Dissertations / Theses: 'Plasma flow in magnetic field'

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Bissell, R. C. "Steady, collisionless plasma flow along a magnetic field." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379920.

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Plechaty, Christopher Ryan. "Penetration of conductive plasma flows across a magnetic field." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453608.

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Lee, Hyunyong. "Study on Effect of Magnetic Field Configuration on Parallel Plasma Flow during Neutral Beam Injection in Heliotron J." Kyoto University, 2013. http://hdl.handle.net/2433/174742.

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Sato, Kunihiro. "Kinetic Analyses of Potential Formation in Plasma Flow along Open Magnetic Fields to a Wall." Kyoto University, 1993. http://hdl.handle.net/2433/154656.

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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第8140号
論工博第2669号
新制||工||906(附属図書館)
UT51-93-F240
(主査)教授板谷良平, 教授秋宗秀夫, 教授大引得弘
学位規則第4条第2項該当

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Kevin, Obrejan. "Study of magnetic shaping effects on plasma flows and micro-instabilities in tokamak plasmas using the full-f gyrokinetic code based on a real space field solver." Kyoto University, 2017. http://hdl.handle.net/2433/227650.

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Margetis, Alexander. "Beltrami Flows." Kent State University Honors College / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1525299172164402.

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Viré, Axelle. "Study of the dynamics of conductive fluids in the presence of localised magnetic fields: application to the Lorentz force flowmeter." Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210062.

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When an electrically conducting fluid moves through a magnetic field, fluid mechanics and electromagnetism are coupled.

This interaction is the object of magnetohydrodynamics, a discipline which covers a wide range of applications, from electromagnetic processing to plasma- and astro-physics.

In this dissertation, the attention is restricted to turbulent liquid metal flows, typically encountered in steel and aluminium industries. Velocity measurements in such flows are extremely challenging because liquid metals are opaque, hot and often corrosive. Therefore, non-intrusive measurement devices are essential. One of them is the Lorentz force flowmeter. Its working principle is based on the generation of a force acting on a charge, which moves in a magnetic field. Recent studies have demonstrated that this technique can measure efficiently the mean velocity of a liquid metal. In the existing devices, however, the measurement depends on the electrical conductivity of the fluid.

In this work, a novel version of this technique is developed in order to obtain measurements that are independent of the electrical conductivity. This is particularly appealing for metallurgical applications, where the conductivity often fluctuates in time and space. The study is entirely numerical and uses a flexible computational method, suitable for industrial flows. In this framework, the cost of numerical simulations increases drastically with the level of turbulence and the geometry complexity. Therefore, the simulations are commonly unresolved. Large eddy simulations are then very promising, since they introduce a subgrid model to mimic the dynamics of the unresolved turbulent eddies.

The first part of this dissertation focuses on the quality and reliability of unresolved numerical simulations. The attention is drawn on the ambiguity that may arise when interpretating the results. Owing to coarse resolutions, numerical errors affect the performances of the discrete model, which in turn looses its physical meaning. In this work, a novel implementation of the turbulent strain rate appearing in the models is proposed. As opposed to its usual discretisation, the present strain rate is in accordance with the discrete equations of motion. Two types of flow are considered: decaying turbulence located far from boundaries, and turbulent flows between two parallel and infinite walls. Particular attention is given to the balance of resolved kinetic energy, in order to assess the role of the model.

The second part of this dissertation deals with a novel version of Lorentz force flowmeters, consisting in one or two coils placed around a circular pipe. The forces acting on each coil are recorded in time as the liquid metal flows through the pipe. It is highlighted that the auto- or cross-correlation of these forces can be used to determine the flowrate. The reliability of the flowmeter is first investigated with a synthetic velocity profile associated to a single vortex ring, which is convected at a constant speed. This configuration is similar to the movement of a solid rod and enables a simple analysis of the flowmeter. Then, the flowmeter is applied to a realistic three-dimensional turbulent flow. In both cases, the influence of the geometrical parameters of the coils is systematically assessed.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Langlois, Yilin. "Modélisation de l’arc électrique dans un disjoncteur à vide." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL062N/document.

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Un modèle numérique d’un arc électrique diffus dans un disjoncteur à vide à champ magnétique axial (AMF) a été développé dans le but de mieux comprendre à terme la transition d’un mode de fonctionnement diffus de l’arc vers un mode plus concentré. Le comportement du plasma d’arc a été simulé depuis la sortie de la zone de mélange cathodique jusqu’à l’entrée de la gaine anodique. Le modèle bidimensionnel est basé sur un système d’équations hydrodynamiques à deux fluides non magnétisés (ions et électrons), incluant les équations de conservation d’énergie ionique et électronique. Il est démontré que les processus d’ionisation et de recombinaison et les effets visqueux sont négligeables. Les transferts radiatifs ne sont pas considérés en première approximation. Outre les forces dues au champ AMF, le modèle inclut les forces dues aux trois composantes du champ magnétique induit par l’arc. Deux régimes d’écoulement des ions, supersonique (aux faibles densités de courant) et subsonique (aux fortes densités de courant), sont considérés. Près de la cathode, les conditions aux limites sont spécifiées à partir de résultats de la littérature. A proximité de l’anode, elles sont basées sur une description simplifiée de la gaine anodique. Les résultats de simulation présentés mettent en évidence une constriction du courant et un comportement différent des ions aux faibles et aux fortes densités de courant, et renseignent sur l’influence de divers paramètres (intensité du courant, distance interélectrode). Ce travail présente également une étude expérimentale, basée sur des visualisations par vidéo rapide de l’arc et des mesures pyrométriques de la température de la surface de l’anode
A model of a diffuse arc in a vacuum circuit breaker with an axial magnetic field (AMF) has been developed with the ultimate aim to better understand the transition of the arc from a diffuse mode to a more confined mode. The interelectrode plasma is simulated from the exit of the mixing region on the cathode side to the entrance of the anode sheath. The two-dimensional model is based on the solution of a system of two-fluid (ions and electrons) hydrodynamic equations, including in particular the energy balance equations relative to both the ions and the electrons, which are treated as non-magnetized particles. It is demonstrated that ionisation and recombination processes, as well as viscous effects, can be neglected. Radiation losses are not taken into account in a first approximation. In addition to the forces due to the AMF, the model considers the forces created by the three components of the magnetic field induced by the arc current. The possibility of both supersonic (at low current density) and subsonic (at high current density) ionic flow regimes is considered. On the cathode side, the boundary conditions are specified using results from the literature. On the anode side, they are based on a simplified description of the anode sheath. The simulation results presented show a constriction of the current lines, emphasize the differences in the behaviour of the ions at low and high current densities, and provide some insight on the influence of various operating parameters (arc current, gap length). The present work comprises also an experimental study, based on high-speed camera visualisations of the arc and measurements of the temperature at the anode surface

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Garren, David Alan. "Magnetic field strength of toroidal plasma equilibria." W&M ScholarWorks, 1991. https://scholarworks.wm.edu/etd/1539623809.

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The goal of nuclear fusion research is to confine a deuterium-tritium plasma at a sufficiently high temperature (15 keV) and density (3 $\times$ 10$\sp{20}$ m$\sp{-3}$) for a sufficient length of time (1 sec) to produce net fusion power. One means to attain the required plasma confinement is to embed the plasma within a magnetic field. The global structure of this magnetic field determines the variation of magnetic field strength within the surfaces of constant plasma pressure. This field strength variation in turn determines many of the stability and confinement properties of the plasma. This dissertation gives the first detailed exposition of the spectrum of possible forms for magnetic field strength corresponding to toroidal plasma equilibria, both within any three-dimensional volume and within any two-dimensional surface of constant plasma pressure. Constraints due to the toroidicity of the configuration and the divergence-free property of the magnetic field are found to limit the form of the field strength. Three-dimensional stellarator equilibria corresponding to a particular form of the magnetic field strength are especially interesting. These "quasi-helically symmetric" equilibria are non-axisymmetric, toroidal configurations in which the magnetic field strength depends on only one angular coordinate, instead of two, within the constant plasma pressure surfaces. Unlike conventional stellarator equilibria, these quasi-helically symmetric equilibria exhibit the favorable confinement properties of axisymmetric tokamak equilibria. We show that stellarators with exact quasi-helical symmetry do not to exist, but that good approximations can be found.

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Simakov, Andrei N. 1974. "Plasma stability in a dipole magnetic field." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/60756.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.
Includes bibliographical references (p. 137-141).
The MHD and kinetic stability of an axially symmetric plasma, confined by a poloidal magnetic field with closed lines, is considered. In such a system the stabilizing effects of plasma compression and magnetic field compression counteract the unfavorable field line curvature and can stabilize pressure gradient driven magnetohydrodynamic modes provided the pressure gradient is not too steep. Isotropic pressure, ideal MHD stability is studied first and a general interchange stability condition and an integro-differential eigenmode equation for ballooning modes are derived, using the MHD energy principle. The existence of plasma equilibria which are both interchange and ballooning stable for arbitrarily large beta = plasma pressure / magnetic pressure, is demonstrated. The MHD analysis is then generalized to the anisotropic plasma pressure case. Using the Kruskal-Oberman form of the energy principle, and a Schwarz inequality, to bound the complicated kinetic compression term from below by a simpler fluid expression, a general anisotropic pressure interchange stability condition, and a ballooning equation, are derived. These reduce to the usual ideal MHD forms in the isotropic limit. It is typically found that the beta limit for ballooning modes is at or just below that for either the mirror mode or the firehose.
(cont.) Finally, kinetic theory is used to describe drift frequency modes and finite Larmor radius corrections to MHD modes. An intermediate collisionality ordering in which the collision frequency is smaller than the transit or bounce frequency, but larger than the mode, magnetic drift, and diamagnetic frequencies, is used for solving the full electromagnetic problem. An integro-differential eigenmode equation with the finite Larmor radius corrections is derived for ballooning modes. It reduces to the ideal MHD ballooning equation when the mode frequency exceeds the drift frequencies. In addition to the MHD mode, this ballooning equation permits an entropy mode solution whose frequency is of the order of the ion magnetic drift frequency. The entropy mode is an electrostatic flute mode, even in equilibrium of arbitrary beta. Stability boundaries for both modes, and the influence of collisional effects on these boundaries has also been investigated.
by Andrei N. Simakov.
Ph.D.

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Tubman, Eleanor. "Magnetic field generation in laser-plasma interactions." Thesis, University of York, 2016. http://etheses.whiterose.ac.uk/16757/.

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The primary focus of this thesis is understanding the production of magnetic fields during laser-plasma experiments. Each chapter investigates a different mechanism of producing magnetic fields. The first is from the by-product of launching asymmetric shocks which drive Biermann battery generated magnetic fields. The second looks at the reconnection of magnetic fields between two laser focal spots and the third is from fields produced around a current carrying loop target. Blast waves are investigated in the laboratory using a fast framing camera to capture multiple images on a single shot. In analysing the images, the blast wave's trajectory is compared to a Sedov-Taylor solution and the coupling of the laser energy into the shock wave is calculated to be 0.5-2%. The evolution of the blast wave's shape is characterised by fitting an ellipse to the outer edge and is observed to progress into a more symmetrical shape. Calculations show that two shocks produced in the interaction cause the change in ellipticity. We experimentally demonstrate that when two laser spots are placed in close proximity reconnection occurs. Diagnostics, including proton radiography, X-ray detectors and an optical probe, record and diagnose the existence of a semi-collisional reconnection event. The experimental data and simulations show that both Nernst and anisotropic pressure effects need to be taken into account for understanding and predicting the correct plasma dynamics observed. Magnetic fields are produced by driving a current through a loop attached to two plates and new measurements recording the voltages induced are presented in this thesis. It is found that the predicted values for the resistance, capacitance and inductance do not match those extracted from the experimental data and reasons for these are presented. Ideas for furthering this research to enhance our understanding in this area are given.

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Galicia, Felicisimo. "Plasma wave induced chaos in a magnetic field." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38863.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1996.
Includes bibliographical references (leaf 125).
by Felicisimo Galicia.
B.S.
M.Eng.

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Miller, Kenneth Elric. "The star thrust experiment, rotating magnetic field current drive in the field reversed configuration /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9996.

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Peter, Andrew Maxwell. "Paramagnetic spin-up of a field reversed configuration with rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9983.

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Goode, Brent. "Plasma response to waves in arbitrary magnetic field geometry." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p3190342.

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Went, Daniel Robert. "Magnetic field and plasma in Saturn's near space environment." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9066.

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This thesis concerns spacecraft observations of magnetic field and plasma in Saturn’s near space environment and compares these observations with those made in and near the Jovian magnetosphere. Such comparisons are equivalent to ‘turning the experimental dial’ in planetary magnetospheres and provide a valuable insight into the way different parameters govern the structure and dynamics of magnetospheres throughout the solar system. Saturn and its magnetosphere is currently being studied by the Cassini spacecraft which, arriving at Saturn in the summer of 2004, became the first spacecraft ever to enter orbit around the planet. As a result there has never been a better time to study the Saturn system and the vast majority of the data utilized in this thesis were obtained by the Cassini spacecraft and its onboard instrumentation. Additional data were also obtained from the Pioneer, Voyager, Ulysses and Galileo spacecraft. Chapter 1 provides a general overview of space plasma and magnetospheric physics while Chapter 2 discusses the Saturn system in more detail. Chapter 3 describes the spacecraft and instrumentation used in this thesis with particular emphasis placed on magnetometer instruments and the Cassini-Huygens spacecraft. Chapter 4 compares the structure of Jupiter’s and Saturn’s outer magnetospheres and discusses the similarities and differences between the two. Chapter 5 presents a new empirical model of Saturn’s dayside bow shock and discusses the three dimensional shape of this surface while, finally, Chapter 6 presents observations of a magnetic cavity in the Saturnian magnetosphere which, as of writing, has yet to be explained. Chapter 7 summarises and concludes the thesis. The three independent investigations described above each shed light on a different aspect of Saturn’s magnetospheric structure and dynamics and contributes to an improved understanding of magnetospheric physics in general.

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Short, David James. "Swirling flow induced by a rotating magnetic field." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338644.

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Taborda, David Ciro. "Magnetic field modeling for non-axisymmetric tokamak discharges." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-04012017-142757/.

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In this work we study the magnetic field modeling of realistic non-axisymmetric plasma equilibrium configurations and the heat flux patterns on the plasma facing components of tokamak divertor discharges. We start by establishing the relation between generic magnetic configurations and Hamiltonian dynamical systems. We apply the concept of magnetic helicity, used to establish topological bounds for the magnetic field lines in ideal plasmas, and to understand the self-consistency of reconnected magnetic surfaces in non-axisymmetric configurations. After this theoretical discussion, we present some results on magnetohydrodynamic equilibrium and the use of analytical solutions to the Grad-Shafranov equation for describing real tokamak discharges based on the experimental diagnostics and realistic boundary conditions. We also compare the equilibrium reconstruction of a DIII-D discharge obtained with a numerical reconstruction routine, developed as part of this research, and the EFIT code used by several tokamak laboratories around the world. The magnetic topology and plasma profiles obtained with our method are in considerable agreement with the numerical reconstruction performed with the other code. Then, we introduce a simplified description of the generic non-axisymmetric magnetic field created by known sources and implement it numerically for describing the magnetic field due to external coils in tokamak devices. After that, we use this routines to develop a numerical procedure to adjust a suitable set of non-linear parameters of internal filamentary currents, which are intended to model the plasma response based on the magnetic field measurements outside the plasma. Finally, these methods are used to model the magnetic field created by a slowly rotating plasma instability in a real DIII-D discharge. The plasma response modeling is based on the magnetic probe measurements and allow us to calculate the magnetic field in arbitrary locations near the plasma edge. Using this information we determine the non-axisymmetric plasma edge through the magnetic invariant manifolds routine developed during this work. The intersection of the calculated invariant manifold with the tokamak chamber agrees considerably well with the heat flux measurements for the same discharge at the divertor plates, indicating the development of a rotating manifold due to the internal asymmetric plasma currents, giving quantitative support to our simplified description of the magnetic field and the plasma edge definition through the invariant manifolds.
Neste trabalho estuda-se a modelagem do campo magnético em configurações realistas de plasmas em equilíbrio não-axissimétrico e o fluxo de calor nos componentes em contato com o plasma em descargas de tokamaks com desviadores poloidais. Começa-se estabelecendo a relação entre configurações magnéticas arbitrárias e sistemas dinâmicos Hamiltonianos. Então aplicamos o conceito de helicidade magnética, que é usado para estabelecer limitações topológicas sobre as linhas de campo magnético em plasmas ideais, assim como para compreender a auto-consistência das superfícies magnéticas reconectadas em configurações não-axissimétricas. Após esta discussão teórica, apresentam-se alguns resultados sobre o equilíbrio magnetohidrodinâmico e o uso de soluções analíticas à equação de Grad-Shafranov para descrever descargas reais em tokamaks, com base em diagnósticos experimentais e condições de contorno realistas. Também realiza-se uma comparação entre a reconstrução do equilíbrio de uma descarga do DIII-D, obtida mediante uma rotina numérica desenvolvida para esta pesquisa, com a obtida mediante o código EFIT, usado amplamente em diversos tokamaks. Após isso, apresenta-se uma descrição simplificada do campo magnético não-axissimétrico, criado por fontes determinadas, e a sua implementação para descrever o campo magnético devido às correntes externas em tokamaks. Então, usam-se estas rotinas para desenvolver um procedimento numérico que ajusta um conjunto adequado de parâmetros não-lineares de correntes filamentares internas, com as quais pretende-se modelar a resposta do plasma com base nas medidas de campo magnético fora do plasma. Finalmente, estes métodos são utilizados para modelar o campo magnético criado por uma instabilidade com rotação lenta numa descarga do DIII-D. Com base nas medidas das sondas magnéticas é possível modelar os campos criados em regiões arbitrárias próximas da borda do plasma. Usando esta informação é possível determinar a borda não-axissimétrica do plasma mediante as invariantes magnéticas calculadas com a utilização de uma rotina desenvolvida durante este trabalho. A intersecção da superfície invariante com a câmara do tokamak coincide satisfatoriamente com as medidas de fluxo de calor nas placas do divertor para a mesma descarga, indicando o desenvolvimento de uma variedade giratória criada pelas correntes de plasma não-axissimétricas, e sustentando quantitativamente a nossa descrição simplificada do campo magnético, assim como a definição da borda do plasma mediante as invariantes magnéticas.

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Adams, Matthew Michael. "Magnetic and acoustic investigations of turbulent spherical Couette flow." Thesis, University of Maryland, College Park, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10160544.

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This dissertation describes experiments in spherical Couette devices, using both gas and liquid sodium. The experimental geometry is motivated by the Earth's outer core, the seat of the geodynamo, and consists of an outer spherical shell and an inner sphere, both of which can be rotated independently to drive a shear flow in the fluid lying between them. In the case of experiments with liquid sodium, we apply DC axial magnetic fields, with a dominant dipole or quadrupole component, to the system. We measure the magnetic field induced by the flow of liquid sodium using an external array of Hall effect magnetic field probes, as well as two probes inserted into the fluid volume. This gives information about possible velocity patterns present, and we extend previous work categorizing flow states, noting further information that can be extracted from the induced field measurements. The limitations due to a lack of direct velocity measurements prompted us to work on developing the technique of using acoustic modes to measure zonal flows. Using gas as the working fluid in our 60 cm diameter spherical Couette experiment, we identified acoustic modes of the container, and obtained excellent agreement with theoretical predictions. For the case of uniform rotation of the system, we compared the acoustic mode frequency splittings with theoretical predictions for solid body flow, and obtained excellent agreement. This gave us confidence in extending this work to the case of differential rotation, with a turbulent flow state. Using the measured splittings for this case, our colleagues performed an inversion to infer the pattern of zonal velocities within the flow, the first such inversion in a rotating laboratory experiment. This technique holds promise for use in liquid sodium experiments, for which zonal flow measurements have historically been challenging.

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Frierson, Robert V. Jr. "Spectroscopic diagnostics of a plasma in a rotating magnetic field." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/17236.

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Hurtig, Tomas. "Plasma cloud penetration across magnetic boundaries." Doctoral thesis, KTH, Alfvén Laboratory, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3804.

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Yu, Edmund Po-ning. "Evolution equations for magnetic islands in a reversed field pinch." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3037030.

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Carpino, Francesca. "Quadrupole Magnetic Field-Flow Fractionation: A Novel Technique For The Characterization Of Magnetic Particles." Cleveland, Ohio : Cleveland State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1207595560.

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Thesis (Ph.D.)--Cleveland State University, 2008.
Abstract. Title from PDF t.p. (viewed on May 8, 2008). Includes bibliographical references (p. 121-126). Available online via the OhioLINK ETD Center. Also available in print.

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Aleksandrova, Svetlana. "Buoyant convection in cavities in a strong magnetic field." Thesis, Coventry University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364613.

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Oliver, Matthew. "Density, temperature and magnetic field measurements in low density plasmas." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:df217453-1e10-4684-beb7-83c1bcecf285.

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Low density plasmas are found throughout the known universe. Therefore, accurate diagnostic methods have implications for our understanding of a variety of topics, ranging from star formation to the semi conductor industry. Low density plasmas are ubiquitous in the material processing industry. However, measurements of the electron temperature and density, two of the most fundamental plasma properties, are not straightforward. In the laboratory, we create a low density, radio frequency, helium plasma with a bi-Maxwellian electron distribution, similar to those found in the semiconductor processing industry. We use optical emission spectroscopy to perform a non invasive measurement of the plasma conditions. We compare this to measurements obtained using a Langmuir probe, a commonly used invasive diagnostic. The optical emission spectroscopy is found to be insensitive to electron density but good agreement is found between the two techniques for values of the temperature of the hot electron component of the bi-Maxwellian. Plasmas created with high-intensity lasers are able to recreate conditions similar to those found during astrophysical events. This development has led to these condi- tions being explored in laboratories around the world. An experiment was performed at the Rutherford Appleton Laboratory in Didcot, UK, investigating the properties of supersonic turbulent jets. For the first time a magneto-optic probe was used to measure the magnetic field in a low-density supersonic turbulent plasma. The results were compared to measurements taken using a magnetic-induction probe. Good agreement was found between measurements of the magnetic field strength within the plasma; however, the magnetic power spectra differ. We attribute this to the dif- ference in integration length between the two measurements. Statistical properties of the velocity field are inferred from the magnetic field measurements, which compare favourably to astrophysical observations and hydrodynamic simulations.

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Bawa'aneh, Muhammad S. "Stimulated brillouin backscattering and magnetic field generation in laser-produced plasmas." Thesis, University of Essex, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284583.

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Brown, Wayne. "Characterisation of low energy ions observed near and during the substorm expansion phase onset." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302621.

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Sinatra, Francy L. "Understanding the Interaction Between Blood Flow and an Applied Magnetic Field." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3518.

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Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.

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Sun, Liping. "A flow-through immunomagnetic cell separation in a quadrupole magnetic field /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu148795065854854.

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Walter, Erwin. "Field-Aligned Currents and Flow Bursts in the Earth’s Magnetotail." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-148525.

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We use electric and magnetic field data from MMS spacecraft between 2016 and 2017 tostatistically investigate earthward propagating plasma flow bursts and field-aligned currents(FACs) inside the plasma sheet of the geomagnetic tail. We observe that the occurrence rateof flow burst peaks around the midnight region with decreasing trend towards Earth and theplasma sheet flanks. Further, we distinguish between long and short FACs. Long FACs laston average 6 sec and have a magnitude of 5-20 nA/m 2 . Short FACs last on average 10 timesshorter and have an magnitude of 10-50 nA/m 2 . Both, long and short FACs occur on averageone time per flow burst, on minimum 0 times and on maximum 4 times per flow burst. Intotal, 43 % of the observed FACs are located in a flow burst, 40 % before and 17 % right after aflow burst.

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Mitma, Pillaca Elver Juan de Dios [UNESP]. "Estudo do comportamento magnético de plasma durante o processo de implantação iônica por imersão em plasma." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/91826.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Universidade Estadual Paulista (UNESP)
O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo “particle-in-cell” (PIC) para simular o movimento de partículas carregadas no campo eletromagnético.
Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field.

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32

Zimmerman, Tassilo Malte Gregor. "Theory of the Plasma-Wall Interaction Under the Influence of a Magnetic Field." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516183.

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33

McDonald, Darren. "A gyrokinetic analysis of electron plasma waves at resonance in magnetic field gradients." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/13975.

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To produce nuclear fusion in a Tokamak reactor requires the heating of a plasma to a temperature of the order of 10 keV. Electron cyclotron resonant heating (ECRH), in which the plasma is heated by radio waves in resonance with the Larmor frequency of the plasma's electrons, is one scheme under consideration for achieving this. A description of such a heating scheme requires a theory to explain the propagation and absorption of high frequency waves in a plasma in the presence of a magnetic field gradient. A WKB analysis can describe some of the processes involved but a complete explanation requires the use of full wave equations. In this thesis we shall develop a technique for deriving such equations which will be shown to be simpler and more general than calculations performed by earlier workers. The technique relies on including the effect of the magnetic gradient across the Larmor orbit of the electrons in the resonance condition of the wave, the so called Gyrokinetic correction, which has been ignored in calculations by previous workers. Once derived, the equations are solved numerically and the results applied to a number of experiments currently being performed on Tokamak fusion. In addition, we shall also look at the energy loss processes of runaway electrons, which have been shown experimentally to be shorter than would be expected.

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34

Gupta, 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.

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Thermonuclear fusion has potential to offer an economically, environmentally and socially acceptable supply of energy. A promising reactor design to execute thermonuclear fusion is the toroidal magnetic confinement device, tokamak. The tokamak still faces challenges in the major areas which can be categorised into confinement, heating and fusion technology. This thesis addresses the problem of confinement, in particular the role of transport along magnetic field lines perturbed by diverse MHD instabilities.

Unstable 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

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35

Sreenivasan, Binod. "Evolution of inertial flow structures in the presence of a magnetic field." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621073.

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36

Mitma, Pillaca Elver Juan de Dios. "Estudo do comportamento magnético de plasma durante o processo de implantação iônica por imersão em plasma /." Guaratinguetá : [s.n.], 2007. http://hdl.handle.net/11449/91826.

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Orientador: Konstantin Georgiev Kostov
Banca: Joaquim José Barroso de Castro
Banca: Mario Ueda
Resumo: O estudo do efeito do campo magnético sobre o processo de implantação iônica por imersão em plasma (3IP) é de grande interesse para o tratamento de materiais. Sendo 3IP uma técnica relativamente nova e de grande relevância para diversas aplicações tecnológicas é importante que ela seja pesquisada e analisada detalhadamente. A aplicação de um campo magnético estático, transversal em relação ao campo elétrico formado durante este processo produz um sistema de campos cruzados ExB. Este sistema de campos cruzados gera um aumento significativo da densidade de plasma na vizinhança do alvo, resultando num maior corrente de implantação, e conseqüentemente um tratamento mais rápido e uma dose retida mais alta em relação ao processo 3IP convencional. Neste trabalho, analisamos mediante simulação numérica, o efeito da distribuição do campo magnético axial no processo 3IP. O campo magnético é produzido por um par de bobinas instaladas fora da câmara de vácuo cujos raios e distância de separação são variadas. Encontramos que a densidade de corrente de implantação depende essencialmente da configuração do campo magnético. Assim, com uma adequada configuração das bobinas (10,0 cm de raio e 42,0 cm de separação) obtivemos uma densidade de corrente quase uniforme de aproximadamente 1,5 mA/cm2 que é 1.5 vezes maior em relação ao caso do sistema 3IP sem campo magnético. O efeito da tensão aplicada assim como da pressão do gás sobre o plasma no processo 3IP é também investigado. O sistema 3IP com campos ExB cruzados é estudado utilizando a técnica de simulação numérica em duas dimensões. Esta simulação é realizada com o código computacional KARAT que emprega o algoritmo "particle-in-cell" (PIC) para simular o movimento de partículas carregadas no campo eletromagnético.
Abstract: Detailed investigation of the effect of magnetic field on the process of plasma immersion ion implantation (PIII) is of great interest for the material treatment. Being a relatively novel and of great relevance for technological applications technique, the PIII demands further research and careful analysis. The application of static magnetic field, transversal in respect to the electric field established during this process, produces a system of crossed fields ExB. This system of crossed fields promotes an increase of the plasma density, resulting in higher implantation current, and consequently in a shorter treatment time and a higher retained dose in comparison to the conventional PIII process. In this work we have analyzed by means of numerical simulation the effect of magnetic field distribution on the PIII processing. The magnetic field is produced by a pair of external coils, whose radii and separation distance were varied. We found that the density of the implantation current essentially depends on the magnetic field configuration. Thus, with an appropriate configuration of the coils (10,0 cm radius and separation of 42,0 cm) we have obtained an almost uniform current density of approximately 1,5 mA/cm2 that is 1,5 times bigger in relation to the case PIII without magnetic field. The effect of the target bias as well as the gas pressure on the ion current incident on the target is also investigated. The PIII system with crossed ExB fields has been studied using two-dimensional numerical simulation. The simulation is accomplished by the computer code KARAT which employs the particle-in-cell (PIC) algorithm for simulating the movement of charged particles in the electromagnetic field.
Mestre

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37

Srikasem, Suthum. "Radiation from an aperture into an anisotropic plasma half-space." Ohio : Ohio University, 1993. http://www.ohiolink.edu/etd/view.cgi?ohiou1173761928.

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38

David, Pierre. "Tomography in a linear magnetised plasma." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0045.

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Quel est le point commun entre des propulseurs à effet hall, des sources d'ions et les grandes machines de recherche sur la fusion magnétique ? Ils sont tous composés de plasmas interagissant avec des champs électrique et magnétique orthogonaux, et leurs tailles, sophistications et inaccessibilités rendent leur étude directe compliquée. Cette étude directe peut être menée à bien sur des machines plus simples, comme la colonne de plasma magnétisée Mistral utilisée dans ce travail, qui sont conçues pour l’étude de mécanismes fondamentaux. La tomographie, quant à elle, est couramment utilisée dans les tokamaks et stellarators, mais plus rarement sur des machines de laboratoire. Son intérêt majeur est de pouvoir reconstituer l’évolution temporelle de section 2D de plasma, et ce sans mesure intrusive. Dans le cadre de cette thèse un diagnostic de tomographie a été entièrement conçu, installé, calibré et testé. Les modèles existant de tomographie ont d'abord été adaptés à ce nouveau contexte, pour ensuite développer et valider le code complet d’inversion tomographique associé. Puis, une étude de faisabilité a été réalisée en mettant au point un diagnostic de tomographie utilisant un seul capteur avec un échantillonnage conditionnel sur des modes réguliers. L’attention est alors portée au développement, à la configuration et à l’application du diagnostic complet à 128 voies. Enfin, une étude paramétrique des modes réguliers a fait ressortir l'importance des paramètres de contrôle sur les modes (présence, fréquence et parité), et l'attention qui doit être portée à l'ensemble des paramètres expérimentaux, ainsi que l’évolution de leur forme et le comportement du plasma central
What do satellites thrusters, ions sources, and fusion devices have in common? They all have plasmas with orthogonal electric and magnetic fields and their size, complexity and accessibility often make them hard to be directly studied. Simpler devices, like the linear magnetised plasma device Mistral used during this work, are conceived in order to understand, predict, and eventually control, some of their fundamental mechanisms. To this purpose, a tomography diagnostic is developed. Tomography is a well known diagnostic in tokamaks and stellarators, but remains seldom used in low temperature plasma studies. Its main advantages are to give access to the temporal evolution of a two-dimensional section of the plasma emissivity, and to be non-intrusive. In the frame of this thesis, a tomography diagnostic has been designed from scratch, implemented, calibrated and tested. The first step consists in the adaptation of existing tomography models in this context, and the full development and validation of the associated numerical code. Then, a proof of concept is conducted with a mono-sensor diagnostic using conditional sampling on coherent rotating modes. Following, the development, configuration, and application of the full 128 channels emission tomography diagnostics on Mistral are reported. New insights to characterise coherent rotating modes, such as the evolution of their shape and the behaviour of the core plasma, are given. Additionally, a parametric study of the rotating modes revealed the complex and intricated effect of control parameters on the modes (existence, frequency, and mode number), and the care that has to be put in monitoring many experimental parameters

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39

Hatch, Spencer Mark. "Stormtime and Interplanetary Magnetic Field Drivers of Wave and Particle Acceleration Processes in the Magnetosphere-Ionosphere Transition Region." Thesis, Dartmouth College, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10603779.

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The magnetosphere-ionosphere (M-I) transition region is the several thousand--kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa. We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfven waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite. Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvenic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases occur during ~30% of the four-year period studied, but together account for more than 65% of global Alfvenic energy deposition and electron precipitation, and more than 70% of the coincident ion outflow. We compare observed interplanetary magnetic field (IMF) control of inertial Alfven wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvenic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvenic power in the Northern Hemisphere. Observed and predicted prenoon Alfvenic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation reverses under dawnward IMF. Despite clear observational and simulated signatures of dayside Alfvenic power, the generation mechanism remains unclear. Last, we present premidnight FAST observations of accelerated precipitation that is best described by a kappa distribution, signaling a nonthermal source population. We examine the implications for the commonly used Knight Relation.

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40

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

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

QC 20171122

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41

Ebbers, Tino. "Cardiovascular fluid dynamics : methods for flow and pressure field analysis from magnetic resonance imaging /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek690s.pdf.

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42

Giersch, Louis Roy Miller. "Experimental investigation of plasma sail propulsion concepts using cascaded arcs and rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9958.

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43

Kumar, Santhosh Tekke Athayil, and santhosh kumar@anu edu au. "Experimental Studies of Magnetic Islands, Configurations and Plasma Confinement in the H-1NF Heliac." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20080611.171513.

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Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement.¶ Work reported in this thesis can be mainly divided into three parts: (a) high resolution imaging of vacuum magnetic islands and flux surfaces of H-1NF, (b) accurate computer modeling of H-1NF magnetic geometry and (c) detailed experiments on magnetic islands in plasma configurations.¶ Electron-beam wire-tomography in the H-1NF has been used for the high resolution mapping of vacuum magnetic flux surfaces and islands. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, has enabled systematic exploration of magnetic islands and surfaces of interest. A fast mapping technique has been developed, which significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields.¶ Flux surface mapping has been carried out at various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields, by point-by-point matching with computer tracing results. This has helped in developing a best-fit computer model for H-1NF magnetic configurations, which can predict rotational transform correct to three decimal places. Results from plasma experiments on magnetic configuration studies are best explained by the new model.¶ Experiments with low order magnetic islands in plasma configurations yielded some new results. It has been observed that the low order magnetic islands (m = 2) near the core of the plasma serve as pockets of improved confinement region under favourable conditions. This results in significant profile modifications including enhancement of the radial electric field near the core to a large positive value. The characteristics of islands are found to be dependent on the plasma collisionality and the island width.¶ Experiments with a magnetic configuration which exhibits no vacuum islands, but the core rotational transform very close to low order rational value, show a spontaneous transition of the radial electric field near the core to a large positive value (nearly 5 kV/m), with a strong electric field shear (nearly 700 kV/m2) and localised improvement in confinement, during the discharge. Evidence indicates that the transition is driven by the excitation of low order magnetic islands near the axis during the plasma discharge, due to the modification of rotational transform profile by toroidal plasma currents. The situation is similar to the Core Electron-Root Confinement (CERC) observed during high temperature ECH plasma discharges on other helical devices. This result provides an experimental evidence for the hypothesis that the threshold conditions for observing CERC can be reduced by exciting magnetic islands near the core of the plasma.

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Stein, Sandra Lynn Wright. "The study of a plasma interacting in an external magnetic field and the production of Kelvin-Helmholtz instabilities as a result /." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1447621.

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45

Beyene, S. "Understanding the formation of magnetic field and plasma structures in the magnetotail via the reconnection process." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1389942/.

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This thesis studies the formation of products of magnetotail reconnection using models and observations. Three studies are presented, the first is an analysis of observations from the Cluster spacecraft, located in different regions of the magnetotail, which allow simultaneous sampling of a Travelling Compression Region (TCR) in the lobe and the underlying magnetic structure in the plasma sheet causing it. Previous work suggests that these structures are created by either single-X-line time-dependent reconnection, forming a flux-bulge, or multiple-X-line reconnection, forming a flux-rope. The observations are analysed and compared to the predictions of these models to determine which mode of reconnection created the structure. The second study presents an adaptation to a single particle model of time-dependent reconnection in the magnetotail previously published by Owen and Cowley (1987). This new model relaxes the cold plasma approximation and assesses the stress balance conditions on reconnected field lines threading the current sheet when the outflow particles have a perpendicular pressure. This is modeled as a result of pitch angle scattering of field-aligned inflow particles as they cross the current sheet on hairpin-like reconnected field lines. The new results show that this accounts for a flux-bulge and a TCR which is consistent with observations. The third study presents a numerical particle model which simulates the evolution of a plasmoid, modeled as a single magnetic field loop in the magnetotail. The model magnetotail has a magnetic, density and velocity gradient along the tail axis. The plasma within the plasmoid splits into two groups, the movement of these groups causes the plasmoid size to oscillate. The initial tailward movement of the plasmoid is caused by the magnetic gradient but continues in its absence due to the net momentum of the plasma inside the plasmoid, with the tailward travelling particles travel faster than the Earthward travelling particles.

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46

Cohen, Joel (Joel A. ). "Excitation of forced ion acoustic waves, large plasma sheets, and magnetic field fluctuations over Gakona, Alaska." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53280.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 47-48).
Two research subjects: (1) excitation of "forced ion acoustic waves", and (2) "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" are reported in my M.S. thesis. The data was acquired in our experiments conducted at Gakona, Alaska from summer 2007 to winter 2008, using DoD/NSF-funded HAARP facilities and our own optical (ASIS) and radio instruments (VLF receiving system of IRIS) aided by GPS satellites as well as AMISR radar at Poker Flat, Alaska. We suggest that "Forced ion acoustic waves" detected by MUIR radar on Oct. 29 during 6:20-6:30 UT arise from keV electron precipitation associated with the occurrence of green aurora. Our work shows, for the first time, that MUIR radar is suitable for probing naturally occurring space plasma processes and not limited to HF heater-induced effects. This would extend the usage of MUIR for the investigation of space weather together with AMISR radar at Poker Flat, to advance our knowledge in space plasma turbulence. The research on "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" is an extension of my B.S. thesis research on thermal filamentation instability, which started in our summer Gakona experiments in 2005. Large plasma sheets (also known as sheet-like filaments) can be excited by HF O-mode and X-mode heater waves via thermal filamentation instability.
(cont.) The dominant nonlinearity is provided by the differential Joule heating acting on electrons, which subsequently gives rise to a cross-field thermal pressure force, to concomitantly generate spatially varying plasma density fluctuations and geomagnetic field fluctuations. It is interesting to find that the fractional density fluctuations are approximately equal to the fractional magnetic field fluctuations. This gives us the theoretical basis to use ground-based magnetometer measurements to infer the density fluctuations in space plasma turbulence. Such a remote sensing technique for probing the space plasma is much more effective and economic than using a beacon satellite.
by Joel Cohen.
S.M.

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47

Cetiner, Selma Olwen. "A plasma sheath with collisions in an oblique magnetic field within a divertor in a tokamak." Thesis, Imperial College London, 2005. http://hdl.handle.net/10044/1/11224.

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Harle, Thomas. "Radio frequency plasma thrusters : performance evaluation of low magnetic field mode operation through direct thrust measurements." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807990/.

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This thesis describes an experimental investigation into the performance of a radio frequency plasma thruster (RFPT). This type of thruster does not rely on the use of high voltage ion acceleration grids or beam neutralisers which are typically life limiting elements of an electric thruster. The RFPT excites an atomic or molecular gas into a plasma using an external RF antenna. This plasma is contained by a cylindrical dielectric source tube which is open at one end. An axial magnetic field is applied to the plasma using one or more solenoids or a permanent magnet source. The magnetic field is usually applied such that it is constant throughout the length of the source tube, after which the field diverges. The plasma couples with the imposed magnetic field, generating internal field structures, which can be used to regulate both the power coupling and the rate at which the plasma diffuses out of the source tube. In this study, the thruster performance is measured directly, thus providing missions designers with accurate performance data which can be used to assess applicability of the technology to future missions. A re-configurable lab prototype thruster was constructed and a pendulum type thrust balance was developed in order to make direct measurements of the thrust produced by the Surrey Space Centre (SSC) RFPT. The balance has been developed to allow mounting of the thruster together with the necessary RF and DC electrical feeds as well as the propellant feeds and incorporates sensors which allow measurements to be made in an RF plasma environment. A low magnetic field mode of RFPT operation was investigated in order to assess whether this mode of operation may be able to provide performance increases at reduced imposed magnetic fields (< 20 mT), which could enable the serious consideration of this technology for future flight opportunities. The lowered magnetic fields used here may reduce the risk of interference with spacecraft subsystems and perturbation to the spacecraft orbit, when compared to many of the proposed plasma thrusters which use fields in excess of 40 mT. Direct thrust measurements of an RFPT operating in a low field mode are presented as a function of the propellant flow, RF power and for two source tube lengths. The thrust is shown to peak at a field strength, B_0, which is demonstrated to vary with RF power and propellant flow. The peaks are also shown to correspond generally to peaks in the source plasma density, plasma potential and in some cases to exhaust ion beam current. Ion energy distribution function measurements show that strong beams are not present in thruster configurations which use a 170 mm length source tube but are shown to increase in strength when using a shorter 85 mm length tube. The low field mode is shown to generally provide performance increases over the non-magnetised case by a factor of 4. Low field mode thrust measurements using the shorter 85 mm source tube and matching double saddle antenna revealed enhanced peak performance gains over the 170 mm length case, resulting in an increase of the thrust efficiency by up to a factor of 15. The performance of the RFPT operating in this configuration is shown to produce enhanced or equivalent performance, when compared to similar state of the art configurations but at generally lower imposed magnetic fields. This particular optimisation may make possible a first flight opportunity for the RFPT as weak magnetic fields may be supplied easily by electromagnets. Electromagnets can be easily deactivated or field reversed to avoid interference with spacecraft subsystems and orbital parameters unlike permanent magnets which may be required to generate higher magnetic fields. Operation of the RFPT in the low field mode with an 85~mm source has also revealed new low field mode behaviour compared to the 170 mm case, producing sudden, large reductions in the performance of the thruster for imposed fields beyond B_0 which are shown to correspond to drops in source plasma density, plasma resistance and exhaust beam current.

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49

Anan, Tetsu. "Open a New Window of Plasma Diagnostics in the Solar Physics with Spectropolarimetric Observation." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/189335.

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50

Galambos, James Paul. "Measurement of the internal toroidal magnetic field on the helicity injected tokamak using the transient internal probe /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10674.

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Dissertations / Theses on the topic 'Plasma flow in magnetic field'

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