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The role of lattice defects on deuterium retention in tungsten was investigated by using specially prepared samples having one dominant defect type. The studies were carried out using nuclear reaction analysis, thermal desorption spectroscopy, positron annihilation lifetime spectroscopy, and electron microscopy. It was demonstrated that vacancies and jogs on dislocations bind deuterium more strongly than dislocations, but less strongly than vacancy clusters., Der Einfluss von Kristallgitterdefekten auf den Deuteriumrückhalt in Wolfram wurde unter Verwendung von speziellen Proben mit nur einer dominierenden Defektspezies untersucht. Die in der Studie angewandten Techniken waren Kernreaktionsanalyse, thermale Desorptionsspektrometrie, Positronenlebensdauerspektroskopie sowie Elektronenmikroskopie. Es wurde gezeigt, dass Leerstellen und Versetzungssprünge Deuterium stärker binden als Versetzungen, jedoch weniger stark als Leerstellencluster.

Nuclear fusion can be regarded as a potentially clean, secure and virtually unlimited source of energy for the future. Currently, the most promising reactor concept – the so-called "tokamak" device employs magnetic confinement of fusion plasma. One of the most ambitious energy-related projects today is the construction of the world’s largest tokamak, also known as ITER, “The Way” in Latin. The experimental campaigns planned at ITER aim at testing integrated technologies, materials and physical regimes necessary for commercial production of fusion-based electricity. In other words, ITER aims at bridging the gap between today’s smaller fusion devices and the demonstrational power plant of the future, the DEMO reactor..., La fusión nuclear puede ser considerada como potencialmente limpia, segura y virtualmente una fuente ilimitada de energía para el futuro. Actualmente, el concepto mas prometedor – el llamado “tokamak” utiliza el confinamiento magnético del plasma de fusión. Uno de los proyectos mas ambiciosos relacionados con la energía es hoy en día la construcción del tokamak mas grande del mundo, también conocido como ITER, El Camino en Latin. La campaña experimental planeada en ITER tiene como objetivo probar las tecnologías, los materiales y los regímenes físicos necesarios para la producción comercial de electricidad basada en la fusión nuclear. En otras palabras, el objetivo de ITER es de tender un puente entre el dispositivo de fusión mas pequeño que existe hoy y la planta de fusión nuclear del futuro, el reactor DEMO...

Using Nuclear Fusion to produce price-competitive electricity is an important element in the European Research and Development Agenda. The next big step is to create ‘first plasma’ in ITER – the key facility for development of commercial fusion power. While this fusion test-bed is under construction, a number of technical and scientific challenges remain problems that must be solved to enable the efficient and safe operation of ITER. Ensuring proper functioning of the divertor is one of those challenges. The field lines of a diverted plasma deflect particles, in particular impurities, in the scrape-off layer (the region from the vessel region up to the magnetic separatrix, which is the boundary of the confined plasma region) towards the divertor, where they are to be neutralized and removed through a pumping system. The divertor exhausts the heat produced by the fusion reactions and enables the removal of helium and other impurities by apumping system, hence it is a vital component of the whole system..., Het gebruik van kernfusie om prijsconcurrentiële elektriciteit te produceren is eenbelangrijk element in de Europese Onderzoeks- en Ontwikkelingsagenda. De volgendegrote stap is het creëren van het eerste plasma in ITER - de belangrijkste faciliteit voorde ontwikkeling van commerciële fusiecentrales. Terwijl deze fusie testreactor inaanbouw is, blijven er een aantal technische en wetenschappelijke uitdagingen,problemen die moeten worden opgelost om de efficiënte en veilige werking van ITERmogelijk te maken.Het verzekeren van een goede werking van de divertor is een van die uitdagingen. Develdlijnen van een afgeleid plasma leiden de deeltjes om, in het bijzonderonzuiverheden, in de afscheidingslaag (het gebied in het vacuümvat tot aan demagnetische separatrix, die de grens van het afgesloten plasmagebied vormt) naar dedivertor, waar ze worden geneutraliseerd en verwijderd via een pompsysteem. Dedivertor vormt de uitlaat voor de warmte die door de fusie reacties wordt veroorzaakten maakt het mogelijk om He en andere onzuiverheden te verwijderen doo..

Tesi en modalitat de cotutela: Universitat Politècnica de Catalunya i Universiteit Gent. Erasmus Mundus. Aplicat embargament des de la data de defensa fins el 30/3/2021, In this thesis, a detailed analysis of the experientially observed energetic particle-driven Alfvénic instabilities in tokamak and stellarator plasmas using three dimensional numerical tools based on the reduced MHD model has been carried out. In TJ-II stellarator plasmas, modelling of chirping and steady modes assesses their coexistence on the persistent appearance of the corresponding combination of the toroidal (n) and poloidal (m) mode numbers through the rotational transform sensitivity analysis both in iota lowering and iota rising dynamic plasmas. Modelling of the experimentally observed frequency sweeping phenomenon during the presence of Alfvénic activity with radially extended low-shear and radially localized strong-shear non-monotonic (NM) iota profiles provides an extended spectrum of Alfvénic modes in the wide frequency range as compared with normal (monotonic) iota profile results. Comparison of mode frequencies calculated using a standard dispersion relation and those modelled with the reduced MHD clustered frequency solver AE3D shows an agreement with the selection of iota minimum values, which supports MHD spectroscopy calculations. Wave particle interaction (WPI) studies for the resonance function calculations developed using Monte Carlo transport model based on the 3D MHD equilibria for the TJ-II plasmas suggest for low bounce harmonics (p) the possibility of describing the non-linear evolution of the AEs in TJ-II by a sum of two ion populations with different weighting factors, one of which is dominated by drag and the other by diffusion. As the bounce harmonic increases, the resonance region starts to expand and can cover a significant area of the particle phase space until this resonance region vanishes at high bounce harmonics. In ASDEX Upgrade tokamak plasmas a bifurcated MHD equilibrium is reconstructed with formation of 3D helical core as saturated magnetic axis and the remaining torus with an axisymmetric equilibrium. The formation of heli, En esta tesis, se ha llevado a cabo un análisis detallado de las inestabilidades Alfvénicas de partículas energéticas observadas experimentalmente en plasmas de tokamak y stellarators utilizando herramientas numéricas tridimensionales basadas en el modelo MHD reducido. En los plasmas de estellarators de TJ-II, el modelado de chirping y modos estables evalúa su coexistencia en la aparición persistente de la combinación correspondiente de los números de modo toroidal (n) y poloidal (m) a través del análisis de sensibilidad de transformación rotacional tanto en disminución de iota como en aumento de iota. El modelado del fenómeno de barrido de frecuencia observado experimentalmente durante la presencia de actividad Alfvénica con perfiles de iota no monotónicos (NM) de cizallamiento fuerte y de cizallamiento fuerte radialmente extendido proporciona un espectro extendido de modos Alfvénicos en el amplio rango de frecuencia en comparación con el normal (monotónico). La comparación de las frecuencias de modo calculadas usando una relación de dispersión estándar y aquellas modeladas con el solver de frecuencia agrupada para MHD reducido AE3D muestra un acuerdo con la selección de valores mínimos de iota, que respalda los cálculos de espectroscopía MHD. Los estudios de interacción de onda-partículas (WPI) para los cálculos de la función de resonancia desarrollados utilizando el modelo de transporte Monte Carlo basado en los equilibrios 3D MHD para los plasmas TJ-II sugieren para armónicos de bajo rebote (p) la posibilidad de describir la evolución no lineal de los AE en TJ-II por una suma de dos poblaciones de iones con diferentes factores de ponderación, uno de los cuales está dominado por arrastre y el otro por difusión. A medida que aumenta el armónico de rebote, la región de resonancia comienza a expandirse y puede cubrir un área significativa del espacio de fase de partículas hasta que esta región de resonancia se desvanece en armónicos de alto rebote. En los plasmas de, (Neerlandès) De experimenteel waargenomen Alfvénic-instabiliteiten die in tokamak- en stellaratorplasma's aangedreven worden door snelle deeltjes worden in detail geanalyseerd. De analyse gebeurde met behulp van driedimensionale numerieke methodes gebaseerd op het gereduceerde MHD-model. In TJ-II stellarator plasma's werd de co-existentie van tjilpende (chirping) en steady-state modi vastgesteld op basis van het aanhoudend voorkomen van de overeenkomstige combinatie van de toroïdale (n) en poloidale (m) modenummers. Deze vaststelling gebeurde op basis van de gevoeligheid ten opzichte van de rotatie-transformatie (rotational transform). Modellering van de veging van de frequentie (frequency sweeping) van de Alfvénic-activiteit met niet-monotone iota-profielen zijn, in vergelijking met normale (monotone) iota-profielresultaten, consistent met experimentele resultaten. Studies van de interactie tussen golf en deeltjes (WPI-wave particle interaction) voor de berekening van de resonantiefunctie met behulp van Monte Carlo transportmodel voor TJ-II plasma's, suggereren dat de niet-lineaire evolutie van AE's een som is van twee ion populaties met verschillende wegingsfactoren. Voor lage bounce harmonische, wordt één gedomineerd door sleep (drag) en de andere door diffusie. In ASDEX Upgrade tokamak-plasma's wordt een vertakt MHD-evenwicht gereconstrueerd met de vorming van een 3D-spiraalvormige kern en de asymmetrische 2D-mantel. Alfvén continuümberekeningen met de vertakte evenwichten leiden tot de frequentiesplitsing tussen de continua van de hoogste frequentietak en de laagste frequentietak en het verschuiven van modi met aangrenzend n continuüm rond het frequentieaccumulatiepunt., Postprint (published version)

Tungsten has been chosen as the divertor armour material in ITER and is the main candidate material for plasma-facing components for future fusion reactors. Interaction of plasma components with the material leads to degradation of the performance and thus the lifetime of the in-vessel components. On top of that special attention is drawn to tritium retention in the reactors vessel from a safety point of view, since tritium is radioactive material. In order to gain better understanding of the mechanisms driving accumulation of plasma components in the material and subsequent degradation of the material, atomistic simulations are employed. The focus of this work is on so-called self trapping of H and He atoms or, in other words, Frenkel pair formation in bulk tungsten in the presence of H and He atoms. Two versions of a model embedded atom interatomic potential and a bond order potential were tested by comparing it with ab initio data regarding the binding properties of pure He and He-H-Vacancy clusters and energetics of Frenkel pair formation. As a result of Molecular Dynamics simulations at finite temperature, the values of critical H concentration needed for the generation of a Frenkel pair in the presence of He clusters were obtained. The results show that the critical H concentration decreases with the size of He cluster present in the simulation cell and thus, Frenkel pair formation by H is facilitated in the presence of He clusters in the material.

Nuclear fusion is a promising candidate to supply energy for future generations. At the high temperatures needed for the nuclei to fuse, ions and electrons are no longer bound into atoms. Magnetic fields confine the resulting plasma. One of the heating methods is the ion cyclotron resonant absorption of waves emitted by an external Ion Cyclotron Radio Frequency (ICRF) antenna. The efficiency of ICRF heating is strongly affected by rectified RF electric fields at antenna and other in-vessel components (so-called ‘sheath effects’). The chapter presents an overview of ICRF principles. Attention is given to characterising the detrimental sheath effects through experiments on a dedicated test facility (IShTAR: Ion cyclotron Sheath Test ARrangement). IShTAR has a linear magnetic configuration and is equipped with an independent helicon plasma source. The configuration and capabilities of the test-bed and its diagnostics are described, as well as an analysis of the plasmas.

The role of lattice defects on deuterium retention in tungsten was investigated by using specially prepared samples having one dominant defect type. The studies were carried out using nuclear reaction analysis, thermal desorption spectroscopy, positron annihilation lifetime spectroscopy, and electron microscopy. It was demonstrated that vacancies and jogs on dislocations bind deuterium more strongly than dislocations, but less strongly than vacancy clusters., Der Einfluss von Kristallgitterdefekten auf den Deuteriumrückhalt in Wolfram wurde unter Verwendung von speziellen Proben mit nur einer dominierenden Defektspezies untersucht. Die in der Studie angewandten Techniken waren Kernreaktionsanalyse, thermale Desorptionsspektrometrie, Positronenlebensdauerspektroskopie sowie Elektronenmikroskopie. Es wurde gezeigt, dass Leerstellen und Versetzungssprünge Deuterium stärker binden als Versetzungen, jedoch weniger stark als Leerstellencluster.

Using Nuclear Fusion to produce price-competitive electricity is an important element in the European Research and Development Agenda. The next big step is to create ‘first plasma’ in ITER – the key facility for development of commercial fusion power. While this fusion test-bed is under construction, a number of technical and scientific challenges remain problems that must be solved to enable the efficient and safe operation of ITER. Ensuring proper functioning of the divertor is one of those challenges. The field lines of a diverted plasma deflect particles, in particular impurities, in the scrape-off layer (the region from the vessel region up to the magnetic separatrix, which is the boundary of the confined plasma region) towards the divertor, where they are to be neutralized and removed through a pumping system. The divertor exhausts the heat produced by the fusion reactions and enables the removal of helium and other impurities by apumping system, hence it is a vital component of the whole system...