Development of fueling technologies for modern and future tokamak reactors is essential for their implementation in a commercial energy production setting. Compared to the presently available fueling technologies, gas or cryogenic pellet injection, compact torus injection presents an effective and efficient method for directly fueling the central core of tokamak plasmas. Fueling of the central core of a tokamak plasma is pivotal for providing efficient energy production. The central core plasma of a reactor contains the greatest density of fusion processes. For consistent and continuous fueling of tokamak fusion reactors, compact torus injectors must be operated in a repetitive mode.<p> The goal of this thesis was to study the feasibility of firing the University of Saskatchewan Compact Torus Injector (USCTI) in a repetitive mode. In order to enable USCTI to fire repetitively, modifications were made to its electrical system, control system and data acquisition system. These consisted primarily of the addition of new power supplies, to enable fast charging of the many capacitor banks used to form and accelerate the plasma. The maximum firing rate achieved on USCTI was 0.33 Hz, an increase from the previous maximum firing rate of 0.2 Hz achieved at UC Davis.<p> Firing USCTI in repetitive modes has been successful. It has been shown that the CTs produced in any given repetitive series are properly formed and repeatable. This is made evident through analysis of data collected from the CTs' magnetic fields and densities as they traveled along the injector barrel. The shots from each experiment were compared to the series' mean data and were shown to be consistent over time. Calculations of their correlations show that there are only minimal deviations from shot to shot in any given series.

Techn. University, Diss., 2004--München.

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.

This thesis deals with the study of turbulence in tokamak plasma and im- provement of an computer model ESEL. The first chapter deals with the theory related to the study of turbulence in the plasma. For the study of these tur- bulences the results of the probe measurements on the ASDEX Upgrade and COMPASS tokamak and model results from a computer model of the turbulent ESEL are used. The second chapter describes the used probes and the third chapter describes the model ESEL. Contribution of the work is mainly in the fourth and fifth chapter, which summarize the results of the comparisons be- tween the experimental data and model ESEL. The sixth chapter summarizes the most important conclusions from these comparisons. Some agreements and discrepancies were shown. One of the main results of the thesis is the impor- tance of one extra term in one governing equation of the ESEL, which means its improvement. However at present the ESEL is still not able to fully describe the tokamak plasma boundary. 1

<p> A surface station consisting of a sample manipulator and transfer system was developed to allow the study of plasma - first wall interactions in ALCATOR at M.I.T. A disc shaped probe is located at the plasma edge and rotated past an aperture in a shield to obtain time resolved data. Samples can be analysed in situ or transported under vacuum to McMaster University. The transfer process from the surface station to the 'vacuum suitcase' is accomplished by means of pressure locks.</p> / Thesis / Master of Engineering (MEngr)

Lors du fonctionnement d’une machine de fusion, les interactions plasma-parois conduisent à des processus d’érosion des matériaux et à la production de particules. Ces poussières sont principalement composées de carbone et de tungstène. Pour des raisons de sureté et afin de garantir un fonctionnement optimum du réacteur, il est important de garder en quantité raisonnable les poussières dont la taille varie entre 10 nm et 100 $m. La mise en suspension de ces poussières est une étape préliminaire à leur récupération, et le laser est une technique prometteuse pour cette application. Afin d’optimiser le nettoyage, les mécanismes physiques à l’origine de l’éjection induite par laser de ces poussières ont été identifiés. Les agrégats sont directement ablatés par le laser et les gouttelettes métalliques sont éjectées intactes par une force électrostatique induite par les photoélectrons. Nous avons également caractérisé l’éjection des particules pour choisir un système de récupération adapté. / During tokamak operation, plasma-wall interactions lead to material erosion processand dusts production. These dusts are mainly composed by carbon and tungsten, with sizesranging from 10 nm to 100 $m. For safety reasons and to guarantee an optimum reactorfunctioning, the dusts have to be kept in reasonable quantity. The dusts mobilization is a firststep to collect them, and the laser is a promising technique for this application. To optimizethe cleaning, physical mechanisms responsible for dust ejection induced by laser have beenidentified. Some particles, such as aggregates, are directly ablated by the laser. The metaldroplets are ejected intact by an electrostatic force, induced by the photoelectrons. We alsocharacterized the particles ejection to choose an appropriate collection device.

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.

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.

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.

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.