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Autricque, Adrien. "Dust transport in tokamaks". Electronic Thesis or Diss., Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0315.
Pełny tekst źródłaThermonuclear fusion could play an important role amongst the numerous alternative energy sources, especially though the tokamak configuration. It could be a prime candidate for the energy transition, owing to its significant advantages (fuel abundance, low amount of wastes generated, low risks of accidents). However, a certain amount of technological and physical challenges require solving before any fusion power plant can be built. Dust production is one of the major difficulties encountered in tokamaks. These small particles, made out of wall material, are created by erosion of the plasma-facing components by the plasma, where the fusion reactions occur. Dust particles can be transported in the plasma, thereby unleashing large amounts of impurities, which in turn reduces the plasma performances (by raising radiative losses and generating instabilities) and can even jeopardize plasma-facing components. Aiming to understand dust transport, injection experiments are performed on the Korean tokamak \KSTAR. Trajectories are recorded on film via fast cameras and are extracted by image processing routines. A numerical tool implementing the latest models for dust-plasma interactions is developed, and comparisons with experimental data is made, confirming the overall tendency of these models to underestimate the trajectory lengths. Leads of improvements are presented. Concerning dust sources and sinks, the focus is made on dust adhesion and resuspension of dust on the machine walls
Duthoit, François-Xavier. "Physique néoclassique pour la génération de courant dans les plasmas de tokamaks". Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00708795.
Pełny tekst źródłaAutricque, Adrien. "Dust transport in tokamaks". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0315/document.
Pełny tekst źródłaThermonuclear fusion could play an important role amongst the numerous alternative energy sources, especially though the tokamak configuration. It could be a prime candidate for the energy transition, owing to its significant advantages (fuel abundance, low amount of wastes generated, low risks of accidents). However, a certain amount of technological and physical challenges require solving before any fusion power plant can be built. Dust production is one of the major difficulties encountered in tokamaks. These small particles, made out of wall material, are created by erosion of the plasma-facing components by the plasma, where the fusion reactions occur. Dust particles can be transported in the plasma, thereby unleashing large amounts of impurities, which in turn reduces the plasma performances (by raising radiative losses and generating instabilities) and can even jeopardize plasma-facing components. Aiming to understand dust transport, injection experiments are performed on the Korean tokamak \KSTAR. Trajectories are recorded on film via fast cameras and are extracted by image processing routines. A numerical tool implementing the latest models for dust-plasma interactions is developed, and comparisons with experimental data is made, confirming the overall tendency of these models to underestimate the trajectory lengths. Leads of improvements are presented. Concerning dust sources and sinks, the focus is made on dust adhesion and resuspension of dust on the machine walls
Pilipenko, Denis. "Influence of ion cyclotron resonance heating on tranport of seeded impurities in the tokamak plasmas". Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210947.
Pełny tekst źródłaPlasma heating by radio-frequency (RF) waves has been proven to be a useful tool to control the behaviour of puffed impurities. In order to asses the prospective of impurity control by RF waves in larger devices and under reactor conditions, proper modelling approaches have been developed. One of the important parameters, which should be evaluated, is the averaged energy or temperature of heated impurity ions. The latter determines, in particular, the power transported to the main species, and, thus, the heating efficiency. Besides, the temperature of impurity ions characterizes the intensity of particle losses for heated impurities. An approach to compute the impurity temperature under such conditions is elaborated. It is based on the construction of a hierarchy of approximate solutions to the impurity heat balance equation and takes into account that the density and, thus, the heat conductivity of heated ion species can change by many orders of magnitude with the position in the plasma. The developed method has been incorporated into 1D transport code RITM. Coupled with the full wave code TORIC, the particle and heat balances for impurity and main plasma species provide a self-consistent approach to model the ion cyclotron resonance heating (ICRH) scenario. The modelling of various heating scenarios for several tokamaks displays the impacts of impurity heating on the heat and particles transport and heating efficiency. To investigate the possibility of impurity control at the large tokamak the experiment on selective impurity heating in the mode conversion H/D plasma was prepared and carried out in the tokamak JET.
Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished
Sourd, Frédéric. "Etudes des électrons découplés accélérés lors des disruptions majeures dans les tokamaks". Aix-Marseille 1, 2004. http://www.theses.fr/2004AIX11049.
Pełny tekst źródłaThe aim of this thesis is a better comprehension of the runaway electrons creation and to qualify a disruption mitigation method. In first part, we use Tore Supra disruptions to simulate the runaway electrons creation. We calculate the electric field in plasma to work out the electrons number with Dreicer and “hot tail” model. The second part of this thesis consists to determinate the electron distribution function. We simulate interaction of these electrons with a wall element. Finally we create a high-pressure gas jet to injected helium in less 5ms to mitigate disruption. The opening command is based on disruption detection method. This should be useful to qualify the principle of this technique what is allowed to ITER
Azeroual, Abderrhaman (19. "Pompage des particules dans les tokamaks au moyen d'une structure à évents : le Divertor Ergodique de Tore Supra". Aix-Marseille 1, 2000. http://www.theses.fr/2000AIX11016.
Pełny tekst źródłaYang, Chang. "Analyse et mise en oeuvre des schémas numériques pour la physique des plasmas ionosphériques et de tokamaks". Thesis, Lille 1, 2011. http://www.theses.fr/2011LIL10183/document.
Pełny tekst źródłaThis thesis focuses on modeling and numerical simulation of ionospheric and Tokamak plasmas.The first part of this work concerns the modeling and simulation of ionospheric perturbations effects for earth-satellite communications. The starting point of this part is an asymptotic analysis of Euler-Maxwell model leading to Dynamo model, which results into a 3D coupling problem between an elliptic equation for the electric potential and a mass conservation equation for the plasma density. Because of the strong anisotropy of the diffusion matrix associated with the elliptic equation, we developed an asymptotic preserving numerical scheme thus allowing the well conditioned linear system. The simulation of the mass conservation equation is made by using high order conservation laws scheme. The validation of this model Dynamo is obtained by a comparison with the 2D Striation model. In the second part, we are interested in tokamak plasma. We extract from TOKAM3D model, a 2D nonlinear energy balance equation containing all the numerical difficulties. Standard numerical methods are very CPU consuming, thus we develop an implicit-explicit scheme shown efficient and stable for this type of problem. Finally, this scheme is combined with dimensional splitting method for the discretization and numerical experiments are then presented
Balbin, Arias Julio José. "Investigation of the dependency of separatrix density of tokamaks as a function of engineering parameters". Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0174.
Pełny tekst źródłaThe analysis of JET H-mode discharges considered for this work is detailed. A first analysis of the dataset shows that some engineering parameters cannot be considered as independent for our analysis because many discharges were performed considering the same typical values of these parameters, such as the toroidal magnetic field and the plasma current. Thus, two main engineering parameters are first identified and will be used for the scaling law on the ratio of the separatrix density to the top pedestal one, namely the plasma current IP and the total injected power PTOTAL. This first scaling law seems to predict the experimental data quite well for low and medium values of the separatrix density, while at high density a strong discrepancy appears. In order to get further insight on such behavior the discharges were analyzed in terms of divertor magnetic configuration. A clear difference is observed between experiments with a corner-corner divertor magnetic configuration compared to the horizontal-vertical ones or vertical-vertical ones. This result suggests the introduction a parameter taking into account the quality of confinement. In this way, a better agreement between predictions and experimental results is obtained for both low and high-density values. Finally, the same type of study is performed on TCV and a scaling law taking into account both devices is derived
Doré, Patrice. "Développement d'une technique de mesure d'érosion et de redéposition par interférométrie de speckle dans un tokamak". Aix-Marseille 1, 2006. http://www.theses.fr/2006AIX11029.
Pełny tekst źródłaSelig, Gaël. "Équilibre évolutif à frontière libre et diffusion résistive dans un plasma de tokamak". Nice, 2012. http://www.theses.fr/2012NICE4075.
Pełny tekst źródłaIn a Tokamak, in order to create the necessary conditions for nuclear fusion to occur, a plasma is maintained by applying magnetic fields. Under the hypothesis of an axial symmetry of the tokamak, the study of the magnetic configuration at equilibrium is done in two dimensions, and is deduced from the poloidal flux function ψ. This function is solution of a non linear partial differential equation system, known as equilibrium problem. This thesis presents the time dependent free boundary equilibrium problem, where the circuit equations in the tokamak’s coils and passive conductors are solved together with the Grad-Shafranov equation to produce a dynamic simulation of the plasma. In this framework, the Finite Element equilibrium code CEDRES++ has been improved in order to solve the aforementioned dynamic problem. Consistency tests and comparisons with the DINA-CH code on an ITER’s vertical instability case have validated the results. Then, the resistive diffusion of the plasma’s current density has been simulated using a coupling between CEDRES++ and the averaged one-dimensional diffusion equation, and it has been successfully compared with the integrated modeling code CRONOS
Seigneur, Aude. "Modélisation du dépôt de puissance dans un tokamak : application aux configurations limiteurs et divertor ergodique dans Tore Supra". Aix-Marseille 1, 1993. http://www.theses.fr/1993AIX11004.
Pełny tekst źródłaGupta, Abhinav. "Losses of heat and particles in the presence of strong magnetic field perturbations". Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210343.
Pełny tekst źródłaUnstable modes such as ideal ballooning-peeling, tearing etc. break closed magnetic surfaces and destroy the axisymmetry of the magnetic configuration in a tokamak, providing deviation of magnetic field lines from unperturbed magnetic surfaces. Radial gradients of plasma parameters have nonzero projections along such lines and drive parallel particle and heat flows which contribute to the radial transport. Such transport can significantly affect confinement as this takes place by the development of neoclassical tearing modes (NTMs) in the core and edge localised modes (ELMs) at the plasma periphery.
In this thesis, transport of heat through non-overlapped magnetic island chains is first investigated using the 'Optimal path' approach, which is based on the principal of minimum entropy production. This model shows how the effective heat conduction through islands increases with parallel heat conduction and with the perturbation level. A more standard analytical approach for the limit cases of "small" and "large" islands is also presented. Transport of heat through internally heated magnetic islands is next investigated by further development of the 'Optimal path' method. In addition the approach by R. Fitzpatrick, has been extended for this investigation. By application of these approaches to experimental observations made at TEXTOR tokamak, heat flux limit, limiting parallel heat conduction in low collisional plasmas, is elucidated.
Models to study transport of heat and particles due to ELMs have also been developed. Energy losses during ELMs have been estimated considering contribution from parallel conduction due to electrons and parallel convection of ions, with constant level of the magnetic field perturbation, steady profiles for density and temperature, and by accounting for the heat flux limit. The estimate shows good agreement with experimental observations. The model is developed further by accounting for the time evolution of the perturbation level due to ballooning mode, and of density and temperature profiles.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Brégeon, Rémi. "Evolution résistive du profil de courant dans les tokamaks, application à l'optimisation des décharges de tore supra". Aix-Marseille 1, 1998. http://www.theses.fr/1998AIX11045.
Pełny tekst źródłaBaudoin, Camille. "Numerical evaluations of mechanisms governing the heat transport in the edge plasma of tokamaks". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0053/document.
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
Emeriau-Viard, Constance. "Turbulence plasma dans les étoiles et les tokamaks : magnétisme, auto-organisation et transport". Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC033/document.
Pełny tekst źródłaIn magnetized plasmas, the interaction between the turbulence, the magnetism and shearing at large scales plays an important role in the organization of plasma and on transport processes. This interaction and its consequences can be studied in the non-linear development with high performance numerical simulations and by a precise analysis (in real space and in spectral space) of the transport processes in plasmas. In this thesis, we focus on stellar and fusion plasmas.The first part introduces the fundamental concepts of plasma physics then the specificities of each type of plasma, with the magnetohydrodynamics and stellar evolution for stellar plasmas and gyrokinetic theory for fusion plasmas. The second part focuses on stellar plasmas. Thanks to 3D numerical simulations of GK stars with the ASH code, we study the influence o the Rossby number on convection. We characterize a transition at Ro = 1 between low Rossby numbers that have a solar-like differential rotation profile or a Jupiter-like profile, and high Rossby numbers that have an anti-solar rotation profile with an equator slower than the poles. Then we choose nine models that enable us to simulate the changes in magnetic field during stellar evolution, from the disk-locking phase to the solar age. During the pre main sequence (PMS), the stellar rotation rate and internal structure change drastically with the birth and growth of the radiative core. We observe that the magnetic energy globally increases when arriving on the zero age main sequence (ZAMS). The topology of the magnetic field becomes more and more complex with a slower dipolar component and a less axisymmetric magnetic field. This field is generated by a dynamo alpha-Omega for which the Omega effect becomes more and more predominant as the star ages from 1Myr to 50Myrs, i.e. the convective zone becomes shallower. The magnetic field contained into the radiative zone possesses a mixed poloidal-toroidal topology that satisfies the stability criteria of instabilities in stably stratified zones. Once arrived on the ZAMS, the internal structure of star settles down and the rotation rate is the only stellar parameter that changes during the main sequence (MS), the star being slowed down by magnetized winds. The slowdown of the star induces a decrease of the magnetic energy contained into the convective zone. We observe a transition of the differential rotation profile since the Rossby number is closer to 1 and thus we analyze the consequences on the topology and on the spectral transfer between the components of the dynamo magnetic field. The third part of this manuscript address the spectral transfers of energy at large scales in fusion plasmas. The use of the 5D gyrokinetic numerical code GYSELA enables us to simulate these avalanches. After a characterization of these transfers, in space and velocity, we use a spectral diagnostic on entropy to have a better understanding of their origin and dynamics. A causal relation ``turbulent heat flux --> temperature gradient --> shearing'' can be emphasize. Finally, by looking at the results we obtained, we discuss on the similarities between the two types of plasmas and propose some leads for future developments
Sarazin, Yanick. "Etude de la turbulence de bord dans les plasmas de tokamaks". Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10265.
Pełny tekst źródłaStrugarek, Antoine. "Turbulence, transport et confinement : des tokamaks au magnétisme des étoiles". Phd thesis, Université Paris-Diderot - Paris VII, 2012. http://tel.archives-ouvertes.fr/tel-00765706.
Pełny tekst źródłaKogut, Dmitry. "Study of wall conditioning in tokamaks with application to ITER". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4741.
Pełny tekst źródłaThesis is devoted to studies of performance and efficiency of wall conditioning techniques in fusion reactors, such as ITER. Conditioning is necessary to control the state of the surface of plasma facing components to ensure plasma initiation and performance. Conditioning and operation of the JET tokamak with ITER-relevant material mix is extensively studied. A 2D model of glow conditioning discharges is developed and validated; it predicts reasonably uniform discharges in ITER. In the nuclear phase of ITER operation conditioning will be needed to control tritium inventory. It is shown here that isotopic exchange is an efficient mean to eliminate tritium from the walls by replacing it with deuterium. Extrapolations for tritium removal are comparable with expected retention per a nominal plasma pulse in ITER.A 1D model of hydrogen isotopic exchange in beryllium is developed and validated. It shows that fluence and temperature of the surface influence efficiency of the isotopic exchange
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
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 źródłaCottier, Pierre. "Modélisation du transport turbulent de moment angulaire dans les plasmas de tokamak - Une approche gyrocinétique quasi-linéaire". Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00939240.
Pełny tekst źródłaDvornova, Anastasiia. "Simulations hybrides fluides-cinétiques de l'excitation des modes TAE via particules rapides et une antenne externe". Electronic Thesis or Diss., Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0265.
Pełny tekst źródłaIn this thesis, the excitation of a specific types of the MHD modes called the Toroidal Alfven Eigenmodes is studied. These global modes can be easily destabilized by one of the several populations of the fast particles present in tokamaks. For the first time the modelling of the excitation of the TAE modes by a 3D external antenna is performed in case of limiter and X-point geometries. With the use of the code CASTOR it has been shown that the damping from the region inside the separatrix with plasma boundary approaching the separatrix can be a source of an increased damping for certain density profile shapes. The results obtained with the JOREK code identifies the region of the open-field lines as the main source of damping. Firther, the purely fluid code JOREK was modified to include the kinetic terms provided by the code's kinetic extension. Between the two commonly used hybrid schemes, pressure and current coupling schemes. In order to confirm the implementation of the scheme, the TAE linear growth rates are obtained for the ITPA benchmark case. A further step that was taken is to combine the previously used approaches by examining the evolution of the TAE modes excited by an external antenna now in the presence of fast particles. The principal interest in this approach is to investigate the possibility of extracting information on the fast particle drive from the plasma response on the TAE excitation. A method allowing an estimate of the fast particle drive by measuring the difference in the frequency response of the two directions of the traveling TAE waves was developed
Martin, Gilles. "Étude des produits de fusion chargés dans un tokamak". Paris 11, 1985. http://www.theses.fr/1985PA112154.
Pełny tekst źródłaMuch literature has been concerned with the planning component of robotic systems; this work has generally stressed generation of plans of action and considered the execution of these plans only as a secondary problem. This approach has practically restricted the planning problem to offline considerations or backstage intervention during the "action phase". Successfully applied in various fields, this approach has shown to have shortcomings for problems where planning and acting need to be interwoven to ensure correct behavior. This is the case in the application of decisional knowledge in the control of robotic systems. It therefore seems necessary to provide a suitable framework in which to express and use such knowledge. The subject of this thesis is the APSIS system, which is such a framework. APSIS is a production system and inference engine. Its characteristics are described and the uses explained through concrete examples. A user's manual may be found at the end of the thesis
Idouakass, Malik. "Linear and nonlinear study of the precessional fishbone instability". Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4756/document.
Pełny tekst źródłaThe wave-particle interaction in plasmas is an important research subject, for fundamental physical understanding as well as for the operation of fusion devices such as tokamaks. This interaction can cause the existence of unstable modes, such as the fishbone instability that is observed in tokamak plasmas. It results from the resonant interaction between an electro-magnetic wave living in the plasma and a population of supra-thermal particles. This mode causes the ejection of a portion of these energetic particles, and is thus detrimental to the confinment of energy in a tokamak, and it is characterized by a frequency down-chirping, i.e. a decrease of frequency of the mode during its evolution. In this thesis, a model for the fishbone instability is developed, that describes the thermal plasma with fluid equations and the supra-thermal particles with the kinetic Vlasov equation. This model is highly simplified in order to understand the basic mechanisms leading to destabilization, frequency chirping, and particle ejection. The linear theory of this model is then done, showing the conditions that lead to the existence of an instability, and that allow the characterization of its linear behavior. The linear analytic results are then compared to numerical linear results obtained with a code, based on the assumptions of the model, that was developed during this PhD and the results are found to be in good agreement. Finally, the code is used to explore the nonlinear behavior of energetic particles in the later phase of the fishbone instability. The main mechanism responsible for the frequency chirping and energetic particle ejection is identified and studied in detail
Faudot, Eric. "Modélisations de phénomènes de polarisation par gaines RF ou-et faisceau de particules dans un plasma magnétisé". Nancy 1, 2005. http://www.theses.fr/2005NAN10146.
Pełny tekst źródłaThis work investigates the problematic of hot spots induced by accelerated particle fluxes in tokamaks. It is shown that the polarization due to sheaths in the edge plasma in which an electron beam at a high level of energy is injected, can reach several hundreds volts and thus extend the deposition area. The notion of obstructed sheath is introduced and explains the acceleration of energy deposition by decreasing of the sheath potential. Then, a 2D fluid modeling of flux tubes in front of ICRF antennae allows us to calculate the rectified potentials taking into account RF polarization currents transverse to magnetic field lines. The 2D fluid code designed validates the analytical results which show that the DC rectified potential is 50% greater with polarization currents than without. Finally, the simultaneous application of an electron beam and a RF potential reveals that the potentials due to each phenomenon are additives when RF potential is much greater than beam polarization. The density depletion of polarized flux tubes in 2D PIC simulations is characterized but not yet explained
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.
Pełny tekst źródłaCottier, 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
Chouli, Billal. "Effet des particules rapides sur la rotation des plasmas de Tokamak sans injection de moment angulaire extérieur". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4084/document.
Pełny tekst źródłaToroidal flows are found to improve the performance of the magnetic confinement devices with increase of the plasma stability and confinement. In ITER or future reactors, the torque from NBI should be less important than in present-day tokamaks. Consequently, it is of interest to study other intrinsic mechanisms that can give rise to plasma rotation in order to predict the rotation profile in experiments. Intriguing observations of plasmas rotation have been made in radio frequency (RF) heated plasmas with little or no external momentum injection. Toroidal rotation in both the direction of the plasma current (co-current) and in the opposite direction (counter-current) has been observed depending on the heating schemes and plasma performance. In Tore Supra, most observations in L-mode plasmas have been in the counter-current direction. However, in this thesis, we show that in lower hybrid current drive (LHCD), the core toroidal rotation increment is in co- or counter-current direction depending on the plasma current amplitude. At low plasma current the rotation change is in the co-current direction while at high plasma current, the change is in the counter-current direction. In both low and high plasma current cases, rotation increments are found to increase linearly with the injected LH power. Several mechanisms in competition which can induce co- or counter-current rotation in Tore Supra LHCD plasmas are investigated and typical order of magnitude are discussed in this thesis
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
Peillon, Samuel. "Influence des effets électrostatiques liés à la radioactivité sur les forces d’adhésion et sur la mise en suspension de particules métalliques". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS400.
Pełny tekst źródłaThe mobility and containment of radioactive dust produced by plasma/wall interactions taking place in the heart of a tokamak have become, over the years, major topics for the safety assessment of the ITER installation. To address these safety issues, I adopted complementary approaches based on experimental and numerical work. A sampling campaign carried out in the tokamak WEST (CEA/IRFM) made it possible to identify tungsten particles of spherical shape and micrometric size. An in-depth parametric study of the adhesion forces acting between these particles and tungsten surfaces was performed using an atomic force microscope (AFM). The results of this study are in very good agreement with an analytical model describing the adhesion forces as a function of particle size and surface roughness. I continued the study by performing measurements of the electric potential of particles when they are labeled with tritium using Kelvin Probe Microscopy (KPFM). The sensitivity of this technique allowed me to demonstrate a difference in surface potential between neutral particles and particles marked with tritium. Finally, resuspension experiments with tungsten particles loaded with tritium were carried out. The results of these experiments, combined with the validation of a particle resuspension model, provide robust data for dust management, safety analyzes and the definition of radiation protection plans for future nuclear fusion facilities
Felici, Romain. "Évolution spatio-temporelle des paramètres macroscopiques d'un plasma de tokamak lors d'un chauffage cyclotronique électronique". Nancy 1, 1988. http://www.theses.fr/1988NAN10129.
Pełny tekst źródłaKrivenski, Vladimir. "Étude cinétique relativiste du chauffage et de la génération de courant cyclotroniques électroniques dans un tokamak". Nancy 1, 1988. http://www.theses.fr/1988NAN10281.
Pełny tekst źródłaMedvedeva, Anna. "Étude expérimentale de la turbulence au bord du plasma du tokamak ASDEX Upgrade par réflectométrie à balayage ultra rapide". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0240/document.
Pełny tekst źródłaPlasma confinement is limited by energy and particle transport, in which turbulence plays an important role. In this work the measurements of the turbulence characteristics carried out on the ASDEX Upgrade tokamak are presented during the transition from the Low (L) to the High (H) confinement mode which goes through an Intermediate (I) phase where turbulence and shear flows strongly interact. One of the most widely accepted theories concerning the L-H transition describes how the turbulence in the plasma edge is stabilized by radial electric field gradients: the E×B flow shear stabilizes turbulence and decreases the radial size of turbulent structures. As a consequence, a transport barrier forms in the edge where the plasma density, the temperature, and their gradients increase. The detailed physical mechanism of the formation of the transport barrier as well as the reason for the residual transport across this barrier are not yet well understood. The density dynamics is measured by an ultra-fast swept reflectometer with a time resolution as high as 1 μs. Studies of the electron density profile dynamics, the density turbulence level, radial wavenumber and frequency spectra during L-H transitions have been performed. The reflectometer measurements show that the density large scale fluctuations decrease after an L-H transition, which confirms the theoretical predictions of the turbulence reduction by sheared flows and supports previous experimental evidences. I-phases for various plasma conditions are documented and the density evolution is compared with the turbulence level. Moreover the results on high frequency coherent modes appearing at the plasma edge are presented
Lesur, Maxime. "The Berk-Breizman Model as a Paradigm for Energetic Particle-driven Alfvén Eigenmodes". Phd thesis, Ecole Polytechnique X, 2010. http://tel.archives-ouvertes.fr/tel-00563110.
Pełny tekst źródłaBourdelle, Clarisse. "Analyse de stabilité de plasmas de Tokamak". Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10101.
Pełny tekst źródłaBetar, Homam. "Kinetic Effects in Magnetic Reconnection". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0043.
Pełny tekst źródłaPlasmas are gaseous systems of ions and electrons which interact via electromagnetic fields and display collective properties. Among these, is the notion of the magnetic line "connection". This expresses the fact that, in regimes in which charged particles spiral sufficiently fast along lines of magnetic induction, the latter is linked to the bulk plasma motion and acquire a topological identity which forbids them to break, intersect and reconnect. This topological identity, however, can be locally violated thanks to a number of kinetic effects, such as particle collisions, when the currents in the plasma are sufficiently intense: one speaks of "magnetic reconnection". Magnetic reconnection is an important ingredient of the plasma self-organization and has significance for both space and laboratory plasmas since it is at the basis of natural phenomena like solar flares and polar lights, or of disruptive processes in thermonuclear fusion experiments. A long-standing problem in the study of laboratory and astrophysical plasmas is to understand the mechanisms of acceleration of electrons and ions, as a magnetic field reconnect and release energy. In this work, we studied kinetic effects on reconnection instabilities developing spontaneously in static current sheets (tearing modes) and in combination with a class of kinetic instabilities (Weibel instabilities) that are relevant both to astrophysical plasma jets and to laser-plasma interaction experiments. We performed this study using reduced-fluid and kinetic models and we investigated the competition between tearing-type modes and Weibel-type instabilities by means of both semi-lagrangian full kinetic Vlasov-Maxwell simulations and particles in cell simulations
Moradi, Sara. "Transport analysis in tokamak plasmas". Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210097.
Pełny tekst źródłaOne of the least understood areas of the impurity transport and indeed any plasma particle or heat transport in general, is the turbulent transport. Extensive efforts of the fusion plasma community are focused on the subject of turbulent transport. Motivated by the fact that impurity transport is an important issue for the whole community and it is an area which needs fundamental research, we focused our attention on the development of turbulent transport models for impurities and their examination against experiments. In a collaboration effort together with colleagues (theoreticians as well as experimentalist) from different research institutes, we tried to find, through our models, physical mechanisms responsible for experimental observations. Although our main focus in this thesis has been on the impurity transport, we also tried a fresh challenge, and started looking at the problem of drift wave turbulent transport in a different framework all together. Experimental observation of the edge turbulence in the fusion devices show that in the Scrape of Layer (SOL: the layer between last closed magnetic surface and machine walls) plasma is characterized with non-Gaussian statistics and non-Maxwellian Probability Distribution Function (PDF). It has been recognized that the nature of cross-field transport trough the SOL is dominated by turbulence with a significant ballistic or non-local component and it is not simply a diffusive process. There are studies of the SOL turbulent transport using the 2-D fluid descriptions or based on probabilistic models using the Levy statistics (fractional derivatives in space). However, these models are base on the fluid assumptions which is in contradiction with the non-Maxwellian plasmas observed. Therefore, we tried to make a more fundamental study by looking at the effect of the non-Maxwellian plasma on the turbulent transport using a gyro-kinetic formalism. We considered the application of fractional kinetics to plasma physics. This approach, classical indeed, is new in its application. Our aim was to study the effects of a non-Gaussian statistics on the characteristic of the drift waves in fusion plasmas.
Ce travail de thèse porte sur le transport turbulent d'impuretés dans les plasmas de fusion
par confinement magnétique. C'est une question de la plus haute importance pour le développement
de la fusion comme source d'énergie. En effet, une accumulation d'impuretés au coeur
du plasma impliquerait des pertes d'énergie par radiation, conduisant par refroidissement à
l'extinction des réactions de fusion. Il est par contre prévu d'injecter des impuretés dans le
bord du plasma, afin d'extraire la chaleur par rayonnement sans endommager les éléments de
la première paroi. Ces contraintes contradictoires nécessitent un contrôle précis du transport
d'impuretés, afin de minimiser la concentration d'impuretés au coeur du plasma tout en la
maximisant au bord. Une très bonne connaissance de la physique sous-jacente au transport
est donc indispensable. L'effet de la turbulence, principal mécanisme de transport, sur les impuretés
est alors une question centrale. Dans cette thèse, un code numérique, AFC-FL, a été développé sur la base d'une approche ``fluide' linéaire pour la turbulence d'ondes de dérive. Il calcule les taux de croissance qui caractérisent la rapidité de l'amorçage des instabilités. L'analyse de stabilité est complétée par l'évaluation des taux de croissance en présence d'un gradient de densité, un cisaillement magnétique ou un nombre arbitraire de différentes espèces d'impureté. Les formules complètes du flux turbulent d'impuretés pour ces taux de croissance calculés des instabilités des ondes de dérive ont été dérivées. Un modèle de transport anormal qui nous permet d'étudier la dépendence du transport en fonction de la charge d'impureté a été développé. Ce modèle prend en compte les effets collisionnels entre les ions, l'impureté et les particules principales de plasma. Une telle dépendence du transport anormal en fonction de la charge de l'impureté est observée dans les expériences et il a été montré que les résultats obtenus sont en bon accord avec les observations expérimentales. Nous avons également étudié l'effet des impuretés sur le confinement de l'énergie dans les plasmas du tokamak JET. La modélisation de transport a été exécutée pour des plasmas avec injection de néon dans la périphérie du tokamak. Cette technique est utilisée afin d'extraire la chaleur par rayonnement sans endommager la paroi et pour réduire certaines instabilités (ELM). Des simulations du code RITM ont été comparées à des mesures effectuées lors d'expériences au JET. Il a été montré que l'injection de néon mène toujours à une dégradation du confinement par rapport aux décharges sans néon. Cependant, l'augmentation de la charge effective, en raison du presence du néon peut diminuer le taux de croissance d'autres instabilité (ITG) et amèliorer le confinement du coeur du plasma. Ce confinement amélioré du coeur peut alors compenser la dégradation au bord et le confinement global du plasma peut s'améliorer.
Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished
Hornung, Grégoire. "étude de la turbulence plasma par réflectométrie à balayage ultra rapide sur le tokamak tore supra". Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-01052756.
Pełny tekst źródłaNicolas, Timothée. "Transport de particules induit par les Dents-de-Scie dans les palsmas de tokamak". Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00926428.
Pełny tekst źródłaDrouot, Thomas. "Étude de la turbulence liée aux particules piégées dans les plasmas de fusion". Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0150/document.
Pełny tekst źródłaIn tokamak plasmas, it is recognized that ion and electron micro- instabilities are held responsible for turbulence giving rise to anomalous transport. These limit particle and energy confinements in tokamak devices. This is the context of this work. The main objective is to have a better understanding of turbulence and thus of anomalous transport. It is known that the behaviour of trapped particles plays a major role in the development of turbulence via trapped ion mode (TIM) instability and trapped electron mode (TEM) instability. This work focus on the development of a model describing kinetic trapped particles (ions and electrons). The involved time scale is of the order of the trapped particle precession frequency which corresponds to characteristic frequency of TIM/TEM turbulence. The originality of this model is the reduction of the dimension from6D to 4D. This reduction is made by averaging over both the fast cyclotron motion and the bounce motion. In addition, using a set of action-angle variables allows one to deal with two parameters instead of two variables. The final model is 4D, dealing with two parameters and 2D space coordinates. The temperature and density gradients which trigger TIM and TEM instabilities are given by the linear analysis of the model. This analysis allows us to calculate the growth rates and frequencies associated with these instabilities. In order to solve the non-linear model describing both trapped kinetic ions and trapped kinetic electrons, we use the existing global code TERESA 4D including only trapped kinetic ions. The spatial and temporal scales associated to TIM and TEM turbulence are of the same order of magnitude. It allows us to include trapped electron kinetic response with very low numerical cost compared to the existing version. The TIM/TEM turbulence can be generated by this new code with low computational resources. Different typical structures observed in tokamak can be studied. This is the case of zonal flow and streamer structures which play a major role in anomalous transport. Finally, the influence of different parameters, such as banana width or electron to ion temperature ratio, is considered
Dine, Sarah. "Tungstène et alliages nanostructurès dans le système W-V-Cr pour la fusion : synthèse, densification et propriétés mécaniques". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCD036.
Pełny tekst źródłaThe aim of this thesis concerns the synthesis of nanostructured tungsten and tungsten alloys, related to the thermonuclear fusion issue, with a double perspective, one concerning the powders themselves,in order to simulate the dust that will be produced during the tokamak operation, the other concerning bulk materials, where the nanostructure could bring a significant improvement on mechanical properties (elastic limit, ductility), and also on specific properties related to this operating environment (resistance to sputtering, blistering, corrosion, ...).To do so, we synthesized tungsten and binary and ternary alloys in the W-V-Cr system using Selfpropagating High-temperature Synthesis. These powders were then sintered using Spark Plasma Sintering, in order to retrieve bulk dense samples. At each step of the process, the materials were characterized using X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, microhardness and compression tests. Our results show that we were able to obtain bulk nanostructured samples, with a relative density ranging from 97 to 100% depending on the alloy, with an elastic limit of up to 1000 MPa and a ductility of about 30%, which is a very promising results for a tungsten alloy with no rhenium
Abiteboul, Jeremie. "Transport turbulent et néoclassique de quantité de mouvement toroïdale dans les plasmas de tokamak". Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00777996.
Pełny tekst źródłaBourbon, Fabienne. "Modélisation, simulation numérique et contrôle optimal de l'évolution de la configuration du plasma pour le Tokamak NET et pour la génération future de réacteurs de fusion". Phd thesis, Grenoble 1, 1993. http://tel.archives-ouvertes.fr/tel-00343468.
Pełny tekst źródłaGoryaev, Farid. "Développement et étude d'une méthode self-consistante permettant, d'une part, de valider des données atomiques par comparaison avec des spectres émis par le plasma du Tokamak TEXTOR et, d'autre part, de faire des diagnostics précis de paramètres du plasma". Paris 11, 2003. http://www.theses.fr/2003PA112286.
Pełny tekst źródłaFor different plasma physical parameters, spectroscopic analysis methods are the most universally employed. The study of X-ray emission spectra enables one to obtain informations on the elementary atomic processes occuring in plasmas, as well as on the plasma physical parameters. The validity of spectroscopic diagnostics depends on: (1), the number of elementary processes included in the model to simulate the spectra: (2), on the accuracy and precision of atomic data computations; (3), the emitting plasma model, based on atomic kinetics equations and plasma dynamics. In general, a theoretical simulation of the emission spectra of multiply charged ions is a complex problem. One of the crucial moment is the calculation of numerous atomic data. For multiply charged ions, z > 10, there are only a few direct measurements of collisional parameters and radiative data, required for the computation and interpretation of the X-ray emission spectra. The only information sources, on binary processes, as well as on hydrodynamic processes are the observed plasma spectra on devices of EBIT type and Tokamaks. The EBIT plasma-sources are already used for measurements and verifications of numerical codes for electron-ion collision cross-sections, and for life time of excited atomic states and wavelengths. But for Tokamaks, until now, the question is still not under consideration for X-ray spectroscopic methods. This thesis is dedicated to the development and the study of a self-consistent method to validate atomic data by comparisons with emitted spectra from TEXTOR tokamak, and to give precise plasma parameter diagnostics
Fraboulet, David. "Emission cyclotronique ionique dans les plasmas de Tokamak". Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10127.
Pełny tekst źródłaBieber, Thomas. "Etude expérimentale d'une source plasma RF à configuration hélicon dans le mélange Ar/H2 : application à la gravure chimique de surfaces graphitiques dans le cadre des interactions plasma-paroi du divertor d'ITER". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0011/document.
Pełny tekst źródłaPlasma-wall interactions are one of the main issues in fusion research and must be thoroughly studied to progress in this topic. The objective of this work is to develop an atomic hydrogen source at low pressure (< Torr) in a helicon configuration reactor working in H2/Ar gas mixture. This source is then used to study the chemical etching of graphite and carbon fiber composites composing the limiter of the Tore Supra tokamak. Depending on the experimental conditions, the RF power coupling of the reactor can be in capacitive, inductive, Trivelpiece-Gould or low field helicon mode. The characterization of these modes determined that in this case the inductive one presents the greatest interest for the atomic hydrogen source. Further studies in inductive mode showed that increasing the confinement magnetic field leads to a decrease of measured relative densities of two metastable levels of argon ion and one metastable state of neutral argon. A simple model simulating neutral metastable state behavior confirmed that these levels are destroyed by electronic collisions towards upper levels. The chemical etching of graphite exposed to the atomic hydrogen source is relatively efficient (up to 3 µm/h) at 10 mTorr and drops with the pressure. A qualitative analysis of atomic hydrogen kinetics concluded that this behavior is due to the decrease of atomic hydrogen flux on the sample with increasing pressure. Finally, first observations of the etched surface underlined different structures (nanoparticles clusters and deposits). These can be compared to the ones observed in different tokamaks
Courtois, Loys. "Détermination de modes électromagnétiques de guides d'ondes corrugués surdimensionnés sur l'installation de chauffage des électrons du Tokamak Tore Supra". Grenoble INPG, 2001. http://www.theses.fr/2001INPG0013.
Pełny tekst źródłaXu, Shaokang. "Study of reduced kinetic models for plasma turbulence". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX057/document.
Pełny tekst źródłaTurbulent transport is one of the keys to improve the energy confinement time required for thermonuclear fusion reactors. The description of the kinetic turbulence of the plasma is a problem with 3 spatial coordinates and 3 velocity coordinates. Both theory and simulation of a problem of such high dimensionality are very difficult, and reduced models are helpfull to understand turbulence in Tokamaks. A widely used technique consists into averaging the cyclotron motion, which is much faster than the turbulence time scale. Such a reduction makes it possible to simplify the problem to three spatial coordinates of the particle guide centers, a parallel velocity or energy, and a perpendicular velocity appearing as the adiabatic invariant. Nonlinear gyrokinetic description requires massively parallel high performance numerical simulations. The difficulty lies in the non-linear terms (Poisson hooks) that describe multi-scale interactions, which is a challenge for both theory and simulation. Any reduced approach, based on well-controlled hypotheses, is therefore interesting to develop.On the basis of this ambition, this thesis concerns the turbulence of particles trapped in magnetized plasma. It is a 4D system, obtained after averaging the particle distribution function on cyclotron and bounce motions, which can be considered as a reduced form of standard gyrokinetic theory. We called it "bounce averaged gyrokinetics" during this work. Even if this description is greatly reduced compared to the gyrokinetic theory, nonlinear direct simulation remains a challenge.A description of the nonlinear polar coordinate terms is chosen, with a logarithmic grid along the norm of the wave vector, while the angles are discretized on a regular grid. The use of a logarithmic grid makes it possible to take into account a wide range of wave vectors, so physics on a very small scale. In a similar way to shell models for fluid turbulence, and in order to simplify the system, only the interactions between neighboring shells are considered.In a first step, the study of the linear system is presented, in particular the paraetric dependence of the instability thresholds and the linear growth rate, allowing to recover the strong anisotropy of the growth rates of the trapped ion modes (or TIM) and the modes of trapped electrons (or TEM). These studies also make it possible to validate the non-linear numerical codes with respect to an independently developer eigenvalue solver.In a second step, the isotropic hypothesis for nonlinear terms is used. Thus, there is no exact phase information for such 1D layer models, which leaves with a free parameter in the interaction coefficients. An original power law is evidenced, which is unaffected by the value of the free parameter, measuring the intensity of the nonlinear effects relative to the linear terms.From the simulation of the isotropic model, the phase information appears very important. Since the linear instability is anisotropic for the fusion, the simulation of the anisotropic model is thus carried out in a third time. The numerically resolved system is reduced to a kinetic species, assuming that the other species are adiabatic. Two different systems can thus be studied: kinetic ions + adiabatic electrons and kinetic electrons + adiabatic ions. Different spectra are observed in each of these two cases, and the validity of the adiabatic hypothesis is discussed for each species, based on a kinetic simulation with two species
Bufferand, Hugo. "Development of a fluid code for tokamak edge plasma simulation. Investigation on non-local transport". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4325/document.
Pełny tekst źródłaIn the scope of designing future nuclear fusion reactors, a clear understanding of the plasma-wall interaction is mandatory. Indeed, a predictive estimation of heat flux impacting the surface and the subsequent emission of impurities from the wall is necessary to ensure material integrity and energy confinement performances. In that perspective, the fluid code SolEdge2D has been developed to simulate plasma transport in the tokamak edge plasma. The plasma-wall interaction is modeled using an innovative penalization technique. This method enables in particular to take complex plasma facing components geometry into account. In parallel to this numerical effort, a theoretical work has been achieved to find appropriate corrections to fluid closures when collisionality drops. The study of stochastic 1D models has been realized in collaboration with physicists from the CSDC group in Florence. A generalized Fourier law taking long range spatio-temporal correlations has been found to properly account for ballistic transport in the low collisional regime. This formulation is expected to be used to model parallel heat flux or turbulent cross-field transport in tokamak plasmas
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