Cette thèse est centrée sur la mesure et l'interprétation du rayonnement X mou ([1 keV; 15 keV] environ) dans les Tokamaks. Le chapitre 2 montre que ce rayonnement véhicule des informations sur la température et la densité du plasma, sur sa configuration magnétique, et sur son contenu en impuretés. Malheureusement les mesures effectuées sont intégrées spatialement et spectralement et résultent des contributions de tous les ions présents.Le diagnostic X mou de Tore Supra s'articule autour de diodes semi-conductrices présentée dans le chapitre 3 aux côté d'un détecteur à gaz testé avec succès. Une nouvelle méthode de détermination de la réponse spectrale d'un photodétecteur n'utilisant qu'un tube X mou portable est également décrite.Les inversions tomographiques, qui permettent d'accéder au champ d'émissivité reconstruit dans une section poloidale, font l'objet du chapitre 4. Les améliorations apportées à un algorithme particulier sont détaillées.Une comparaison systématique entre les positions horizontales du maximum d'émissivité et de l'axe magnétique est présentée au chapitre 5.Le chapitre 6 décrit une hypothèse concernant la résilience de la fonction de rayonnement X mou d'une impureté vis-à-vis du transport de cette impureté. Cette hypothèse permet de déduire la densité d'une impureté de son émissivité X mou. Les processus physiques justifiant cette hypothèse, ainsi que leur domaine de validité sont analysés avec soin.Le chapitre 7 présente les asymétries poloidales d'émissivité X mou. Les premiers résultats d'expériences mises en oeuvres à ASDEX-U pour vérifier les dépendences paramétriques de deux types particuliers d'asymétries sont détaillés. / This thesis focuses on measuring and interpreting the Soft X-Ray (SXR) radiation (approximately [1 keV; 15 keV]) in Tokamaks.As explained in Chapter 2, this radiation conveys information about the plasma density, temperature, magnetic equilibrium and impurity content. However, the measured data is spectrally and spatially-integrated and results from several physical phenomena affecting every ion species. Tore Supra's SXR diagnostics is based on semiconductor diodes presented in Chapter 3, along with a new gas detector successfully tested in laboratory and on Tore Supra. A new methodology for absolute spectral characterisation of photo detectors using a portable SXR tube is presented. Tomographic inversion algorithms, that grant access to reconstructions of the SXR emissivity field in a poloidal cross-section, are presented in Chapter 4. Improvements implemented on one particular algorithm are detailed with examples of application. A comparison between the position of the SXR emissivity maximum and the magnetic axis reconstructed by an equilibrium code is presented in Chapter 5.Chapter 6 presents an approach used to derive an impurity density from its SXR emissivity using the robustness of its SXR cooling factor with respect to impurity transport. The physics accounting for this robustness is studied and a first map of the domain of validity of this method is provided. Chapter 7 addresses poloidal asymmetries of the SXR emissivity field. Two types of asymmetries are presented as well as experiments conducted on ASDEX-U to verify their parametric dependences. A new type of SXR asymmetry, observed on Tore Supra is introduced.

Dans cette thèse nous étudions l'impact de perturbations magnétiques résonnantes sur la dynamique de la barrière de transport dans un tokamak. Pour cela nous avons réalisé des simulations numériques tridimensionnelles de turbulence dans le plasma de bord du tokamak. Nos simulations numériques ont reproduit les résultats expérimentaux observés dans différents tokamaks. Dans le régime de confinement amélioré (mode H), la barrière de transport n'est pas stable : elle effectue des oscillations de relaxation, qui partagent des caractéristiques communes avec les "modes localisés au bord'' (Edge Localized Modes, ELMs). Ces ELMs ont à la fois des avantages et des inconvénients. D'un côté, ils permettent d'évacuer les impuretés présentes dans le coe ur du plasma. Mais d'un autre côté, la charge thermique induite sur la paroi pendant un ELM peut endommager les matériaux de première paroi. Pour cette raison, ils doivent être contrôlés. Cette thèse s'inscrit dans le contexte du projet ITER actuellement en construction en France. Sur ITER, le contrôle des ELMs sera indispensable en raison de la quantité d'énergie évacuée. Parmi les différentes façons de contrôler les ELMs, les perturbations magnétiques résonnantes (Resonant Magnetic Perturbations, RMPs) semblent prometteuses. Ces perturbations magnétiques résonnantes sont créées par des bobines externes. Nous nous plaçons dans le cas du tokamak TEXTOR et nous considérons deux configurations pour les bobines externes : dans un premier temps, une perturbation magnétique résonnante comprenant plusieurs harmoniques, qui permet d'avoir une zone stochastique au bord du plasma lorsque les chaînes d'îlots magnétiques se superposent. / In this PhD thesis we study the impact of resonant magnetic perturbations on the transport barrier dynamics in a tokamak. In this goal we have performed turbulence tridimensional numerical simulations in the edge plasma of a tokamak, which reproduced the experimental results observed in different tokamaks. In the improved confinement regime (H mode), the transport barrier is not stable : it does relaxation oscillations, which share common features with the ``Edge Localized Modes'' (ELMs). These ELMs both have advantages and drawbacks. On the one hand, they enable to push away the impurities present in the plasma core. But on the other hand, the thermal load induced on the wall during an ELM can damage the first wall materials. For this reason, they must be controlled. This PhD thesis belongs to the frame of the ITER project, which is today in construction in France. On ITER the ELMs control will be compulsory due to the quantity of energy released. Among the different ways of controlling the ELMs, the resonant magnetic perturbations (RMPs) seem promising. These resonant magnetic perturbations are created by external coils. We consider the TEXTOR tokamak case and we consider two configurations for the external coils : first, a resonant magnetic perturbation with several harmonics, which enables to have a stochastic zone at the plasma edge when the magnetic island chains overlap ; then, a resonant magnetic perturbation with a single harmonic, which therefore creates a single magnetic island chain. In this PhD thesis, we focus on the non-axisymmetric equilibrium created in the plasma by the resonant magnetic perturbation.

Le nettoyage des surfaces métalliques est nécessaire dans différents domaines de l'industrie moderne. L'industrie nucléaire cherche de nouvelles méthodes de décontamination des surfaces oxydées, et les installations thermonucléaires nécessitent le nettoyage des composants face au plasma pour enlever la couche déposée contenant tritium. L'ablation laser est proposée comme une méthode efficace et sûre pour le nettoyage des surfaces métalliques et leur décontamination. Le facteur important influençant le chauffage et l'ablation laser est la distribution en profondeur de l’intensité laser. Le modèle de propagation de la lumière dans une couche diffusant sur un substrat métallique est développé et appliqué pour analyser les caractéristiques de distribution de lumière. Pour simuler les surfaces contaminées, l'inox AISI 304L a été oxydé par laser et chauffé dans un four. La contamination radioactive de la couche d'oxyde a été simulée par l'introduction d’europium et / ou de sodium. Un facteur de décontamination de plus de 300 a été démontré avec le régime de nettoyage optimal trouvé. Une diminution de la résistance à la corrosion a aussi été montrée après un nettoyage laser. Les seuils d'ablation des surfaces ITER-like (représentatives d’ITER) ont été mesurés. Une vitesse de nettoyage de 0,07 m2/W∙h a été trouvée. Pour les surfaces miroir, les seuils de dommages étaient déterminés pour éviter les dommages lors du nettoyage au laser. La possibilité de restaurer la réflectivité après le dépôt d’une couche mince de carbone a été démontrée. Les perspectives de développement ultérieur de nettoyage laser sont discutées. / Metal surface cleaning is highly required in different fields of modern industry. Nuclear industry seeks for new methods for oxidized surface decontamination, and thermonuclear installations require the cleaning of plasma facing components from tritium-containing deposited layer. The laser ablation is proposed as an effective and safe method for metal surface cleaning and decontamination. The important factor influencing the laser heating and ablation is the in-depth distribution of laser radiation. The model of light propagation in a scattering layer on a metal substrate is developed and applied to analyse the features of light distribution. To simulate the contaminated surfaces, the stainless steel AISI 304L was oxidized by laser and in a furnace. Radioactive contamination of the oxide layer was simulated by introducing europium and/or sodium. The decontamination factor of more than 300 was demonstrated with found optimal cleaning regime. The decreasing of the corrosion resistance was found after laser cleaning. The ablation thresholds of ITER-like surfaces were measured. The cleaning productivity of 0.07 m2/hour∙W was found. For mirror surfaces, the damage thresholds were determined to avoid damage during laser cleaning. The possibility to restore reflectivity after thin carbon layer deposition was demonstrated. The perspectives of further development of laser cleaning are discussed.

The future fusion power plants that are based on magnetic confinement will deal with plasmas that inevitably contain energetic (non-thermal) particles. These particles come, for instance, from fusion reactions or from external heating of the plasma. Ensembles of energetic ions can excite eigenmodes in the Alfvén frequency range to such an extent that the resulting wave fields redistribute the energetic ions, and potentially eject them from the plasma. The redistribution of ions may cause a substantial reduction of heating efficiency. Understanding the dynamics of such instabilities is necessary to optimise the operation of fusion experiments and of future fusion power plants. Two models have been developed to simulate the interaction between energetic ions and Alfvén eigenmodes. One is a bump-on-tail model, of which two versions have been developed: one fully nonlinear and one quasilinear. The quasilinear version has a lower dimensionality of particle phase space than the nonlinear one. Unlike previous similar studies, the bump-on-tail model contains a decorrelation of the wave-particle phase in order to model stochasticity of the system. When the characteristic time scale for macroscopic phase decorrelation is similar to or shorter than the time scale of nonlinear wave-particle dynamics, the nonlinear and the quasilinear descriptions quantitatively agree. A finite phase decorrelation changes the growth rate and the saturation amplitude of the wave mode in systems with an inverted energy distribution around the wave-particle resonance. Analytical expressions for the correction of the growth rate and the saturation amplitude have been derived, which agree well with numerical simulations. A relatively weak phase decorrelation also diminishes frequency chirping events of the eigenmode. The second model is called FOXTAIL, and it has a wider regime of validity than the bump-on-tail model. FOXTAIL is able to simulate systems with multiple eigenmodes, and it includes effects of different individual particle orbits relative to the wave fields. Simulations with FOXTAIL and the nonlinear bump-on-tail model have been compared in order to determine the regimes of validity of the bump-on-tail model quantitatively. Studies of two-mode scenarios confirmed the expected consequences of a fulfillment of the Chirikov criterion for resonance overlap. The influence of ICRH on the eigenmode-energetic ion system has also been studied, showing qualitatively similar effects as seen by the presence of phase decorrelation. Another model, describing the efficiency of fast wave current drive, has been developed in order to study the influence of passive components close to the antenna, in which currents can be induced by the antenna generated wave field. It was found that the directivity of the launched wave, averaged over model parameters, was lowered by the presence of passive components in general, except for low values of the single pass damping of the wave, where the directivity was slightly increased, but reversed in the toroidal direction. / De framtida fusionskraftverken baserade på magnetisk inneslutning kommer att hantera plasmor som oundvikligen innehåller energetiska (icke-termiska) partiklar. Dessa partiklar kommer exempelvis från fusionsreaktioner eller från externa uppvärmningsmekanismer av plasmat. Ensembler av energetiska joner kan excitera egenmoder i Alfvén-frekvensområdet i en sådan utsträckning att de resulterande vågfälten omfördelar de energetiska jonerna i rummet, och potentiellt slungar ut jonerna ur plasmat. Omfördelningen av joner kan orsaka en väsentligen minskad uppvärmningseffekt. Det är nödvändigt att förstå dynamiken hos denna typ av instabilitet för att kunna optimera verkningsgraden hos experiment och hos framtida fusionskraftverk. Två modeller har utvecklats för att simulera interaktionen mellan energetiska joner och Alfvén-egenmoder. Den första är en bump-on-tail-modell, av vilken två versioner har utvecklats: en fullt icke-linjär och en kvasi-linjär. I den kvasi-linjära versionen har partiklarnas fasrum en lägre dimensionalitet än i den icke-linjära versionen. Till skillnad från tidigare liknande studier innehåller denna bump-on-tail-modell en dekorrelation av våg-partikelfasen för att modellera stokasticitet hos systemet. När den karakteristiska tidsskalan för makroskopisk fasdekorrelation är ungefär samma som eller kortare än tidsskalan för icke-linjär våg-partikeldynamik så stämmer den icke-linjära och den kvasi-linjära beskrivningen överens kvantitativt. En ändlig fasdekorrelation förändrar vågmodens tillväxthastighet och satureringsamplitud i system med en inverterad energifördelning omkring våg-partikelresonansen. Analytiska uttryck för korrektionen av tillväxthastigheten och satureringsamplituden har härletts, vilka stämmer väl överens med numeriska simuleringar. En relativt svag fasdekorrelation försvagar även "frequency chirping events" (snabba frekvensskiftningar i korttids-Fourier-transformen av egenmodens amplitudutveckling) hos egenmoden. Den andra modellen, kallad FOXTAIL, har ett mycket bredare giltighetsområde än bump-on-tail-modellen. FOXTAIL kan simulera system med flera egenmoder, och den inkluderar effekter av olika enskilda partikelbanor relativt vågfälten. Simuleringar med FOXTAIL och med bump-on-tail-modellen har jämförts för att kvantitativt bestämma bump-on-tail-modellens giltighetsområde. Studier av scenarier med två egenmoder bekräftar de förväntade effekterna av när Chirikov-kriteriet för resonansöverlapp uppfylls. Även inflytandet av ICRH på dynamiken mellan egenmoder och energetiska joner har studerats, vilket har visat kvalitativt liknande effekter som har observerats i närvaron av fasdekorrelation. En annan modell, vilken beskriver effektiviteten hos "fast wave current drive" (strömdrivning med snabba magnetosoniska vågor), har utvecklats för att studera inflytandet av passiva komponenter nära antennen, i vilka strömmar kan induceras av vågfälten som genereras av antennen. Det visades att den utskickade vågens direktivitet, medelvärdesbildat över modellparametrar, generellt sett minskade vid närvaron av passiva komponenter, förutom vid låg "sinlge pass damping" (dämpning av vågen vid propagering genom hela plasmat), då direktiviteten istället ökade något, men bytte tecken i toroidal riktning. / <p>QC 20160927</p>

Metal surface cleaning is highly required in different fields of modern industry. Nuclear industry seeks for new methods for oxidized surface decontamination, and thermonuclear installations require the cleaning of plasma facing components from tritium-containing deposited layer. The laser ablation is proposed as an effective and safe method for metal surface cleaning and decontamination. The important factor influencing the laser heating and ablation is the in-depth distribution of laser radiation. The model of light propagation in a scattering layer on a metal substrate is developed and applied to analyse the features of light distribution. To simulate the contaminated surfaces, the stainless steel AISI 304L was oxidized by laser and in a furnace. Radioactive contamination of the oxide layer was simulated by introducing europium and/or sodium. The decontamination factor of more than 300 was demonstrated with found optimal cleaning regime. The decreasing of the corrosion resistance was found after laser cleaning. The ablation thresholds of ITER-like surfaces were measured. The cleaning productivity of 0.07 m2/hour∙W was found. For mirror surfaces, the damage thresholds were determined to avoid damage during laser cleaning. The possibility to restore reflectivity after thin carbon layer deposition was demonstrated. The perspectives of further development of laser cleaning are discussed.

This thesis concerns heating and current drive in tokamak plasmas using the fast magnetosonic wave in the ion cyclotron range of frequencies. Fast wave heating is a versatile heating method for thermonuclear fusion plasmas and can provide both ion and electron heating and non-inductive current drive. Predicting and interpreting realistic heating scenarios is however difficult due to the coupled evolution of the cyclotron resonant ion velocity distributions and the wave field. The SELFO code, which solves the coupled wave equation and Fokker-Planck equation for cyclotron resonant ion species in a self-consistent manner, has been upgraded to allow the study of more advanced fast wave heating and current drive scenarios in present day experiments and in preparation for the ITER tokamak. Theoretical and experimental studies related to fast wave heating and current drive with emphasis on fast ion effects are presented. Analysis of minority ion cyclotron current drive in ITER indicates that the use of a hydrogen minority rather than the proposed helium-3 minority results in substantially more efficient current drive. The parasitic losses of power to fusion born alpha particles and beam injected ions are concluded to be acceptably low. Experiments performed at the JET tokamak on polychromatic ion cyclotron resonance heating and on fast wave electron current drive are presented and analysed. Polychromatic heating is demonstrated to increase the bulk plasma ion to electron heating ratio, in line with theoretical expectations, but the fast wave electron current drive is found to be severely degraded by parasitic power losses outside of the plasma. A theoretical analysis of parasitic power losses at radio frequency antennas indicates that the losses can be significantly increased in scenarios with low wave damping and with narrow antenna spectra, such as in electron current drive scenarios. / QC 20100506

Les besoins énergétiques croissants de la population mondiale requièrent le développement, la maîtrise et la fourniture de nouvelles formes d'énergie. Dans ce contexte, la fusion nucléaire est une piste de recherche extrêmement prometteuse. Le projet mondial ITER est destiné à démontrer la faisabilité scientifique et technique de la fusion nucléaire comme nouvelle source d'énergie. Un des nombreux verrous tient à la maîtrise de la distribution spatiale du profil de courant dans les plasmas de tokamak, paramètre clé pour la stabilité et la performance des expériences. L'évolution spatiotemporelle de ce courant est décrite par un ensemble d'équations aux dérivées partielles non linéaires. Ce document traite de la stabilisation par un contrôle robuste de la distribution spatiale du profil de courant en dimension infinie. Deux approches sont proposées : la première s'inspire d'une approche de type mode glissant et la seconde (de type proportionnelle et proportionnelle intégrale) est basée sur les fonctions de Lyapunov en dimension infinie. La conception des lois de contrôle est basée sur l'équation 1D de la diffusion résistive du flux magnétique. Les lois de contrôle sont calculées en dimension infinie sans discrétisation spatiale préalables

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2017-03-10T16:38:03Z No. of bitstreams: 0 / Made available in DSpace on 2017-03-10T16:38:03Z (GMT). No. of bitstreams: 0 / Neste trabalho foi padronizada uma solução de 14C emissor beta puro com energia máxima de 156 keV, por meio de três diferentes métodos: CIEMAT/NIST e TDCR (triple-to-double coincidence ratio) em sistemas de cintilação líquida e pelo método do traçador, em sistema de coincidências 4&pi;&beta;-&gamma;. O sistema de cintilação líquida TRICARB, equipado com dois tubos fotomultiplicadores, foi usado para aplicação do método CIEMAT/NIST, usando um padrão de 3H emissor beta puro com energia máxima de 18,7 keV como traçador de eficiência. O sistema de cintilação líquida HIDEX 300SL, equipado com três tubos fotomultiplicadores, foi utilizado para as medidas pelo método TDCR. As amostras de 14C e 3H, medidas nos sistemas de cintilação foram preparadas usando-se três coquetéis cintiladores comerciais Ultima Gold, Optiphase Hisafe3 e InstaGel-Plus a fim de comparar seu desempenho nas medidas.Todas as amostras foram preparadas com 15 mL de coquetel cintilador, em frascos de vidro com baixa concentração de potássio. Alíquotas conhecidas de solução radioativa foram depositadas nos coquetéis cintiladores. Para a variação do parâmetro indicador de quenching, foram utilizados: um carregador de nitro metano e 1 mL de água destilada. Para a padronização pelo método do traçador no sistema de coincidências 4&pi;&beta;-&gamma;, foi utilizado 60Co como emissor beta gama. As medidas foram feitas no sistema de coincidências por software SCS, usando discriminação eletrônica para alterar a eficiência beta. O comportamento da curva de extrapolação foi predito por meio do código Esquema, que utiliza a técnica de Monte Carlo. Os resultados da atividade da solução de 14C obtida pelos três métodos utilizados mostraram uma boa concordância dentro da incerteza experimental. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Controlled thermonuclear fusion may become an attractive future electrical power source. The most promising of all fusion machine concepts is called a tokamak. The fuel, a plasma made of deuterium and tritium, must be confined to enable the fusion process. It is also necessary to protect the wall of tokamaks from erosion by the hot plasma. To increase wall lifetime, the high-Z metal tungsten is foreseen as wall material in future fusion devices due to its very high melting point. This thesis focuses on the following consequences of plasma impact on a high-Z wall: (i) erosion, transport and deposition of high-Z wall materials; (ii) fuel retention in tokamak walls; (iii) long term effects of plasma impact on structural machine parts; (iv) dust production in tokamaks. An extensive study of wall components has been conducted with ion beam analysis after the final shutdown of the TEXTOR tokamak. This unique possibility offered by the shutdown combined with a tracer experiment led to the largest study of high-Z metal migration and fuel retention ever conducted. The most important results are:   - transport is greatly affected by drifts and flows in the plasma edge; - stepwise transport along wall surfaces takes place mainly in the toroidal direction; - fuel retention is highest on slightly retracted wall elements; - fuel retention is highly inhomogeneous.   A broad study on structural parts of a tokamak has been conducted on the TEXTOR liner. The plasma impact does neither degrade mechanical properties nor lead to fuel diffusion into the bulk after 26 years of duty time. Peeling deposition layers on the liner retain fuel in the order of 1g and represent a dust source. Only small amounts of dust are found in TEXTOR with overall low deuterium content. Security risks in future fusion devices due to dust explosions or fuel retention in dust are hence of lesser concern. / <p>QC 20170630</p>

The thesis deals with integral and distributed optical fiber sensors of electric current. In the area of integral sensors the analysis is performed by Jones matrix calculus and the simultaneous influence of induced circular and undesired linear birefringence using an ortho-conjugation retroreflector. Furthermore, the proposed conjugation loop variant using half-wave phase retarders is analyzed. The theoretical conclusions are confirmed by simulation and experimental measurement. In the field of distributed fiber optic sensors, analysis and simulation for the detection of plasma currents in thermonuclear fusion reactors, based on the POTDR technique, is performed. An improvement procedure is proposed for circular-shaped vacuum vessel reactors. Plasma current detection procedure in divertor-type reactors have been newly designed and simulated to investigate the effect of the OTDR detector noise on plasma current detection accuracy.