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1
Riggs, John Forrest. "Anode sheath contributions in plasma thrusters." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA280395.
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Thesis (Degrees of Aeronautical & Astronautical Engineer and M.S. in Astronautical Engineering) Naval Postgraduate School, March 1994.Thesis advisor(s): Oscar Biblarz. "March 1994." Includes bibliographical references. Also available online.
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Kawamura, Gakushi. "Gyrokinetic Theory for Peripheral Plasmas and its Application to Plasma Sheath." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/57265.
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Starkey, Ryan P., Mark J. Lewis, and Charles H. Jones. "PLASMA SHEATH CHARACTERIZATION FOR TELEMETRY IN HYPERSONIC FLIGHT." International Foundation for Telemetering, 2003. http://hdl.handle.net/10150/606733.
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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, NevadaDuring certain hypersonic flight regimes, shock heating of air creates a plasma sheath resulting in telemetry attenuation or blackout. The severity of the signal attenuation is dependent on vehicle configuration, flight trajectory, and transmission frequency. This phenomenon is investigated with a focus placed on the nonequilibrium plasma sheath properties (electron concentration, plasma frequency, collision frequency, and temperature) for a range of flight conditions and vehicle design considerations. Trajectory and transmission frequency requirements for air-breathing hypersonic vehicle design are then addressed, with comparisons made to both shuttle orbiter and RAM-C II reentry flights.
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Figueroa, Shana Suzanne. "Ion scattering in a self-consistent cylindrical plasma sheath." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-051006-112304/.
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Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: orbital trajectory, ion collection, turning point method, spherical probes, turning angle, ion scattering, cylindrical probes. Includes bibliographical references (p.60-63).
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Brown, George Scott. "Exploring plasma sheath solutions for planar and cylindrical anodes." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/43771.
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Anode sheaths impact the operation of many practical plasma devices. This complex region is explored in detail for collisional, isothermal (identical specie temperatures), low-temperature plasmas, where sheath dimensions are in the micron range. The selected approach involves postulation of a specific electric field distribution with two shape factors. Previous research regarding planar anodes is verified and expanded upon using greater parameter ranges. 'Z', a dimensionless quantity specifying plasma composition and condition, groups diverse plasmas into 'families' exhibiting similar sheath characteristics. Eta, a nondimensional ratio of electrical energy to thermal energy in the sheath, allows temperature effects to be studied. The investigation focuses on three disparate plasma families that span a range of 1.1729 to 2,1493, at eta values defined by plasma temperatures of 6000 K, 3000 K, and 3000 K. Results indicate that at lower temperatures, charge production in the outer sheath is generic to the electric field distribution, and that the sheaths themselves are nearly unaffected by substantial changes in temperature (i.e., eta). Conversely, sheath density and extent are shown to vary significantly for differing z values. Newly-derived equations governing cylindrical anodes generate sheaths that are virtually identical to corresponding planar cases. It is shown that only those anodes whose radii are comparable to the plasma's characteristic radius (gamma) must be treated with the cylindrical formulation; non-vacuous plasma would require micron-width anodes to be thus affected. Finally, an analytical approach yields solutions that confirm the numerical results, and offers an algebraic approximation for high-eta plasmas.
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Han, W. E. "The stability of the plasma sheath with secondary emission." Thesis, City University London, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382894.
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Takamura, S., T. Misawa, N. Ohno, S. Nunomura, M. Sawai, K. Asano, and P. K. Kaw. "Dynamic behaviors of dust particles in the plasma–sheath boundary." American Institute of Physics, 2001. http://hdl.handle.net/2237/7044.
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Taneda, Hiroshi. "The effect of a plasma sheath on hypersonic flight communications." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/42438.
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Ku, Victor Po-Tsung. "Experimental studies of capacitively coupled RF discharges." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318752.
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Langendorf, Samuel J. "Effects of electron emission on plasma sheaths." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54383.
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Current state-of-the-art plasma thrusters are limited in power density and thrust density by power losses to plasma-facing walls and electrodes. In the case of Hall effect thrusters, power deposition to the discharge channel walls and anode negatively impact the efficiency of the thruster and limit the attainable power density and thrust density. The current work aims to recreate thruster-relevant wall-interaction physics in a quiescent plasma and investigate them using electrostatic probes, in order to inform the development of the next generation of high-power-density / high-thrust-density propulsion devices.
Thruster plasma-wall interactions are complicated by the occurrence of the plasma sheath, a thin boundary layer that forms between a plasma and its bounding wall where electrostatic forces dominate. Sheaths have been recognized since the seminal work of Langmuir in the early 1900’s, and the theory of sheaths has been greatly developed to the present day. The theories are scalable across a wide range of plasma parameters, but due to the difficulty of obtaining experimental measurements of plasma properties in the sheath region, there is little experimental data available to directly support the theoretical development.
Sheaths are difficult to measure in situ in thrusters due to the small physical length scale of the sheath (order of micrometers in thruster plasmas) and the harsh plasma environment of the thruster. Any sufficiently small probe will melt, and available optical plasma diagnostics do not have the sensitivity and/or spatial resolution to resolve the sheath region.
The goal of the current work is to experimentally characterize plasma sheaths
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in a low-density plasma that yields centimeter-thick sheath layers. By generating thick sheaths, spatially-resolved data can obtained using electrostatic probes. The investigation focuses on the effects of electron emission from the wall and several factors that influence it, including wall material, wall temperature, wall surface roughness and topology, as well as the scaling of sheaths from the low-density plasma environment towards thruster conditions.
The effects of electron emission and wall material are found to agree with classical fluid and kinetic theory extended from literature. In conditions of very strong emission from the wall, evidence is found for a full transition in sheath polarities rather than a non-monotonic structure. Wall temperature is observed to have no effect on the sheath over boron nitride walls independent of outgassing on initial heat-up, for sub-thermionic temperatures. Wall roughness is observed to postpone the effects of electron emission to higher plasma temperatures, indicating that the rough wall impairs the wall’s overall capacity to emit electrons. Reductions in electron yield are not inconsistent with a diffuse-emission geometric trapping model. Collectively, the experimental data provide an improved grounding for thruster modeling and design.Current state-of-the-art plasma thrusters are limited in power density and thrust density by power losses to plasma-facing walls and electrodes. In the case of Hall effect thrusters, power deposition to the discharge channel walls and anode negatively impact the efficiency of the thruster and limit the attainable power density and thrust density. The current work aims to recreate thruster-relevant wall-interaction physics in a quiescent plasma and investigate them using electrostatic probes, in order to inform the development of the next generation of high-power-density / high-thrust-density propulsion devices.
Thruster plasma-wall interactions are complicated by the occurrence of the plasma sheath, a thin boundary layer that forms between a plasma and its bounding wall where electrostatic forces dominate. Sheaths have been recognized since the seminal work of Langmuir in the early 1900’s, and the theory of sheaths has been greatly developed to the present day. The theories are scalable across a wide range of plasma parameters, but due to the difficulty of obtaining experimental measurements of plasma properties in the sheath region, there is little experimental data available to directly support the theoretical development.
Sheaths are difficult to measure in situ in thrusters due to the small physical length scale of the sheath (order of micrometers in thruster plasmas) and the harsh plasma environment of the thruster. Any sufficiently small probe will melt, and available optical plasma diagnostics do not have the sensitivity and/or spatial resolution to resolve the sheath region.
The goal of the current work is to experimentally characterize plasma sheaths
xxvi
in a low-density plasma that yields centimeter-thick sheath layers. By generating thick sheaths, spatially-resolved data can obtained using electrostatic probes. The investigation focuses on the effects of electron emission from the wall and several factors that influence it, including wall material, wall temperature, wall surface roughness and topology, as well as the scaling of sheaths from the low-density plasma environment towards thruster conditions.
The effects of electron emission and wall material are found to agree with classical fluid and kinetic theory extended from literature. In conditions of very strong emission from the wall, evidence is found for a full transition in sheath polarities rather than a non-monotonic structure. Wall temperature is observed to have no effect on the sheath over boron nitride walls independent of outgassing on initial heat-up, for sub-thermionic temperatures. Wall roughness is observed to postpone the effects of electron emission to higher plasma temperatures, indicating that the rough wall impairs the wall’s overall capacity to emit electrons. Reductions in electron yield are not inconsistent with a diffuse-emission geometric trapping model. Collectively, the experimental data provide an improved grounding for thruster modeling and design.
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Stephens, Kenneth Frank. "Space-Charge Saturation and Current Limits in Cylindrical Drift Tubes and Planar Sheaths." Thesis, University of North Texas, 2000. https://digital.library.unt.edu/ark:/67531/metadc2598/.
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Space-charge effects play a dominant role in many areas of physics. In high-power microwave devices using high-current, relativistic electron beams, it places a limit on the amount of radiation a device can produce. Because the beam's space-charge can actually reflect a portion of the beam, the ability to accurately predict the amount of current a device can carry is needed. This current value is known as the space-charge limited current. Because of the mathematical difficulties, this limit is typically estimated from a one-dimensional theory. This work presents a two-dimensional theory for calculating an upper-bound for the space-charge limited current of relativistic electron beams propagating in grounded coaxial drift tubes. Applicable to annular beams of arbitrary radius and thickness, the theory includes the effect introduced by a finite-length drift tube of circular cross-section. Using Green's second identity, the need to solve Poisson's equation is transferred to solving a Sturm-Liouville eigenvalue problem, which is easily solved by elementary methods. In general, the resulting eigenvalue, which is required to estimate the limiting current, must be numerically determined. However, analytic expressions can be found for frequently encountered limiting cases. Space-charge effects also produce the fundamental collective behavior found in plasmas, especially in plasma sheaths. A plasma sheath is the transition region between a bulk plasma and an adjacent plasma-facing surface. The sheath controls the loss of particles from the plasma in order to maintain neutrality. Using a fully kinetic theory, the problem of a planar sheath with a single-minimum electric potential profile is investigated. Appropriate for single charge-state ions of arbitrary temperature, the theory includes the emission of warm electrons from the surface as well as a net current through the sheath and is compared to particle-in-cell simulations. Approximate expressions are developed for estimating the sheath potential as well as the transition to space-charge saturation. The case of a space-charge limited sheath is discussed and compared to the familiar Child-Langmuir law.
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Cagas, Petr. "Continuum Kinetic Simulations of Plasma Sheaths and Instabilities." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/84979.
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A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters, fusion devices, spacecraft-environment interactions, to name a few. This work aims to advance our understanding of fundamental plasma processes pertaining to plasma-material interactions, sheath physics, and kinetic instabilities through theory and novel numerical simulations. Key contributions of this work include (i) novel continuum kinetic algorithms with novel boundary conditions that directly discretize the Vlasov/Boltzmann equation using the discontinuous Galerkin method, (ii) fundamental studies of plasma sheath physics with collisions, ionization, and physics-based wall emission, and (iii) theoretical and numerical studies of the linear growth and nonlinear saturation of the kinetic Weibel instability, including its role in plasma sheaths.
The continuum kinetic algorithm has been shown to compare well with theoretical predictions of Landau damping of Langmuir waves and the two-stream instability. Benchmarks are also performed using the electromagnetic Weibel instability and excellent agreement is found between theory and simulation. The role of the electric field is significant during nonlinear saturation of the Weibel instability, something that was not noted in previous studies of the Weibel instability. For some plasma parameters, the electric field energy can approach magnitudes of the magnetic field energy during the nonlinear phase of the Weibel instability.
A significant focus is put on understanding plasma sheath physics which is essential for studying plasma-material interactions. Initial simulations are performed using a baseline collisionless kinetic model to match classical sheath theory and the Bohm criterion. Following this, a collision operator and volumetric physics-based source terms are introduced and effects of heat flux are briefly discussed. Novel boundary conditions are developed and included in a general manner with the continuum kinetic algorithm for bounded plasma simulations. A physics-based wall emission model based on first principles from quantum mechanics is self-consistently implemented and demonstrated to significantly impact sheath physics. These are the first continuum kinetic simulations using self-consistent, wall emission boundary conditions with broad applicability across a variety of regimes.Ph. D.
13
Morrison, John T. "Selective Deuteron Acceleration using Target Normal Sheath Acceleration." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365523293.
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Starkey, Ryan P., Mark J. Lewis, and Charles H. Jones. "PLASMA TELEMETRY IN HYPERSONIC FLIGHT." International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/607506.
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International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, CaliforniaProblems associated with telemetry blackout caused by the plasma sheath surrounding a hypersonic vehicle are addressed. In particular, the critical nature of overcoming this limitation for test and evaluation purposes is detailed. Since the telemetry blackout causes great concern for atmospheric cruise vehicles, ballistic missiles, and reentry vehicles, there have been many proposed approaches to solving the problem. This paper overviews aerodynamic design methodologies, for which the required technologies are only now being realized, which may allow for uninterrupted transmission through a plasma sheath. The severity of the signal attenuation is dependent on vehicle configuration, trajectory, flightpath, and mission.
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George, Kevin Mitchell. "Modifying the target normal sheath accelerated ion spectrum using micro-structured targets." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1482857706862922.
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Usoltceva, Mariia. "Advancements in Langmuir probe diagnostic for measurements in RF sheath and in modelling of the ICRF slow wave." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0061.
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Injecter de la puissance au plasma avec les ondes au voisinage de la fréquence cyclotron ionique (ICRF) est une technique prometteuse pour chauffer les plasmas de tokamak aux températures de fusion requises. Pour le rendement élevé, l'antenne ICRF doit être placée à proximité du plasma, mais ils accroissent les interactions plasma-paroi néfastes. Les ions accélérés par le champ électrique dans la gaine radiofréquence (RF) se sont avérés être à l'origine de ces interactions. La conception de l'antenne ICRF pourrait être optimisée pour réduire les effets observés. Ces études peuvent être réalisées sur une simple expérience dédiée. Aline (A Linear Experiment) est une machine linéaire avec un plasma cylindrique à basse température que s'appuie sur la caractérisation du plasma avec la sonde de Langmuir. Le champ magnétique modifie complètement le transport de particules dans le plasma. Par conséquent, les méthodes classiques d'analyse de sondes ne sont plus applicables. Cela est particulièrement vrai pour une sonde de Langmuir cylindrique de petit diamètre parallèle au champ magnétique ou avec un petit angle avec celui-ci. Les théories développées pour le traitement des données de la sonde de Langmuir pour le plasma magnétisé sont présentés. Les résultats sont comparés aux densités obtenues par interférométrie. Les techniques d'analyse des données présentées sont non seulement importantes pour l'application sur Aline, mais aussi pour d’autre machines à plasma magnétisé. IShTAR (Ion cyclotron Sheath Test Arrangement) fournit des conditions plus proches de celles du tokamak que celles d'Aline car possédant une antenne ICRF imitant celles d'un tokamak. L'objectif est d'étudier la propagation des ondes ICRF dans la configuration IShTAR. Les diagnostics de sonde ont été utilisés pour quantifier les paramètres plasma et les champs des ondes ICRF pertinents. Des simulations numériques de l'onde lente ICRF ont été réalisées à COMSOL. Le plasma a été mis en œuvre en tant que matériau avec des propriétés physiques ajustées manuellement. Les structures de champ obtenues pour l'onde lente diffèrent significativement de celles de l'onde rapide (autre solution de la relation de dispersion), et présentent une forte dépendance du profil de densité sur le bord du plasma. Les résultats de cette thèse contribuent aux études de la physique de la gaine RF sur des dispositifs linéaires dédiés, ainsi que de la physique des ondes ICRF sur le bord du plasma du tokamak en généralCoupling power to the plasma with ion cyclotron range of frequencies (ICRF) waves is a promising method for heating tokamak plasmas to fusion relevant temperatures. For high efficiency, the ICRF antenna must be placed close to the plasma, but they enhance destructive plasma-wall interactions. Plasma ions accelerated by the electric field in the radio-frequency (RF) sheath have been found to be the main cause of these interactions. The ICRF antenna design could be optimized to reduce the observed effects. The physics of these effects can be studied on a simple specially designed experiment. Aline (A LINear Experiment) is a linear low-temperature plasma device. The machine is focused on plasma characterization with the Langmuir probe diagnostic. The presence of magnetic field changes completely the particle transport in plasma, therefore conventional methods of data analysis are not applicable. Especially it is true for a small cylindrical Langmuir probe parallel to the magnetic field or at a small angle to it. In this thesis theories are presented which were developed for Langmuir probe data processing for magnetized plasma. The first results are also presented, as well as a comparison to line-averaged densities by interferometry. Presented data analysis techniques are not only important for application on Aline but can be used on any machine with magnetized plasma. IShTAR (Ion cyclotron Sheath Test Arrangement) is closer to tokamak conditions than Aline because it has an ICRF antenna which mimics tokamak antennas. In the framework of this thesis the objective is to study comprehensively the ICRF wave propagation in IShTAR configuration. Probe diagnostics were employed to quantify the relevant plasma parameters and the relevant ICRF wave fields. Numerical simulations of the ICRF slow wave were done in COMSOL. Plasma was implemented as a material with manually assigned physical properties. Field structures obtained for the slow wave differ significantly from the other mode, fast wave, and exhibit strong dependence on the density profile on the plasma edge. The results of this thesis work contribute to the studies of the RF sheath physics on dedicated linear devices, as well as the physics of ICRF waves on the tokamak plasma edge in general. In ICRF simulations for tokamak devices the slow wave propagation on the edge is avoided. Results of this thesis can be used to improve the complex tokamak ICRF simulations
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Takamura, S., N. Ohno, and T. Misawa. "Response to ‘‘Comment on ‘Dynamic behaviors of dust particles in the plasma–sheath boundary’’’[Phys. Plasmas 9, 1057 (2002) ]." American Institute of Physics, 2002. http://hdl.handle.net/2237/7017.
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Jeong, Hyunju. "Kinetic Simulations of Spacecraft Charging and Plasma Interactions in the Solar Wind." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/30237.
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Analytical and numerical studies are carried out to investigate spacecraft charging and plasma interactions in the solar wind. The physics of spacecraft charging in solar wind is determined by the mesothermal flow and the photoelectron sheath. In order to properly resolve both plasma flow and the photoelectron sheath, a 3-D full particle PIC model is applied. In this model, all plasma species (ambient ions and electrons, and photoelectrons) are modeled as macro-particles so the detailed dynamics of each species can be resolved around a charged spacecraft. In order to correctly resolve the mesothermal velocity ratio, PIC simulations are carried out using the real ion to electron mass ratio. A charging model based on the capacitance matrix method is integrated into the PIC model so the floating potential can be calculated self-consistently with the PIC code from charges deposited on the surface.
We first investigate the photoelectron sheath in the solar wind. Previous analytical studies of monotonic and non-monotonic sheath profiles in stationary electrons have suggested that there can exist two solutions of the sheath profiles when photoelectron emissions are significant. We extend the previous analytical approach to include the effects of drifting electrons. Full particle PIC simulations suggest that the non-monotonic sheath profile is the stable solution under solar wind conditions. We found that the current balance calculation is not an accurate method to predict the floating potential when photoelectron emissions are significant.
We next apply the simulation model to study spacecraft charging under various solar wind conditions. Due to photoelectron emissions, spacecraft charging is typically not a serious problem. The floating potential is ~2.5V under the mean solar wind condition. We also investigate the plasma interactions of a multi-body system consisting of a large platform and a small free flyer in the absence of photoelectron emissions where we set a free flyer at 2*Debye length behind the platform in the wake. For the particular system studied in this dissertation, the simulation shows that wake charging is not severe under both the mean solar wind condition and severe magnetosheath charging condition.Ph. D.
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Nunomura, S., N. Ohno, and S. Takamura. "Confinement and structure of electrostatically coupled dust clouds in a direct current plasma–sheath." American Institute of Physics, 1998. http://hdl.handle.net/2237/7004.
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Luddeni, Giovanni. "Improvement of a simulation platform for Helicon Plasma Thrusters: analysis of the boundary conditions and modelling of the sheath." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24296/.
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The proper treatment of the boundary conditions when dealing with fluid simulations of plasma processes constitutes a non-negligible issue that might affect the results, especially when dealing with plasma sources for propulsion applications, e.g., as in Helicon Plasma Thrusters (HPT). In this work, we handle the problem of boundary conditions modelling. Firstly, we have reviewed several established physical models to assess how to properly treat the HPTs. Then, three approaches to account for the sheath have been considered, namely, I) the direct solution of the sheath region through the finite volume discretization, II) the modelling of the sheath through analytical solutions, and III) a hybrid approach in which we coupled two distinguished solvers that handle respectively the bulk region of the plasma and the sheath.
The bulk region solver is based on the classical multi-fluid approach. The sheath is solved either by a fluid or a Lagrangian approach, to account for deviations from the Maxwellian velocity distribution function for each species present in the plasma. The proposed approaches have been tested in terms of plasma profiles (e.g., density) against the experimental case of a Piglet reactor. Generally, all three approaches have given a satisfactory agreement with the experimental measurements. In particular, the first and third approaches have shown similar results, with the latter being assessed with the fluid approach only. As for the computational cost, both methods required similar computation time. Regarding the second approach, the results under-estimate the plasma density if compared to the other methods. Nonetheless, this approach required 97% less computational effort. Ultimately, the hybrid approach achieved good results and it offers interesting possibilities of further development, some of which have been discussed.
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Dansereau, Jeffrey Paul. "An analytic-numerical scheme for a collisional Fokker-Planck time dependent sheath-presheath structure." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/17697.
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Kohno, Haruhiko. "Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/76360.
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Thesis (Sc. D. in Applied Plasma Physics)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 183-191).
Electromagnetic plasma waves in the ion cyclotron range of frequencies (ICRF) are routinely used in magnetic fusion experiments to heat plasmas and drive currents. However, many experiments have revealed that wave energy losses in the plasma edge and at the wall are significant, and detected that the acceleration of ions into the walls due to the formation of radio-frequency (RF) sheaths is one of the root causes of this problem. Since the RF-enhanced sheaths have many undesirable effects, such as impurity production and hot spot generation, a predictive numerical tool is required to quantitatively evaluate these effects with complicated boundary shapes of tokamaks taken into account. In this thesis the numerical code that solves self-consistent RF sheath-plasma interactions in the scrape-off layer for ICRF heating is developed based on a nonlinear finite element technique and is applied to various problems in the one-dimensional (1D) and two-dimensional (2D) domains corresponding to simplified models for the poloidal plane of a tokamak. The present code solves for plasma waves based on the cold plasma model subject to the sheath boundary condition, in which the most important physics that happens in the sheath is captured without using the field quantities in the sheath. Using the developed finite element code, several new properties of the RF sheath plasma interactions are discovered. First, it is found in the 1D domain that multiple roots can be present due to the resonance of the propagating slow wave and its nonlinear interaction with the sheath. Second, sheath-plasma waves are identified in a 2D slab geometry, and it is proved in conjunction with an electrostatic 2D sheath mode analysis that the sheath-plasma wave only appears in the vicinity of the sheath surface if the plasma density is greater than the lower hybrid density, and its wavelength depends on various parameters. Third, as a consequence of the self-consistent interaction between the propagating slow wave and the sheath, it is shown that the electric field distribution pattern in the plasma smoothly varies along the magnetic field lines between the conducting-wall and quasi-insulating limits. In the numerical analysis employing the 2D domain whose scale is equivalent to the Alcator C-Mod device, it is demonstrated that the calculated sheath potential can reach the order of kV, which is sufficient to yield enhanced sputtering at the wall. In addition, it is shown that the sheath potential in the close vicinity of the antenna current strap can be insensitive to the direction of the background magnetic field in the RF sheath dominated regime. Further, it is found from a series of nonlinear calculations that the sheath potential sensitively varies depending on the plasma density and electron temperature, which is consistent with the scaling derived from the Child-Langmuir law and the definition of the RF sheath potential. Lastly, a new finite element approach, which is named the finite element wave-packet method, is developed for the purpose of solving for multiscale plasma waves in the tokamak poloidal plane accurately with reasonable computational cost. This method is established by combining the advantages of the finite element and spectral methods, so that important properties in the finite element method, such as the sparsity of the global matrix and the ease in satisfying the boundary conditions, are retained. The present scheme is applied to some illustrative 1D multiscale problems, and its accuracy improvement is demonstrated through comparisons with the conventional finite element method.
by Haruhiko Kohno.
Sc.D.in Applied Plasma Physics
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Kubic, Martin. "Étude expérimentale d'interactions entre antennes HF et plasma périphérique d'un Tokamak." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0220/document.
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Les antennes en opération dans la gamme de fréquence cyclotron ionique représentent un moyen utile pour chauffer du plasma dans les tokamaks et autres plasmas de fusion. Ces systèmes de chauffage sont amenés à jouer un rôle important dans le projet ITER. Conjointement avec le chauffage souhaité, les interactions parasites avec le bord du plasma et de la limite des matériaux apparaissent. Plusieurs de ces effets délétères sont causés par la formation de la radio-fréquence des gaines. L'objectif de cette thèse est d'étudier, principalement de façon expérimentale, les modifications du plasma de bord «scrape-off layer» causées par les effets non-linéaires des gaines RF. Cela se fait en utilisant les sondes électrostatiques (de Langmuir, Retarded Field Analyser, tunnel) pour différentes configurations du plasma et des antennes: avec des études paramétriques en fonction du déséquilibre entre les émetteurs de l'antenne, de la puissance injectée et de la densité SOL. De plus, l'influence des gaines RF sur les mesures du potentiel de la gaine avec le RFA sont analysées. Cette étude s'effectue à l'aide d'un code 1D basé sur le modèle cinétique «particle-in-cell». Ces simulations ont montré que la RFA est capable de mesurer de manière fiable le potentiel gaine, toutefois cela reste limité pour les fréquences de plasma ionique wpi proche de la fréquence injectée wrf. Par contre, pour des conditions réelles du SOL (wpi>wrf), quand RFA est magnétiquement connectée à la structure de l'antenne RF, il est fortement sous-estimé. Enfin, les mesures de RFA dans Tore Supra indiquent que les potentiels RF se propagent au moins jusqu'à de 12m de l'antenne le long de lignes de champ magnétiquesAntennas operating in the ion cyclotron range of frequency (ICRF) provide a useful tool for plasma heating in many tokamaks and are foreseen to play an important role in ITER. However, in addition to the desired heating in the core plasma, spurious interactions with the plasma edge and material boundary are known to occur. Many of these deleterious effects are caused by the formation of radio-frequency (RF) sheaths. The aim of this thesis is to study, mainly experimentally, scrape-off layer (SOL) modifications caused by RF sheaths effects by means of Langmuir probes that are magnetically connected to a powered ICRH antenna. Effects of the two types of Faraday screens' operation on RF-induced SOL modifications are studied for different plasma and antenna configurations - scans of strap power ratio imbalance, injected power and SOL density. In addition to experimental work, the influence of RF sheaths on retarding field analyzer (RFA) measurements of sheath potential is investigated with one-dimensional particle-in-cell code. One-dimensional particle-in-cell simulations show that the RFA is able to measure reliably the sheath potential only for ion plasma frequencies wpi similar to RF cyclotron frequency wrf, while for the real SOL conditions (wpi > wrf), when the RFA is magnetically connected to RF region, it is strongly underestimated. An alternative method to investigate RF sheaths effects is proposed by using broadening of the ion distribution function as an evidence of the RF electric fields in the sheath. RFA measurements in Tore Supra indicate that RF potentials do indeed propagate from the antenna 12m along magnetic field lines
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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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Tomme, Edward B. "An investigation of dusty plasmas." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325244.
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Lu, LingFeng. "Modelling of plasma-antenna coupling and non-linear radio frequency wave-plasma-wall interactions in the magnetized plasma device under ion cyclotron range of frequencies." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0173/document.
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Le Chauffage Cyclotron Ionique (ICRH) par des ondes dans la gamme 30-80MHz est couramment utilisé dans les plasmas de fusion magnétique. Excitées par par des réseaux phasés de rubans de courant à la périphérie du plasma, ces ondes existent sous deux polarisations. L’onde rapide traverse le bord ténu du plasma par effet tunnel puis se propage à son centre où elle est absorbée. L’onde lente, émise de façon parasite, existe seulement à proximité des antennes. Quelle puissance peut être couplée au centre avec 1A de courant sur les rubans? Comment les champs radiofréquence (RF) proches et lointains émis interagissent-ils avec le plasma de bord par rectification de gaine RF à l’interface plasma-paroi? Pour répondre simultanément à ces deux questions, en géométrie réaliste sur l’échelle spatiale des antennes ICRH, cette thèse a amélioré et testé le code numérique SSWICH (Self-consitent Sheaths and Waves for ICH). SSWICH couple de manière auto-cohérente la propagation des ondes RF et la polarisation continue (DC) du plasma via des conditions aux limites non-linéaires de type gaine (SBC) appliquées à l’interface plasma / paroi. La nouvelle version SSWICH-FW est pleine onde et a été développée en deux dimensions (toroïdale/radiale). De nouvelles SBCs couplant les deux polarisations d’ondes ont été obtenues et mises en œuvre le long de parois courbes inclinées par rapport au champ magnétique de confinement. Avec ce nouvel outil en l'absence de SBCs, nous avons étudié l'impact d'une densité décroissant continûment à l'intérieur de la boîte d'antenne en traversant la résonance hybride basse (LH). Dans les limites mémoire de notre poste de travail, les champs RF au-dessous de la résonance LH ont changé avec la taille de maille. Par contre spectre de puissance couplée n’a que très peu évolué, et n’était que faiblement influencé par la densité à l'intérieur de l'antenne. En présence de SBCs, les simulations SSWICH-FW ont identifié le rôle de l'onde rapide sur l’excitation de gaines RF et reproduit certaines observations expérimentales clés. SSWICH-FW a finalement été adapté pour réaliser les premières simulations 2D électromagnétiques et de gaine-RF de la machine plasma cylindrique magnétisée ALINEIon Cyclotron Resonant Heating (ICRH) by waves in 30-80MHz range is currently used in magnetic fusion plasmas. Excited by phased arrays of current straps at the plasma periphery, these waves exist under two polarizations. The Fast Wave tunnels through the tenuous plasma edge and propagates to its center where it is absorbed. The parasitically emitted Slow Wave only exists close to the launchers. How much power can be coupled to the center with 1A current on the straps? How do the emitted radiofrequency (RF) near and far fields interact parasitically with the edge plasma via RF sheath rectification at plasma-wall interfaces? To address these two issues simultaneously, in realistic geometry over the size of ICRH antennas, this thesis upgraded and tested the Self-consistent Sheaths and Waves for ICH (SSWICH) code. SSWICH couples self-consistently RF wave propagation and Direct Current (DC) plasma biasing via non-linear RF and DC sheath boundary conditions (SBCs) at plasma/wall interfaces. Its upgrade is full wave and was implemented in two dimensions (toroidal/radial). New SBCs coupling the two polarizations were derived and implemented along shaped walls tilted with respect to the confinement magnetic field. Using this new tool in the absence of SBCs, we studied the impact of a density decaying continuously inside the antenna box and across the Lower Hybrid (LH) resonance. Up to the memory limits of our workstation, the RF fields below the LH resonance changed with the grid size. However the coupled power spectrum hardly evolved and was only weakly affected by the density inside the box. In presence of SBCs, SSWICH-FW simulations have identified the role of the fast wave on RF sheath excitation and reproduced some key experimental observations. SSWICH-FW was finally adapted to conduct the first electromagnetic and RF-sheath 2D simulations of the cylindrical magnetized plasma device ALINE
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Grobler, N. J. Marno. "Induktiefgekoppelde plasmas: die rol van die skermgas in hoëdrywingstoerusting." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/75751.
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Induktiefgekoppelde-plasmareaktore (IGP’s) het toepassings in verskeie industrieë, insluitend die voorbereiding van metaalpoeiers vir laagvervaardiging. Die skermgas (ook skutgas gnoem) speel ’n belangrike rol in die termiese afskerming van die reaktorwand in ’n IGP. Die energie wat verloor word deur die wand van die reaktor kan verminder word deur die hittesone weg van die wand af te beweeg. Hierdie verplasing van die hittesone word bereik deur ’n skermgas te gebruik wat moeiliker ioniseer as die plasmagas. Die ioniseringsgraad van waterstof is laer as dié van argon weens die hoër elektriese geleidingsvermoë van argon by soortgelyke temperature. Waterstof word dus in klein hoeveelhede in die skutgas gebruik met argon as die hoof bestandeel en hoofplasmagas. Die waterstof voorkom dus plasmavorming naby die wand. Die skutgas het ook ’n heelwat hoër vloeisnelheid en verminder sodoende die beskikbare tyd vir hitte-oordrag na die wand.
Die besondere hoë temperature wat in ’n IGP bereik word, belemmer egter die meting van eenvoudige lesings soos vloeisnelheid en temperatuur. Rekenaarmodelle voorsien ons van die geleentheid om die fisiese en chemiese eienskappe van ’n plasma te ondersoek asook die nodige gereedskap om die gedrag van die plasma te analiseer sonder eksperimentele lesings. Daar is verskeie numeriese modelle van IGP-sisteme in die literatuur alhoewel nie een van dié modelle die effek van die skutgassamestelling in ag neem nie. Die hoeveelheid waterstof in die skutgas kan groot newe-effekte hê op die plasmagas a.g.v. die hoër ionisasiepotensiaal van waterstof. ’n Oormaat waterstof in die skutgas is ook ’n verkwisting van voermateriaal. Albei die faktore het ’n invloed op die ekonomiese uitvoerbaarheid van die plasmaproses.
Hierdie navorsing het beoog om die optimale skutgassamestelling te vind vir die reaktor wat by Necsa gebruik word vir sferoïedisering. Die werk is uitgevoer met die kommersiële eindige-elementsagtewarepakket COMSOL Multiphysics R. Hierdie rekenaarmodel dui daarop dat die wand beskerm kan word van plasmavorming met ’n waterstof/argon skutgas wat sodoende ook die energieverliese deur die wand verminder. Waterstof verbeter die skutgas se hitte-oordragvermoë, maar verskuif die hittesone weg van die wand af. As gevolg van hierdie twee kompeterende meganismes bestaan daar ’n optimale bedrywingspunt by 3 vol% H2 in die skutgas. Die model is bevestig deur die energiebalans van die model te vergelyk met eksperimentele resultate.Dissertation (MEng)--University of Pretoria, 2020.
Advanced Metals Initiative Suid Afrikaanse Akademie vir Wetenskap en Kuns
Chemical Engineering
MEng
Unrestricted
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Tavant, Antoine. "Study of the plasma/wall interaction and erosion on a plasma thruster of low power." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX085.
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Les moteurs électriques pour satellites, qui accélèrent les ions d'un plasma, sont primordiaux pour le succès des missions spatiales (GPS, météo, communication, etc.).Le moteur à effet Hall fait partie des technologies les plus performantes et utilisées.Cependant, sa conception et son optimisation sont longs et coûteux, car des processus clefs sont encore mal compris, en particulier, le transport des électrons et l'interaction plasma-paroi.Afin d'étudier ces deux phénomènes, nous utilisons une simulation cinétique bidimensionnelle.Grace aux résultats de simulation 2D, nous avons mis en évidence que les électrons sont non-locaux, car ils sont absorbés plus vite aux parois qu'ils ne sont thermalisés par les collisions.En conséquence, nous avons développé un modèle de gaine avec une loi d'état polytropique pour les électrons, qui décrit plus précisément l'interaction plasma-surface.Ce modèle peut être utilisé en présence, ou non, d'émission électronique secondaire.Lorsque l'émission secondaire est présente, le modèle de gaine présente jusqu'à trois solutions, ce qui explique les oscillations de gaines observées dans les simulationsElectric propulsion systems that accelerate plasma ions are important for the success of spatial missions (GPS, weather forecast, communication, etc.).The Hall effect thruster is one of the most used and efficient technology.However, its conception and optimization is slow and costly, as key processes are still poorly understood, in particular the electron transport and the plasma-wall interaction.In order to study both phenomena, we use a bi-dimensional kinetic simulation.We showed with 2D PIC simulation results that electrons are non-local, as they are absorbed more quickly at the wall compared to the collision frequency.Consequently, we derived a non-isothermal sheath model using a polytropic state law for the electrons that describes more accurately the plasma-wall interaction.The model can be used with and without secondary electron emission.With electron emission, the sheath model can present up to three solutions, explaining the oscillations observed in the simulations.The azimuthal instability observed, responsible for the electron transport, is compared to the dispersion relation of the ion acoustic wave and the electron cyclotron drift instability.We show that, while the first linear stage of the instability is well understood, the saturated quasi-steady-state is affected by particle-wave interactions and non-linear mechanisms that are not included in the dispersion relation
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McMahon, Matthew M. "Modeling Ion Acceleration Using LSP." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440426562.
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Fanara, C. "A Langmuir multi-probe system for the characterization of atmospheric pressure arc plasmas." Thesis, Cranfield University, 2003. http://dspace.lib.cranfield.ac.uk/handle/1826/96.
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The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.
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Koch, Bernd. "Angular resolved measurements of particle and energy fluxes to surfaces in magnetized plasmas." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973051116.
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Carrere, Marcel Henri Michel. "Etude expérimentale d'un plasma de décharge à confinement multipolaire." Grenoble 1, 1994. http://www.theses.fr/1994GRE10039.
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Les decharges a confinement magnetique multipolaire excitees par des filaments emissifs sont largement utilisees pour des etudes fondamentales dans les plasmas. Le but de cette these est de comprendre leur fonctionnement et notamment comment l'energie est distribuee entre les electrons en l'absence de collisions. Apres la description d'un modele simple de bilan entre creation et pertes dans le plasma et le rappel de quelques instabilites, nous presentons une analyse detaillee de l'interaction filament-plasma et une etude de la correlation turbulence-temperature. L'equilibre thermique du filament est fortement couple a l'emission des electrons: il existe un profil de temperature le long du filament et l'emission d'electrons du filament vers le plasma presente deux etats stables. La transition du courant de decharge entre ces deux etats presente parfois un saut et un hysteresis lorsqu'on varie continument un parametre de controle de la decharge. Nous attribuons ce saut a un ecrasement de la gaine emissive. En l'absence de champ magnetique, la largeur de l'hysteresis est principalement regie par les profils de temperature et de potentiel le long du filament. Le champ magnetique local a la gaine introduit une brisure de symetrie supplementaire dans la dynamique des porteurs de charge. En l'absence de champ magnetique multipolaire nous avons trouve une correlation turbulence-temperature. Avec le champ magnetique multipolaire, pour des pressions superieures a 10##4 mb, nous observons la pression electronique est constante. En dessous de cette pression, le comportement du plasma est plus complexe. L'ensemble de ces resultats experimentaux ouvre des perspectives pour l'etude theorique et la modelisation numerique de ces decharges
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Jacquot, Jonathan. "Description non linéaire auto-cohérente de la propagation d'ondes radiofréquences et de la périphérie d'un plasma magnétisé." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0257/document.
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Une bonne compréhension des interactions entre les ondes à la fréquence cyclotronique ionique (FCI) (40-80MHz) et le plasma de bord est nécessaire pour injecter de fortes puissances dans un plasma de fusion en continu. Les objectifs de cette thèse étaient de modéliser séparément, avec Comsol Multiphysics, mais de façon compatible le couplage d'ondes et la formation de gaines radiofréquences (RF), qui rétroagissent sur le couplage, pour aboutir à terme à une modélisation auto-cohérente. Modéliser le couplage de l'onde rapide nécessite une description détaillée de l'antenne émettrice (2D ou 3D) et du plasma environnant par une approche pleine onde en plasma froid. L'absorption des ondes sortant du domaine de simulation est émulée par des couches parfaitement adaptées, rendues compatibles avec un tenseur diélectrique plasma. Les tendances expérimentales des résistances de couplage des antennes de Tore Supra sont qualitativement reproduites mais l'efficacité de couplage est surestimée. Parallèlement une description novatrice auto-cohérente, incluant les effets des gaines RF, de la propagation de l'onde lente et de la polarisation DC (Direct Current) du bord d'un plasma magnétisé a été développée avec le minimum d'ingrédients physiques. Dans le cas des antennes Tore Supra, le couplage du code avec TOPICA a permis d'expliciter qualitativement certaines observations inattendues sur un écran de Faraday dont le schéma électrique visait à minimiser les gaines RF. Un transport de courants DC dans la SOL est apparu nécessaire pour expliquer les structures radiales des mesures. Les barreaux coupés sont les éléments de l'antenne responsable de l'augmentation du potentiel plasmaA correct understanding of the interactions between the edge plasma and the ion cyclotron (IC) waves (40-80MHz) is needed to inject reliably large amount of power required for self-sustainable fusion plasmas. These thesis objectives were to model separately, with Comsol Multiphysics, but in compatible approaches the wave coupling and the radio-frequency (RF) sheath formation to anticipate development of a single code combining both. Modelling of fast wave coupling requires a detailed description of the antenna (2D or 3D) and of the plasma environment by a full wave approach for a cold plasma. Absorption of outgoing waves is emulated by perfectly matched layers, rendered compatible with a plasma dielectric tensor. Experimental trends for the coupling resistance of the antennas of Tore Supra are qualitatively reproduced but the coupling efficiency is overestimated. In parallel a novel self-consistent description, including RF sheaths, of the interplay between the cold wave propagation and DC biasing of the magnetized edge plasma of a tokamak was developed with the minimum set of physics ingredients. For Tore Supra antenna cases, the code coupled with TOPICA allowed to unveil qualitatively some unexpected observations on the latest design of Tore Supra Faraday screens whose electrical design was supposed to minimize RF sheaths. From simulations, a DC (Direct Current) current transport appears necessary to explain the radial structures of measurements. Cantilevered bars have been identified as the design element in the antenna structure enhancing the plasma potential
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Pigeon, Valentin. "Laser induced fluorescence study of plasma-insulator wall interaction involving secondary electron emission." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0307.
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Dans les propulseurs à effet Hall, l’interaction entre le plasma et les parois en céramique a un impact sur la durée de vie et les performances de ces machines. Ceci est dû en partie à l’émission d’électrons secondaires (EES), capable de refroidir le plasma et peut déclencher de la turbulence et des instabilités. Pour ces raisons, il est nécessaire de comprendre l’interaction plasma-céramique et d’évaluer l’impact de l’EES. Cette étude est destinée principalement à caractériser les gaines plasma faisant face aux céramiques des propulseurs à effet Hall. Celles-ci sont comparées aux gaines d’autres matériaux utilisés en physique des plasmas en précisant l’influence de l’EES. La partie expérimentale de cette étude repose principalement sur le diagnostic de fluorescence induite par laser permettant de sonder les gaines plasmas de manière non-intrusive. La structure des gaines, les variations de la densité ionique et la forme des fonctions de distribution ionique sont présentées et discutées. Il apparaît que la gaine varie d’un matériau à l’autre et que l’EES des céramiques de propulseurs est plus faible que celle des autres céramiques étudiées. Ce dernier résultat est cohérent avec de précédentes études. D’autre part, la densité ionique atteint un maximum près de l’entrée de la gaine, un résultat non prédit par les théories de gaine. Les résultats expérimentaux sont comparés à un modèle de gaine 1D cinétique et à des simulations cinétiques, qui tous deux utilisent des taux d’émission secondaire disponibles dans la littérature. Enfin, la première étape pour la mesure de gaines plasma hautement émissive par fluorescence induite par laser est présentéeIn Hall-effect ion thrusters, the interaction between the plasma and the ceramic walls has an impact on the devices’ lifetime and performances. This is partially due to the secondary electron emission (SEE), a phenomenon that may cool down the plasma, resulting in a lower ionization rate, and may trigger turbulence and instabilities. For these reasons, it is necessary to understand the plasma-ceramic wall interaction and evaluate the impact of the SEE. This study mainly focuses on plasma sheaths – the fundamental mechanism involved in plasma-wall interaction – standing in front of Hall thrusters’ ceramics. Those sheaths are compared to other materials’ ones used in plasma devices, and the influence of the SEE on them is studied. The experimental part of the study mainly relies on the laser induced fluorescence diagnostic that allows to probe plasma sheaths in a non-intrusive way. The sheaths’ structure, the ion density variations and the ion distribution functions’ shape are presented and discussed. It is shown that the sheath is material dependent and that the thrusters’ ceramics’ SEE is lower than for the other studied ceramics, which is coherent with previous measurements. Also, a peak in the ion density is observed near the sheath entrance, a result not captured by the classical sheath theory. These experimental results are compared with a 1D kinetic sheath model and kinetic simulations that use the SEE yields found in the literature. Finally, the first step of highly emissive plasma sheath measured with laser induced fluorescence is presented
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Ruffe, Remi. "Etude des surfaces de carbone en interaction avec le plasma de Tore Supra." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4799/document.
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Les tokamaks visent à réaliser la fusion contrôlée de noyaux de deutérium et de tritium par le confinement magnétique d'un plasma chaud. L'interaction entre le plasma et les parois a été étudiée en détail pour le tokamak Tore Supra. Au cours des décharges, le plasma interagit fortement avec le limiteur, formé de milliers de tuiles en composite carbone/carbone. L'érosion de ces tuiles par les flux de particules du plasma mène à la formation de co-dépôts de carbone et de deutérium qu'il est essentiel de limiter. Nous avons effectué une étude multi-échelle, principalement avec les différents outils de la microscopie électronique, sur des tuiles provenant du limiteur de Tore Supra. Une analyse des co-dépôts a permis de mettre en évidence leur topographie en forme de pointes, orientées dans une même direction quelque soit la position de la tuile sur le limiteur. L'étude de la surface de tuiles appartenant à des zones majoritairement érodées a révélé la présence d'une striation périodique de surface. Ces deux phénomènes ont été mis en relation avec la direction des flux et l'effet de la gaine faiblement magnétisée de Tore Supra a été mis en évidence. L'analyse des dépôts présents dans les interstices entre les tuiles a révélé une physique propre à ces interstices permettant la formation de dépôts en profondeur. Des nanoparticules graphitiques sphériques ont été observées, signe d'une croissance homogène locale en phase plasma. Nous avons développé des méthodes de mesure des volumes de dépôt et des volumes érodés, menant à l'établissement d'un bilan carbone et à l'évaluation de la masse de deutérium piégé, en bon accord avec les mesures in-situ réalisées dans Tore SupraTokamaks are devices aiming at achieving controlled fusion of deuterium and tritium by magnetically confining a hot plasma. The interaction between the plasma and the inner walls is a crucial issue and has been studied in detail in Tore Supra. During discharges the plasma strongly interacts with limiter, designed with thousands of carbon tiles (C/C composite). The plasma particle fluxes erode the tiles, leading to co-deposition of carbon and deuterium that should be limited. We have performed a multi-scale study of tiles extracted from the Tore Supra limiter, mainly using electron microscopy. The analysis of the co-deposits has revealed a tip-shaped topography, tips being oriented in the same direction wherever the tile over the limiter. Analyses of tiles extracted from erosion-dominated zones have revealed the presence of a periodic ripple on their surfaces. Both phenomena have been related with the direction of ion fluxes and the effect of the weakly magnetized sheath of Tore Supra has been shown. Analyses of the deposits inside the gaps in-between the tiles have revealed the existence of specific processes leading to the formation of deposits deeply inside the gaps. Graphitic nano-particles have been observed, showing the existence of local homogeneous growth processes. Finally, by measuring the deposit volume and the C/C composite eroded volume we have obtained an inventory of both carbon and deuterium which is consistent with the analyses of Tore Supra in-situ measurements
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Ngadjeu, Djomzoue Alain narcisse. "Etude des effets de gaine induites par une antenne de chauffage à la fréquence cyclotronique ionique (FCI, 30-80 MHz) et de leur impact sur les mesures par sondes dans les plasmas de fusion." Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10118/document.
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Ces travaux abordent la problématique des mesures de sonde de Langmuir dans un environnement RF. Les mesures expérimentales ont montré que des courants DC négatifs (électroniques) étaient collectés sur la structure d'une antenne ICRF sous tension, pendant que des courants DC positifs (ioniques) sont recueillis par une sonde de Langmuir à l'autre bout du tube de flux magnétique ouvert connecté à l'antenne, la sonde étant au potentiel de la machine. Un modèle de tube de flux asymétrique, de type de sonde double, est présenté. Celui-ci modélise un plasma, confiné le long des lignes de champ magnétique, ayant à chaque extrémité une électrode dont l'une est polarisée à un potentiel RF et l'autre à la masse. L'électrode polarisée modélise le potentiel RF résultant de l'intégration, le long d'une ligne champ magnétique, du champ électrique rayonné par les straps d'une antenne ICRF, tandis que l'autre électrode modélise la sonde au potentiel de la machine. Ce modèle permet d'expliquer l'apparition de courants DC en émettant simplement l'hypothèse qu'il faut à la fois une asymétrie de la source RF par rapport à une masse fixe, une conductivité RF transverse non nulle autorisant des courants RF transverses ainsi qu'une caractéristique courant-tension non linéaire due aux gaines pour favoriser des courants négatifs du côté RF et des courants positifs côté sonde. Ce modèle permet également de modéliser les caractéristiques Courant DC - Tension DC d'une sonde en présence de RF et ainsi d'évaluer les propriétés du plasma. Dans ce cas l'électrode modélisant la sonde n'est plus à la masse, mais à un potentiel donné. Des résultats analytiques sont trouvés dans certaines limitesThis work investigates the problematic of probe measurements in RF environment. DC currents flowing along magnetic field lines connected to powered ICRF antennas have been observed experimentally. Negative (i.e. net electron) current is collected on the powered ICRF antenna structure, while positive (i.e. net ion) current is collected by magnetically connected Langmuir probes. An asymmetric model based upon a double probe configuration was developed. The ICRF near field effect is mimicked by a ?driven? RF electrode at one extremity of an "active" open magnetic flux tube, where a purely sinusoidal potential is imposed. The other connection point is maintained at ground potential to model a collecting probe. This "active" flux tube can exchange transverse RF currents with surrounding "passive" tubes, whose extremities are grounded. With simple assumptions, an analytical solution is obtained. We can thus explain how DC currents are produced from RF sheaths. This model also makes it possible to model the characteristics DC Current' DC Voltage of a probe in the presence of RF and thus to evaluate some plasma properties. In this case the electrode at ground potential (probe) is polarized at a given potential. Analytical results are found within certain limits
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Urbanczyk, Guillaume. "Interaction of High-Power waves with the plasma periphery of WEST & EAST tokamaks." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0181.
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Cette thèse vise à étudier les interactions entre le plasma et les parois de tokamaks liées aux ondes à la fréquence cyclotronique ionique (FCI), les interactions plasma-métaux étant à éviter absolument car elles sont synonymes de dégradations matérielles de l’enceinte et la libération d’impuretés métalliques dans le plasma dont les performances s’en trouvent grandement réduites. Cette problématique affecte concrètement toute machine visant à chauffer les ions via des ondes à la fréquence FCI, ce qui sera notamment le cas d’ITER. Cette thèse s'inscrit dans une collaboration entre le CEA Cadarache (France) et l’Institut de Physique des Plasmas à Hefei (Chine). Divers travaux expérimentaux ont été effectués sur les tokamaks EAST (Chine) et WEST (France) afin d'identifier les paramètres pertinents pour d'une part optimiser l'efficacité par laquelle les ondes FCI utilisées pour chauffer le plasma doivent être excitées afin de maximiser la quantité de puissance couplée au plasma tout en minimisant les interactions du plasma avec les parois dues à ce type d'ondes et souvent attribuées au concept de gaine radiofréquence au cœur de cette thèseThis thesis aims at studying phenomena by which Ion Cyclotron Resonance Heating (ICRH) induces interactions between the plasma and the walls of tokamaks, the plasma-metal interactions being deleterious not only to prevent vessel materials degradation but also not to affect plasma performance due to the presence of heavy metallic impurity compared to foreseen fuel (namely deuterium and tritium). This problematic basically affects any machine aiming at heating the ions with waves at the ion cyclotron frequency, which in particular will be the case of ITER. This thesis is the result of a collaboration between CEA Cadarache (France) and the Institute of Plasma Physics in Hefei (China). Various experimental work have been carried out on the EAST (China) and WEST (France) tokamaks in order to identify the relevant parameters allowing to optimize the efficiency by which the ICRF waves – used to heat the plasma – must be excited in order to maximize the amount of power coupled, while simultaneously minimizing the plasma interactions with the walls due to this type of waves and the so called radiofrequency sheath excitation
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Takamura, S., M. Y. Ye, T. Kuwabara, and N. Ohno. "Heat flows through plasma sheaths." American Institute of Physics, 1998. http://hdl.handle.net/2237/6995.
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Javidi, Shirvan Alireza. "Modelling of Electric Arc Welding : arc-electrode coupling." Licentiate thesis, Högskolan Väst, Avd för maskinteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-5826.
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Arc welding still requires deeper process understanding and more accurateprediction of the heat transferred to the base metal. This can be provided by CFD modelling.Most works done to model arc discharge using CFD consider the arc corealone. Arc core simulation requires applying extrapolated experimental data asboundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arcmodel. The most critical part is then the interface layer between the electrodesand the arc core. This interface is complex and non-uniform, with specific physicalphenomena.The present work reviews the concepts of plasma and arc discharges that areuseful for this problem. The main sub-regions of the model are described, andtheir dominant physical roles are discussed.The coupled arc-electrode model is developed in different steps. First couplingsolid and fluid regions for a simpler problem without complex couplinginterface. This is applied to a laser welding problem using the CFD softwareOpenFOAM. The second step is the modelling of the interface layer betweencathode and arc, or cathode layer. Different modelling approaches available inthe literature are studied to determine their advantages and drawbacks. One ofthem developed by Cayla is used and further improved so as to satisfy the basicprinciples of charge and energy conservation in the different regions of thecathode layer. A numerical procedure is presented. The model, implementedin MATLAB, is tested for different arc core and cathode conditions. The maincharacteristics calculated with the interface layer model are in good agreementwith the reference literature. The future step will be the implementation of theinterface layer model in OpenFOAM.
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Scherner, Michael J. "The effects of moving electron density fluctuations on time domain reflectometry in plasmas." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-03172010-020634/.
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Neuman, William Albert. "Determination of surface plasma structures in the kinetic regime." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184326.
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A numerical study is done of a plasma in contact with a cold solid surface that is emitting a neutral gas. Two numerical models have been developed to describe the dominant phenomena of surface plasma structures. The first model entails a steady-state, kinetic treatment of the transport equations in one space dimension and one velocity dimension, to determine self-consistently the distribution functions of the interacting species and the electrostatic potential near the solid surface. The dominant phenomena in this region are the ionization of the neutral gas and the acceleration of the resulting ions by the electrostatic field in a pre-sheath region. Other effects involved are a Debye sheath structure between the solid surface and pre-sheath, and collisional trapping and untrapping of electrons in an electrostatic potential well that is predicted in the pre-sheath region. Results are presented from a nondimensional model with a monatomic returning neutral species and for diatomic molecular hydrogen returning from the surface. For each set of physical parameters chosen, a one parameter family of solutions is obtained. The second numerical model involves a steady-state treatment of the transport equations in a (x,v∥,v⊥) phase space for the interacting species. Included in this model are ionization of the refluxing monatomic neutrals, a self-consistently determined electrostatic potential and a nonlinear Fokker-Planck treatment of ion-ion Coulomb collisions. Both the region near the surface dominated by kinetic effects and the region away from the surface in which Coulomb collisional effects are significant are treated. Results are presented which identify the correct physical solution for the region near the surface from the permitted family found with the kinetic model. Additionally, results are shown which span a temperature range from the high temperature kinetic regime where Coulomb collisional effects are negligible, to the low temperature, highly collisional fluid regime. At low temperatures the collisional model agrees well with standard fluid techniques.
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Miller, Evan. "Magnetogenesis through Relativistic Velocity Shear." Thesis, Dartmouth College, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10001975.
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Magnetic fields at all scales are prevalent in our universe. However, current cosmological models predict that initially the universe was bereft of large-scale fields. Standard magnetohydrodynamics (MHD) does not permit magnetogenesis; in the MHD Faraday’s law, the change in magnetic field B depends on B itself. Thus if B is initially zero, it will remain zero for all time. A more accurate physical model is needed to explain the origins of the galactic-scale magnetic fields observed today. In this thesis, I explore two velocity-driven mechanisms for magnetogenesis in 2-fluid plasma. The first is a novel kinematic ‘battery’ arising from convection of vorticity. A coupling between thermal and plasma oscillations, this non-relativistic mechanism can operate in flows that are incompressible, quasi-neutral and barotropic. The second mechanism results from inclusion of thermal effects in relativistic shear flow instabilities. In such flows, parallel perturbations are ubiquitously unstable at small scales, with growth rates of order with the plasma frequency over a defined range of parameter-space. Of these two processes, instabilities seem far more likely to account for galactic magnetic fields. Stable kinematic effects will, at best, be comparable to an ideal Biermann battery, which is suspected to be orders of magnitude too weak to produce the observed galactic fields. On the other hand, instabilities grow until saturation is reached, a topic that has yet to be explored in detail on cosmological scales. In addition to investigating these magnetogenesis sources, I derive a general dispersion relation for three dimensional, warm, two species plasma with discontinuous shear flow. The mathematics of relativistic plasma, sheared-flow instability and the Biermann battery are also discussed.
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Gines, Arnold Rey Burgos. "Physics and engineering of sheet plasma devices." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13128127/?lang=0, 2019. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13128127/?lang=0.
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また、この研究は、特定の動作条件で生成されたシートプラズマで、プラズマやシートプラズマの寸法を決定する動作パラメータなどのプラズマ条件を理解し、最適化パラメータと将来の産業用アプリケーションの条件を導き出すことも目的としています。 そのため、この研究は、表面技術アプリケーション用のシートプラズマデバイスの開発と理解に貢献することを試みています。Sheet plasmas have the advantage of producing thin films and functional surfaces by generating localized high-density and temperature gradient regions suitable for specific reactions. A stream of high energy electrons from a plasma cathode efficiently excites and/or ionizes atomic and molecular species which are confined in a linear magnetic field. An electron cyclotron resonance (ECR) sheet plasma device employing a 2.45 GHz microwave source and combination of permanent magnets and field coils was designed and operated. The combined field realized a linear magnetic field that sustained a rectilinear confinement of the plasma.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
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Nagata, Daisuke. "Solar wind control of plasma number density in the near-earth plasma sheet." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136894.
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Storey, Jonathan. "Observations in the plasma sheet during substorm activity." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/30639.
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This thesis presents a statistical study of the plasma sheet location and thickness of the plasma sheet boundary layer, including the effect of magnetic and solar wind conditions. Next are presented two case studies of in-situ particle data from the Polar spacecraft as it entered and passed through the near-Earth plasma sheet during substorm activity. These data sets are compared with in-situ magnetic field measurements, from the Magnetic Fields Experiment (MFE), and remote observations of the aurora from the Ultra-Violet Imager (UVI). The latter, in conjunction with ground magnetograms, allow us to place the in-situ plasma flows in the overall context of the substorm phases. In the first case study the spacecraft entered the plasma sheet boundary layer (PSBL) and observed field-aligned ion beams, which were connected with field-aligned signature in MFE. When Polar entered the PSBL its footprint mapped to the poleward edge of an auroral double oval. Then, a decrease in the number and energy of the ions occurred, which coincided with the spacecraft footprint entering the central low-luminosity region of the UV double oval. After the spacecraft entered the CPS an expansion phase onset occurred, and Polar observed large ion count rate increases and depolarisation of the magnetic field. When Polar entered the PSBL in the second case study, which again coincided with entry into the auroral oval, there was evidence of pseudobreakups. Then the PSBL retreated over the spacecraft, which was mirrored in the ionosphere by equatorward motion of the auroral oval. Polar entered to the PSBL and rapidly entered the CPS when a substorm expansion phase onset occurred. Due to the large amount of substorm activity during these case studies, emphasis is placed on the use of both remote observations of the aurora and ground-based data to place the in-situ measurements in context.
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Xu, Lei. "Plasma arc welding fabrication using thin titanium sheet." Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605800.
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This work was motivated by the industrial and academic needs for process development of automated keyhole plasma arc welding (K-PA W) in thin Ti- 6AI-4V sheet and the control required for the process to be suitable for aerospace components. K-PAW, is a high energy density precision welding process which is a lowcost alternative to laser and electron beam welding. It is potentially capable of fabricating high integrity titanium alloy welds in aero-engine thin panel structures. However, the process has always represented a challenge owing to the complexity of welding torch configurations and the associated large number of process parameters to take into consideration. Three types of weld joint, which represent the welding fabrications in a simplified aero-engine casing component, were manufactured in the work: flat bead-on-plate, flat Tjoint and curved T -joint. A new welding procedure was developed to produce thin sheet T-joints by K-PAW, which has overcome the difficulty of operating the structurally complicated welding torch in limited space. An analytical model was experimentally validated and was employed to identify the process parametric envelopes for valid keyhole welding modes from the numerous possible parameter combinations. Weld joints were characterised in tenns of thermal history, micro-hardness and metallurgical microstructure. Distortion and residual stresses are maJor concerns associated with fusion welding fabrication. While distortions can lead to geometrical inaccuracy, paIticularly in the thin panel stl11ctures, residual stresses can combine with applied stresses to reduce the life of components. In this thesis, the out-of-plane l distortions of welded thin Ti-6AI-4V bead-on-plate and T-joint welds were measured using contact and non-contact coordinate-measuring techniques, from which the effects of welding sequence on the distortions can also be identified. Residual stress distributions in the welded sheet were detennined by synchrotron X-ray and neutron diffraction techniques. The use of synchrotron X-ray methods is relatively newly developed as titanium alloys respond weakly to neutron beams. These not only have provided improved understanding of residual stresses in thin sheet welds but also have greatly contributed to validation of finite element (FE) modelling work undertaken by other researchers.
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Wade, Neal S. "Dynamics of ions and neutral particles in the sheath region of processing plasmas." Thesis, University of Glasgow, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392428.
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Craig, Joseph Lackey. "Investigation of the shear layer versus the last closed flux surface on TEXT-upgrade." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3025208.
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Henderson, Paul David. "Cluster multi-point observations of the magnetotail plasma sheet." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1444299/.
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This thesis presents observations of the terrestrial magnetotail plasma sheet made by the European Space Agency Cluster mission. The Cluster mission is composed of four identical spacecraft, the first such multi-spacecraft mission, and enables, for the first time, the disambiguation of time versus space phenomena. Using the data from 2003, when the spacecraft were at their smallest average separation to date, many small-scale processes, both microphysical and macrophysical, are investigated. In the first study presented, two small flux ropes, a possible signature of multiple X-line reconnection, are investigated. By the development and utilisation of various multi-spacecraft methods, the currents and magnetic forces internal and external to the flux ropes, as well as the internal structure of the flux ropes, are investigated. In addition, a theory of their early evolution is suggested. In the second study presented, various terms of the generalised Ohm's law for a plasma are determined, including, for the first time, the divergence of the full electron pressure tensor, during the passage past the spacecraft of an active reconnection X-line. It is found that the electric field contribution from the divergence of the electron pressure tensor is anti-correlated with the contribution from the Hall term in the direction normal to the neutral sheet. In addition, further signatures of reconnection are quantified, such as parallel electric field generation and Hall quadrupolar magnetic field and current systems. In the final study presented, the anti-correlation between the divergence of the electron pressure tensor and Hall terms is investigated further. It is found that the anti-correlation is general, appearing in the direction normal to the neutral sheet because of a cross tail current. In a simple magnetohydrostatic treatment, a force balance argument leads to the conclusion that the gradient of the anti-correlation is a function of the ratio of the electron to ion temperatures, as well as providing information regarding the spatial scales of the pressure tensors.
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Dahlburg, Russell B. "Stability and transition of the driven magnetohydrodynamic sheet pinch." W&M ScholarWorks, 1985. https://scholarworks.wm.edu/etd/1539623755.
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The stability and transition properties of a bounded, current carrying magnetofluid are explored, using the hydrodynamic theory developed for plane shear flows as a guide. A driven magnetohydrodynamic sheet pinch equilibrium is employed. A sixth order, complex eigenvalue equation which governs the normal modes of small oscillations is derived, and solved numerically by the Chebyshev tau method. Eigenfunctions are shown, as well as the curve of neutral stability. The locus of critical Lundquist numbers has the form of a hyperbola. The nonlinear stability of a primary disturbance of the system is considered. For regions in parameter space close to criticality, a nonlinear stability equation of the Landau type is derived. These regions are characterized by low values of the Lundquist numbers, in contrast with the inviscid, highly conducting limit considered by Rutherford (1973). Amplitude phase planes for these disturbances are exhibited. The full set of two dimensional magnetohydrodynamic equations is solved numerically by a semi-implicit, mixed Fourier pseudospectral-finite difference algorithm. Both linear and random perturbations of the system are followed numerically into the nonlinear regime. Current sheets and deflection currents are nonlinear structures found to be significant to the evolution of the system. A secondary instability mechanism, the dynamic rupturing of the current density sheet, is also observed.