutron camera. In the second part of the thesis the developed methods are applied to model the neutron camera observations performed in a variety of plasma scenarios. The first method, which involves only TRANSP/NUBEAM and LINE2 codes, was used to validate the neutron count rate profiles measured by the neutron camera in three different plasma scenarios covering the wide range of total neutron rate typically observed on MAST. In addition, the first framework was applied to model the changes in the total and local neutron rates caused by fishbone instability as well as to estimate the Hydrogen and Deuterium ion ratio. The second modelling method, which involves TRANSP/NUBEAM, LINE2, DRESS and NRESP, was used to validate the measured recoil proton pulse height spectra in a MHD-quiescent plasma scenario.

Investigations of tokamak dynamics, especially as they relate to the challenge of burn control, require an accurate representation of energy and particle confinement times. While the ITER-98 scaling law represents a correlation of data from a wide range of tokamaks, confinement scaling laws will need to be fine-tuned to specific operational features of specific tokamaks in the future. A methodology for developing, by regression analysis, tokamak- and configuration-specific confinement tuning models is presented and applied to DIII-D as an illustration. It is shown that inclusion of tuning parameters in the confinement models can significantly enhance the agreement between simulated and experimental temperatures relative to simulations in which only the ITER-98 scaling law is used. These confinement tuning parameters can also be used to represent the effects of various heating sources and other plasma operating parameters on overall plasma performance and may be used in future studies to inform the selection of plasma configurations that are more robust against power excursions.

This thesis presents a complete theoretical framework for turbulence and transport in tokamak plasmas. The fundamental scale separations present in plasma turbulence are codified as an asymptotic expansion in the ratio of the gyroradius to the equilibrium scale length. Proceeding order-by- order in this expansion, a framework for plasma turbulence is developed. It comprises an instantaneous equilibrium, the fluctuations driven by gra- dients in the equilibrium quantities, and the transport-timescale evolu- tion of mean profiles of these quantities driven by the fluctuations. The equilibrium distribution functions are local Maxwellians with each flux surface rotating toroidally as a rigid body. Large-scale deviations of the distribution function from a Maxwellian are given by neoclassical theory. The fluctuations are determined by the high-flow gyrokinetic equation, from which we derive the governing principle for gyrokinetic turbulence in tokamaks: the conservation and local cascade of free energy. Transport equations for the evolution of the mean density, temperature and flow ve- locity profiles are derived. These transport equations show how the neo- classical corrections and the fluctuations act back upon the mean profiles through fluxes and heating. This framework is further developed by exploiting the scale separation between ions and the electrons. The gyrokinetic equation is expanded in powers of the electron to ion mass ratio, which provides a rigorous method for deriving the electron response to ion-scale turbulence. We prove that such turbulence cannot change the magnetic topology, and ar- gue that, therefore, the magnetic field lies on fluctuating flux surfaces. These flux surfaces are used to construct magnetic coordinates, and in these coordinates a closed system of equations for the electron response is derived. All fast electron timescales have been eliminated from these equations. Simplified transport equations for electrons in this limit are also derived.

Ce travail de thèse porte sur la modélisation et la simulation numérique des plasmas ionosphérique et Tokamak. La première partie de ce travail concerne la modélisation et la simulation numérique des effets de perturbations ionosphériques sur les communications terre-satellite. Le point départ de cette partie est l’analyse asymptotique du modèle de Euler-Maxwell conduisant ainsi au modèle Dynamo, qui se traduit en un couplage en 3D entre une équation elliptique pour le potentiel électrique et une équation de conservation de masse pour la densité du plasma. Du fait de la forte anisotropie de la matrice de diffusion associée a l’équation elliptique, on a developpé un schéma numérique préservant l’asymptotique permettant ainsi le bon conditionnement du systeme linéaire. La simulation de l’équation de conservation de masse est faite à l’aide de schémas de lois de conservation d’ordre elevé. La validation de ce modèle Dynamo s’obtient par une étude comparative avec le modèle Striation en 2D. Dans la deuxième partie, on s’intéresse au plasma Tokamak. On extrait du modele TOKAM3D, une équation de balance d’énergie de type non-linéaire en dimension 2 contenant toutes les difficultés numériques. Les méthodes numériques standard étant très coûteux en temps CPU, on developpe un schéma implicite-explicite prouvé efficace et stable pour ce type de problème. Enfin, ce schéma est combiné à une méthode de splitting dimensionnelle pour la discrétisation et des expériences numériques sont alors presentées. / This thesis focuses on modeling and numerical simulation of ionospheric and Tokamak plasmas.The first part of this work concerns the modeling and simulation of ionospheric perturbations effects for earth-satellite communications. The starting point of this part is an asymptotic analysis of Euler-Maxwell model leading to Dynamo model, which results into a 3D coupling problem between an elliptic equation for the electric potential and a mass conservation equation for the plasma density. Because of the strong anisotropy of the diffusion matrix associated with the elliptic equation, we developed an asymptotic preserving numerical scheme thus allowing the well conditioned linear system. The simulation of the mass conservation equation is made by using high order conservation laws scheme. The validation of this model Dynamo is obtained by a comparison with the 2D Striation model. In the second part, we are interested in tokamak plasma. We extract from TOKAM3D model, a 2D nonlinear energy balance equation containing all the numerical difficulties. Standard numerical methods are very CPU consuming, thus we develop an implicit-explicit scheme shown efficient and stable for this type of problem. Finally, this scheme is combined with dimensional splitting method for the discretization and numerical experiments are then presented.

La thèse décrit les mesures de températures ioniques (Ti) dans la Scrape-Off-Layer (SOL) – un paramètre important cependant rarement mesuré – à l'aide d'une sonde Analyseur à Retard de Champ (RFA) installée sur le Tokamak Tore Supra. La thèse s'organise en 4 chapitres. Dans le premier sont brièvement rappelés les enjeux de la fusion nucléaire, la géométrie des limiteurs et la physique la SOL, le principe des sondes de Langmuir, etc. Sont aussi adressés les différents diagnostics dédiés aux mesures de Ti dans la SOL, utilisés dans le passé. Le second chapitre est consacré au RFA. Le principe de l'analyseur, les détails techniques et opérationnels sur Tore Supra ainsi que les effets instrumentaux sur les mesures y sont abordés. Il est conclut que l'influence instrumentale sur les mesures RFA de Ti sont relativement faibles. Dans le troisième chapitre, les mesures systématiques de Ti (ainsi que d'autres paramètres) dans la SOL de Tore Supra sont présentées. Il est montré que le rapport Ti / Te > 1 (Te étant la température électronique) dans la SOL, mais aussi dans le plasma confiné ; et que ce rapport augmente avec le rayon plasma. Un autre résultat important est que Ti dans la SOL change significativement, suivant étroitement les paramètres centraux, alors que Te dans la SOL n'évolue presque pas. Dans le dernier chapitre est présenté le statut actuel de trois projets en cours visant à valider indépendamment la mesure de Ti dans la SOL de Tore Supra : le développement d'une tête de sonde à tunnel segmenté permettant une mesure des fluctuations de Ti dans la SOL ; la mesure de Ti au bord des plasmas du Tokamak Joint European Torus (JET) ; et la comparaison des mesures de RFA avec les mesures de spectroscopie d'échange de charge et recombinaison (CXRS) sur Tore Supra. / The thesis describes measurements of the scrape-off layer (SOL) ion temperature Ti – an important but yet rarely measured parameter – with a retarding field analyzer (RFA) probe in the limiter tokamak Tore Supra. The thesis is organized in four chapters. In the first chapter, some well known facts about nuclear fusion, limiter SOL, Langmuir probes, etc. are briefly recalled. Various diagnostics for SOL Ti measurements developed in the past are addressed as well. The second chapter is dedicated to the RFA. The principle of the RFA, technical details and operation of the Tore Supra RFA, and the influence of instrumental effects on RFA measurements are addressed. It is concluded that the influence of instrumental effects on RFA Ti measurements is relatively small. In the third chapter, the systematic measurements of Ti (as well as other parameters) in the Tore Supra SOL are presented. It is shown that Ti / Te >1 (with Te being the electron temperature) in the SOL but also in the confined plasma, and increases with radius. Also important result is that while SOL Ti changes significantly, following the core properties rather closely, SOL Te hardly changes at all. In the final chapter the present status of three ongoing projects aimed at the independent validation of SOL Ti measurements in Tore Supra is presented: the development of the segmented tunnel probe for fast SOL Ti measurements, the measurement of edge ion temperature in Joint European Torus (JET) tokamak, and the comparison of RFA with charge exchange recombination spectroscopy in Tore Supra.

Um sistema de bobinas de Mirnov foi construído, calibrado e utilizado para a análise das descargas de plasma no tokamak TCABR. Este sistema é composto de 22 bobinas magnéticas que foram instaladas ao redor de uma seção transversal no interior da câmara de vácuo do TCABR, tendo-se em conta os efeitos produzidos pela geometria toroidal do sistema. Cuidados especiais foram tomados para proteger os enrolamentos das bobinas com relação a ação do plasma, e também para evitar que correntes de Foucault viessem a comprometer o funcionamento do sistema. Para este diagnóstico também foi construído um sistema eletrônico específico para a filtragem e amplificação dos sinais das bobinas, para serem, depois, digitalizadas pelo sistema VME e gravados através do sistema de aquisição de dados do TCABR. Foi desenvolvido, também, um programa para a análise destes dados, baseados no processo da análise de Fourier, de forma a permitir a identificação dos modos de perturbação MHD presentes nas descargas do TCABR. Com esse sistema de deteção colocado em operação, foi então possível investigar as descargas de plasma do TCABR para dois regimes de operação: descargas de 'run-away' e plasma resistivo. Nas descargas com elétrons fugitivos 'run-away', foram observadas estruturas nos sinais de tensão de enlace, H alfa, raios-X duros e bobinas de Mirnov, bastante correlacionados entre si. Nas descargas com plasma resistivo, foi observado que as oscilações de Mirnov no tokamak TCABR possuem freqüências no intervalo de 10 kHz - 15 kHz. Em algumas das descargas também foram observadas correlações entre os sinais de emissão de raios-X duros e as oscilações de Mirnov, bem como correlações entre as flutuações da densidade de partículas e as oscilações de Mirnov. Experimentos com deslocamento horizontal da coluna de plasma permitiram observar como variava o comportamento das amplitudes dos sinais das bobinas de Mirnov. Também foram estudadas algumas descargas disruptivas com plasma resistivo no limite de altas densidades. Pode-se analisar as oscilações de Mirnov e os modos de perturbação antes da ocorrência de disrupturas. Observou-se, por exemplo, que o modo precursor m = 3 é predominante ao longo da descarga mas, antes da disruptura, os modos m = 1, 2, 3 e 4 passam a ser dominantes. Nesta situação a velocidade angular das ilhas magnéticas foi determinada como sendo de 5000 rad/s. Finalmente, utilizaram-se os sinais do sistema de bobinas de Mirnov para algumas análises preliminares envolvendo descargas resistivas com ondas de Alfvèn. Foi observado, por exemplo, que depois de 3 ms de serem ligadas as antenas de Alfvèn, as oscilações de Mirnov geralmente crescem em amplitude enquanto diminuem em freqüência, mantendo-se assim até o final da descarga.

La connaissance des champs de flux thermique sur les composants d'un tokamak estun élément important de la conception de ce type de machines. L'objectif de cette thèse est dedévelopper et mettre en œuvre une méthode de calcul de ces flux à partir des mesures detempérature par thermographie infrarouge. Ce travail repose sur trois objectifs qui concernentles tokamaks actuels et futurs (ITER) : mesurer un champ de température d'une paroiréfléchissante par pyrométrie photothermique (pré-étude), caractériser les propriétésthermiques des dépôts sur les surfaces des composants et développer un calcultridimensionnel et non-linéaire du flux.Une comparaison de différentes techniques de pyrométries monochromatique,bichromatique et photothermique est effectuée sur une expérience de laboratoire de mesure detempérature. Une sensibilité importante de la technique de pyrométrie photothermique auxgradients de température sur la zone observée a été mise en évidence.Les dépôts en surface des composants exposés au plasma, sans inertie thermique, sontmodélisés par des champs de résistance thermique équivalente transverse. Ce champ derésistance est déterminé, en tout point de mesure, par confrontation du champ de températurede paroi issu de la thermographie avec le résultat d'une simulation par un modèlemonodimensionnel linéaire du composant. Une information sur la répartition spatiale du dépôtà la surface d'un composant est alors obtenue.Un calcul tridimensionnel et non-linéaire du champ de flux pariétal sur un composantest développé, par une méthode d'éléments finis, à partir de maillages de composants issus deCAO. La sensibilité du flux calculé à la précision des mesures de températures est discutée.Cette méthode est appliquée à des campagnes de mesures de températurebidimensionnelles par thermographie infrarouge sur des composants du tokamak JET. Leschamps de flux sur les tuiles du divertor, la protection supérieure et les protections poloïdalesinternes et externes sont déterminés et étudiés dans les deux directions, poloïdale ettoroïdale, du tokamak. La symétrie toroïdale du flux, d'une tuile à l'autre, est établie.L'influence de la résolution spatiale des mesures sur les flux calculés est discutée, à partir decomparaisons de résultats obtenus à partir de deux systèmes de thermographie de résolutionsdifférentes.

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.

Density fluctuations in high temperature fusion plasmas have been a central challenge to the development of fusion power. They are the cause of excessive anomalous losses from the plasma and are still not fully understood. A microwave scattering experiment is performed on the Saskatchewan Torus-Modified (STOR-M) tokamak for the first time to study these density fluctuations with wave-numbers in the range <b><i>k</i></b> = 5 /cm to 10 /cm. The fluctuations are found to follow <i>k¦Ñ_s</i> scaling consistent with ion drift waves; signatures of the electron temperature gradient (ETG) mode connected with anomalous electron losses are not detected. The fluctuation level in the STOR-M is measured to be <i>n_tilda/n</i> ¡Ö 0.1 at a mean perpendicular wave-number of <b><i>k</b>_perp</b></i> ¡Ö 7 /cm and is reported for the first time. The fluctuation levels are inversely proportional to the energy confinement time suggesting that these fluctuations are driving anomalous particle and energy losses from the STOR-M. The system is now fully operational and this work paves the way for future experiments with this equipment.

Adequate control of the position of the plasma column within the STOR-M tokamak is a chief requirement in order for experimental quality discharges to be obtained. Optimal control over tokamak discharge parameters, including the plasma position, is very difficult to achieve. This is due in large part to the difficulty in modelling the tokamak discharge parameters, as they are highly nonlinear and time varying in nature. The difficulty of modelling the tokamak discharge parameters suggests that a control system, such as a fuzzy logic based controller, which does not require a system model may be well suited to the control of fusion plasma. In order to improve the quality of control over the plasma position within the STOR-M tokamak, the existing analog PID controller was modified. These modifications facilitate the application of a digital controller by a personal computer via the Advantech PCL-711B data acquisition card. The performance of the modified plasma position controller and an Arbitrary Signal Generator developed by the author was evaluated. This modified plasma position controller was applied successfully to the STOR-M tokamak during both normal mode and A.C. mode operation. In both cases, the modified controller provided adequate control over the position of the plasma column within the discharge chamber. Furthermore, the modified controller was more convenient to optimize than the original, existing analog PID controller. By taking advantage of the modifications that were made to the plasma position controller, a fuzzy logic controller was developed by the author. The fuzzy logic based plasma position controller was also successfully applied to the STOR-M tokamak during both normal mode and A.C. operation. The fuzzy controller was demonstrated to reliably provide a higher degree of control over the position of the plasma column within the STOR-M tokamak than the modified PID controller.