Дисертації з теми "Plasma physics- Alfvenic turbulence"
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Kumari, Anju. "Localized structures and alfvenic turbulence in magnetized plasmas." Thesis, IIT Delhi, 2016. http://localhost:8080/xmlui/handle/12345678/7094.
Повний текст джерелаNielson, Kevin Derek. "Analysis and gyrokinetic simulation of MHD Alfvén wave interactions." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3504.
Повний текст джерелаLeonardis, Ersilia. "Quantifying finite range plasma turbulence." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/57673/.
Повний текст джерелаKlein, Kristopher Gregory. "The kinetic plasma physics of solar wind turbulence." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/5000.
Повний текст джерелаSaucier, Antoine. "Cascade processes and fully developed turbulence." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74674.
Повний текст джерелаDewhurst, Joseph Michael. "Statistical description and modelling of fusion plasma edge turbulence." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3903/.
Повний текст джерелаWilliams, Timothy Joe. "Statistically constrained decimation of a turbulence model." W&M ScholarWorks, 1988. https://scholarworks.wm.edu/etd/1539623778.
Повний текст джерелаGullman-Strand, Johan. "Turbulence and scalar flux modelling applied to separated flows." Doctoral thesis, Stockholm : Department of Mechanics, Royal Institute of Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92.
Повний текст джерелаLiu, Li. "Hierarchical structures in fully developed turbulence." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289027.
Повний текст джерелаHighcock, Edmund. "The zero-turbulence manifold in fusion plasmas." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:7ed1774d-88a5-4764-ba06-1de00c348d26.
Повний текст джерелаWah, Darren M. "Turbulence in binary fluid flow systems: A lattice Boltzmann approach." W&M ScholarWorks, 1999. https://scholarworks.wm.edu/etd/1539623963.
Повний текст джерелаMacnab, Angus Ian Duncan. "Magnetohydrodynamic turbulence: The development of lattice Boltzmann methods for dissipative systems." W&M ScholarWorks, 2003. https://scholarworks.wm.edu/etd/1539623425.
Повний текст джерелаRea, Cristina. "3D physics, turbulence and transport in the plasma boundary of RFX-mod." Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424023.
Повний текст джерелаIl crescente aumento nella richiesta di produzione energetica è diventato un costante leitmotif che caratterizza la società in cui viviamo. L'impossibilità di riuscire a soddisfare tali richieste sfruttando opzioni già esistenti che siano economicamente vantaggiose ed al contempo rispettino l’ambiente, è ormai una consapevolezza globalmente diffusa. La International Energy Agency ha esaustivamente documentato attraverso i suoi report annuali che le riserve di gas naturale e combustibile fossile si esauriranno nel giro di qualche decade a causa della sempre più crescente richiesta di energia. Come provvedere a soddisfare le esigenze energetiche di una popolazione mondiale in continuo aumento diventerà ben presto un problema critico. E' all'interno di questo quadro globale che entra in gioco la ricerca sulla fusione come risorsa energetica. Al fine di poter dimostrare la sfruttabilità della fusione nucleare quale risorsa energetica, la comunità scientifica internazionale ha da anni continuato ad investire nella ricerca sulla fusione termonucleare controllata. Ad oggi è nelle fasi finali di costruzione il più grande esperimento che coinvolga trasversalmente ricercatori da ogni parte del mondo. L'esperimento è denominato ITER (International Thermonuclear Experimental Reactor) e rappresenterà un banco di prova per la fisica della fusione e l’ingegneria. Tra le possibili configurazioni magnetiche adottabili sperimentalmente in una macchina da fusione, quella a campo magnetico rovesciato si è rivelata essere un eccellente strumento per studiare la fisica del plasma e le innumerevoli sfide scientifiche che essa pone. Tuttavia, per svariati motivi non è previsto l'utilizzo di tale configurazione in un reattore a fusione che produca energia a fini commerciali. L'esperimento RFX-mod ospitato presso il Consorzio RFX a Padova è il reversed-field pinch (RFP) più grande al mondo. L'attività di ricerca che verrà presentata in questo lavoro di tesi è stata svolta principalmente a Padova su RFX-mod ma ha anche previsto e contemplato la partecipazione ad una campagna sperimentale sul tokamak COMPASS a Praga. L’attività di ricerca che verrà presentata in questa tesi si concentra sulla caratterizzazione degli effetti 3D sui meccanismi di trasporto nella regione più esterna del plasma di RFX-mod. La macchina risulta essere estremamente versatile in quanto sono possibili operazioni in configurazione a campo rovesciato e in configurazione tokamak. Nello svolgimento della tesi verrà fornita una descrizione dettagliata delle proprietà di trasporto al bordo del plasma in entrambe le configurazioni magnetiche. L'approccio che verrà seguito può essere descritto in termini di un duplice percorso condiviso tra l'investigazione delle fluttuazioni elettrostatiche delle proprietà di trasporto effettuato attraverso l'utilizzo di sonde inseribili nel plasma e lo studio dei cambiamenti della topologia magnetica dovuti a meccanismi spontanei di tipo 3D. La tesi viene così organizzata: Parte I, Introduzione. Nella prima parte della tesi verranno introdotte tutte le nozioni di base utili allo svolgimento del lavoro. Nel capitolo 1 sarà discusso il concetto di plasma e fisica della fusione assieme ad una descrizione dettagliata delle due configurazioni magnetiche rilevanti ai fini delle analisi effettuate: la configurazione reversed-field pinch (RFP) e tokamak. Nel capitolo 2 la dinamica di un RFP verrà dettagliatamente descritta attraverso la teoria di Taylor. Inoltre verranno discussi gli stati a singola e multipla elicità (stati SH e MH), caratteristici della dinamica di un RFP. Successivamente verrà descritta la regione più esterna del plasma di RFX-mod, anche attraverso gli strumenti principali utilizzati nelle analisi effettuate. Il capitolo si concluderà quindi con l'introduzione di una analogia, che sarà dominante in tutto il corpo della tesi, tra la regione esterna di un plasma di tipo RFP e di uno di tipo tokamak durante esperimenti che prevedano l'applicazione di perturbazioni magnetiche. Parte II, Analisi di trasporto. Il capitolo 3 si apre con la presentazione delle due configurazioni sperimentali adottate per RFX-mod ai fini delle analisi di trasporto. Negli esperimenti è stata utilizzata la sonda inseribile U-probe, che verrà descritta successivamente assieme alla teoria su cui si basano le misure da essa raccolte. Verranno quindi discussi i risultati derivanti dall'investigazione delle fluttuazioni elettrostatiche nella regione di bordo del plasma. Verranno di seguito presentati gli studi sui meccanismi di trasporto in differenti regioni topologiche in presenza di una perturbazione magnetica esternamente applicata. Tali risultati verranno mostrati per esperimenti condotti su RFX-mod sia in configurazione reversed-field pinch che in configurazione tokamak. Parte III, Analisi topologiche. Lo studio dei cambiamenti della topologia magnetica si sviluppa attraverso l'analisi di eventi spontanei di riconnessione magnetica in configurazione a campo rovesciato. Nel capitolo 4 verranno inizialmente discussi alcuni modelli di riconnessione magnetica. Verranno quindi presentati i cosiddetti eventi di crash all'interno di RFX-mod e verrà dettagliatamente descritta la tecnica di analisi adottata. Nella seconda parte del capitolo verranno descritti gli esperimenti effettuati sul tokamak COMPASS e su RFX-mod sfruttando un'altra sonda inseribile che ha lo scopo di analizzare il profilo di temperatura ionica. Parte IV, Conclusioni. Nel capitolo 5 sono raccolti e discussi i risultati della tesi. Infine, viene fornita una sezione in cui i principali risultati sono trattati sinteticamente insieme ai problemi rimasti aperti in vista di future prospettive di ricerca. Parte V, Appendici. In Appendice A è possibile trovare una descrizione dettagliata del formalismo della Magnetoidrodinamica mentre in Appendice B vengono trattate in dettaglio le equazioni per il trasporto utili ai fini della tesi.
Kim, Young-chul. "Characteristics of plasma turbulence in the Mega Amp Spherical Tokamak." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:23eea01f-e910-418c-993e-06b3b85d5d43.
Повний текст джерелаXu, Shaokang. "Study of reduced kinetic models for plasma turbulence." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX057/document.
Повний текст джерелаTurbulent 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
Leconte, Michael. "Interactions entre ecoulements cisailles et turbulence dans un plasma de fusion magnetique." Phd thesis, Université de Provence - Aix-Marseille I, 2008. http://tel.archives-ouvertes.fr/tel-00439354.
Повний текст джерелаZhou, Ye. "Renormalization group theory technique and subgrid scale closure for fluid and plasma turbulence." W&M ScholarWorks, 1987. https://scholarworks.wm.edu/etd/1539623774.
Повний текст джерелаRunov, A. V., M. I. Pudovkin, and Claudia-Veronika Meister. "The dynamics of tail-like current sheets under the influence of small-scale plasma turbulence." Universität Potsdam, 1999. http://opus.kobv.de/ubp/volltexte/2007/1490/.
Повний текст джерелаvan, Wyk Ferdinand. "Subcritical turbulence in the Mega Ampere Spherical Tokamak." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:6d84d615-d8dc-45e6-8920-0d71053a13db.
Повний текст джерелаGallagher, Stephen J. "Zonal flow generation through four wave interaction in reduced models of fusion plasma turbulence." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/59703/.
Повний текст джерелаHornung, 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.
Повний текст джерелаRathod, Chirag. "Examining Plasma Instabilities as Ionospheric Turbulence Generation Mechanisms Using Pseudo-Spectral Methods." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/102892.
Повний текст джерелаDoctor of Philosophy
In the modern day, all wireless communication signals use electromagnetic waves that propagate through the atmosphere. In the upper atmosphere, there exists a region called the ionosphere, which consists of plasma (a mixture of ions, electrons, and neutral particles). Because ions and electrons are charged particles, they interact with the electromagnetic communication signals. A better understanding of ionospheric turbulence will allow for aid in forecasting space weather as well as improve future communication equipment. Communication signals become distorted as they pass through turbulent regions of the ionosphere, which negatively affects the signal quality at the receiving end. For a tangible example, when Global Positioning System (GPS) signals pass through turbulent regions of the ionosphere, the resulting position estimate becomes worse. This work looks at two specific causes of ionospheric turbulence: the gradient drift instability (GDI) and the Kelvin-Helmholtz instability (KHI). Under the correct background conditions, these instabilities have the ability to generate ionospheric turbulence. To learn more about the GDI and the KHI, a novel simulation model is developed. The model uses a method of splitting the equations such that the focus is on just the development of the turbulence while considering spatially constant realistic background conditions. The model is shown to accurately represent results from previously studied problems in the ionosphere. This model is applied to an ionospheric phenomenon known as subauroral polarization streams (SAPS) to study the development of the GDI and the KHI. SAPS are regions of the ionosphere with large westward velocity that changes with latitude. The shape of the latitudinal velocity profile depends on many other factors in the ionosphere such as the geomagnetic conditions. It is found that for certain profiles, the GDI will form in SAPS with some of these examples matching observational data. At higher altitudes, the model predicts that the KHI will form instead. While the model is applied to just the development of the GDI and the KHI in this work, it is written in a general manner such that other causes of ionospheric turbulence can be easily studied in the future.
Sondak, David. "Novel residual-based large eddy simulation turbulence models for incompressible magnetohydrodynamics." Thesis, Rensselaer Polytechnic Institute, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3601031.
Повний текст джерелаThe goal of this work was to develop, introduce, and test a promising computational paradigm for the development of turbulence models for incompressible magnetohydrodynamics (MHD). MHD governs the behavior of an electrically conducting fluid in the presence of an external electromagnetic (EM) field. The incompressible MHD model is used in many engineering and scientific disciplines from the development of nuclear fusion as a sustainable energy source to the study of space weather and solar physics. Many interesting MHD systems exhibit the phenomenon of turbulence which remains an elusive problem from all scientific perspectives. This work focuses on the computational perspective and proposes techniques that enable the study of systems involving MHD turbulence. Direct numerical simulation (DNS) is not a feasible approach for studying MHD turbulence. In this work, turbulence models for incompressible MHD were developed from the variational multiscale (VMS) formulation wherein the solution fields were decomposed into resolved and unresolved components. The unresolved components were modeled with a term that is proportional to the residual of the resolved scales. Two additional MHD models were developed based off of the VMS formulation: a residual-based eddy viscosity (RBEV) model and a mixed model that partners the VMS formulation with the RBEV model. These models are endowed with several special numerical and physics features. Included in the numerical features is the internal numerical consistency of each of the models. Physically, the new models are able to capture desirable MHD physics such as the inverse cascade of magnetic energy and the subgrid dynamo effect. The models were tested with a Fourier-spectral numerical method and the finite element method (FEM). The primary test problem was the Taylor-Green vortex. Results comparing the performance of the new models to DNS were obtained. The performance of the new models was compared to classic and cutting-edge dynamic Smagorinsky eddy viscosity (DSEV) models. The new models typically outperform the classical models.
Hahlin, Axel. "Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-356265.
Повний текст джерелаStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår.
Morel, Pierre. "Le modèle "water bag" appliqué aux équation cinétiques des plasmas de Tokamak." Phd thesis, Université Henri Poincaré - Nancy I, 2008. http://tel.archives-ouvertes.fr/tel-00453088.
Повний текст джерелаMedvedeva, 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.
Повний текст джерелаPlasma 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
Sundkvist, David. "Space Plasma Dynamics : Instabilities, Coherent Vortices and Covariant Parametrization." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6051.
Повний текст джерелаChasapis, Alexandros. "Étude de la reconnexion magnétique dans les plasmas turbulents à partir des données satellites." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112205/document.
Повний текст джерелаMagnetic reconnection is a fundamental energy conversion process in plasma. It occurs in thin regions of strong current known as current sheets and results in particle heating and acceleration. In turbulence, which is ubiquitous in space plasma, magnetic reconnection has been observed to occur in small scale structures that form therein, and is thought to contribute to dissipation of turbulent energy at kinetic scales. For this work we examine data from the Cluster spacecraft in the Earth's magnetosheath, downstream of the quasi-parallel shock. The detection of ion-scale current sheets was performed by implementing the PartialVariance of Increments (PVI) method for multiple spacecraft. The properties of the observed current sheets were different for high (> 3) and low (< 3) values of the PVI index. We observed a distinct population of high PVI (> 3) structures that accounted for ~ 20% of the total. Those current sheets have high magneticshear (> 90degrees). In order to estimate the local heating occurring within those current sheets, a proxy of the electron temperature was obtained at high time resolution(125ms) from the partial distributions measured by Cluster. This allowed for the first time to study the localized electron heating within ion-scale currentsheets. The observed enhancement of the estimated electron temperature withinthe high PVI current sheets suggest that they are important for local electron heating and energy dissipation. We also examined measurements inside the diffusion region of a thin reconnecting current sheet. Multi-spacecraft observationsallow as to study electron distributions and wave activity at different distances from the x-line. Significant differences were observed in the electron populations as they were heated going through the current sheet. In particular electrons were heated in the direction parallel to the magnetic field in close proximity to thex-line, whereas no significant variation was observed in the perpendicular direction. However, the distribution was more isotropic downstream of the x-line with electrons heated in the perpendicular direction
Baudoin, 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.
Повний текст джерелаFusion 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
Strugarek, 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.
Повний текст джерелаPonty, Yannick. "Rôle de la turbulence sur l'effet dynamo et l'induction magnétique." Habilitation à diriger des recherches, Université Nice Sophia Antipolis, 2012. http://tel.archives-ouvertes.fr/tel-00922148.
Повний текст джерелаRetinò, Alessandro. "Magnetic Reconnection in Space Plasmas : Cluster Spacecraft Observations." Doctoral thesis, Uppsala University, Department of Astronomy and Space Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7891.
Повний текст джерелаMagnetic reconnection is a universal process occurring at boundaries between magnetized plasmas, where changes in the topology of the magnetic field lead to the transport of charged particles across the boundaries and to the conversion of electromagnetic energy into kinetic and thermal energy of the particles. Reconnection occurs in laboratory plasmas, in solar system plasmas and it is considered to play a key role in many other space environments such as magnetized stars and accretion disks around stars and planets under formation. Magnetic reconnection is a multi-scale plasma process where the small spatial and temporal scales are strongly coupled to the large scales. Reconnection is initiated rapidly in small regions by microphysical processes but it affects very large volumes of space for long times. The best laboratory to experimentally study magnetic reconnection at different scales is the near-Earth space, the so-called Geospace, where Cluster spacecraft in situ measurements are available. The European Space Agency Cluster mission is composed of four-spacecraft flying in a formation and this allows, for the first time, simultaneous four-point measurements at different scales, thanks to the changeable spacecraft separation. In this thesis Cluster observations of magnetic reconnection in Geospace are presented both at large and at small scales.
At large temporal (a few hours) and spatial (several thousands km) scales, both fluid and kinetic evidence of reconnection is provided. The evidence consist of ions accelerated and transmitted across the Earth’s magnetopause. The observations show that component reconnection occurs at the magnetopause and that reconnection is continuous in time.
The microphysics of reconnection is investigated at smaller temporal (a few ion gyroperiods) and spatial (a few ion gyroradii) scales. Two regions are important for the microphysics: the X-region, around the X-line, where reconnection is initiated and the separatrix region, away from the X-line, where most of the energy conversion occurs. Observations of a separatrix region at the magnetopause are shown and the microphysics is described in detail. The separatrix region is shown to be highly structured and dynamic even away from the X-line.
Finally the discovery of magnetic reconnection in turbulent plasma is presented by showing, for the first time, in situ evidence of reconnection in a thin current sheet found in the turbulent plasma downstream of the quasi-parallel Earth’s bow shock. It is shown that turbulent reconnection is fast and that electromagnetic energy is converted into heating and acceleration of particles in turbulent plasma. It is also shown that reconnecting current sheets are abundant in turbulent plasma and that reconnection can be an efficient energy dissipation mechanism.
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.
Повний текст джерелаSimon, Patrick. "Investigation of geodesic acoustic mode flow oscillations using Doppler reflectometry in ASDEX Upgrade." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0076/document.
Повний текст джерелаMagnetic confinement fusion is a promising candidate for a future energy source. Its efficiency is limited by particle and heat transport due to plasma turbulence. A thorough understanding of the turbulence and turbulence moderation mechanisms, is therefore needed. The geodesic acoustic mode (GAM) is a radially localised plasma flow oscillation which contributes to the reduction of turbulent transport through velocity shearing. This thesis investigates the fundamental behaviour of the GAM through a systematic experimental study of its properties in the ASDEX Upgrade tokamak. In particular, the role of the plasma geometry on the scaling of the GAM frequency and amplitude, as well as the GAM radial structure are investigated in detail. The experimental data was obtained with the aid of the microwave Doppler reflectometry diagnostic. The GAM frequency scaling is compared with multiple models which reproduce the expected fundamental scaling behaviour, but do not give a satisfyingly accurate prediction. The GAM amplitude is studied in connection with damping rates predicted by models for collisional and collisionless Landau damping processes. It is found that finite orbit width effects need to be considered and that collisional damping effects cannot be neglected. In studying the GAM radial structure, three distinct states are identified for different plasma conditions. Transitions between these states are observed under variations of the plasma geometry
Meyrand, Romain. "Turbulence à hautes fréquences dans le vent solaire : Modèle magnétohydrodynamique Hall et expériences numériques." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00878745.
Повний текст джерелаAl, Moulla Khaled. "Turbulence at MHD and sub-ion scales in the magnetosheath of Saturn : a comparative study between quasi-perpendicular and quasi-parallel bow shocks using in-situ Cassini data." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-354775.
Повний текст джерелаSyftet med detta projekt är att undersöka de spektrala egenskaperna hos turbulens i Saturnus magnetoskikt, med in-situ-mätningar av magnetfältet från Cassini-rymdsonden. Enligt modeller av inkompressibla, turbulenta fluider, är energispektrumet i det intertiala omfånget proportionellt mot frekvensen upphöjd i -5/3, vilket har observerats i den jordnära Solvinden men inte i det jordiska magnetoskiktet förutom nära magnetopausen. 120 tidsintervall för när Cassini befinner sig inuti magnetoskiktet identifieras — 40 styck i kategorierna bakom kvasi-vinkelräta bogchockar, bakom kvasi-parallella bogchockar, och inuti mellersta delen av magnetoskiktet. Effektspektraltätheten beräknas därefter för varje intervall, med logaritmiska regressioner på MHD- och subjon-skalorna som separeras av jongyrofrekvensen. Resultaten verkar tyda på liknande beteende som i Jordens magnetoskikt, utan märkvärdig skillnad mellan kvasi-vinkelräta och kvasi-parallella fall förutom något brantare exponenter på MHD-skalan för de förnämnda. Dessa observationer bekräftar bogchokens roll i förstörandet av den fullt utvecklade turbulensen i Solvinden, därmed förklarande avsaknaden av det inertiala omfånget.
Zarzoso, David. "Description de l'interaction entre les particules energetiques et les ondes dans les plasmas de fusion." Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00765271.
Повний текст джерелаLemoine, Nicolas. "Transport turbulent d'un plasma à travers un champ magnétique : observation par diffusion collective de la lumière." Phd thesis, Ecole Polytechnique X, 2005. http://pastel.archives-ouvertes.fr/pastel-00002317.
Повний текст джерелаFonseca, Júlio César David da. "Barreiras de transporte em plasmas e mapas simpléticos não-twist." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-11052012-184108/.
Повний текст джерелаWe consider a hamiltonian model of the electrostatic drift motion to investigate chaotic particle transport in the Tokamak plasma edge. This model takes into account the electrostatic drift turbulence, which is responsible for the anomalous transport. The Hamiltonian model provides the basic equations of motion, which are dependent on the form of an electric potential function. This function is characterized by the equilibrium potential and the term corresponding to the drift waves. We assume three diferent radial profiles for the equilibrium radial electric field: one linear and the other two non-monotonic with a smooth extremum. For these profiles, we show that the model can be reduced to three symplectic maps: the standard map, the nontwist standard map, and a nontwist model map introduced in this work. The nontwist standard map and the model map violate the twist condition, a property of fundamental importance for the applicability of the KAM and Birkhoff theorems. For these nontwist maps, we study numerically the transport barriers created around their shearless curves. We show for the model map that the transport barrier is robust,i.e., remains for a wide range of one of its parameters. Inside the barrier region, we describe the birth of island chains with even or odd periods due to the control parameter variation. We analyse these two scenarios by calculating the winding numbers inside the barrier region and identifying the bifurcations that create the islands. Finally, we conjecture that all the island chains inside the barrier are created by these two scenarios. Moreover, if the winding number of the shearless curve reachs a rational number, the island chains are created according to the described scenarios.
Meunier, Claude. "Quelques problèmes non-linéaires en hydrodynamique et en physique des plasmas : théorèmes de moyennisation et théorèmes adiabatiques." Paris 6, 1986. http://www.theses.fr/1986PA066126.
Повний текст джерелаToufen, Dennis Lozano. "Controle da turbulência em plasmas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26032013-154737/.
Повний текст джерелаThe Texas Helimak is a toroidal confinement of plasma device with helically magnetic field lines and which plasma parameters (like the density and temperature) are similar to the edge and the scrape-off-layer of a tokamak. This thesis analyzed the equilibrium and fluctuations in the Helimak Texas plasma. We present the analysis and interpretation of electrostatic control of turbulence and turbulent particle transport by electrical potential, bias, applied externally. Changes in transport and turbulence caused by the change of external electric potential were investigated in a region of uniform radial gradients plasma. Fluctuations in discharges with positive or zero bias have broadband power spectra and a PDF with an accentuated tail that reveals the intermittent occurrence of extreme events. Moreover, fluctuations in discharges with negative bias have narrow power spectra, a more Gaussian PDF and more structures in the recurrence diagram. A four coupled wave model was used to relate the bandwidth of turbulence with the interaction time between the waves in the model. Radial profiles of turbulent transport of particles in the radial direction were calculated as a function of bias and compared to the profiles of the plasma flow velocity and its shear. It was shown that the transport depends on the radial profile of the plasma flow velocity. In that discharges where the velocity radial profile presents a point of maximum, the transport profile has a minimum which was interpreted, using a drift wave model Hamiltonian, as a result of a shearless flow transport barrier. In other discharges, the maxima in the transport radial profiles were related with resonances that occur where the wave phase velocity is equal to the plasma velocity.
Norin, Lars. "Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere." Doctoral thesis, Uppsala universitet, Astronomi och rymdfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9393.
Повний текст джерелаTresset, Guillaume. "Caractérisation, Modélisation et Contrôle des Scénarios Avancés dans le Tokamak Européen JET." Phd thesis, Université de Provence - Aix-Marseille I, 2002. http://tel.archives-ouvertes.fr/tel-00001803.
Повний текст джерелаAkbari, Hassanali. "Beam-plasma interactions and Langmuir turbulence in the auroral ionosphere." Thesis, 2015. https://hdl.handle.net/2144/16310.
Повний текст джерелаRoberts, Thomas Maximillian. "Local Regulation of Interchange Turbulence in a Dipole-Confined Plasma Torus using Current-Injection Feedback." Thesis, 2015. https://doi.org/10.7916/D8GT5M4S.
Повний текст джерелаVan, Vuuren Gary Wayne. "The influence of rotating and locked magnetic islands on edge transport in Tokoloshe tokamak." Thesis, 1993. http://hdl.handle.net/10413/6469.
Повний текст джерелаThesis (Ph.D.)-University of Natal, 1993.
Banerjee, Debarghya. "Some Studies of Statistical Properties of Turbulence in Plasmas and Fluids." Thesis, 2014. http://etd.iisc.ac.in/handle/2005/2909.
Повний текст джерелаBanerjee, Debarghya. "Some Studies of Statistical Properties of Turbulence in Plasmas and Fluids." Thesis, 2014. http://etd.iisc.ernet.in/handle/2005/2909.
Повний текст джерелаOlsen, Christopher. "Experimental Characterization of Plasma Detachment from Magnetic Nozzles." Thesis, 2013. http://hdl.handle.net/1911/72016.
Повний текст джерелаBoelens, Arnout. "On the effect of elasticity on drag reduction due to polymer additives using a hybrid D.N.S. and Langevin dynamics approach." 2012. https://scholarworks.umass.edu/dissertations/AAI3518211.
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