Дисертації: "Fusion magnet"

1

KHOLIA, AKSHAT. "Thermal Hydraulic numerical analysis of Fusion superconducting magnet systems." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2507886.

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In the present scenario, the International Thermonuclear Experimental Reactor (ITER) is in progress and efforts are being made to extend ITER to DEMOnstration Power plant (DEMO) with the purpose to harness the fusion energy for peaceful and constructive purposes. ITER uses the sueperconducting magnet systems for trapping and maneuvering plasma inside the giant tokamak machines. Superconductivity only entails under the critical conditions of temperature, magnetic field and current density. If any of these parameters surpass the critical value, the quench ensues in the cable. In the real system scenarios, electromagnetic, radiative & conductive loads are present, which may affect the performance of the machine. The magnet designer can change the parameters in terms of current and magnetic field to ensure that the critical conditions are met, but when it comes to temperature, it is really hard to locate the hot spot locations. To envisage such situations, it is essential to study thermal hydraulics and hence system code is needed for the whole superconducting magnet system. For such purposes, Cryogenic Circuit, Conductor and Coil code (4C) was built, imbibing the thermal hydraulic modeling of the cable in Conduit conductors (including strands) coupled with structures (which give support to the winding pack, wound by conductors) and an external cryogenic circuit. During the thesis work, the pre-existing 4C code, was modeled for various coils with or without external cooling circuit as required. Henceforth, it was implemented against the wide range of transients, fast transients (~ few seconds) as well as slow transients (~ few days or weeks) to test the flexibility of the code in studying the wide range of physical phenomenon on different time scales. Eventually, the results were validated against the available experimental data to observe the precision of the model in 4C code. One of the analysis carried out during this dissertation included the cool down of one of the non planar coils (NPC) used in Wendelstein 7-X, which was an example of slow transient. In the domain of fast transients, an extensive analysis of AC losses in one of poloidal field (PF) coils with an external cooling circuit, was performed for Korean Superconducting Tokamak Advanced Research (KSTAR), functional fusion device.

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2

Coatanea-gouachet, Marc. "Quench detection and behaviour in case of quench in the ITER magnet systems." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4739/document.

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Le quench d'un système magnétique d'ITER est une transition irréversible d'un conducteur, de l'état supraconducteur à l'état normal résistif. Cette zone normale se propage le long du câble au cours du temps, en dissipant une grande quantité d'énergie. La détection se doit d'être suffisamment rapide afin de permettre une décharge de l'énergie magnétique et éviter un endommagement permanent du système. La détection primaire de quench d'ITER est basée sur la détection de la tension due au quench, qui est le moyen le plus rapide. L'environnement magnétique perturbé pendant le scenario plasma rend la détection de cette tension très difficile, à cause des hautes tensions inductives qu'il génère dans les bobinages. En conséquence, des compensations de tension sont nécessaires afin de discriminer la tension résistive due au quench.Une solution conceptuelle de la détection de quench basée sur la mesure des tensions est proposée pour les trois grands systèmes magnétiques d'ITER. Pour ceci, une méthodologie claire est développée, incluant le calcul classique selon le critère du point chaud, l'étude de la propagation de quench grâce au code commercial Gandalf, et l'estimation des perturbations inductives, grâce au développement du code TrapsAV. Des solutions adaptées sont proposée pour ces systèmes ainsi que les paramètres de cette détection, qui sont le seuil de détection (entre 0.1 V et 0.55 V) et le temps de discrimination (entre 1 s et 1.2 s). Les valeurs choisies, et en particulier le temps de discrimination, sont suffisamment élevées pour garantir la fiabilité du système, et pour éviter le déclenchement intempestif de décharges rapides non nécessaires
The quench of one of the ITER magnet system is an irreversible transition from superconducting to normal resistive state, of a conductor. This normal zone propagates along the cable in conduit conductor dissipating a large power. The detection has to be fast enough to dump out the magnetic energy and avoid irreversible damage of the systems. The primary quench detection in ITER is based on voltage detection which is the most rapid detection. The very magnetically disturbed environment during the plasma scenario, makes the voltage detection particularly difficult, inducing large inductive components in the coils and voltage compensations have to be designed to discriminate the resistive voltage associated with the quench. A conceptual design of the quench detection based on voltage measurements is proposed for the three majors magnet systems of ITER. For this, a clear methodology was developed. It includes the classical hot spot criterion, the quench propagation study using the commercial code Gandalf and the careful estimation of the inductive disturbances by developing the TrapsAV code.Specific solutions have been proposed for the compensation in the three ITER magnet systems and for the quench detection parameters which are the voltage threshold (in the range of 0.1 V- 0.55 V) and the holding time (in the range of 1 -1.4 s). The selected values, in particular the holding time, are sufficiently high to ensure the reliability of the system and avoid fast safety discharges not induced by a quench which is a classical problem

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3

ZAPPATORE, ANDREA. "Modelling Innovative High Temperature Superconductors for Fusion Applications." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2935600.

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4

Barber, Julien (Julien Victor). "Investigation of cryogenic cooling for a high-field toroidal field magnet used in the SPARC fusion reactor design." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118738.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 111-114).
Rare Earth Barium Copper Oxide (REBCO) High Temperature Superconducting (HTS) tapes are being considered for the Toroidal Field (TF) magnets of the highly compact, high-field SPARC Version 0 (V0) reactor design. The V0 design is set to operate at magnetic fields as high as 20 T, and operating temperatures ranging from 10-30 K. Due to the increase in range of operating conditions made available through the HTS-based magnets, a new set of cryogenic fluids are being considered for forced flow cooling. This thesis analyzes the thermophysical properties of helium, hydrogen, and neon, and constructs a numerical model to investigate the forced flow cooling for REBCO HTS tapes under the extreme heating conditions present in the SPARC V0 design. Four design criteria are used to assess each cryogen, including the current sharing temperature, fluid inlet temperature, cable pressure drop ([delta]P), and operating pressure. From the results of the model, neon is removed from consideration due to its high required pressure drop and low temperature margins imposed by the superconductor current sharing limit. Hydrogen provides the highest effective heat transfer rate operating at inlet conditions of 1.5 MPa and 15 K, but is constrained by safety considerations. Helium is also able to meet the current sharing condition, but with higher initial pressure and lower initial temperature. Using the numerical model, an analysis using the four design criteria finds an optimal operating condition for helium of 2.5 MPa and 10 K based on minimizing cable pressure drop ([delta]P) and inlet pressure, while maximizing the fluid's inlet temperature. With a target operating point defined, an experimental cryogenic flow loop is designed with the purpose of verifying the high heat transfer rates required for the high-pressure, supercritical helium flow in the SPARC reactor. The flow loop uses a pressure differential to drive flow at a target mass flow rate of 46 g/s. To simulate a plasma pulse, the fluid flow is subject to heat fluxes up to 45 kW/m² for a minimum duration of ten seconds.
Supported by the U.S. Department of Energy, Office of Fusion Energy Science Grant: DE-FC02-93ER54186
by Julien Barber.
S.M.

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5

Dehnen, Matthias [Verfasser]. "Degenerative Veränderungen des angrenzenden Segments nach anteriorer zervikaler Diskektomie und Fusion : eine Magnet Resonanz Untersuchung im Langzeitverlauf / Matthias Dehnen." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1214240763/34.

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6

Bayer, Christoph M. [Verfasser]. "Characterization of High Temperature Superconductor Cables for Magnet Toroidal Field Coils of the DEMO Fusion Power Plant / Christoph M. Bayer." Karlsruhe : KIT Scientific Publishing, 2017. http://www.ksp.kit.edu.

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7

Talami, Matteo. "Modeling of the Toroidal Field Insert coil for the ITER Project." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/12916/.

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Il contenuto della tesi riguarda le analisi numeriche e sperimentali effettuate su un campione di cavo superconduttivo del sistema magnetico del reattore sperimentale per la fusione nucleare “ITER”. In particolare, il campione di cavo denominato “Toroidal Field Insert” o “TFI”, appartiene al sistema magnetico toroidale della macchina e viene inserito in un solenoide esterno in modo da replicare le condizioni di campo magnetico tipiche del normale funzionamento di questo conduttore. Le analisi sperimentali effettuate sul campione sono mirate alla caratterizzazione del comportamento durante un ipotetico ciclo di vita del cavo. I parametri principalmente studiati risultano essere: la caratterizzazione dello stato superconduttivo prima e dopo le varie sollecitazioni imposte, l’efficacia idraulica del raffreddamento e la stabilità termica del magnete. In modo complementare alla analisi dei dati sperimentali, due modelli numerici a diverse scale sono stati sviluppati e testati: un primo modello, alla scala di sistema, si occupa dello studio termico e idraulico dell’intera porzione di cavo testata; il secondo, alla scala di componente, si occupa della simulazione elettromagnetica di un riscaldatore induttivo installato sul conduttore volto a misurarne la stabilità. Il confronto tra l’analisi numerica e quella sperimentale ha permesso la comprensione dei principali fenomeni in gioco e la caratterizzazione del conduttore testato.

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8

Lopes, Carmelo Riccardo. "Design and Simulation of Fast Discharge Units (FDUs) for Toroidal Field Coils of Divertor Tokamak Test (DTT)." Doctoral thesis, Università degli Studi di Palermo, 2023. https://hdl.handle.net/10447/580087.

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Questa tesi riassume il lavoro svolto durante il triennio di dottorato nel periodo compreso tra il 2019 e il 2022. Come è ben noto nella comunità scientifica, l'ambiziosissimo progetto di fusione nucleare ha richiesto e richiede notevoli risorse ed investimenti; La tabella di marcia per la generazione di energia da fusione nucleare su larga scala comprende missioni impegnative. I progetti ITER e DEMO, essendo progetti internazionali, richiedono la collaborazione (sia dal punto di vista economico che tecnico) di diversi Paesi a livello europeo ed extraeuropeo; per questo motivo i vari aspetti tecnologici, che verranno poi implementati e applicati nei reattori a fusione finali, vengono prima analizzati, simulati e gestiti da vari enti degli stati membri del progetto (compresa l'Italia). Una delle strutture di ricerca più importanti per questi progetti si trova presso la sede ENEA di Frascati (RM) ed è denominata DTT (divertor tokamak test facility). La struttura DTT è progettata per esplorare tutte le linee di regimi operativi del plasma rilevanti per ITER e DEMO; In particolare sarà possibile dimostrare la fattibilità fisica e tecnologica di varie configurazioni di divertore. In questo modo sarà possibile integrare le conoscenze su concetti di divertori alternativi già sperimentati su macchine esistenti. Poiché l'energia magnetica immagazzinata nei magneti superconduttori è dell'ordine di 2GJ-4GJ (per DTT), in caso di guasto o quench deve esserci la possibilità di estrarla molto velocemente per salvaguardare l'integrità del Tokamak e dei superconduttori. In questo caso intervengono i cosiddetti sistemi FDU (Fast Discharge Unit), costituiti essenzialmente da resistenze per consentire la scarica e la rapida dissipazione dell'energia. La protezione viene realizzata collegando una resistenza di scarica in serie ad ogni blocco di magneti suddivisi in vari gruppi a seconda della loro configurazione elettrica. L'obiettivo principale di questa tesi è quindi quello di riportare tutti i modelli, le simulazioni ei risultati elaborati per l'intera durata del corso di studio nell'ambito dello sviluppo di Fast Discharge Units (FDU).
This thesis summarizes the work carried out during the 3-year PhD course in the period between 2019 and 2022. As is well known in the scientific community, the very ambitious nuclear fusion project has required and still requires considerable resources and investments; The roadmap for large-scale nuclear fusion power generation is comprised of challenging missions. The ITER and DEMO projects, being international projects, require the collaboration (both from an economic and technical point of view) of different countries at European and non-European level; for this reason, the various technological aspects, which will then be implemented and applied in the final fusion reactors, are first analyzed, simulated, and managed by various bodies of the project member states (including Italy). One of the most important research facilities for these projects is located at the ENEA headquarters in Frascati (RM) and is called DTT (divertor tokamak test facility). The DTT structure is designed to explore all lines of plasma operating regimes relevant to ITER and DEMO; In particular, it will be possible to demonstrate the physical and technological feasibility of various divertor configurations. In this way it will be possible to integrate knowledge on alternative divertor concepts already tested on existing machines. Since the magnetic energy stored in superconducting magnets is of the order of 2GJ-4GJ (for DTT), in the event of a failure or quench there must be the possibility to extract it very quickly to safeguard the integrity of the Tokamak and superconductors. In this case, the so-called FDU systems (fast discharge unit) intervene, which basically consist of resistors to allow discharge and fast dissipation of energy. Protection is carried out by connecting a discharge resistor in series to each block of magnets divided into various groups depending on their electrical configuration. The main objective of this thesis so is to report all the models, simulations and results processed for the entire duration of the course of study as part of the development of Fast Discharge Units (FDU).

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9

Hasnain, Bakhtiyar Asef, and Ademir Hodzic. "Design and Simulation of a Slotless Aircored PM Synchronous Generator." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-425268.

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This thesis is a study on an unconventional slow speed direct drive permanent magnet (PM) generator. Unlike a standard permanent magnet synchronous generator (PMSG) which has the copper coils wound around iron teeth, the work in this thesis will present a generator where the copper coils are directly mounted on the stator which eliminates the slots and teeth in the generator. By having a slotless design it is possible to eliminate cogging torque, iron losses in teeth and achieve a lightweight design. These characteristics can prove useful when developing generators for an application such as wind turbines, or more specifically vertical axis wind turbines (VAWTs) in remote areas where weight and serviceability is of concern. This thesis consists of two main parts where the main focus was on the design and simulation of slotless generators. The second part of the thesis was to investigate an available slotless axial flux machine. For the simulations, three different models were created in 2D using CAD software. Two of the models were double-rotor slotless generators and one was a single rotor variant. The electromagnetic properties of these models were analysed using FEMM and COMSOL. The results showed that the double rotor variant with the smaller magnets were more favourable considering the price of magnets and no iron core losses. The experimental results of the axial flux machine gave insight into the construction of commercially available axial slotless generators which could be used to further analyse these types of machines.

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10

Bruzzone, Pierluigi. "AC losses in high current superconductors for nuclear fusion magnets /." [S.l.] : [s.n.], 1987. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8224.

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11

Barth, Christian [Verfasser]. "High Temperature Superconductor Cable Concepts for Fusion Magnets / Christian Barth." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.

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12

Louzguiti, Alexandre. "Magnetic screening currents and coupling losses induced in superconducting magnets for thermonuclear fusion." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0574.

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Les tokamaks visent à produire de l'énergie par fusion thermonucléaire en chauffant un plasma d'hydrogène jusqu'à 150 millions K et en le confinant à l’aide d’un champ magnétique intense créé par des aimants transportant d’importants courants. La supraconductivité est un atout précieux ici car permettant de réduire la taille des aimants et leur consommation énergétique en contrepartie d’un refroidissement cryogénique. Cependant, dans les tokamaks, des variations de champ magnétique apparaissent (ex : décharge du solénoïde central) et génèrent des pertes par induction dans les aimants. Si leur température augmente trop, ils peuvent perdre leur état supraconducteur lors d’une transition brutale appelée "quench": afin de les protéger, ils sont déchargés de leur courant entraînant ainsi la perte du plasma. Nous avons concentré notre travail sur la modélisation de ces pertes car leur connaissance est cruciale pour le bon dimensionnement du refroidissement des aimants et la prédiction des limites opérationnelles du tokamak. Afin d'améliorer la compréhension physique de ce phénomène complexe et de proposer des solutions simples mais réalistes, facilement intégrables dans des plateformes multiphysiques déjà fortement sollicitées par la modélisation d'autres effets, nous avons choisi d'adopter une approche analytique. Les câbles présents dans les tokamaks ayant une architecture assez complexe (centaines de brins torsadés ensemble), nous avons mené des études analytiques et expérimentales aux différentes échelles du câble; nous comparons ensuite les résultats de notre approche à ceux d'autres modèles existants (ex : numériques) et, lorsque cela est possible, à l'expérience
Tokamaks aim at producing energy by thermonuclear fusion heating a hydrogen plasma up to 150 million K and confining it with an intense magnetic field created by magnets carrying important currents. Superconductivity is a very valuable asset in this field since it allows to reduce the size of the magnets and their energy consumption in exchange for cooling them down to cryogenic temperatures. However, in tokamaks, magnetic field variations occur (e.g. due to the central solenoid discharge) and generate induction losses in the magnets. If their temperature increases too much, they lose their superconducting properties in a brutal transition called "quench": to protect their integrity, they are then discharged and the magnetic confinement of the plasma is lost. We have therefore focused on the modeling of these losses - more precisely on the “coupling losses” - since their knowledge is crucial to safely adapt the cryogenic cooling of the magnets and predict the operating limits of the tokamak. In order to both enhance the physical understanding of this complex phenomenon and provide simple but realistic solutions that can easily be integrated in multiphysics platforms already heavily solicited by the modeling of other effects, we have chosen to adopt an analytical approach on this problem. The cables commonly considered for tokamaks presenting a rather complex architecture (several hundreds of strands twisted together in specific patterns), we have carried out analytical and experimental studies at the different scales of the cable; we then compare the results of our approach to other existing ones (e.g. numerical models) and, when possible, to the experiment

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13

Nguyen, Christine. "Magneto-Hydrodynamic Activity and Energetic Particles - Application to Beta Alfvén Eigenmodes." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005642.

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La faisabilite de la fusion magnetique est dependante de notre capacite a confiner l'energie des particules supra-thermiques liberees a haute energie par les reactions de fusion, dans les meilleures conditions de securite et d'efficacite. Dans ce but, il est necessaire de comprendre l'interaction entre les particules energetiques et le plasma thermo-nucleaire qui constitue l'environnement des reactions de fusion, afin de la controler. La these que nous presentons ici s'inscrit dans cet effort. Le coeur du travail mene est l'etude d'un type d'instabilite, le Beta Alfven Eigenmode (BAE), que peuvent exciter les particules energetiques, et dont on peut craindre qu'il degrade fortement non seulement le confinement des particules energetiques mais aussi le confinement du plasma dans sa globalite. Dans un premier temps, nous nous attacherons a decrire les caracteristiques de ce mode et nous deriverons sa relation de dispersion ainsi que sa structure. Dans une seconde partie, nous effectuerons l'etude de la stabilite lineaire de ce mode en presence de particules energetiques. Cette etude nous a permis de definir un critere analytique rendant compte de la capacite des particules energetiques a exciter le BAE. Ce critere sera discute et confronte aux resultats d'experiences menees durant la these. Cette etude lineaire presentant cependant quelques limites, il nous est apparu important de nous poser la question de la possibilite d'une modication de la stabilite du BAE liee a l'utilisation d'une description non-lineaire. Nous suggererons dans cette presentation un processus, verifie analytiquement et numeriquement, dont peut resulter l'existence d'etats meta-stables pour le BAE.

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14

Sorbom, Brandon Nils. "The effect of irradiation temperature on REBCO Jc degradation and implications for fusion magnets." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/120392.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 143-154).
Recent advances in high temperature superconductors (HTS) have opened up a new parameter space for the design of tokamak fusion pilot plants. While previously the maximum on-axis field in a superconducting tokamak was limited to ~6 T, HTS allows tokamaks to be designed with much higher on-axis fields, leading to smaller reactor designs. For these designs, it is critical to determine the lifetime of modern HTS technology in an environment relevant to compact, high-field fusion reactors as well as develop strategies to mitigate this damage. While some studies have been undertaken to assess the lifetime of coated conductors in a fast neutron environment, facilities do not exist to perform cryogenic neutron irradiations at the present. In addition, reactor studies are costly and activate the samples, requiring long cooldown times and specialized analysis facilities to handle radioactive material. In order to complement reactor irradiation studies of HTS and determine whether elevated temperature irradiation has an effect on Jc degradation, REBCO coated conductors were irradiated with a 1.2 MeV proton beam at 80 K, 323 K, and 423 K. Proton irradiation at cryogenic temperatures was found to substantially reduce the amount of Jc degradation in the REBCO samples irradiated to high fluences, a result of great importance to superconducting REBCO magnets in fusion applications where the radiation will occur at T < 80 K. An analysis of temperature, field, and angle dependencies of Jc was performed to investigate the microstructural mechanisms behind the Jc degradation at different temperatures. The key mechanism driving the differences in Jc degradation was found to be radiation-enhanced diffusion at higher temperatures, leading to grain boundary widening between superconducting crystals which in turn blocked supercurrent transport through the conductor. Molecular dynamics simulations suggest that the same mechanism (enhanced diffusion to grain boundaries) also applies to neutron irradiations. This motivates a re-evaluation of previous REBCO neutron irradiation studies at temperatures between 323 K and 383 K, specifically with regards to predictions about REBCO lifetimes in a fusion environment. The work in this thesis suggests that at cryogenic temperatures, the Jc degradation observed in these studies could be substantially less than previously reported.
by Brandon Nils Sorbom
Ph. D.

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15

Cordaro, Luigi. "Magnetic reconnection in fusion plasmas." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3422201.

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This thesis is devoted to the experimental study of magnetic reconnection and the related phenomena taking place in the plasmas produced in the RFX-mod device, a flexible toroidal facility for the study of magnetic plasma confinement for nuclear fusion. Magnetic reconnection consists in a rearrangement of the magnetic field topology, which results in a conversion of magnetic energy into heat and kinetic energy of charged particles. It occurs everywhere in the universe, being observed in the evolution of solar flares, in the interaction of solar-wind with the Earth’s magnetosphere and in star accretion disks. Magnetic reconnection occurs also in laboratory plasmas, especially in the self-organization processes in current carrying fusion plasmas. In the latter, magnetic reconnection events are particularly evident during sawtooth activities in tokamaks and in the discrete relaxation events (DREs) in Reversed Field Pinchs (RFPs). They are also involved in island formation associated to the stearing instability. During these phenomena, a topology change of the magnetic field lines occurs, leading to new equilibrium configurations of lower magnetic energy. A complete and detailed understanding of magnetic reconnection is still missing, therefore this phenomenon represents an important topic to be studied for a better understanding of a large variety of astrophysical and laboratory phenomena. The research activity, here presented, is based on the analysis of the experimental RFX-mod data, coming mainly from the in-vessel system of electrostatic and magnetic probes. The experimental analyzes have been performed alongside theoretical modelling activities. The overall activity can be divided in two main parts: in the first one, a characterization of reconnection phenomena in fusion plasmas, with special emphasis on the RFP configuration, has been performed; the second one is dedicated to the study of the rotation of magnetic islands in tokamak circular discharges. The characterization of magnetic reconnection has been carried out by analyzing the DREs in RFP discharges. During these phenomena, a toroidally localized m = 0 magnetic perturbation develops, associated with the formation of a poloidal current sheet. The analysis, performed on the high frequency magnetic perturbation data, has shown that the current sheet is naturally subject to a fragmentation process, determining, in turn, a multiscale electric field structure, which has been suggested to be able to efficiently accelerate charged particles. Indeed, the acceleration of supra-thermal ions, mainly localized at the position where magnetic reconnection occurs, has been observed during the discrete relaxation events. Such particles have energies high enough to induce enhanced fusion reactivity, as evidenced by the time behavior of the detected neutron fluxes. These evidences show that magnetic reconnection can efficiently contribute to the plasma heating of RFP plasmas. The second main research activity has been devoted to the analysis of tearing mode dynamics in the RFX-mod plasmas in tokamak configuration. Tearing modes are resistive instabilities, developing both in tokamak and RFP plasmas. In the presence of resistivity, field lines can tear and reconnect, determining a change in the magnetic topology. The resulting magnetic configuration is characterized by the presence of magnetic islands, which, in turn, favor the radial transport of particles and the confinement reduction. Tearing modes are therefore a concern for magnetic confinement and their characterization is important in order to control them and achieve better confinement performances. The study of tokamak circular discharges has included both the analysis of experimental data and a theoretical modeling of mode rotation based on the two-fluid MHD equations. The comparison of experimental and theoretical results has shown that the rotation of magnetic islands in RFX-mod tokamak plasmas is driven mainly by the diamagnetic drift. The variation of the latter can determine the slowing down of tearing mode rotation, a phenomenon which is sometimes associated with the growth of the instability and the sudden loss of magnetic confinement (disruption). Finally, a characteristic quasi-cyclic oscillation of both amplitude and frequency of tearing mode, known as ‘limit cycle’, has been observed. This behavior has been found to be coupled to sawtooth activities occurring in the plasma core.
Questa tesi è dedicata allo studio sperimentale della riconnessione magnetica e ai fenomeni correlati che si verificano nei plasmi generati da RFX-mod, una macchina sperimentale molto flessibile per lo studio del confinamento magnetico dei plasmi per la fusione termonucleare. La riconnessione magnetica consiste in un riarrangiamento della topologia del campo magnetico, che determina una conversione di energia magnetica in calore e energia cinetica di particelle cariche. Essa si verifica ovunque nell’universo, essendo osservata nell’evoluzione dei brillamenti solari, nella interazione del vento solare con la magnetosfera della Terra e nei dischi di accrescimento delle stelle. La riconnessione magnetica avviene anche nei plasmi di laboratorio, specialmente nei processi di auto-organizzazione che si verificano nei plasma da fusione. In quest’ultimi, gli eventi di riconnessione magnetica sono particolarmente evidenti durante le attività sawtooth dei tokamak e negli eventi di rilassamento discreti (DRE) nei reversed field pinch (RFP) e sono coinvolti nella formazione di isole magnetiche associate alle instabilità ‘tearing’. Durante questi processi si verifica un cambiamento topologico delle linee del campo magnetico, che porta a nuove configurazioni di equilibrio di energia magnetica inferiore. Una comprensione completa e dettagliata della riconnessione magnetica è ancora mancante. Tale fenomeno rappresenta un importante argomento da studiare per una migliore comprensione di una grande varietà di fenomeni astrofisici e di laboratorio. Il lavoro di analisi presentato in questa tesi è principalmente basato sull’analisi dei dati sperimentali di RFX-mod, provenienti da sistemi di sonde elettrostatiche e magnetiche, posizionate all’interno della camera da vuoto. Le analisi sperimentali sono state affiancate anche da attività di modellizazione teorica. L’attività complessiva può essere divisa in due parti principali: nella prima è stata svolta una caratterizzazione dei fenomeni di riconnessione nei plasmi in configurazione RFP; la seconda è dedicata allo studio della rotazione delle isole magnetiche in scariche tokamak circolari. La caratterizzazione della riconnessione magnetica è stata effettuata analizzando i DRE in scariche RFP. Durante questi fenomeni, la perturbazione magnetica determina la formazione di modi toroidalmente localizzati m = 0, associati alla formazione di strutture di corrente poloidale. L’analisi ha dimostrato che queste strutture sono naturalmente soggette a frammentazione, la quale determina a sua volta una struttura di campo elettrico multi-scala che, come mostrato in letteratura, è in grado di accelerare efficacemente le particelle cariche. In effetti, è stata osservata l’accelerazione di ioni sovratermici, particolarmente evidenti nelle posizioni in cui si verifica la riconnessione magnetica, durante gli eventi discreti di rilassamento. Tali particelle hanno energia abbastanza alta da indurre una reattività da fusione, come dimostrano gli andamenti temporali dei flussi neutronici. Queste evidenze sperimentali dimostrano che la riconnessione magnetica può contribuire in modo efficace al riscaldamento del plasma nei dispositivi RFP. La seconda attività di ricerca principale è stata dedicata all’analisi della dinamica dei modi tearing nei plasmi di RFX-mod in configurazione tokamak. Tali modi tearing sono instabilità resistive, che si sviluppano sia nei plasmi tokamak che in quelli RFP. In presenza di resistività, le linee di campo possono rompersi e riconnettere, determinando un cambiamento nella topologia magnetica. La configurazione magnetica risultante è caratterizzata dalla presenza di isole magnetiche che, a loro volta, favoriscono il trasporto radiale di particelle e la riduzione del confinamento magnetico. I modi tearing costituiscono quindi un problema per il confinamento magnetico e la loro caratterizzazione è importante per poter proporre metodi di controllo al fine di migliorare le prestazioni del confinamento. Lo studio delle scariche tokamak ha incluso sia l’analisi dei dati sperimentali che una modellazione teorica della rotazione dei modi tearing basata sulle equazioni MHD a due fluidi. Il confronto dei risultati sperimentali con le previsioni del modello teorico ha mostrato che la rotazione delle isole magnetiche nei plasmi tokamak di RFX-mod è guidata principalmente dalla deriva diamagnetica. La variazione di quest’ultima può determinare, associate ad una modifica dei profili di pressione, al rallentamento della rotazione di tali modi, un fenomeno talvolta associato alla crescita delle instabilità e che può portare alla disruzione. Infine, è stata osservata una caratteristica oscillazione quasi-ciclica di ampiezza e frequenza dei modi tearing, chiamata ‘ciclo limite’. Questo comportamento è dimostrato essere accoppiato alla cosiddetta attività ‘sawtooth’ che si verifica nella regione centrale del plasma.

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16

Michael, Andrew M. "Imaging schizophrenia : data fusion approaches to characterize and classify /." Online version of thesis, 2009. http://hdl.handle.net/1850/9673.

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17

Andersson, Sundén Erik. "Neutron Spectrometry Techniques for Fusion Plasmas : Instrumentation and Performance." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121615.

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Neutron are emitted from a deuterium plasma with energies around 2.5 MeV. The neutron spectrum is intimately related to the ion velocity distribution of the plasma. As a consequence, the analysis of neutron energy spectra can give information of the plasma rotation, the ion temperature, heating efficiency and fusion power. The upgraded magnetic proton recoil spectrometer (MPRu), based on the thin-foil technique, is installed at the tokamak JET. The upgrade of the spectrometer was done to allow for measurements of deuterium plasmas. This thesis describes the hardware, the data reduction scheme and the kind of fusion plasma parameters that can be estimated from the data of the MPRu. The MPRu data from 3rd harmonic ion cyclotron resonance and beam heating are studied. Other neutron spectrometer techniques are reviewed as well, in particular in the aspect of suitability for neutron emission spectrometry at ITER. Each spectrometer technique is evaluated using synthetic data which is obtained from standard scenarios of ITER. From this evaluation, we conclude that the thin-foil technique is the best technique to measure, e.g., the ion temperature in terms of time resolution.

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18

Renzetti, Reny Angela. "Estudo comparativo da recristalização de dois aços de atividade reduzida endurecidos por dispersão de óxidos (9%Cr e 13%Cr)." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-27082013-094247/.

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O crescente interesse em novos métodos para a geração de energia limpa e sustentável contribui para o desenvolvimento de materiais avançados destinados a aplicações estruturais em reatores de fusão nuclear. Os principais resultados obtidos quanto à caracterização microestrutural de dois aços endurecidos por dispersão de óxidos, candidatos potenciais a este tipo de aplicação, são apresentados. Um dos aços contém 9%Cr e o outro 13%Cr (% em massa). Os aços foram laminados até 80% de redução e recozidos até temperaturas próximas a 0,9 Tf, onde Tf é o ponto de fusão. A cinética de amolecimento foi acompanhada por meio de medidas de dureza Vickers em função da temperatura de recozimento e do tempo. Amostras representativas foram caracterizadas via microscopia eletrônica de transmissão e de varredura e por difração de elétrons retroespalhados. As temperaturas das transformações de fases foram determinadas por técnicas como dilatometria e análise térmica diferencial. Curvas de magnetização em função do campo magnético aplicado até 15 kOe foram obtidas para o aço com 9%Cr. Medidas de difração de raios X para determinar a densidade de discordâncias também foram realizadas em amostras representativas do aço com 9%Cr. Os resultados até o momento mostram que o engrossamento microestrutural destes aços só se torna significativo quando o recozimento é feito em temperaturas acima de 0,8 Tf. Em temperaturas mais baixas, ainda no campo ferrítico, a recuperação prevalece e a fração recristalizada é baixa. A resistência destes materiais à recristalização se deve à presença das partículas de óxido de ítrio dispersas na matriz que dificultam a movimentação e o rearranjo das discordâncias e contornos durante sua migração. Por outro lado, partículas grosseiras como as dos carbonetos M23C6 estimulam a recristalização atuando como sítios preferenciais para a nucleação. O recozimento em temperaturas elevadas no campo austenítico resultou no aumento considerável na dureza Vickers e na densidade de discordâncias para o aço com 9%Cr devido à transformação martensítica. No aço com 13%Cr os resultados também sugerem a ocorrência da transformação martensítica.
There is an increasing interest in the development of new, sustainable, clean and safe sources of energy. In view of these requirements, the development of advanced materials for future nuclear fusion reactors becomes essential. This work investigates the annealing behavior and the microstructural stability of two oxide dispersion strengthened steels with 9%Cr and 13%Cr ODS steels. These materials are potential candidates for structural applications in future fusion reactors. The two ODS steels were cold rolled to 80% thickness reduction. Samples were annealed in vacuum at temperatures of about 0.9 Tm, where Tm is the melting point. The microstructural characterization was performed by Vickers hardness testing, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) performed by a highresolution SEM. Important temperatures related to the phase transformations were determined with aid of dilatometry and differential thermal analysis (DTA). Magnetization curves as a function of applied magnetic fields up to 15 kOe were obtained for 9%Cr ODSEurofer. X-ray diffraction experiments were also performed on 9%Cr steel to evaluate the dislocation density in several metallurgical conditions. Results show that microstructural coarsening becomes significant when annealing is performed above 0.8 Tm. Below 800°C, static recovery is the main softening mechanism of these steels and the volume fraction of recrystallized grains is quite low. The resistance of these steels to recrystallization can be explained by the strong interaction between boundaries and mobile dislocations with fine particles of Y-based oxides. Contrastingly, coarse M23C6 particles act as preferential nucleation sites through the well-known particle stimulated nucleation (PSN) mechanism. Samples annealed above 800oC (austenitic phase field) display larger dislocation densities in the 9%Cr ODS steel. Results concerning to 13%Cr steel suggest the occurrence of martensitic transformation.

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19

Samulski, Camille Clement. "Deceleration Stage Rayleigh-Taylor Instability Growth in Inertial Confinement Fusion Relevant Configurations." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103703.

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Experimental results and simulations of imploding fusion concepts have identified the Rayleigh-Taylor (RT) instability as one of the largest inhibitors to achieving fusion. Understanding the origin and development of the RT instability will allow for the development of mitigating measures to dampen the instability growth, thus improving the chance that fusion concepts such as inertial confinement fusion (ICF) are successful. A study of 1D and 2D simulations are presented for investigating RT instability growth in deceleration stage of imploding geometries. Two cases of laser-driven implosion geometry, Cartesian and cylindrical, are used to study late stage deceleration-phase RT instability development on the interior surface of imploding targets. FLASH's hydrodynamic (HD) and magnetohydrodynamic (MHD) modeling capabilities are used for different laser and target parameters in order to study the RT instability and the impact of externally applied magnetic fields on their evolution. Several simulation regimes have been identified that provide novel insight into the impact that a seeded magnetic field can have on RT instability growth and the conditions under which magnetic field stabilization of the RT instability is observable. Finally, future work and recommendations are made.
Master of Science
The direction for the future of renewable energy is uncertain at this time; however, it is known that the future of human energy consumption must be green in order to be sustainable. Fusion energy presents an opportunity for an unlimited clean renewable energy source that has yet to be realized. Fusion is achieved only by overcoming the earthly limitations presented by trying to replicate conditions at the interior of stellar structures. The pressures, temperature, and densities seen in the interior of stars are not easily reproduced, and thus human technology must be developed to reach these difficult stellar conditions in order to harvest fusion energy. There are two main branches of developmental technology geared towards achieving the difficult conditions controlled nuclear fusion presents, magnetic confinement fusion (MCF) and inertial confinement fusion (ICF)[17]. Yet in both approaches barriers exist which have thwarted the efforts toward reaching fusion ignition which must be addressed through scientific discovery. Successfully reaching ignition is only the first step in the ultimate pursuit of a self sustaining fusion reactor. This work will focus on the experimental ICF configuration, and on one such inhibitor toward achieving ignition, the Rayleigh-Taylor (RT) instability. The RT instability develops on the surfaces of the fusion fuel capsules, targets, and causes nonuniform compression of the target. This nonuniform compression of the target leads to lower pressures and densities through the material mixing of fusion fuel and the capsule shell, which ultimately leads to challenges with reaching fusion ignition. The work presented here was performed utilizing the University of Chicago's FLASH code, which is a state-of-the-art open source radiation magneto-hydrodynamic (MHD) code used for plasma and astrophysics computational modeling [11]. Simulations of the RT instability are performed using FLASH in planar and cylindrical geometries to explore fundamental Rayleigh-Taylor instability evolution for these two different geometries. These geometries provide easier access for experimental diagnostics to probe RT dynamics. Additionally, the impact of externally applied magnetic fields are explored in an effort to examine if and how the detrimental instability can be controlled.

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20

Villamizar, Avendaño Juan Manuel. "Evaluación del rendimiento de la biopsia con fusión cognitiva en el diagnóstico del Cáncer de Próstata." Doctoral thesis, Universitat Autònoma de Barcelona, 2021. http://hdl.handle.net/10803/673202.

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Objectius: avaluar l’eficàcia de la biòpsia transrectal de pròstata per fusió cognitiva (BTRP-fc) en el diagnòstic de càncer de pròstata (CaP) i càncer de pròstata clínicament significatiu (CaPs). Material i mètodes: anàlisi retrospectiva de 111 pacients sotmesos a BTRP-fc a l’Hospital Verge de la Cinta entre 2014 i 2018 amb lesions PIRADS ≥ 3. Resultats: es van detectar 38 CaP (34,4%) i 25 CaPs (65,8% de tots els CaP). Es van evidenciar diferències estadísticament significatives afavorint el grup de biòpsia positiva versus negativa a l’estudiar les variables: edat (mitjana de 69,84 anys), PIRADS (categoria PIRADS 4), mida de la lesió índex (mitjana de 16 mm) i la ubicació de la lesió índex per zones anatòmiques (predominant les lesions a la zona perifèrica amb un 65,8%). L’anàlisi multivariant va revelar que l’edat igual o superior a 70 anys i la mida de la lesió índex igual o superior a 12 mm estaven associats de manera independent a un augment de risc de biòpsia de pròstata positiva per a qualsevol tipus de càncer de pròstata. Conclusions: els nostres resultats són prometedors en el marc de el model actual de diagnòstic de càncer de pròstata que pretén detectar la malaltia clínicament significativa i disminuir el sobrediagnòstic i sobretractament de la malaltia indolent i probablement optimitzant l’estratègia de biòpsia i minimitzant l’heterogeneïtat dels mètodes poguessin assolir taxes de detecció de Caps encara més grans.
Objetivos: evaluar la eficacia de la biopsia transrectal de próstata por fusión cognitiva (BTRP-fc) en el diagnóstico del cáncer de próstata (CaP) y cáncer de próstata clínicamente significativo (CaPs). Material y métodos: análisis retrospectivo de 111 pacientes sometidos a BTRP-fc en el Hospital Verge de la Cinta entre 2014 y 2018 con lesiones PIRADS ≥ 3. Resultados: se detectaron 38 CaP (34,4%) y 25 CaPs (65,8% de todos los CaP). Se evidenciaron diferencias estadísticamente significativas favoreciendo el grupo de biopsia positiva versus negativa al estudiar las variables: edad (media de 69,84 años), PIRADS (categoría PIRADS 4), tamaño de la lesión índice (media de 16 mm) y ubicación de la lesión índice por zonas anatómicas (predominando las lesiones en la zona periférica con un 65,8%). El análisis multivariante reveló que la edad igual o superior a 70 años y el tamaño de la lesión índice igual o superior a 12 mm estaban asociados de manera independiente a un aumento de riesgo de biopsia de próstata positiva para cualquier tipo de cáncer de próstata. Conclusiones: nuestros resultados son prometedores en el marco del modelo actual de diagnóstico de cáncer de próstata que pretende detectar la enfermedad clínicamente significativa y disminuir el sobrediagnóstico y sobretratamiento de la enfermedad indolente y probablemente optimizando la estrategia de biopsia y minimizando la heterogeneidad de los métodos pudieran alcanzarse tasas de detección de CaPs aún mayores.
Objectives: to evaluate the efficacy of the cognitive fusion transrectal biopsy of the prostate (BTRP-fc) in the diagnosis of prostate cancer (CaP) and clinically significant prostate cancer (CaPs). Material and methods: retrospective analysis of 111 patients undergoing BTRP-fc at the Hospital Verge de la Cinta between 2014 and 2018 with PIRADS lesions ≥ 3. Results: 38 CaP (34.4%) and 25 CaPs (65.8% of all CaP) were detected. Statistically significant differences were observed favoring the positive versus negative biopsy group when studying the variables: age (mean 69.84 years), PIRADS (PIRADS category 4), size of the index lesion (mean 16 mm) and location of the Index lesion by anatomical areas (predominantly lesions in the peripheral zone with 65.8%). Multivariate analysis revealed that age equal to or greater than 70 years and index lesion size equal to or greater than 12 mm were independently associated with an increased risk of a positive prostate biopsy for any type of prostate cancer. Conclusions: our results are promising in the framework of the current prostate cancer diagnosis model that aims to detect clinically significant disease and reduce overdiagnosis and overtreatment of indolent disease and probably optimizing the biopsy strategy and minimizing the heterogeneity of the methods could even higher CaPs detection rates can be achieved.
Universitat Autònoma de Barcelona. Programa de Doctorat en Cirurgia i Ciències Morfològiques

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21

Hussain, Asad. "Synergistic effects of neutrons and plasma on materials in fusion reactors & relaxation of merging magnetic flux ropes in fusion and solar plasmas." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/synergistic-effects-of-neutrons-and-plasma-on-materials-in-fusion-reactors--relaxation-of-merging-magnetic-flux-ropes-in-fusion-and-solar-plasmas(9802cf3f-f977-460c-9e9d-314e9c0e8bd5).html.

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This thesis comprises of essentially two parts. The first deals with materials in a fusion reactor and examines how neutron damage affects material in a fusion reactor, with focus on how this is important for plasma damage. The methods used are neutron transport, primary event analysis and molecular dynamics. It found that the neutron damage by 14 MeV neutrons is restricted to back scatter events within the surface (first 20 microns). Molecular dynamics analysis showed that the issue of cascades is heavily dependent on direction of primary event and the energy of such. Statistical analysis was done to provide a standard approach for modelling of damage through neutrons. The second deals with the relaxation of magnetic flux ropes with an emphasis on kink unstable flux ropes. A relaxation model was developed which shows good approximation to simulation results of merging magnetic flux ropes. Subsequently, work was done to establish the physical processes involved in relaxation. This was done by examining magnetohydrodynamic (MHD) simulations of two flux ropes, one unstable and one stable. It was found that there is is a clear distance at which merger does not occur any more. Furthermore, a critical current seems to be a requirement at the edge a stable flux rope.

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22

Peterson, Joshua T. Knowlton S. F. "Vacuum magnetic flux surface measurements made on the compact toroidal hybrid." Auburn, Ala., 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Physics/Dissertation/Peterson_Joshua_48.pdf.

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23

Fridström, Richard. "Resonant magnetic perturbation effect on the tearing mode dynamics : Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch." Doctoral thesis, KTH, Fusionsplasmafysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218052.

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The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode. In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity. In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.

QC 20171122

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24

Hilscher, Paul Peter. "Study of multi-scale interaction and dissipation based on gyro-kinetic model in fusion plasmas." Kyoto University, 2013. http://hdl.handle.net/2433/180447.

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25

Sheeba, Roshin Raj. "Synthetic diagnostics for plasma spectroscopy of magnetic fusion devices." Thesis, Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/201217_SHEEBA_753c513mttwj498soje466ehx_TH.pdf.

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Dans cette thèse, un outil numérique a été élaboré en combinant un code d’élargissement Stark avec un code développé pour le calcul du continuum de recombinaison (transitions libre-lié et libre-libre). L’outil permet de modéliser des spectres d’émission complet de la série Balmer de l’hydrogène/deutérium pour des plasmas de divertors de tokamaks en particulier les plasmas recombinants (détachés). En plus d’élargir les raies, l’environnement plasma abaisse le potentiel d’ionisation des atomes induisant un avancement du continuum. Ces effets statistiques du plasma sont pris en compte avec l’approche du facteur de dissolution des raies dans le continuum. Dans cette approche, au delà d’un niveau critique dépendant des paramètres plasma, les niveaux liés sont considérés comme des états libres. Cette approche a été implémentée en étendant le continuum au-delà de la limite théorique de la série et en transformant des états liés en états libres. Pour simplifier, au-delà de la limite d’Inglis-Teller, les profils des raies Balmer sont extrapolés de celui de la dernière raie résolue. Pour les faibles densités électroniques, un modèle collisionnel-radiatif a été utilisé pour le calcul des intensités. L’outil a été testé via la comparaison avec un spectre expérimental et a été utilisé pour prédire des spectres synthétiques pour WEST en utilisant des distributions spatiales de la densité de neutres et des paramètres plasma simulés par le code de transport SOLEDGE2D-EIRENE le long des lignes de visée. Cette approche des diagnostics synthétiques de la spectroscopie des plasmas peut être facilement élargie pour des prédictions efficaces des futures machines comme ITER et DEMO
In this thesis, a numerical tool is elaborated by combining a Stark lineshape code with another code developed for the calculation of the recombination continuum due to bound-free and free-free transitions. The tool is intended to model whole Balmer spectra emitted by hydrogen or deuterium atoms for tokamak divertor plasma conditions with a focus on recombining plasmas (detachment regime). In addition to Stark line broadening, the plasma environment affects hydrogen atoms by lowering the ionization potential leading to the advance of the continuum. For hydrogen emission, these statistical plasma effects are retained using the dissolution factor approach which allows the modeling of the gradual line merging into the continuum. In this approach, bound levels are considered as free levels beyond a critical level depending on the plasma parameters. The approach is implemented by extending the continuum beyond the theoretical series limit and transforming bound levels to free ones. For simplicity, beyonf the Inglis-Teller limit, the profiles of the Balmer lines are extrapolated from that of the last resolved line. For low electron densities, the line intensities are calculated using a collisional-radiative model. The numerical tool was checked by comparison with an experimental spectrum from literature. The numerical tool was applied to predict synthetic spectra for WEST using spatial distributions of the hydrogen density and of the plasma parameters simulated along viewing chords by the transport code SOLEDGE2D-EIRENE. This approach of synthetic diagnostics of plasma spectroscopy, can easily be extended for efficient predictions for future fusion devices like ITER and DEMO

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26

Sanabria, Edgar Rodolfo Rondán. ""Teoria e modelamento computacional de aquecimento de plasma por ondas de alfvén no tokamak TCABR"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-20102006-111511/.

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Neste trabalho apresentamos o estudo da possivilidade de melhores regimes para o uso dos experimentos de aquecimento e geracao de corrente e fluxo de plasma no tokamak TCABR. Apresentamos um estudo dos efeitos de rotacao de plasma em baixa frequencia (low-frequency (LF)), penetração de campo eletromagnético, absorção e forças ponderomotoras no Tokamak Chauffage Alfvén Brésilien (TCABR) com ênfase na faixa de frequências de 0, 510, 0kHz. Os campos de LF são dirigidos pelo limitador magnético ergódico (ergodic magnetic limiter (EML)) no TCABR. Foi feito um estudo analítico das ondas de Alfvén e ressonância usando modelos simples. Um estudo num´erico tembém foi realizado utilizando três códigos, quais sejam, o código cinético toroidal, o código cilíndrico e o código ALTOK.
In this work we present the study of the determination the best regimes and parameters¶for the heating experiments and current generation and plasma flow in the tokamak TCABR. Study of effects of plasma rotation in low frequency (LF), field penetration, absorption and ponderomotive forces in Tokamak Chauffage Alfvén Brésilien (TCABR)is investigated with emphasis in the frequency range of 0, 510, 0kHz. The fields of LF are driven by the ergodic magnetic limiter (EML) in TCABR. A qualitative analytical study of the Alfvén waves and their resonances is performed using simple models. A numeric study was carried out using through three codes, called the kinetic totoidal code, the cylindrical code and the ALTOK code.

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27

Gallo, Alberto. "Impact of the plasma geometry on the divertor power exhaust in a magnetic fusion reactor." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0001/document.

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Une compréhension profonde du transport du plasma au bord d'un réacteur à fusion par confinement magnétique est obligatoire pour gérer l'extraction de puissance. Dans les dispositifs de fusion de nouvelle génération, des limites technologiques contraignent le flux de chaleur maximal au divertor. Pour une puissance d'échappement donnée le flux de chaleur maximal est déterminé par l'amplitude de l'empreinte du plasma au mur. Les profils de flux de chaleur au divertor peuvent être paramétrés par deux échelles de longueur du transport. Nous remettons en question l'interprétation actuelle de ces deux échelles de longueur en étudiant l'impact de la géométrie du divertor sur l'échappement. En particulier, un élargissement des profils de flux de chaleur avec la longueur de la jambe du divertor externe est diagnostiqué. Des efforts de modélisation ont montré que les simulations diffusives reproduisent les profils expérimentaux de flux de chaleur pour les plasmas à jambes courtes. Inversement, l'étalement du flux de chaleur pour une longe jambe du divertor est reproduit par un modèle turbulent, soulignant l'importance de la turbulence aussi dans le divertor. Ces résultats remettent en question l'interprétation de la largeur du flux de chaleur comme grandeur liée a la main SOL uniquement. Les configurations magnétiques avec une longe jambe du divertor mettent en évidence l'importance du transport asymétrique dans le divertor. Nous concluons que le transport dans la main SOL et celui dans le divertor ne sont pas à découpler et nous soulignons l'importance de la géométrie magnétique sur le transport turbulent avec l'avantage potentiel d'un inattendu étalement du dépôt de puissance
A deep understanding of plasma transport at the edge of a magnetically confined fusion device is mandatory for a sustainable and controlled handling of the power exhaust. In the next-generation fusion device ITER, technological limits constrain the peak heat flux on the divertor. For a given exhaust power the peak heat flux is determined by the extent of the plasma footprint on the wall. Heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two length scales for the transport of heat in SOL. In this work, we challenge the current interpretation of these two length scales by studying the impact of divertor geometry modifications on the heat exhaust. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg. Modelling efforts showed that diffusive simulations well reproduce the experimental heat flux profiles for short-legged plasmas. Conversely, the broadening of the heat flux for a long divertor leg is reproduced by a turbulent model, highlighting the importance of turbulent transport not only in the main SOL but also in the divertor. These results question the current interpretation of the heat flux width as a purely main SOL transport length scale. In fact, long divertor leg magnetic configurations highlighted the importance of asymmetric divertor transport. We therefore conclude that main SOL and divertor SOL transport cannot be arbitrarily disentangled and we underline the importance of the divertor magnetic geometry in enhancing asymmetric turbulent transport with the potential benefit of an unexpected power spreading

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28

Abdelall, Fahd Fathi. "Experimental and numerical studies of the Rayleigh-Taylor instability for bounded liquid films with injection through the boundary." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04072004-102937/unrestricted/abdelall%5Ffahd%5Ff%5F200405%5Fphd.pdf.

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29

Costa, José Tarcisio. "Éléments finis stabilisés VMS appliqués aux modèles magnétohydrodynamiques (MHD) des plasmas de fusion." Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4117/document.

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L'objectif principal de cette thèse concerne la mise en oeuvre d'une méthoded'éléments finis stabilisés pour la simulation des plasmas de fusion. Pour cela,nous avons d'abord dérivé les modèles magnétohydrodynamiques depuis lemodèle cinétique. Les modèles MHD sont généralement utilisés pour simuler lesinstabilités macroscopiques des plasmas. Nous nous sommes concentrés sur lemodèles de la MHD complète. Ensuite, l'approche numérique est décrite dans lecadre de la stabilisation Variationelle Multi-Échelles (VMS). Cette stabilisationvient ajouter un terme à la formulation faible pour mimer les effets des échellesnon-résolues sur celles résolues. Si les effets de ces sous-échelles ne sont paspris en compte lorsque l'on traite des écoulements dominés par convection,comme dans le cadre des plasmas de fusion, le schéma numérique conduit àdes résultats non-physiques. Une étude détaillée de l'instabilité de « Kinkinterne » a été faite ainsi qu'une étude préliminaire des plasmas avec point-Xayant pour but la validation du schéma numérique développé ici
The main objective of this thesis concerns the implementation of a robuststabilized finite element method for simulating fusion plasmas. For that, we firstderive the magnetohydrodynamic models from the kinetic model. MHD modelsare generally used for macroscopic simulations of plasma instabilities. Weconcentrate ou efforts on the full MHD model. Next, the numerical approach isdescribed in the context of the Variational Multi-Scale (VMS) stabilization. Thisstabilization comes to add a term to the weak formulation to mimics the effectsof the unresolved scales over the coarse scales. If the effects of these subscalesare not taken into account when dealing with fluxes dominated byconvection, as it is the cases for fusion plasmas, the numerical scheme canlead to unphysical results. A detailed study of the resistive internal kinkinstability has been done as well as an introductory study of the so called Xpointplasmas in order to validate the numerical scheme developed here

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30

González-Villà, Sandra. "Automated brain structure segmentation in magnetic resonance images of multiple sclerosis patients." Doctoral thesis, Universitat de Girona, 2019. http://hdl.handle.net/10803/667616.

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This thesis is focused on the automated segmentation of the brain structures in magnetic resonance images, applied to multiple sclerosis patients. This disease is characterized by the presence of lesions, which affect the segmentation result of commonly used automatic methods. We propose a new correspondence search model able to minimize this problem and extend the theory of two remarkable label fusion strategies of the literature, i.e. Non-local Spatial STAPLE and Joint Label Fusion, in order to integrate this model into their corresponding estimation algorithms. Furthermore, with the aim of providing fully automated algorithms, a whole automated pipeline is presented. Finally, a second extension of the theory to enable the integration of manual and automatic edits into the segmentation estimation of both strategies is also proposed. The analysis of the results obtained points out a performance improvement on the lesion areas, which is also reflected on the whole brain segmentation performance
Aquesta tesi se centra en la segmentació automàtica de les estructures cerebrals en imatges de ressonància magnètica, aplicada a pacients d’esclerosi múltiple. Aquesta malaltia es caracteritza per la presència de lesions, que afecten els resultats de segmentació dels mètodes automàtics tradicionals. Per aquest motiu proposem un nou model de cerca de correspondències capaç de minimitzar aquest problema i estenem la teoria de dues estratègies notables de la literatura, Non-local Spatial STAPLE i Joint Label Fusion, per integrar aquest model en els seus corresponents algoritmes d’estimació. Amb l’objectiu de proporcionar algoritmes totalment automatitzats, es presenta una pipeline completa. Finalment, també es proposa una segona extensió de la teoria per permetre la integració d’anotacions manuals i automàtiques en les dues estratègies. L’anàlisi dels resultats obtinguts demostra una millora en el rendiment dels algorismes de segmentació en les àrees de lesió, que també es veu reflectida en la segmentació de tot el cervell

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31

Addab, Younes. "Formation, caractérisation et bombardements ioniques de films minces de WO3 d'intérêt pour la fusion magnétique." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4765/document.

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Dans ce travail, nous étudions la stabilité thermique et les effets des irradiations par un plasma d'hélium ou de deutérium de films minces de WO3 d’intérêt pour la fusion magnétique (projet ITER). L’objectif est de comprendre comment une oxydation du divertor modifie les interactions plasma paroi. Pour cela, nous avons synthétisé des films de WO3 par oxydation thermique de substrats de W à 400°C et caractérisé les effets du type de substrat, de la pression d’oxygène et du temps d’oxydation sur la structure et sur l’épaisseur des oxydes formés. La structure (monoclinique nanocristalline), la morphologie et les défauts des échantillons ont été analysés avant et après traitement, à différentes échelles, en utilisant la microscopie électronique, la microscopie Raman, la diffraction de rayons X, et la microscopie à force atomique.Le chauffage sous vide (400 - 800°C) a conduit à la formation de WO2. Le bombardement aux ions D+ (11 eV) a mené à une diffusion profonde du deutérium à travers le film d’oxyde, engendrant un effet électrochimique, observé ici pour la première fois sous irradiation plasma. Cet effet, réversible, est associé à la formation de bronzes de tungstène (DxWO3) et à une transition de phase vers une structure hexagonale. Des bombardements aux ions He+ (20 eV) ont été réalisés afin de dissocier les effets physiques et chimiques. A température ambiante, le bombardement a causé peu de changements morphologiques et structuraux. Par contre, le autre bombardement à 400°C a causé une érosion du film d’oxyde accompagnée d’un changement de couleur, une amorphisation en surface et la formation de bulles à l’interface W / WO3
As part of laboratory studies devoted to magnetic fusion we have investigated the thermal stability and the effects of helium and deuterium plasma irradiation on tungsten oxide thin films. The objective is to predict the consequences of the oxidation of the W plasma facing component (divertor) for plasma wall interactions.To this aim, we have synthesized WO3 films by thermal oxidation of W substrates at 400°C and we have characterized the effects of the W substrate, the oxygen pressure and the oxidation duration on the structure and the thickness of the oxide films. The sample crystalline structure (monoclinic nanocrystalline), defects and morphologies were characterized before and after treatment using scanning and transmission electron microscopies, Raman microscopy, X-Ray diffraction and atomic force microscopy. Heating under vacuum up to 800°C leads to changes in the film structure and composition which results in the formation of WO2. D+ bombardment (11 eV) leads to D+ diffusion throughout the oxide film and to an electrochromic effect, here observed for the first time under plasma irradiation. This effect - which turned out to be reversible - is related to the formation of W bronzes (DxWO3) and to a phase transition of the oxide toward a hexagonal structure. Helium bombardments (20 eV) have then been performed to unravel physical and chemical processes at play. He+ bombardment at room temperature causes slight structural and morphological changes. On the contrary, He+ bombardment at 400°C leads to a significant erosion of the oxide film, accompanied by a colour change, the surface amorphisation and the formation of bubbles at the W / WO3 interface

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32

Heideklang, René. "Data Fusion for Multi-Sensor Nondestructive Detection of Surface Cracks in Ferromagnetic Materials." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19586.

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Ermüdungsrissbildung ist ein gefährliches und kostenintensives Phänomen, welches frühzeitig erkannt werden muss. Weil kleine Fehlstellen jedoch hohe Testempfindlichkeit erfordern, wird die Prüfzuverlässigkeit durch Falschanzeigen vermindert. Diese Arbeit macht sich deshalb die Diversität unterschiedlicher zerstörungsfreier Oberflächenprüfmethoden zu Nutze, um mittels Datenfusion die Zuverlässigkeit der Fehlererkennung zu erhöhen. Der erste Beitrag dieser Arbeit in neuartigen Ansätzen zur Fusion von Prüfbildern. Diese werden durch Oberflächenabtastung mittels Wirbelstromprüfung, thermischer Prüfung und magnetischer Streuflussprüfung gewonnen. Die Ergebnisse zeigen, dass schon einfache algebraische Fusionsregeln gute Ergebnisse liefern, sofern die Daten adäquat vorverarbeitet wurden. So übertrifft Datenfusion den besten Einzelsensor in der pixelbasierten Falscherkennungsrate um den Faktor sechs bei einer Nutentiefe von 10 μm. Weiterhin wird die Fusion im Bildtransformationsbereich untersucht. Jedoch werden die theoretischen Vorteile solcher richtungsempfindlichen Transformationen in der Praxis mit den vorliegenden Daten nicht erreicht. Nichtsdestotrotz wird der Vorteil der Fusion gegenüber Einzelsensorprüfung auch hier bestätigt. Darüber hinaus liefert diese Arbeit neuartige Techniken zur Fusion auch auf höheren Ebenen der Signalabstraktion. Ein Ansatz, der auf Kerndichtefunktionen beruht, wird eingeführt, um örtlich verteilte Detektionshypothesen zu integrieren. Er ermöglicht, die praktisch unvermeidbaren Registrierungsfehler explizit zu modellieren. Oberflächenunstetigkeiten von 30 μm Tiefe können zuverlässig durch Fusion gefunden werden, wogegen das beste Einzelverfahren erst Tiefen ab 40–50 μm erfolgreich auffindet. Das Experiment wird auf einem zweiten Prüfkörper bestätigt. Am Ende der Arbeit werden Richtlinien für den Einsatz von Datenfusion gegeben, und die Notwendigkeit einer Initiative zum Teilen von Messdaten wird betont, um zukünftige Forschung zu fördern.
Fatigue cracking is a dangerous and cost-intensive phenomenon that requires early detection. But at high test sensitivity, the abundance of false indications limits the reliability of conventional materials testing. This thesis exploits the diversity of physical principles that different nondestructive surface inspection methods offer, by applying data fusion techniques to increase the reliability of defect detection. The first main contribution are novel approaches for the fusion of NDT images. These surface scans are obtained from state-of-the-art inspection procedures in Eddy Current Testing, Thermal Testing and Magnetic Flux Leakage Testing. The implemented image fusion strategy demonstrates that simple algebraic fusion rules are sufficient for high performance, given adequate signal normalization. Data fusion reduces the rate of false positives is reduced by a factor of six over the best individual sensor at a 10 μm deep groove. Moreover, the utility of state-of-the-art image representations, like the Shearlet domain, are explored. However, the theoretical advantages of such directional transforms are not attained in practice with the given data. Nevertheless, the benefit of fusion over single-sensor inspection is confirmed a second time. Furthermore, this work proposes novel techniques for fusion at a high level of signal abstraction. A kernel-based approach is introduced to integrate spatially scattered detection hypotheses. This method explicitly deals with registration errors that are unavoidable in practice. Surface discontinuities as shallow as 30 μm are reliably found by fusion, whereas the best individual sensor requires depths of 40–50 μm for successful detection. The experiment is replicated on a similar second test specimen. Practical guidelines are given at the end of the thesis, and the need for a data sharing initiative is stressed to promote future research on this topic.

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33

Burrell, Lauren S. "Feature analysis of functional mri data for mapping epileptic networks." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26528.

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This research focused on the development of a methodology for analyzing functional magnetic resonance imaging (fMRI) data collected from patients with epilepsy in order to map epileptic networks. Epilepsy, a chronic neurological disorder characterized by recurrent, unprovoked seizures, affects up to 1% of the world's population. Antiepileptic drug therapies either do not successfully control seizures or have unacceptable side effects in over 30% of patients. Approximately one-third of patients whose seizures cannot be controlled by medication are candidates for surgical removal of the affected area of the brain, potentially rendering them seizure free. Accurate localization of the epileptogenic focus, i.e., the area of seizure onset, is critical for the best surgical outcome. The main objective of the research was to develop a set of fMRI data features that could be used to distinguish between normal brain tissue and the epileptic focus. To determine the best combination of features from various domains for mapping the focus, genetic programming and several feature selection methods were employed. These composite features and feature sets were subsequently used to train a classifier capable of discriminating between the two classes of voxels. The classifier was then applied to a separate testing set in order to generate maps showing brain voxels labeled as either normal or epileptogenic based on the best feature or set of features. It should be noted that although this work focuses on the application of fMRI analysis to epilepsy data, similar techniques could be used when studying brain activations due to other sources. In addition to investigating in vivo data collected from temporal lobe epilepsy patients with uncertain epileptic foci, phantom (simulated) data were created and processed to provide quantitative measures of the efficacy of the techniques.

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34

Taccon, Cristiano. "Iter di magnetic diagnostics: design study of in-vessel electro-magnetic sensors." Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3426384.

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The interest on nuclear fusion devices as power generators has been growing since the last 25 years. As new competitors enter in the energy market and natural resources become not enough to satisfy the demand, the answer for the long term period is certainly the nuclear fusion. Although none of the operating nuclear devices has produced energy, as they operate as experimental machines, it is fundamental to study and understand the process in the light of future developments like ITER. In order to understand the several scenario that will be present in ITER many diagnostic systems will be installed, among them the magnetic diagnostic system is an essential tool to study and to control the plasma. This system, installed in-vessel and ex-vessel, gives instantaneous measurement of the magnetic field that allows determinating the main electromagnetic plasma parameters such as: plasma current; item plasma shape; item loop voltage; item Halo current distribution.

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35

AHMAD, ALI. "Study of impulsive magnetic reconnection due to resistive tearing mode with the effect of viscosity and dynamic flow in fusion plasmas." Kyoto University, 2015. http://hdl.handle.net/2433/199415.

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36

Borkowetz, Angelika, Ivan Platzek, Marieta Toma, Theresa Renner, Roman Herout, Martin Baunacke, Michael Laniado, et al. "Evaluation of Magnetic Resonance Imaging/ Ultrasound-Fusion Biopsy in Patients with Low-Risk Prostate Cancer Under Active Surveillance Undergoing Surveillance Biopsy." Karger, 2018. https://tud.qucosa.de/id/qucosa%3A70640.

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Introduction: Targeted biopsy of tumour-suspicious lesions detected in multiparametric magnetic resonance imaging (mpMRI) plays an increasing role in the active surveillance (AS) of patients with low-risk prostate cancer (PCa). The aim of this study was to compare MRI/ultrasound-fusion biopsy (fusPbx) with systematic biopsy (sysPbx) in patients undergoing biopsy for AS. Methods: Patients undergoing mpMRI and transperineal fusPbx combined with transrectal sysPbx (comPbx) as surveillance biopsy were investigated. The detection of Gleason score upgrading and reclassification according to Prostate Cancer Research International Active Surveillance criteria were evaluated. Results: Eighty-three patients were enrolled. PCa upgrading was detected in 39% by fusPbx and in 37% by sysPbx (p = 1.0). The percentage of patients who were reclassified in fusPbx and sysPbx (p = 0.45) were 64 and 59% respectively. ComPbx detected more frequently tumour upgrading than fusPbx (71 vs. 64%, p = 0.016) and sysPbx (71 vs. 59%, p < 0.001) and more patients had to be reclassified after comPbx than after fusPbx or sysPbx alone. Conclusions: The combination of fusPbx and sysPbx outperforms both modalities alone with regard to the detection of upgrading and reclassification in patients under AS. Because a high missing rate of significant PCa still exists in both biopsy modalities, a combination of fusPbx and sysPbx should be recommended in these patients.

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37

Sommariva, Cristian. "Test particles dynamics in 3D non-linear magnetohydrodynamics simulations and application to runaway electron formation in tokamak disruptions." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0512/document.

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La thèse étudie la dynamique des Electrons Découplés (DE) dans une disruption plasma déclenchée par injection massive de gaz dans le tokamak JET et simulée par le code JOREK. Cette investigation est permise par l’implémentation d’un module de suivi des particules tests relativistes dans JOREK. L’étude montre que les électrons peuvent ‘survivre’dans le chaos magnétique caractérisant la phase dite de ‘Disjonction Thermique’ (DT) de cette disruption (simulée) grâce à la reformation des surfaces magnétiques fermées. Deuxièmement, l’accélération des électrons causée par les champs électriques dus aux fluctuations magnétohydrodynamiques (MHD) pendant la DT est analysée. Cela montre que les électrons peuvent être accélérés par ces champs et devenir DE, après reconfinement, pendant la phase dite de ‘Disjonction de Courant’. Une étude préliminaire sur les dépendances entre le courant des DE et l’activité MHD dans les expériences de disruption du tokamak ASDEX Upgrade est également reportée
In view of better understanding Runaway Electron (RE) generation processes during tokamak disruptions, this work investigates test electron dynamics during a JET disruption simulated with the JOREK code. For this purpose, a JOREK module computing relativistic test particle orbits in the simulated fields has been developed and tested. The study shows that a significant fraction of pre-disruption thermal electrons remain confined in spite of the magnetic chaos characterizing the Thermal Quench (TQ) phase. This finding, which is related to the prompt reformation of closed flux surfaces after the TQ, supports the possibility of the so-called “hot tail” RE generation mechanism. In addition, it is found that electrons may be significantly accelerated during the TQ due to the presence of strong local electric field (E) fluctuations related to magnetohydrodynamic (MHD) activity. This phenomenon, which has virtually been ignored so far, may play an important role in RE generation. In connection to this modelling work, an experimental study on ASDEX Upgrade disruptions has been performed, suggesting that strong MHD activity reduces RE production

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38

Makni, Aida. "Fusion de données inertielles et magnétiques pour l’estimation de l’attitude sous contrainte énergétique d’un corps rigide accéléré." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAT025/document.

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Dans ce travail de thèse on s’intéresse à l’estimation de l’attitude d’un corps rigideen mouvement dans l’espace 3D en utilisant les quaternions comme représentation. Cetteproblématique a été largement étudiée dans la littérature sous divers domaines d’application.L’objectif de la thèse est de proposer de nouvelles méthodes de fusion de données en combinantdes mesures inertielles et magnétiques. Dans un premier temps, nous nous sommesintéressés à l’estimation de l’attitude en cas de mouvement accéléré où l’accélération linéairedu corps n’est plus négligeable devant la gravité. Deux approches ont été proposées dans cecadre. La première utilise un filtre de Kalman adaptatif pour la compensation des accélérationslinéaires. Précisément, des lois de détection ont été développées pour distinguer d’unefaçon automatique les différentes phases de mouvement (statiques et dynamiques). Ainsi, lamatrice de covariance associée à l’accélération linéaire est estimée afin d’ajuster le gain dufiltre. La deuxième approche consiste à intégrer un filtre singulier élaboré sur la base d’unnouveau modèle, dans lequel le modèle du processus est défini en se basant sur les mesuresissues de l’accéléromètre tandis que le modèle d’observation est défini par les mesures issuesdu gyromètres et du magnétomètres. Cette formulation permet de prendre en compte l’effetdes accélérations linéaires d’une manière efficace. Dans un deuxième temps, on s’est focalisésur l’estimation de l’attitude avec utilisation intermittente de gyromètres, considérés commecapteurs énergivores. Nous avons étudié dans ce cas la façon la plus adéquate afin de réduirel’acquisition des mesures de vitesse angulaire tout en gardant une qualité acceptable de l’estimationde l’attitude. Toutes les approches développées ont été validées par des simulationsnumériques ainsi que des expérimentations utilisant des données réelles
In this PhD. thesis we deal with attitude estimation of accelerated rigid body moving in the 3D space using quaternion parameterization. This problem has been widely studied in the literature in various application areas. The main objective of the thesis is to propose new methods for data fusion to combine inertial gyros) and magnetic measurements. The first challenge concerns the attitude estimation during dynamic cases, in which external acceleration of the body is not negligible compared to the Gravity. Two main approaches are proposed in this context. Firstly, a quatenion-based adaptive Kalman filter (q-AKF) was designed in order to compensate for such external acceleration. Precisely, a smart detector is designed to decide whether the body is in static or dynamic case. Then, the covariance matrix of the external acceleration is estimated to tune the filter gain. Second, we developed descriptor filter based on a new formulation of the dynamic model where the process model is fed by accelerometer measurements while observation model is fed by gyros and magnetometer measurements. Such modeling gives rise to a descriptor system. The resulting model allows taking the external acceleration of the body into account in a very efficient way. The second challenge is related to the energy consumption issue of gyroscope, considered as the most power consuming sensor. We study the way to reduce the gyro measurements acquisition by switching on/off the sensor while maintaining an acceptable attitude estimation. The effciency of the proposed methods is evaluated by means of numerical simulations and experimental tests

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39

Beaucourt-Jacquet, Céline. "Étude expérimentale du guidage du faisceau d’électrons dans le cadre de l’allumage rapide de cibles de fusion." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14741/document.

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Les travaux de cette thèse s’inscrivent dans le cadre de l’allumage rapide pour la fusion par confinement inertiel (FCI), pour la production d’énergie. Dans ce schéma les phases de compression et d’allumage sont découplées. Au cours de la seconde phase, le faisceau d’électrons doit parcourir une distance de 300 µm dans le combustible dense avantde déposer son énergie au coeur de la cible et d’initier les réactions de fusion. Le principal défaut de ce schéma réside dans la divergence du faisceau d’électrons au cours de son transport dans la matière dense. Parmi plusieurs schémas proposés pour réduire cette divergence, nous considérons ici, les schémas sans cône basés sur la collimation des électrons dans un champ magnétique. En particulier, A.P.L. Robinson et ses collaborateurs [Phys. Rev. Lett. 100, 025002, 2008] ont proposé une méthode simple à mettre en place pour contrôler la divergence du faisceau d’électrons :utiliser une séquence de deux impulsions laser. La première impulsion permet de créer un environnement magnétique favorable au confinement du faisceau d’électrons engendré par la seconde interaction. La validation de cette proposition est le sujet de cette thèse. Nous présenterons les résultats expérimentaux et les modélisations théoriques motivées par cette proposition. L’expérience du guidage d’un faisceau d’électrons avec deux impulsions laser a été réalisée sur l’installation laser petawatt Vulcan au Rutherford Appleton Laboratory (RAL) à Didcot en Angleterre. Elle est basée sur la proposition d’un groupe international dans le cadre du projet FCI HiPER. Cette expérience nous a permis d’obtenir les conditions de guidage en fonction du rapport des intensités et du délai entre les deux impulsions. Les résultats de l’expérience ont été modélisés par le code hydrodynamique CHIC couplé au module de transport de particules chargées M1. L’interprétation des résultats expérimentaux nous a permis d’expliquer la base de la physique du guidage du faisceau d'électrons et d'en définir les conditions magnétiques favorables
The work presented in this thesis is realised in the framework of the fast ignition of inertial confinement fusion for energy production. In this scheme the compression and the ignition phases are decoupled. During the second phase, the electron beam must cross over 300 µm in the dense fuel to deposit its energy in the dense core and ignite the fusion reactions.The major problem of the scheme is related to the divergence of the electron beam while it crosses the dense matter. Among the different propositions to inhibit the electron divergence we consider here the schemes without cone that are based on the effect of magnetic collimation. In particular, A.P.L. Robinson and his co-authors [Phys. Rev. Lett. 100, 025002, 2008] suggested a simple way to control the electron beam divergence by using a sequence of two laser pulses. The first one creates a magnetic background favourable for the confinement of the second electron beam resulting from the second interaction. The validation of this scheme is the major goal of this thesis.We present the results of experimental sudies and numerical modeling of the electron beam guiding with help of two consequent laser pulses. The experiment was performed on the Vulcan facility at the Rutherford Appleton Laboratory at Didcot in UK, based on the proposal submitted by an international group of scientists in the framework of the European project for inertial fusion energy HiPER. This experiment allowed us to define a combination of laser and target parameters where the electron beam guiding takes place. The analysis of experimental data and numerical modelling is realised with the hydrodynamic code CHIC coupled to the charged particules transport module M1. The interpretation of the experimental results allowed us to explain the experimental data and the physical basis of guiding and to define the magnetic conditionflavourable to the electron beam guidance

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40

Ivanova, Darya. "Plasma-Facing Components in Tokamaks : Material Modification and Fuel Retention." Doctoral thesis, KTH, Fusionsplasmafysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105099.

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Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for the steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in this thesis in order to contribute to a better understanding and the development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in the Nuclear Research Center Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). Following issues were addressed: (a) properties of material migration products, i.e. co-deposited layers and dust particles; (b) impact of fuel removal methods on dust generation and on modification of plasma-facing components; (c) efficiency of fuel and deposit removal techniques; (d) degradation mechanism of diagnostic components - mirrors - and methods of their regeneration.

QC 20121116

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41

Woestenenk, Esmeralda A. "Protein production, characterization and structure determination in structural genomics." Doctoral thesis, KTH, Biotechnology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-29.

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This thesis covers the process from expression of a heterologous gene in Escherichia coli to structure determination of a protein by nuclear magnetic resonance (NMR) spectroscopy.

The first part concerns structural genomics-related parallel screening studies on the effect of fusion tags (in particular the His tag) on protein solubility and the use of fusion tags in fast, parallel purification protocols intended for initial biophysical characterization of human proteins produced in E. coli. It was found that for most proteins the His tag has a negative influence on protein solubility. This influence appears to be more pronounced for our C-terminal His tag than for the N-terminal His tags used in this study. Moreover, high ratios of soluble per total protein do not always guarantee a high yield of soluble protein after purification, as different vector - target protein combinations result in large differences in host cell growth rates. Protein purification protocols for different fusion tags were developed that make it possible to express, purify and study structural properties of low concentration samples of 15N-labeled proteins in one or two days.

The second part of this thesis describes the assignment and solution structure determination of ribosomal protein L18 of Thermus thermophilus. The protein is a mixed α/β structure with two α-helices on one side of a four-stranded β-sheet. Comparison to RNA-bound L18 showed that the protein to a large extent adopts identical structures in free and bound states, with exception of the loop regions and the flexible N-terminus.

Keywords: protein production, protein solubility, fusion tags, nuclear magnetic resonance, structure determination, ribosomal protein

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42

Gonzalez, Winder Alexander. "Study, development and analysis of In-vessel pick-up coil sensors for ITER magnetic diagnostic and n & gamma detection in fusion plasmas." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3424759.

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The research work described in this thesis has been dedicated to the subject of the magnetic diagnostic for ITER and neutron & y-ray detection for the RFX experiment. The main topic has been focused on the design of a novel concept of magnetic pick-up coil, based on the Low- Temperature Co-fired Ceramic (LTCC) technology, which had been proposed during the conceptual design phase for the ITER in-vessel magnetic diagnostic system. The design has been developed up to the preliminary design level in the framework of an international collaboration, led by Consorzio RFX and supported by the European Agency Fusion for Energy (F4E) and by ITER Organization (ITER-O). The activities carried out during the doctoral period concerned several aspects of plasma diagnostic design: from thermo-mecanical to neutronic numerical analyses; from vacuum technology studies to the setting-up and execution of thermo-electrical tests on sensor prototypes. In the final part of the doctoral period the competence gained has been applied to the setting-up and the exploitation of a neutron and photon detection system for RFX-mod. The major results obtained in the various thematic areas are described in the following chapters: Theoretical framework and background (Chapters 1, 2 and 3): In these chapters, after a basic introduction about fusion science, the theoretical bases and the main arguments that motivated this study are described, with specific emphasis on magnetic diagnostics. This phase is supported by an extensive literature review and a summary of results from previous R&D activities on pick-up coils based on Low Temperature Co-fired Ceramic (LTCC) technology, which lead to the design of a new set of prototypes improved in order to achieve the ITER requirements. LTCC sensor prototypes characterization (Chapter 4): This chapter describes a series of tests to characterize the magnetic sensor prototypes, developed in order to finalize the detailed design of sensors for ITER magnetic diagnostic. For this purpose a formal test protocol for a full characterization of the sensors is reported. In particular these tests have been focused on dimensional and planarity analysis, electrical, magnetic and thermo-electrical characterization, executed on a new set of 40 LTCC sensor prototypes (third generation). Vacuum compatibility (Chapter 5): This chapter describes the main issues related to the vacuum compatibility of the in-vessel components, such as magnetic sensors. The design proposal of a test rig for outgassing rate measurements has been developed. A detailed description of the system, cost estimation and CAD assembly design is reported. Mechanical sensor assembly (Chapter 6): This chapter describes the thermo-mechanical aspects related to the support structure designed to attach the sensors inside the vacuum vessel. Several topics have been investigated with proper thermo-mechanical fem analyses and experimental tests, such as: assessment of temperature gradients within sensor assembly, to minimize possible measurement noise due to thermoelectric sensitivity; mechanical optimization of stress and deformation induced by welding; technical feasibility study for a suitable method of welding for LTCC electrical connections. Simulations of LTCC sensors under n irradiation (Chapter 7): This chapter is focused on the estimation of the nuclear heat [W/cm^3 ] induced by neutron reactions within LTCC sensors, considering a set of expected neutron flux spectra [n/cm^2/s] under the Blanket modules of ITER. For this propouse a set of Monte Carlo neutron interaction simulations have been carried out using a detailed model of the sensor and two potential locations for installation. RFX-mod as n and gamma source (Chapter 8): This chapter summarises the activities of installation of two scintillator detectors (Nal Scintillator and NE213 Liquid Scintillator) executed during the experimental campaign (January-September 2014) at RFX experiment, as part of the first experimental measurements of neutron and photon production in RFX-mod deuterium plasmas. A total of 1185 shots have been monitored over 7 months of experimental campaign, background particle detection and magnetic shielding, as well as data acquisition and calibration issues are reported
Il lavoro di ricerca descritto in questa tesi è stato dedicato al tema della diagnostica magnetica per ITER e alla rivelazione dei neutroni e dei raggi gamma nell'esperimento RFX-mod. L'obiettivo principale è stato il disegno di un nuovo concetto di bobine pick-up, basate sulla tecnologia Low-Temperature Co-fired Ceramic (LTCC), che è stata proposta nella fase concettuale del disegno per il sistema diagnostico magnetico di vuoto di ITER. Il disegno, nella fase preliminare è stato sviluppato nell'ambito di una collaborazione internazionale, diretta dal consorzio RFX e finanziata dall'agenzia europea Fusion for Energy (F4E) e dall'organizzazione ITER. Le attività realizzate durante il periodo di dottorato si sono concentrate sui vari aspetti del disegno dei sistemi di diagnostico in plasma, come l'analisi termico-meccanica, l'interazione neutronica, il disegno dei sistemi di vuoto e le prove termoelettriche in sensori prototipo. Nella fase finale del dottorato le abilità e conoscenze acquisite sono state applicate all'installazione e all'operazione di un sistema per la rivelazione di neutroni e fotoni in RFX-mod. I risultati più importanti ottenuti nei diversi argomenti studiati sono descritti nei seguenti capitoli: Parte teorica e contesto della tesi (Capitoli 1, 2 e 3): In questi capitoli, dopo una descrizione basilare della fusione nucleare, le basi teoriche e gli argomenti principali che hanno motivato questa ricerca sono descritti, con un'enfasi specifica sulla diagnostica magnetica. Lo studio riportato in questa parte è supportato dalla consultazione di una estesa letteratura riguardo ai lavori teorici e tecnici realizzati precedentemente nel disegno e nello sviluppo di bobine magnetiche basate sulla tecnologia LTCC, che ha condotto al disegno di un nuovo gruppo di prototipi, migliorati per soddisfare i requisiti di ITER. Caratterizzazione dei sensori prototipo (Capitolo 4): Questo capitolo descrive una serie di prove per la caratterizzazione dei sensori prototipo, sviluppati con lo scopo di elaborare un disegno dettagliato per il sistema magnetico di ITER. Per raggiungere questo obiettivo si è creato un protocollo formale delle prove necessarie per la caratterizzazione totale dei sensori. Nello specifico, queste prove sono state concentrate sull'analisi della planarità, delle dimensioni fisiche, delle caratteristiche elettriche magnetiche e termoelettriche di quaranta sensori prototipo (terza generazione). Compatibilità con vuoto (Capitolo 5): In questo capitolo sono descritti i principali poblemi legati alla compatibilità dei componenti in vuoto, come nel caso dei sensori magnetici. `E avanzata una proposta di disegno di un sistema di prova per la misurazione del degasamento. Viene presentata inoltre una dettagliata descrizione del sistema in CAD, e la stima del costo. Assemblaggio meccanico del sensore (Capitolo 6): In questo capitolo vengono descritti gli aspetti legati all'analisi termomeccanica del supporto del sensore dentro la camera di vuoto di ITER. Vari argomenti sono stati studiati con adeguate simulazioni FEM. Per prima cosa si è valutato il gradiente di temperatura dentro il corpo del sensore, per minimizzare la misurazione del rumore di fondo dovuto alla sensibilità termica; in seguito si è ottimizzato lo stress indotto dalla saldatura; infine si è studiata la fattibilità tecnica dell'applicazione dei metodi per saldatura delle connessioni elettriche del sensore. Simulazioni dei sensori LTCC sotto radiazione neutronica (Capitolo 7): Questo capitolo è dedicato alla valutazione della potenza nucleare indotta [W/cm^3 ] dalle interazioni neutroniche dentro il sensore LTCC, considerando un gruppo di spettri neutronici [n/cm^2 /s] tipico del blanket di ITER. Questo studio consiste nella realizzazione di una serie di simulazioni di interazione neutronica, basate sul metodo Monte Carlo, utilizzando un modello dettagliato del sensore e due potenziali ubicazioni per l'installazione. RFX-mod come fonte di neutroni e raggi gamma (Capitolo 8): Questo capitolo riassume le attività realizzate durante l'installazione e l'operazione di due rivelatori a scintillio (Nal Scintillator e NE213 Liquid Scitillator) nel periodo della sessione sperimentale (gennaio-settembre 2014) di RFX-mod. Questo esperimento rappresenta la fase iniziale nella rivelazione dei neutroni e nella produzione di fotoni in plasma di deuterio in RFX-mod. Un totale di 1185 impulsi sono stati analizzati nei sette mesi di sessione sperimentale: è stato misurato il fondo di emissione neutronica, si è discusso il blindaggio magnetico e sono stati inoltre studiati e documentati problemi di calibrazione e acquisizione dei dati

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43

Bailly-Grandvaux, Mathieu. "Laser-driven strong magnetic fields and high discharge currents : measurements and applications to charged particle transport." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0557/document.

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La problématique de génération de champs magnétiques quasi-statiques intenses constitue un défi pour la physique de l’interaction laser-plasma. Proposé il y a 30 ans, l’utilisation de cibles "boucles" irradiées par laser se distinguent par leur design compact ne nécessitant aucune génération de courant pulsé en plus de la puissance laser et ont dévoilé récemment leur grand potentiel.Ce travail de thèse s’attache à la caractérisation des phénomènes physiques et au développement de cette technique. On a ainsi montré la génération de forts champs magnétiques quasi-statiques par interaction laser-matière (500 J, durée laser de 1 ns et intensité ~10^17 W/cm^2) atteignant une amplitude de plusieurs centaines de Teslas pendant 2 à 3 ns. L'évolution temporelle et la distribution spatiale des champs magnétiques ont été mesurés par trois diagnostics indépendants : sondes B-dot, rotation de Faraday et défléctométrie de protons. La caractérisation des mécanismes physiques sous-jacents ont aussi fait appel à des diagnostics de rayonnements X de la région irradiée par laser ainsi qu’à des mesures d’ombroscopie optique du fil de la boucle en expansion.Une application de ces champs au guidage magnétique d’électrons relativistes dans la matière dense a permis d'ouvrir de nouvelles perspectives au transport de hautes densités d’énergies dans la matière. En effet, en laissant suffisamment de temps pour que le champ magnétique pénètre dans la cible dense, une amélioration d’un facteur 5 de la densité d’énergie portée par les électrons après 50 µm de propagation a été mise en évidence.En outre, des décharges de courants intenses consécutives à l'irradiation par impulsion laser courtes (50 J, durée laser < 1 ps et intensité ~10^19 W/cm^2) ont été observées. Une imagerie protonique de la décharge a permis de mesurer la propagation d’une onde électromagnétique à des vitesses proches de la vitesse de la lumière. Cette onde d’une durée de ~ 40 ps a été utilisée comme lentille électromagnétique pour focaliser et sélectionner sur une bande étroite d'énergie un faisceau de protons de plusieurs MeV (jusqu’à 12 MeV) passant dans la boucle.Les résultats de ces différentes mesures et applications expérimentales ont été par ailleurs confrontées à des simulations et à des modèles analytiques.Les applications de cette thèse se déploient sur des aspects comme :- la fusion par confinement inertiel, en guidant des faisceaux d'électrons relativistes jusqu'au cœur de la capsule de combustible, tout en confinant les particules qui y déposent leur énergie ainsi que celles créées par les réactions de fusion nucléaire;- l'astrophysique et la planétologie de laboratoire, en générant des sources secondaires de particules énergétiques ou de rayonnement afin de porter la matière dense a de très hautes températures (matière tiède et dense), ou en magnétisant des plasmas pour reproduire des phénomènes astrophysiques à plus petite échelle au laboratoire;- et enfin le contrôle de faisceaux de particules chargées dans le vide pour le développement de sources laser dans le cadre d'applications s'effectuant à distance de la source notamment en science, dans l'industrie, ou même en médecine
The problem of strong quasi-static magnetic field generation is a challenge in laser-plasma interaction physics. Proposed 30 years ago, the use of the laser-driven capacitor-coil scheme, which stands out for its compact design while not needing any additional pulsed power source besides the laser power, only recently demonstrated its potential.This thesis work aims at characterizing the underlying physics and at developing this scheme. We demonstrated the generation of strong quasi-static magnetic fields by laser (500 J, 1 ns-duration and ~10^17 W/cm^2 intensity) of several hundreds of Teslas and duration of 2-3 ns. The B-field space- and time-evolutions were characterized using three independent diagnostics: B-dot probes, Faraday rotation and proton-deflectometry). The characterization of the underlying physical processes involved also X-ray diagnostics of the laser-irradiated zone and optical shadowgraphy of the coil rod expansion.A novel application of externally applied magnetic fields to guide relativistic electron beam in dense matter has been carried out and the obtained results set the ground for improved high-energy-density transport in matter. Indeed, allowing sufficient time for the dense target magnetization, a factor 5 improvement of the electron energy-density flux at 50µm-depth was evidenced.Besides, the generation of high discharge currents consecutive to short laser pulse irradiation (50 J, <1 ps-duration and ~10^19 W/cm^2 intensity) was also pointed out. Proton imaging of the discharge permitted to measure the propagation of an electromagnetic wave at a velocity close to the speed of light. This wave, of ~40ps-duration, was used as an electromagnetic lens to focalize and energy-select a narrow energy range within a multi-MeV proton beam (up to 12 MeV) passing through the coil.All-above experimental measurements and application results were thoroughly compared to both computer simulations and analytic modeling.The applications of this thesis work in a near future will concern:- inertial confinement fusion, by guiding relativistic electron beams up to the dense core nuclear fuel, and by confining particles depositing their energy in it, or even those resulting from the fusion reactions;- laboratory planetology and astrophysics, by generating secondary sources of energetic particles and radiation to reach the warm-dense-matter state or by magnetizing plasmas to reproduce astrophysical phenomena in scaled experiments;- and finally, the control of charged particle beams in vacuum, useful in particular for the development of laser-driven sources for distant applications in science, industry or even medecine

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44

Borkowetz, Angelika, Theresa Renner, Ivan Platzek, Marieta Toma, Roman Herout, Martin Baunacke, Christer Groeben, et al. "Evaluation of Transperineal Magnetic Resonance Imaging/Ultrasound-Fusion Biopsy Compared to Transrectal Systematic Biopsy in the Prediction of Tumour Aggressiveness in Patients with Previously Negative Biopsy." Karger, 2018. https://tud.qucosa.de/id/qucosa%3A71674.

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Objectives: We compared the transperineal MRI/ultrasoundfusion biopsy (fusPbx) to transrectal systematic biopsy (sys-Pbx) in patients with previously negative biopsy and investigated the prediction of tumour aggressiveness with regard to radical prostatectomy (RP) specimen. Material and Methods: A total of 710 patients underwent multiparametric magnetic resonance imaging (mpMRI), which was evaluated in accordance with Prostate Imaging Reporting and Data System (PI-RADS). The maximum PI-RADS (maxPI-RADS) was defined as the highest PI-RADS of all lesions detected in mpMRI. In case of proven prostate cancer (PCa) and performed RP, tumour grading of the biopsy specimen was compared to that of the RP. Significant PCa (csPCa) was defined according to Epstein criteria. Results: Overall, scPCa was detected in 40% of patients. The detection rate of scPCa was 33% for fusPbx and 25% for sysPbx alone (p < 0.005). Patients with a maxPI-RADS ≥3 and a prostate specific antigen (PSA)-density ≥0.2 ng/mL2 harboured more csPCa than those with a PSA-density < 0.2 ng/mL2 (41% [33/81] vs. 20% [48/248]; p < 0.001). Compared to the RP specimen (n = 140), the concordance of tumour grading was 48% (γ = 0.57), 36% (γ = 0.31) and 54% (γ = 0.6) in fusPbx, sysPbx and comPbx, respectively. Conclusions: The combination of fusPbx and sysPbx outperforms both biopsy modalities in patients with re-biopsy. Additionally, the PSA-density may represent a predictor for csPCa in patients with maxPI-RADS ≥3.

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45

Forshed, Jenny. "Processing and analysis of NMR data : Impurity determination and metabolic profiling." Doctoral thesis, Stockholm : Dept. of analytical chemistry, Stockholm university, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-712.

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46

Olofsson, K. Erik J. "Nonaxisymmetric experimental modal analysis and control of resistive wall MHD in RFPs : System identification and feedback control for the reversed-field pinch." Doctoral thesis, KTH, Fusionsplasmafysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94096.

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The reversed-field pinch (RFP) is a device for magnetic confinement of fusion plasmas. The main objective of fusion plasma research is to realise cost-effective thermonuclear fusion power plants. The RFP is highly unstable as can be explained by the theory of magnetohydrodynamics (MHD). Feed-back control technology appears to enable a robustly stable RFP operation. Experimental control and identification of nonaxisymmetric multimode MHD is pursued in this thesis. It is shown that nonparametric multivariate identification methods can be utilised to estimate MHD spectral characteristics from plant-friendly closed-loop operational input-output data. It is also shown that accurate tracking of the radial magnetic field boundary condition is experimentally possible in the RFP. These results appear generically useful as tools in both control and physics research in magnetic confinement fusion.

QC 20120508

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47

Floyd, John-Patrick. "Evolution of edge pedestal transport between ELMs in DIII-D." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53079.

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Evolution of measured profiles of densities, temperatures and velocities in the edge pedestal region between successive ELM (edge-localized mode) events are analyzed and interpreted in terms of the constraints imposed by particle, momentum and energy balance in order to gain insights regarding the underlying evolution of transport processes in the edge pedestal between ELMs in a series of DIII-D discharges. The data from successive inter-ELM periods during an otherwise steady-state phase of the discharges were combined into a composite inter-ELM period for the purpose of increasing the number of data points in the analysis. These composite periods were partitioned into sequential intervals to examine inter-ELM transport evolution. The GTEDGE integrated modeling code was used to calculate and interpret plasma transport and properties during each interval using particle, momentum, and energy balance. Variation of diffusive and non-diffusive (pinch) particle, momentum, and energy transport over the inter-ELM period are examined for discharges with plasma currents from 0.5 to 1.5 MA and inter-ELM periods from 50 to 220 ms. Diffusive transport is dominant for ρ< 0.925, while non-diffusive and diffusive transport are very large and nearly balancing in the sharp gradient region 0.925 <ρ <1.0. Transport effects of ion orbit loss are significant for ρ > 0.95, and are taken into account. During the inter-ELM period, diffusive transport increases slightly more than non-diffusive transport, increasing total outward transport. Both diffusive and non-diffusive transport have a strong inverse correlation with plasma current. Weakening the electromagnetic pinch may increase outward particle transport, and enable control over the rebuilding of the edge pedestal between ELMs.

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48

Sener, Emre. "Automatic Bayesian Segmentation Of Human Facial Tissue Using 3d Mr-ct Fusion By Incorporating Models Of Measurement Blurring, Noise And Partial Volume." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615091/index.pdf.

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Segmentation of human head on medical images is an important process in a wide array of applications such as diagnosis, facial surgery planning, prosthesis design, and forensic identification. In this study, a new Bayesian method for segmentation of facial tissues is presented. Segmentation classes include muscle, bone, fat, air and skin. The method incorporates a model to account for image blurring during data acquisition, a prior helping to reduce noise as well as a partial volume model. Regularization based on isotropic and directional Markov Random Field priors are integrated to the algorithm and their effects on segmentation accuracy are investigated. The Bayesian model is solved iteratively yielding tissue class labels at every voxel of an image. Sub-methods as variations of the main method are generated by switching on/off a combination of the models. Testing of the sub-methods are performed on two patients using single modality three-dimensional (3D) images as well as registered multi-modal 3D images (Magnetic Resonance and Computerized Tomography). Numerical, visual and statistical analyses of the methods are conducted. Improved segmentation accuracy is obtained through the use of the proposed image models and multi-modal data. The methods are also compared with the Level Set method and an adaptive Bayesiansegmentation method proposed in a previous study.

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49

Ngadjeu, Djomzoue Alain narcisse. "Etude des effets de gaine induites par une antenne de chauffage à la fréquence cyclotronique ionique (FCI, 30-80 MHz) et de leur impact sur les mesures par sondes dans les plasmas de fusion." Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10118/document.

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Ces travaux abordent la problématique des mesures de sonde de Langmuir dans un environnement RF. Les mesures expérimentales ont montré que des courants DC négatifs (électroniques) étaient collectés sur la structure d'une antenne ICRF sous tension, pendant que des courants DC positifs (ioniques) sont recueillis par une sonde de Langmuir à l'autre bout du tube de flux magnétique ouvert connecté à l'antenne, la sonde étant au potentiel de la machine. Un modèle de tube de flux asymétrique, de type de sonde double, est présenté. Celui-ci modélise un plasma, confiné le long des lignes de champ magnétique, ayant à chaque extrémité une électrode dont l'une est polarisée à un potentiel RF et l'autre à la masse. L'électrode polarisée modélise le potentiel RF résultant de l'intégration, le long d'une ligne champ magnétique, du champ électrique rayonné par les straps d'une antenne ICRF, tandis que l'autre électrode modélise la sonde au potentiel de la machine. Ce modèle permet d'expliquer l'apparition de courants DC en émettant simplement l'hypothèse qu'il faut à la fois une asymétrie de la source RF par rapport à une masse fixe, une conductivité RF transverse non nulle autorisant des courants RF transverses ainsi qu'une caractéristique courant-tension non linéaire due aux gaines pour favoriser des courants négatifs du côté RF et des courants positifs côté sonde. Ce modèle permet également de modéliser les caractéristiques Courant DC - Tension DC d'une sonde en présence de RF et ainsi d'évaluer les propriétés du plasma. Dans ce cas l'électrode modélisant la sonde n'est plus à la masse, mais à un potentiel donné. Des résultats analytiques sont trouvés dans certaines limites
This work investigates the problematic of probe measurements in RF environment. DC currents flowing along magnetic field lines connected to powered ICRF antennas have been observed experimentally. Negative (i.e. net electron) current is collected on the powered ICRF antenna structure, while positive (i.e. net ion) current is collected by magnetically connected Langmuir probes. An asymmetric model based upon a double probe configuration was developed. The ICRF near field effect is mimicked by a ?driven? RF electrode at one extremity of an "active" open magnetic flux tube, where a purely sinusoidal potential is imposed. The other connection point is maintained at ground potential to model a collecting probe. This "active" flux tube can exchange transverse RF currents with surrounding "passive" tubes, whose extremities are grounded. With simple assumptions, an analytical solution is obtained. We can thus explain how DC currents are produced from RF sheaths. This model also makes it possible to model the characteristics DC Current' DC Voltage of a probe in the presence of RF and thus to evaluate some plasma properties. In this case the electrode at ground potential (probe) is polarized at a given potential. Analytical results are found within certain limits

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50

Riquier, Raphaël. "Magnetic field in laser plasmas : non-local electron transport and reconnection." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX004/document.

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Dans le cadre de la fusion par confinement inertiel, une capsule contenant le combustible de deutérium-tritium est implosée soit par irradiation laser (attaque directe, interaction laser – cible de numéro atomique faible), soit par un rayonnement de corps noir émis par une cavité convertissant le rayonnement laser (attaque indirecte, interaction laser – cible de numéro atomique élevé).Dans les deux cas, une modélisation correcte du transport électronique est cruciale pour avoir des simulations hydro-radiatives prédictives. Cependant, il a été montré très tôt que les hypothèses d'un mécanisme de transport linéaire ne sont pas applicables dans le cadre de l'irradiation d'une cible solide par un laser de puissance (I~10^14 W/cm²). Cela est dû d'une part à des gradients de température très importants (effets cinétiques dits « non-locaux ») ainsi qu'à la présence d'un champ magnétique auto-généré par effet thermo-électrique. Enfin, le flux de chaleur et le champ magnétique sont fortement couplés au travers de deux mécanismes : le transport du champ magnétique par le flux de chaleur (effet Nernst) et la rotation et inhibition du flux de chaleur par la magnétisation du plasma (effet Righi-Leduc).Dans le présent manuscrit, nous commencerons par exposer les différents modèles de transport électronique, et en particulier le modèle non-local avec champ magnétique, implémenté dans le code hydro-radiatif FCI2. Par la suite, nous chercherons à valider ce modèle par des comparaisons avec un code cinétique, puis avec une expérience lors de laquelle le champ magnétique a été mesuré par radiographie proton. Cela fait, nous utiliserons le code FCI2 pour expliquer la source et le transport du champ, ainsi que son effet sur l'interaction.Enfin, nous étudierons la reconnexion du champ magnétique, lors de l'irradiation d'une cible par deux faisceaux lasers
In the framework of the inertial confinement fusion, a pellet filled with the deuterium-tritium fuel is imploded, either through laser irradiation (direct drive, laser – low atomic number target interaction) or by the black body radiation from a cavity converting the laser radiation (indirect drive, laser – high atomic number target interaction).In both cases, a correct modeling of the electron transport is of first importance in order to have predictive hydro-radiative simulations. Nonetheless, it has been shown early on that the hypothesis of the linear transport are not valid in the framework of a solid target irradiated by a high power laser (I~1014 W/cm²). This is due in part to very steep temperature gradients (kinetic effects, so-called « non-local ») and because of a magnetic field self-generated through the thermo-electric effect. Finally, the heat flux and the magnetic field are strongly coupled through two mecanisms: the advection of the field with the heat flux (Nernst effect) and the rotation and inhibition of the heat flux by the plasma's magnetization (Righi-Leduc effect).In this manuscript, we will first present the various electron transport models, particularly the non-local with magnetic field model included in the hydro-radiative code FCI2. Following, in order to validate this model, we will compare it first against a kinetic code, and then with an experiment during which the magnetic field has been probed through proton radiography. Once the model validated, we will use FCI2 simulations to explain the source and transport of the field, as well as its effect on the interaction.Finally, the reconnection of the magnetic field, during the irradiation of a solid target by two laser beams, will be studied

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