Rozprawy doktorskie na temat „Fusion thermonucléaire par confinement magnétique”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „Fusion thermonucléaire par confinement magnétique”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
Dachicourt, Remi. "Contrôle du rayonnement dans les plasmas de fusion par confinement magnétique". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4097.
Pełny tekst źródłaThe route presently envisaged towards the development of a commercial fusion power plant includes that a few remaining physics issues are solved. The present work addresses two of them: plasma radiation control, as a part of the more general power handling issue, and high density tokamak operation. These two issues will be most critical in the demonstration reactor, called DEMO, intermediate step between ITER and a future commercial reactor. For DEMO, the need to radiate a large fraction of the power so as to limit the peak power load on the divertor will be a key constraint. High confinement will have to be combined with high radiated power fraction, and the required level of plasma purity. A fractional radiated power, including bremsstrahlung radiation, of 80-90% of the total power loss will be required. Present studies suggest that this level of radiation could be achieved with acceptable levels of plasma contamination, but improvements are required in models of plasma radiation, and compatibility with the edge transport barrier of the H-mode has to be further assessed. Correlatively, high plasma density (typically with a Greenwald fraction above unity) is required, both because it allows efficient radiation of exhaust power to the reactor walls, and because the final cost of electricity is directly influenced by the achieved Greenwald value
Geulin, Eléonore. "Contribution to the modeling of pellet injection : from the injector to ablation in the plasma". Electronic Thesis or Diss., Aix-Marseille, 2023. http://www.theses.fr/2023AIXM0066.
Pełny tekst źródłaThe preferred method of fueling fusion device is the use of D and/or T pellets injected into the plasma. They are currently used, but the results cannot be extrapolated to future larger reactors where the design of the injection system and the construction of scenarios will be mainly based on simulations. It is therefore important to fill in the gaps in the existing models from the manufacture of pellets to the deposition of material in the plasma. Two lacks of knowledge appear: the modeling of the pellet transport in the injection pipe and the validation of the ablation process. This work aims to fill these gaps and consists of 3 parts.- Describe the physics of material deposition, then the state of the art of the main results and finally the description of the pellet injection systems planned for the next machines.- Model the transport of the pellet in the injection pipe. The effects taken into account in the model are the weakening of the ice during rebounds, the increase in its temperature and its erosion. The model gives in particular the slowing down and the loss of mass of the pellet during the journey, as well as the stored elastic energy linked to its integrity on leaving the tube.- Contribute to the validation of the HPI2 ablation code, by comparing its predictions to data measured in ablation clouds. The method used is a calculation of synthetic data sets from simulations and comparing them to measurements. This method made it possible to validate the assumptions and approximations of the ablation model
Ialovega, Mykola. "Influence des conditions de surface sur le piégeage de l'hydrogène dans le tungstène". Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0058.
Pełny tekst źródłaInvestigations of hydrogen isotopes and helium retention in plasma facing components (PFC) that are exposed to various plasma conditions are important for future fusion devices such as ITER and DEMO. Due to its favorable physical properties, tungsten (W) has been chosen as the plasma-facing material of the ITER divetor. In the deuterium/tritium (D/T) phase of ITER, W PFC will experience incident particles flux composed of hydrogen isotopes (HI), helium (He), impurities and neutrons. In particular, it has been found that He significantly affects W PFC near surface, with the formation of dislocation loops, bubbles, or even W-fuzz. Furthermore, since oxygen is a typical main impurity in tokamak vacuum vessels, W PFC can get oxidized due to the high surface temperatures during ITER operation. Such surface and bulk modifications of W PFC may significantly affect the retention and other physical properties of W leading to an increase of the T inventory in the tokamak. Also, the modification of retention properties of PFC may impact plasma edge physics due to the outgassing of cold HI molecules or He atoms.\\In this PHD thesis, laboratory experiments involving ion implantation and thermal desorption spectrometry (TDS) technique were used to investigate the fundamental retention properties of HI in W PFC due to: - The presence of an oxide layer grown on the polycrystalline W surfaces in ITER relevant conditions, - An impact of ITER relevant He irradiation on the W surface and near-surface layer. TDS measurements were coupled with observations of modification occurring on the surface, in the bulk and in the structure of various PCW samples
Walraet, François. "Propagation et rétrodiffusion d'un faisceau laser lissé dans un plasma de fusion thermonucléaire". Palaiseau, Ecole polytechnique, 2003. http://www.theses.fr/2003EPXX0011.
Pełny tekst źródłaBardin, Sébastien. "Etude des interactions plasma-paroi par imagerie rapide : application aux plasmas de laboratoire et de tokamak". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0012/document.
Pełny tekst źródłaThe necessity to find a new energy source has lead scientists to explore the way of thermonuclear fusion by magnetic confinement considered as one of the most promising possibility. However the production of such plasmas in the current tokamaks lies to several challenges like the interactions between the plasma and the first wall which spark off the creation of a lot of dust in the plasma which could be problematic for the operation of the next fusion reactors. The knowledge of dust production rates, localisation and transport through the vacuum vessel during plasma phases is of primary importance and must be investigated in preparation of ITER. A time and resource efficient algorithm named TRACE, validated thanks to a dedicated laboratory experiment, is used to detect and track dust particles in ASDEX Upgrade during plasma phase. It allows for automatically analyzing videos originating from fast framing cameras. A statistic about micron sized dust detection rate as a function of cumulated discharge duration is made on a large number of discharges (1470). First analyses covering five last campaigns clearly confirm that the amount of dust is significantly low in most of discharges realized in ASDEX Upgrade, excepted for specific conditions corresponding to off-normal plasma phases (disruptions, strong plasma fluctuations including ELMs, plasma displacement toward PFCs and inefficient absorption of heating power). These observations allow to identify the risky plasma discharges and choose the most efficient plasmas scenarios for ITER. It seems to also confirm the applicability of an all tungsten first wall for future fusion reactors as ITER
Coulette, David. "Simulation numérique de modèles cinétiques réduits pour l'étude de la dynamique des plasmas de fusion par confinement magnétique". Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0159/document.
Pełny tekst źródłaThe research exposed therein is developed in the context of the study of turbulent energy and particle transport phenomena occuring in magnetically confined fusion plasmas. A study of the ion temperature gradient instability, one of the main sources of such turbulent transport, is carried out using a gyrokinetic model. The main originality of this work lies in the use of a reduced model, the so-called Multi-Water-Bag model, which allows to reduce the problem dimension while preserving kinetic effects. The model is developed in two types of confinement field geometries. In cylindrical geometry, the growth of the instability is analysed by the mean of three dynamical models : linear, quasi-linear and non-linear. Starting from a given unstable stationary state, linear stability analysis allows one to obtain spectral and geometrical characteristics of the instability. In a second phase, comparing results of numerical simulations implementing the three dynamical models, the growth of turbulence is analysed as well as the first stages of non-linear saturation of the instability. In toroidal geometry, a linear stability analysis is performed. Two different methods, time-based and spectral, were implemented in order to obtain the spectral and geometrical characteristics of the most unstable modes. In both field geometries encompassed by this research, the numerical methods used to obtain the results are described and their performances analyzed. Throughout the work, particular care is given to the balance between the benefits and costs of the Multi-Water-Bag reduction
Isoardi, Livia. "Modelisation du transport dans le plasma de bord d'un tokamak". Aix-Marseille 3, 2010. http://www.theses.fr/2010AIX30066.
Pełny tekst źródłaHelou, Walid. "Design and operation of antennas at the ion cyclotron and lower hybrid range of frequencies for nuclear fusion reactors". Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0395.
Pełny tekst źródłaThe thesis provides at first a brief introduction to magnetic nuclear fusion and tokamaks. It explains the need for auxiliary plasma heating and current-drive electromagnetic systems at the Ion Cyclotron and Lower Hybrid Range of Frequencies (ICRF and LHRF). The thesis then sets antenna specifications that allow satisfying proper plasma wave propagation and proper wave-particle resonance. The Radio Frequency (RF) network solver SIDON developed for this thesis is then presented. The thesis then discusses the different types of ICRF antennas and details the challenges of the impedance matching in ICRF arrays of straps. WEST ICRF launchers are discussed in great detail and simulations of impedance matching scenarios for these launchers using SIDON are reported. The thesis reports on the low-power (milliwatt range) testbed that has been developed for WEST ICRF launchers, as well as the low-power tests of the first one among them. Furthermore, high power (megawatt range) experiments on plasma with the JET ICRF ITER-Like Antenna are reported. The thesis then provides an overview about existing LHRF antennas and discusses the numerical modeling of the coupling of waveguide phased arrays to the plasma. The RF design of ASTARTE-LP and its feeding circuit is discussed. ASTARTE-LP is a low-power (milliwatt range) prototype LHRF antenna based on the Slotted Waveguide Antenna concept that has been designed and built to perform proof of principle experiments on the COMPASS tokamak. The experimental validation of ASTARTE-LP and its feeding circuit before the experiments on COMPASS, as well as the experiments performed on COMPASS plasmas are reported
Helou, Walid. "Design and operation of antennas at the ion cyclotron and lower hybrid range of frequencies for nuclear fusion reactors". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0395/document.
Pełny tekst źródłaThe thesis provides at first a brief introduction to magnetic nuclear fusion and tokamaks. It explains the need for auxiliary plasma heating and current-drive electromagnetic systems at the Ion Cyclotron and Lower Hybrid Range of Frequencies (ICRF and LHRF). The thesis then sets antenna specifications that allow satisfying proper plasma wave propagation and proper wave-particle resonance. The Radio Frequency (RF) network solver SIDON developed for this thesis is then presented. The thesis then discusses the different types of ICRF antennas and details the challenges of the impedance matching in ICRF arrays of straps. WEST ICRF launchers are discussed in great detail and simulations of impedance matching scenarios for these launchers using SIDON are reported. The thesis reports on the low-power (milliwatt range) testbed that has been developed for WEST ICRF launchers, as well as the low-power tests of the first one among them. Furthermore, high power (megawatt range) experiments on plasma with the JET ICRF ITER-Like Antenna are reported. The thesis then provides an overview about existing LHRF antennas and discusses the numerical modeling of the coupling of waveguide phased arrays to the plasma. The RF design of ASTARTE-LP and its feeding circuit is discussed. ASTARTE-LP is a low-power (milliwatt range) prototype LHRF antenna based on the Slotted Waveguide Antenna concept that has been designed and built to perform proof of principle experiments on the COMPASS tokamak. The experimental validation of ASTARTE-LP and its feeding circuit before the experiments on COMPASS, as well as the experiments performed on COMPASS plasmas are reported
Salazar, Luigui. "Data-driven discovery approach to tackle turbulence in fusion plasmas". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0327.
Pełny tekst źródłaOne way to achieve fusion on Earth is through toroidal magnetic confinement, in which the main devices are tokamaks and stellarators. One of the main limiting phenomena is turbulence. This is the result of a mixture of instabilities on different temporal and spatial scales. The aim of this thesis was to contribute to the understanding of turbulent transport, which is the interaction of this turbulence with the plasma properties, in magnetically confined plasmas, focusing on the characterisation of density fluctuations and their dynamics using reflectometry. From the signal spectrum provided by reflectometry, each spectral component was extracted using an algorithm developed in this thesis. It performs this spectral decomposition(Low frequency component, Broadband component, QC modes and noise) in an intelligent way (without ad hoc constraints), preserving its statistical and physical information. Particular attention has been paid to a spectral component, the so-called QC modes because of its link with TEM, an instability acting in turbulent transport. Thanks to the algorithm, the properties and dynamics of the QC modes have been studied, allowing a statistical study and a detailed analysis of the interaction with other spectral components in different magnetic configurations: ToreSupra(limiter), WEST(divertor) and W7X(island divertor). This work is qualified as exploratory because there were no methods to access these QC mode properties and dynamicsThe statistical studies carried out with the ToreSupra and WEST database provided a probability map of the occurrence of the QC modes in the ohmic confinement regime, confirming their link with the TEM,but also 2 more classes, one at low current and another at high current were found. The broadband component was also analysed as it is believed to be related to the microturbulence. Since the spectral amplitude of the BB component is found with the AGG, mainly μ and β, which correspond to the assymetry and shape of the spectrum, show a variation during the transition. On the other hand, the analysis of the dynamics of the QC modes by means of an algorithm developed in this thesis showed a recurrent interaction between the QC modes and the modes in the LF component. Finally, in order to better discriminate the QC modes, the concept of transfer entropy is used to analyse the causality in this interaction. Some cases shows the interaction between the LF component corresponding to the sawtooth instability and the QC modes. All this analysis of dynamics and also causality is then applied to ToreSupra, WEST and W7X, where there is a similar dynamic for signals with bi-directional causality, i.e. not only from the LF component to the QC modes, but also from the QC modes to the BB component. In addition, the ECRH is also examined for the TS database, which shows a decrease in the probability of QC modes as the PECRH increases. Since these QC modes appear in different magnetic configurations, the ultimate objective is to discover if all these QC modes are produced by the same mechanism, since it is believed that there must be a universal mechanism underlying the physics in fusion plasmas, this is still under investigation
Lerbinger, Klaus. "Problèmes spectraux en MHD : effets non idéaux, stabilité du kink interne". Paris 11, 1988. http://www.theses.fr/1988PA112109.
Pełny tekst źródłaEttoumi, Wahb. "Dynamique hamiltonienne et phénomènes de relaxation: d'un modèle champ moyen au confinement magnétique". Phd thesis, Ecole Polytechnique X, 2013. http://tel.archives-ouvertes.fr/tel-00925491.
Pełny tekst źródłaSommariva, Cristian. "Test particles dynamics in 3D non-linear magnetohydrodynamics simulations and application to runaway electron formation in tokamak disruptions". Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0512.
Pełny tekst źródłaIn 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
Hamann, Franck Nicolas. "Conception de cavités radiatives chauffées par plasma de striction magnétique en régime 100 nanosecondes". Palaiseau, Ecole polytechnique, 2003. http://www.theses.fr/2003EPXX0051.
Pełny tekst źródłaVillegas, Daniel. "Etude expérimentale de l'influence du gradient de température électronique sur le transport turbulent des impuretés dans un plasma de fusion". Aix-Marseille 1, 2010. http://theses.univ-amu.fr.lama.univ-amu.fr/2010AIX11055.pdf.
Pełny tekst źródłaUnderstanding impurity transport is a key to an optimal regime for a future fusion device. In this thesis, the theoretical and experimental influence of the electron temperature gradient R/LTe on heavy impurity transport is analyzed both in Tore Supra and ASDEX Upgrade. The electron temperature profile is modified locally by heating the plasma with little ECRH power deposited at two different radii. Experimental results have been obtained with the impurity transport code (ITC) which has been completed with a genetic algorithm allowing to determine the transport coefficient profiles with more accuracy. Transport coefficient profiles obtained by a quasilinear gyrokinetic code named QuaLiKiz are consistent with the experimental ones despite experimental uncertainties on gradients. In the core dominated by electron modes, the lower R/LTe the lower the nickel diffusion coefficient. The latter tends linearly to the neoclassical level when the instability threshold is approached. The experimental threshold is in agreement with the one computed by QuaLiKiz. Further out, where the plasma is dominated by ITG, which are independent of R/LTe , both experimental and simulated results show no modification in the diffusion coefficient profile. Furthermore, the convection velocity profile is not modified. This is attributed to a very small contribution of the thermodiffusion (1/Z dependence) in the total convection. On ASDEX, the preliminary results, very different from the Tore Supra ones, show a internal transport barrier for impurities located at the same radius as the strong ECRH power deposit
Hamann, Franck. "Conception de cavités radiatives chauffées par plasmas de striction magnétique en régime 100ns". Phd thesis, Ecole Polytechnique X, 2003. http://pastel.archives-ouvertes.fr/pastel-00000811.
Pełny tekst źródłaSommariva, 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.
Pełny tekst źródłaIn 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
Levy, Yoann. "Etude numérique et modélisation des instabilités hydrodynamiques dans le cadre de la fusion par confinement inertiel en présence de champs magnétiques auto-générés". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00742130.
Pełny tekst źródłaReux, Cédric. "Etude d'une méthode d'amortissement des disruptions d'un plasma de tokamak". Phd thesis, Ecole Polytechnique X, 2010. http://pastel.archives-ouvertes.fr/pastel-00599210.
Pełny tekst źródłaStorelli, Alexandre. "Étude du transport turbulent dans les plasmas du tokamak Tore Supra : observation des écoulements perpendiculaires stationnaires et du mode acoustique géodésique". Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01167913v2/document.
Pełny tekst źródłaTokamaks are toroidal machines designed to magnetically confine plasma and to host reactions of nuclear fusion. Their performance is limited by turbulent transport, which precise mechanisms are not fully elucidated. Turbulent fluctuations cause the onset of macroscopic mean flows, in the direction perpendicular to both magnetic field and small radius, called zonal flows. Their shear is known to decrease both fluctuation level and transport. Diagnostics of Doppler backscattering have been installed on Tore Supra (CEA Cadarache). They could measure the perpendicular velocity of turbulent fluctuations in different zones of the plasma. First, it is shown that, on average, fluctuations flow twice as fast at the low field side of the machine than at its top. The difference, significantly higher than predicted by common models, is put in perspective with the properties of magnetic equilibrium and the behaviour of fluctuations. Then, variations of the velocity, due to the zonal flow branch called geodesic acoustic mode (GAM), are examined in a series of experiments where collisionality is varied. Those observations have been quantitatively compared with a gyrokinetic simulation with the code GYSELA, using the equilibrium profiles from the experiments. GAM frequency in experiments is lower than predicted, especially at low collisionalities. In addition, the instationarity of GAM has been characterized with the Hilbert-Huang transform. Burts of GAM oscillations have similar statistics between experiments and simulation and their duration could be related with the nonlinear interaction between the GAM and turbulence and with the continuum damping which is observed in the simulation
Dumont, Rémi. "Contrôle du profil de courant par ondes cyclotroniques électroniques dans les tokamaks". Phd thesis, Université Henri Poincaré - Nancy I, 2001. http://tel.archives-ouvertes.fr/tel-00001589.
Pełny tekst źródłaGallo, Alberto. "Impact of the plasma geometry on the divertor power exhaust in a magnetic fusion reactor". Electronic Thesis or Diss., Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0001.
Pełny tekst źródłaA 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
Cottier, Pierre. "Modelling the turbulent transport of angular momentum in tokamak plasmas - A quasi-linear gyrokinetic approach". Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/docs/00/93/92/40/PDF/Manuscrit.pdf.
Pełny tekst źródłaThe magnetic confinement in tokamaks is for now the most advanced way towards energy production by nuclear fusion. Both theoretical and experimental studies showed that rotation generation can increase its performance by reducing the turbulent transport in tokamak plasmas. The rotation influence on the heat and particle fluxes is studied along with the angular momentum transport with the quasi-linear gyro-kinetic eigenvalue code QuaLiKiz. For this purpose, the QuaLiKiz code is modified in order to take the plasma rotation into account and compute the angular momentum flux. It is shown that QuaLiKiz framework is able to correctly predict the angular momentum flux including the $$\exb$$ shear induced residual stress as well as the influence of rotation on the heat and particle fluxes. The major approximations of QuaLiKiz formalisms are reviewed, in particular the ballooning representation at its lowest order and the eigenfunctions calculated in the hydrodynamic limit. The construction of the quasi-linear fluxes is also reviewed in details and the quasi-linear angular momentum flux is derived. The different contributions to the turbulent momentum flux are studied and successfully compared both against non-linear gyro-kinetic simulations and experimental data
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.
Pełny tekst źródłaIn 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
Scotto, d'Abusco Manuel. "Modélisation numérique du transport turbulent cœur-bord dans un tokamak en géométrie réaliste par une méthode numérique avancée". Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0173.
Pełny tekst źródłaNowadays a challenge remains the design of optimized plasma scenarios for tokamak operation to control the heat flow from the core region to the wall. This calls for the development of efficient and reliable numerical codes with predictive capabilities for plasma simulations. The present work aims to develop a high-order finite elements code based on hybrid discontinuous Galerkin numerical scheme and an efficient implicit time integration method for solving non isothermal Braginskii reduced fluid equations in versatile tokamak and magnetic equilibrium geometries. The use of such numerical scheme allows to perform simulations with time evolving magnetic configurations, avoiding expensive re-meshing of the computational domain. The structure and the realization of such a numerical tool is presented. The feasibility of the latter is then investigated through a careful validation and benchmarking operation with SolEdge3X. Self-consistent sources of particle, due to plasma recycling, and energy due to Ohmic heating are introduced to perform 2D simulation of a full poloidal tokamak cross section. With such a model the main features of a detached plasma are investigated for the WEST tokamak machine. The first core-edge transport simulations of an entire WEST discharge (shot #54487) are shown from the start-up phase to the final plasma landing. Comparisons between experimental interferometry and synthetic simulation data show a remarkable agreement. The time evolution of the particles and heat fluxes at the wall, are analyzed and exploited to assess the tungsten sputtering, using both a simple cinematic model and the impurity tracker monte-carlo code ERO2.0
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.
Pełny tekst źródłaIn 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
Laribi, Elias. "Modélisation numérique de l'impact de la géométrie magnétique sur le plasma de bord des tokamaks". Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0298.
Pełny tekst źródłaThis phD work has shown that, in a limiter configuration, the elongation of magnetic surfaces has a stabilizing effect with respect to the edge plasma turbulence. This leads to a reduction of the edge plasma width when the elongation increases. Regarding triangularity, this phD work revealed that its effects on the edge plasma were weaker than those of elongation. A better understanding of these trends has been possible thanks to a theoretical work on a simplified interchange model. This work has also revealed the importance of the magnetic field spatial variability on the poloidal size of turbulent structures and therefore on the radial turbulent fluxes. In a second step, the study of a divertor configuration with one X point has shown that the the magnetic field spatial variability was so important that it could be one of the reasons that explain the enhancement of the low field side ballooned nature of edge plasma turbulence in a divertor geometry. Still concerning the divertor geometry, this phD also revealed that the internal material receives more heat compared to the external material when the toroidal magnetic field is oriented in the direct direction (= magnetic drift of the ions pointing towards the X point). A possible explanation of this observation is the existence of a significant plasma circulation from the low field side to the high field side at the X point that we observed in this configuration. Finally, we were able to confirm that one way to improve this heat flux distribution on the walls was to merge two X points perfectly (= ideal snowflake proposed in 2007 by Ryutov and Sukhanovsky)
Jesko, Karol. "Studying divertor relevant plasmas in linear devices : experiments and transport code modelling". Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0010.
Pełny tekst źródłaPredictions for the operation of tokamak divertors typically rely on edge transport codes, consisting of a fluid plasma code in combination with a Monte Carlo code for neutral species. The linear devices Magnum-PSI and Pilot-PSI at DIFFER, operating with a cascaded arc plasma source that produces plasmas comparable to those expected in the ITER divertor (Te ∼ 1 eV, n_e ∼ 10²⁰ m⁻³). In this thesis, plasma discharges have been studied both experimentally and by modelling using the Soledge2D-Eirene code in order to a) investigate which phenomena need to be included in the modeling to reproduce experimental trends and b) provide new insights to the interpretation of experiments. Experimentally, the effect of neutral pressure Pn was investigated using Thomson scattering, a Langmuir probe, visible spectroscopy and calorimetry. We have shown that a plasma beam can be effectively terminated by a blanket of neutral gas. Next, from comparisons of experiments and simulations, we have found that it is critical to include elastic collisions between the plasma and molecules if experiments are to be reproduced. Furthermore, the near-target Te is systematically overestimated by the code, underestimating the recombination rate thereby. Lastly, we have experimentally shown the importance of the inclusion of surface recombination to the surface energy flux in low temperature plasmas, an effect that is generally known but difficult to measure in fusion devices. The work presented in this thesis contributes to the understanding of plasma-neutral interactions especially in new generation, closed divertor concepts (i.e. MAST-upgrade, DIII-D)
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.
Pełny tekst źródłaAs 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
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.
Pełny tekst źródłaThe 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
Meireni, Mutia. "Spectroscopic diagnostic of magnetic fusion plasmas : application to ITER". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0218.
Pełny tekst źródłaThis thesis focuses on the modeling of the atomic line radiation emitted by magnetic fusion plasmas for diagnostic purposes. An improvement of the accuracy of diagnostics is proposed, in order to have a better characterization of runaway electrons in the context of ITER preparation. In the first chapter, we discuss about fusion reaction, about how it is produced in tokamak machines, and we discuss about the disruptions, which are a consequence of instabilities. They are one cause of runaway electrons. In the second chapter, the formalism used in spectral line broadening models is introduced based on quantum mechanics and statistical physics. Numerical calculations are also presented. They are done for applications to synthetic diagnostics in tokamak divertor plasma conditions. Hydrogen Balmer lines with a moderate principal quantum number are considered. In the third chapter, we discuss the physics underlying Langmuir waves. This includes the Landau damping process and its inverse counterpart, the plasma-beam instability mechanism. It is possible to calculate the magnitude of the electric field which is created by a beam of electrons using the quasilinear theory. We present this theory and we present a generalization to strongly nonlinear regimes for which the Langmuir waves are coupled with the ion sound and electromagnetic waves. Finally, we discuss this model and, next, apply the formalism for different beam densities in tokamak edge plasmas and we examine the possibility for making a diagnostic of runaway electrons based on atomic spectroscopy in the fourth chapter
Elarif, Ali Aboudou. "Approximation par éléments finis C1 des modèles magnétohydrodynamiques pour les plasmas de fusion". Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4108.
Pełny tekst źródłaThis thesis participates in the development of advanced numerical methods to simulate plasma instabilities for fusion by magnetic confinement in tokamaks. These flows are described in a general framework by magnetohydrodynamic(MHD) fluid models and can be considered incompressible in some approximations known as reduced MHD models. In this work, the incompressibility constraint is dealt with by the introduction of stream functions. A consequence of this formulation is the appearence of differential terms of order 4 in the equations. The use of C 1 functions is then required to apply the conforming Galerkin finite element method. We have used the the so-called reduced Clough-Tocher(CT) finite element method on general triangulations. The method has been validated on simple problems and then extented to problems relevant for the study of fusion plasmas. First, plasma equilibrium described by the Grad-Shafranov equation, has been investigated. Then we have studied incompressible models in a pure streamfunction formulation. First, we introduced a discretization of the incompressible Navier-Stokes equations which constitute a sub-model of the incompressible MHD equations. We have shown the stability in energy of the method and demontrated its performance on some standard test cases. We have then extended this numerical scheme to the incompressible MHD equations. We have also proved the stability in energy of the numerical approach and applied the numerical scheme to the simulation of the well known "tilt instability". In view of the results obtained, the CT method appears to be suitable for the simulation of plasma instabilities described by MHD models. Due to its capability to represent complex geometry, it compares favorably to other numerical methods in term of accuracy, CPU time, memory cost and versatility. jfavorably to other numerical methods in term of accuracy, CPU time, memory cost and versatility
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.
Pełny tekst źródłaA 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
Gracias, William Agnelo. "The numerical study of filament dynamics in tokamak scrape-off layer plasmas". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0731.
Pełny tekst źródłaFilamentary transport has been experimentally observed in a multitude of magnetically confined fusion devices, especially of the tokamak type. Filaments are carriers of large quantities of particles and heat and as such, their presence in the SOL has implications for the target surface design in future fusion reactors. To better understand their nature, this doctoral thesis studies filaments through computer simulations as isolated structures and spontaneously forming structures, using a 3D fluid model called the TOKAM3X. Parametric studies using the model for studying the effect of the plasma's parallel resistivity and magnetic shear, and also the filament's parallel extension and size/density amplitude are performed and analysed. The studies reveal the strong impact of the parallel resistivity on filament velocities and hence their lifetimes in the SOL. The doctoral work also looked at the impact of strong local magnetic shear and the separatrix on the motion and generation of filaments. The results from the simulations performed reveal that strong shear mechanisms may be key to the destruction and formation of filaments. Further, a comparison of spontaneously forming and seeded filaments shows that seeded filaments do not behave completely the same way as spontaneously forming ones. But their mean velocity characteristics are still retained to a good degree
Sepetys, Arvydas. "Tungsten sources in the divertor and the main chamber and contamination of the WEST tokamak plasmas". Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0506.
Pełny tekst źródłaUnderstanding the mechanisms responsible for the contamination of magnetically confined plasmas by impurities is necessary to achieve sustainable and controlled operation of tokamaks. To prepare ITER operation with its tungsten divertor, it is necessary to monitor tungsten sources in present tokamaks and to characterize how eroded tungsten atoms get transported across the scrape off layer into the confined plasma. One of the questions is to identify the location of the sources driving the contamination.In this work, spectroscopic measurements in the visible and VUV spectral ranges were performed to characterize impurities, and particularly tungsten, in WEST plasmas. Their consistency with other available experimental data from various diagnostics (probes, thermocouples) was studied. We make use of spectral line intensities, but also present a modelling study of the line shape change of neutral tungsten lines at different plasma conditions.In order to better understand the W contamination pathways, WEST plasmas were modelled using the ERO2.0 code. First, as an input to ERO2.0, the Soledge2D-EIRENE code generated background plasmas including a generic light impurity, where radial transport is adjusted so that the plasma background is consistent with available diagnostics. In a second step, ERO2.0 uses the Soledge2D-EIRENE results as an input to generate the poloidal ion distributions of eroded tungsten and investigate how different source areas influence the poloidal tungsten density field. The contamination probability of the sources due to various wall elements was also evaluated. The role of the divertor and the antenna protection limiters are discussed in more detail
Breton, Sarah. "Tungsten transport in a tokamak : a first-principle based integrated modeling approach". Electronic Thesis or Diss., Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0007.
Pełny tekst źródłaMagnetic confinement fusion is currently the most advanced way to produce energy thanks to Deuterium/Tritium reaction. One of the challenges is the limitation of the reaction contamination because of Tungsten (W), a material capable of resisting high heat fluxes. W large atomic number causes W to radiate inside tokamak plasmas. If W accumulates in the central part, it cools down the plasma. It is therefore crucial to understand the mechanisms of W transport and identify the actuators of the accumulation process. W transport is involved in complex interplays with the plasma parameters (density, temperature, rotation). Therefore the use of integrated modeling is mandatory in order to evolve self-consistently all those parameters for several confinement times. For the first time, an integrated modeling tool is coupled to first-principle transport codes to self-consistently simulate the time evolution of the W behavior, as well as the evolution of density, temperature, rotation profiles, radiation and external heating. For numerical reasons, several phenomena are not modeled, and the physics of the interaction with the inner wall is simplified. At each time step, this simulation successfully reproduces experimental profiles and the W central accumulation. Moreover, actuators of the central W accumulation (rotation and central particle fueling) were identified. Finally, integrated modeling simulation allowed bringing out a very interesting non-linear mechanism: the stabilizing effect of W on turbulence. This work demonstrates that first-principles integrated modeling now allows to design and optimize in advance plasma scenarios with limited W central accumulation
Lo-Cascio, Guillaume. "Barrières et transport des impuretés dans les plasmas de Tokamak". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0280.
Pełny tekst źródłaNuclear fusion is the process that powers stars and consists in fusing light nuclei, typically hydrogen isotopes, into a heavier nucleus such as helium. The mass deficit obtained through this type of reaction yields significant amount of energy without emitting greenhouse gases. Fusion through gravitational confinement is impossible to do on Earth. Another way of confining fusion plasma, which are at several millions Kelvin, is required if we want to exploit this source of energy. Nowadays, the most widely studied way of achieving fusion is by magnetically confining the plasma. Since charged particles follow a circular trajectory around magnetic field lines. It is therefore possible to build a reactor, usually toroidal in shape, to confine a plasma that is less dense than in the cores of stars, but at temperatures 10 times higher. A magnetic field along the main axis of the toroid is generated by transverse (i.e. poloidal) coils that inject a current along the same toroidal axis. This generates a transverse magnetic field which, when combined with the first field, creates a total helical field based on interlocking toroidal surfaces. The particles evolving in these closed surfaces are then said to be confined. However, plasma confinement in a tokamak is not perfect; Coulomb collisions allow ions to drift towards the walls by crossing the last closed flux surface of the tokamak (i.e. the separator). This transport phenomenon is known as "neoclassical" transport. However, the transport coefficients calculated using neoclassical theory are 2 to 3 orders of magnitude lower than the experimental values. The transport observed in tokamaks is mainly due to instabilities developing in turbulence by drawing on the free energy stored in the temperature gradients, thus greatly increasing the transport of heat and particles towards the walls of the tokamak. Nonetheless, this transport can be limited by a state transition that takes place by injecting energy into the tokamak via fast neutrals. A very significant reduction in transport and a stiffening of the pressure profiles at the edge is then observed; a "transport barrier" has been set up. This L-H (i.e. "Low - High") transition is experimentally reproducible in many tokamaks and is the standard operating mode envisaged for ITER. However, even in H mode, large flows of particles and heat can reach the wall and pulverise it. Impurities (i.e. species not involved in the fusion reaction) can then contaminate the plasma core and dilute or even extinguish it. This is particularly the case with tungsten, which is not completely ionised under core plasma conditions and therefore re-emits much of the energy it absorbs in the form of radiation. In this thesis, we used GYSELA, a 5D gyrokinetic massively parallelized code developed by CEA Cadarache, the various mechanisms that generate transport barriers. To this end, a sheared poloidal momentum source was used to reduce turbulent intensity locally. The resulting quench of turbulent structures size led to an equivalent reduction in heat flux and associated diffusivity coefficient. Those elements led us to conclude that a transport barrier was successfully triggered in our simulations. Finally, simulations with impurities (He, Ar, W) with and without a transport barrier showed that the transport barrier successfully prevented heavy impurities from outside the barrier to penetrate and contaminate the core plasma. Thermal screening effect is mainly responsible for the resulting confinement enhancement we observed
Jesko, Karol. "Studying divertor relevant plasmas in linear devices : experiments and transport code modelling". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0010.
Pełny tekst źródłaPredictions for the operation of tokamak divertors typically rely on edge transport codes, consisting of a fluid plasma code in combination with a Monte Carlo code for neutral species. The linear devices Magnum-PSI and Pilot-PSI at DIFFER, operating with a cascaded arc plasma source that produces plasmas comparable to those expected in the ITER divertor ($T_e \sim 1 $ eV, $n_e \sim 10^{20}$m$^{-3}$). In this thesis, plasma discharges have been studied both experimentally and by modelling using the Soledge2D-Eirene code in order to a) investigate which phenomena need to be included in the modeling to reproduce experimental trends and b) provide new insights to the interpretation of experiments. Experimentally, the effect of neutral pressure $P_n$ was investigated using Thomson scattering, a Langmuir probe, visible spectroscopy and calorimetry. We have shown that a plasma beam can be effectively terminated by a blanket of neutral gas. Next, from comparisons of experiments and simulations, we have found that it is critical to include elastic collisions between the plasma and molecules if experiments are to be reproduced. Furthermore, the near-target $T_e$ is systematically overestimated by the code, underestimating the recombination rate thereby. Lastly, we have experimentally shown the importance of the inclusion of surface recombination to the surface energy flux in low temperature plasmas, an effect that is generally known but difficult to measure in fusion devices. The work presented in this thesis contributes to the understanding of plasma-neutral interactions especially in new generation, closed divertor concepts (i.e. MAST-upgrade, DIII-D)
Grosjean, Alex. "Impact of geometry and shaping of the plasma facing components on hot spot generation in tokamak devices". Electronic Thesis or Diss., Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0556.
Pełny tekst źródłaThis PhD falls within ITER project support, aiming to study the thermal behavior of ITER-like PFC prototypes in two superconducting tokamaks: EAST (Hefei) and WEST (Cadarache). These prototypes correspond to castellated tungsten monoblocks placed along a cooling tube with small gaps (0.5 mm) between them, called plasma-facing units, to extract the heat from the components. The introduction of gaps between monoblocks (toroidal) and plasma-facing units (poloidal), to relieve the thermomechanical stresses in the divertor, implies that poloidal leading edges may be exposed to near-normal incidence angle. A local overheating is expected in a thin lateral band at the top of each monoblocks, which can be enhanced when the neighboring components are misaligned. In this work, we propose to study the impact of two geometries (sharp and chamfered LEs) of these components, as well as their misalignments on local hot spot generation, by means of embedded diagnostics (TC/FBG), and a submillimeter infrared system (~0.1 mm/pixel), whose emissivity varies with wavelength, and the temperature, but above all, the surface state of the component, which evolves under plasma exposure, during the experimental campaigns. The divertor Langmuir probes measure the plasma temperature, and thus estimate the ion Larmor radius that may play a role in the local heat flux distribution around poloidal and toroidal edges. The results presented in this thesis, confirming the modelling predictions by experimental measurements, support the final decision by ITER to include 0.5 mm toroidal beveling of monoblocks on the vertical divertor targets to protect poloidal leading edges from excessive heat flux
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.
Pełny tekst źródłaThe 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
Fil, Nicolas. "Caractérisation et modélisation des propriétés d’émission électronique sous champ magnétique pour des systèmes RF hautes puissances sujets à l’effet multipactor". Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0025/document.
Pełny tekst źródłaSpace communication payload as well as magnetic confinement fusion devices, among other applications, are affected by multipactor effect. This undesirable phenomenon can appear inside high frequency (HF) components under vacuum and lead to increase the electron density in the vacuum within the system. Multipactor effect can thus disturb the wave signal and trigger local temperature increases or breakdowns. This PhD research aims to improve our understanding and the prediction of the multipactor effect. The multipactor phenomenon is a resonant process which can appear above a certain RF power threshold. To determine this power threshold, experimental tests or/and simulations are commonly used. We have made a study to evaluate the multipactor power threshold sensitivity to the TEEY. Two particular critical parameters have been found: first cross-over energy and the energies between the first cross-over and the maximum energies. In some situations, the HF components are submitted to DC magnetic fields which might affect the electron emission properties and hence the multipactor power threshold. Current multipactor simulation codes don’t take into account the effect of the magnetic field on the TEEY. A new experimental setup specially designed to investigate this effect was developed during this work. Our new experimental setup and the associated TEEY measurement technique were analysed and optimized thanks to measurements and SPIS simulations. We used the setup to study the influence of magnetic field perpendicular to the sample surface on the TEEY of copper. We have demonstrated that the magnetic field affects the copper TEEY, and hence multipactor power threshold
Vauzour, Benjamin. "Étude expérimentale du transport d'électrons rapides dans le cadre de l'allumage rapide pour la fusion inertielle". Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14496/document.
Pełny tekst źródłaThe framework of this PhD thesis is the validation of the fast ignition scheme for the nuclear fusion by inertial confinement. It consists in the experimental study of the various processes involved in fast electron beams propagation, produced by intense laser pulses (10^{19} W.cm-2), through dense matter either solid or compressed. In this work we present the results of three experiments carried out on different laser facilities in order to generate fast electron beams in various conditions and study their propagation in different states of matter, from the cold solid to the warm and dense plasma.The first experiment was performed with a high intensity contrast on the UHI100 laser facility (CEA Saclay). The study of fast electron energy deposition inside thin aluminium targets highlights a strong target heating at shallow depths, where the collectivs effects are predominant, thus producing a steep temperature profile between front (300eV) and rear (20eV) sides over 20µm thickness. A numerical simulation of the experiment shows that this temperature gradient induces the formation of a shock wave, breaking through the rear side of the target and thus leading to increase the thermal emission. The experimental chronometry of the shock breakthrough allowed validating the model of the collective transport of electrons.Two other experiments were dedicated to the study of fast electron beam propagation inside compressed targets. In the first experiment on the LULI2000 laser facility, the plane compression geometry allowed to precisely dissociate the energy losses due to resistive effects from those due to the collisional ones. By comparing our experimental results with simulations, we observed a significative increase of the fast electron beam energy losses with the compression and the target heating to temperatures close to the Fermi temperature. The second experiment, performed in a cylindrical geometry, demonstrated a fast electron beam guiding phenomenon due to self-generated magnetic fields in presence of sharp radial resistivity gradients. Furthermore, in the temperature and density conditions achieved here, the increase of collisional energy losses with density is compensated by the decreasing resistive energy losses due to the transition of the conductivity into the high-temperatures Spitzer regime
Mao, Rui. "Simulation de l’extraction de puissance dans un tokamak à configuration divertor alternative avec le code SOLEDG2D". Electronic Thesis or Diss., Ecole centrale de Marseille, 2019. http://www.theses.fr/2019ECDM0011.
Pełny tekst źródłaPower exhaust is one of the critical issue toward the elaboration of a magnetic confinement fusion reactor. Magnetic confinement is responsible for an extremely localized plasma bombardment on plasma facing components, requiring strong volume dissipation in a dedicated plasma volume called divertor. ITER exhaust strategy relies on a standard closed divertor geometry designed from smaller scale experiments and plasma simulations. Until conclusions from ITER results, current experimental trends however suggest that such divertor concept has to be improved for dealing with power exhaust constraints imposed by a larger reactor like DEMO. This PhD project aimed at studying the potential benefit of divertor configurations alternative to the one of ITER, as targeted in the new Chinese tokamak HL-2M. A particular interest was devoted to so-called snowflake configurations, consisting in two neighbor X-points on the divertor magnetic field. For the first time, these geometries have been fully simulated with the SOLEDGE2D-EREINE code, consisting in a fluid solver for the plasma particle, momentum and energy conservation, coupled to a Monte Carlo solver for neutral dynamics. In a staged approach, SOLEDG2D simulations were first applied to the more conventional divertor geometry of the WEST tokamak, aiming for a direct comparison with experimental results. A set of synthetic diagnostics have been developed from SOLEDGE simulations to mimic a broad set of experimental diagnostics. Density ramps were simulated, featuring divertor detachment in qualitative agreement with experimental observations. Then, snowflake geometries of HL2M were addressed. First, magnetic geometries were constructed with a magnetic equilibrium solver, optimizing current distribution in poloidal field coils. Mesh were generated on these magnetic maps for the SOLEDGE plasma solver. To tackle the large number of mesh elements required by the snowflake geometry, a coarse-graining convergence technique was developed, providing a speed up of the convergence time of SOLEDGE simulations by a factor of about 10. Three configurations have been generated: standard single null (SN), snowflake plus (SF+), snowflake minus (SF-). Detachment of the outer target is studied in these configurations during plasma density ramps, at constant input power and constant radial transport coefficients. Some typical characteristics of detachment, like threshold, depth and upstream window of detachment are investigated. In the three geometries, detachment onset and evolution with upstream plasma density is characterized by the gradual displacement of a radiation front from the outer target to the main X-point, as observed in experiments. It is found that, whatever the detachment in terms of particle, momentum or power dissipation, the detachment threshold is dominated primarily by the geometrical structure of divertor plate and it does not exhibit dependence on the magnetic configuration of the diverted plasma volume. In particular, the parallel connection length in the divertor is not found to affect the detachment threshold, in contrast with expectations from the 2-point model, but in agreement with experimental findings. These simulation results are a first step necessary toward the ambitious objective of predicting the benefit of alternative configuration for DEMO size conditions. It rather evidences the necessity of addressing this complex issue with a global approach coupling experimental tests, reduced model development and simulations results from complex numerical tools
Yang, Xin. "Study of the hydrogen-tungsten interaction for fusion : measurement of the atomic reflection coefficient by laser spectroscopy". Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0232.
Pełny tekst źródłaPlasma surface interaction (PSI) is considered to be one of the key scientific challenges in nuclear fusion. The interaction between hydrogen isotopes and plasma-facing materials such as tungsten is of particular importance. The atomic hydrogen isotope surface loss coefficient (γ) is a key point in PSI studies. It can give information on hydrogen isotope inventory and is an important input for modeling and theoretical work. The aim of this project is to determine atomic hydrogen and deuterium surface loss coefficients on tungsten (W) sample by using two-photon-absorption laser induced fluorescence (TALIF) and pulsed induced fluorescence (PIF) technique. This project is carried out in CAMITER reactor which is a low-pressure radio-frequency ICP reactor at PIIM laboratory in Aix-Marseille University
Baudoin, Camille. "Numerical evaluations of mechanisms governing the heat transport in the edge plasma of tokamaks". Electronic Thesis or Diss., Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0053.
Pełny tekst źródłaFusion devices are a promising solution for a new source of energy. However, using fusion reaction to produce power within a magnetic confinement is a scientific and technological challenge as it requires a high confinement in the core plasma at the same time as a good control of plasma exhaust on the material walls. This work is motivated by the key problematic of power handling in fusion power plants necessary to avoid damaging the expensive plasma facing components (PFC). The understanding of the physics underlying the heat transport, and more specifically is a critical task for the engineering design of future Tokamak devices. In this context, it is mandatory to make reliable predictions of the power spreading in order to correctly size the future Tokamaks. This calls for a theoretical ground describing the way energy escapes the core plasma through the separatrix and deposits on the PFCs. Some theoretical and experimental studies attempt to achieve such a task, however no definitive conclusion have been drawn yet. To achieve this goal, numerical modelling is a necessary complement to experimental results. This PhD work has been dedicated to the study of the different aspects of the heat transport in the edge plasma using a numerical fluid approach. Special focus was devoted to two types of mechanisms suspected to play an important role in the heat transport: intermittent turbulence; the large-scale convective transport
Lu, LingFeng. "Modelling of plasma-antenna coupling and non-linear radio frequency wave-plasma-wall interactions in the magnetized plasma device under ion cyclotron range of frequencies". Electronic Thesis or Diss., Université de Lorraine, 2016. http://docnum.univ-lorraine.fr/public/DDOC_T_2016_0173_LU.pdf.
Pełny tekst źródłaIon Cyclotron Resonant Heating (ICRH) by waves in 30-80MHz range is currently used in magnetic fusion plasmas. Excited by phased arrays of current straps at the plasma periphery, these waves exist under two polarizations. The Fast Wave tunnels through the tenuous plasma edge and propagates to its center where it is absorbed. The parasitically emitted Slow Wave only exists close to the launchers. How much power can be coupled to the center with 1A current on the straps? How do the emitted radiofrequency (RF) near and far fields interact parasitically with the edge plasma via RF sheath rectification at plasma-wall interfaces? To address these two issues simultaneously, in realistic geometry over the size of ICRH antennas, this thesis upgraded and tested the Self-consistent Sheaths and Waves for ICH (SSWICH) code. SSWICH couples self-consistently RF wave propagation and Direct Current (DC) plasma biasing via non-linear RF and DC sheath boundary conditions (SBCs) at plasma/wall interfaces. Its upgrade is full wave and was implemented in two dimensions (toroidal/radial). New SBCs coupling the two polarizations were derived and implemented along shaped walls tilted with respect to the confinement magnetic field. Using this new tool in the absence of SBCs, we studied the impact of a density decaying continuously inside the antenna box and across the Lower Hybrid (LH) resonance. Up to the memory limits of our workstation, the RF fields below the LH resonance changed with the grid size. However the coupled power spectrum hardly evolved and was only weakly affected by the density inside the box. In presence of SBCs, SSWICH-FW simulations have identified the role of the fast wave on RF sheath excitation and reproduced some key experimental observations. SSWICH-FW was finally adapted to conduct the first electromagnetic and RF-sheath 2D simulations of the cylindrical magnetized plasma device ALINE
Auphan, Thomas. "Analyse de modèles pour ITER ; Traitement des conditions aux limites de systèmes modélisant le plasma de bord dans un tokamak". Phd thesis, Aix-Marseille Université, 2014. http://tel.archives-ouvertes.fr/tel-00977893.
Pełny tekst źródłaArtola, Such Francisco Javier. "Free-boundary simulations of MHD plasma instabilities in tokamaks". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0441/document.
Pełny tekst źródłaOne of the most promising concepts for future fusion reactors is the tokamak. In these devices, a hot ionized plasma is confined with the use of large magnetic fields. The subject of this thesis is the study of a particular type of tokamak instabilities with MagnetoHydroDynamic (MHD) simulations. The code JOREK-STARWALL is adapted and applied to the simulation of the so-called free-boundary instabilities. The investigation of this type of instabilities requires a special treatment for the plasma boundary conditions, where the interaction of the plasma with the vacuum and the surrounding conducting structures needs to be taken into account. In this work, the modelling of the electromagnetic plasma-wall-vacuum interaction is reviewed and generalized for the so-called halo currents. The adapted JOREK-STARWALL code is applied in order to study the physics of two particular free-boundary instabilities: Edge Localized Modes (ELMs) triggered by vertical position oscillations and Vertical Displacement Events (VDEs). Two major results are obtained: 1. The triggering of ELMs during vertical position oscillations is for the first time reproduced with self-consistent simulations. These allow for the investigation of the physical mechanism underlying this phenomenon. The simulations reveal that for the international ITER project, a large-scale tokamak, these triggered ELMs are mainly due to an increase in the plasma edge current due to the vertical plasma motion. 2. For VDEs, several benchmarks are performed with other existing MHD codes showing a good agreement and therefore allowing the performance of ITER simulations to estimate the expected amount of halo currents in ITER
Jardin, Axel. "Utilisation du rayonnement X-mou pour l'étude du transport des impuretés dans les plasmas de tokamaks". Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0482.
Pełny tekst źródłaGlobal energy consumption has increased significantly during the last century and will continue to grow in the coming decades. The development of sustainable energies alternative to fossil fuels is a crucial issue for the future generations. In this context, controlled thermonuclear fusion is a good candidate for the energy transition. Magnetic confinement fusion and tokamaks are currently the most promising solution to control the fusion reaction and use it for civil purposes.In tokamak plasmas, heavy impurities such as tungsten sputtered from plasma-facing components can migrate to the core plasma and strongly degrade fusion performance by radiation. The goal of this PhD thesis is to use this radiation in the soft X-ray range in order to obtain valuable information on tungsten transport in the core plasma. The final perspective is to control the impurity concentration and identify actuators that can act on this distribution
Morales, Mena Jorge. "Confined magnetohydrodynamics applied to magnetic fusion plasmas". Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00995867.
Pełny tekst źródła