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1
Lai, Chi-hsuan. "Neutrino electron plasma instability /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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McGregor, Duncan Ekundayo. "Electron cyclotron heating and current drive using the electron Bernstein modes." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/212.
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Jacobson, Craig Michael. "Electron transport in plasmas with lithium-coated plasma-facing components." Thesis, Princeton University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3615076.
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The Lithium Tokamak Experiment (LTX) is a spherical tokamak designed to study the lowrecycling regime through the use of lithium-coated shells conformal to the last closed flux surface (LCFS). A lowered recycling rate is expected to flatten core Te profiles, raise edge Te, strongly affect n e profiles, and enhance confinement.
To study these unique plasmas, a Thomson scattering diagnostic uses a ≤ 20 J, 30 ns FWHM pulsed ruby laser to measure Te and ne at 11 radial points on the horizontal midplane, spaced from the magnetic axis to the outer edge at a single temporal point for each discharge. Scattered light is imaged through a spectrometer onto an intensified CCD. The diagnostic is absolutely calibrated using a precision light source and Raman scattering. Measurements of n e are compared with line integrated density measurements from a microwave interferometer. Adequate signal to noise is obtained with ne ≥ 2 ×10 18 m–3.
Thomson profiles of plasmas following evaporation of lithium onto room-temperature plasmafacing components (PFCs) are used in conjunction with magnetic equilibria as input for TRANSP modeling runs. Neoclassical calculations are used to determine Ti profiles, which have levels that agree with passive charge exchange recombination spectroscopy (CHERS) measurements. TRANSP results for confinement times and stored energies agree with diamagnetic loop measurements. Results of χe result in values as low as 7 m2/s near the core, which rise to around 100 m2/s near the edge. These are the first measurements of χe in LTX, or its predecessor, the Current Drive Experiment-Upgrade (CDX-U), with lithium PFCs.
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Sandoval, Parra Astor Emar. "Electron heating in a collisionless plasma." Tesis, Universidad de Chile, 2019. http://repositorio.uchile.cl/handle/2250/172658.
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Tesis para optar al grado de Magíster en Ciencias, Mención FísicaLos plasmas son comunes en diferentes sistemas astronómicos. Una parte importante de estos plasmas están en el régimen no colisional, en que el camino libre medio de las partículas que lo componen es más grande que el tamaño del sistema. Un ejemplo de este tipo de objetos es el disco de acreción que se encuentra en las cercanías del agujero negro ubicado en el centro de la Vía Láctea, Sagitario A* (Sgr A*). Por su baja colisionalidad, se espera que el plasma en Sgr A* no siga una distribución de Maxwell-Boltzmann. Además, por la mayor eficiencia radiativa de los electrones, es también esperable que estos tengan menor temperatura que los iones. El grado en que se calientan los electrones en un sistema no colisional, así como su espectro de energía, tienen importantes consecuencias observacionales. Existen diversos mecanismos que pueden transferir energía a los electrones. Entre ellos están: reconexión magnética, interacción onda-partícula, y viscosidad anisotrópica. En esta tesis nos enfocamos en el calentamiento de electrones por medio de la interacción onda partícula y por calentamiento viscoso. Para ello realizamos simulaciones ``particle-in-cell'' (o PIC) de un plasma no colisional, magnetizado y sujeto a un cizalle permanente. Este cizalle produce una amplificación del campo magnético, obteniéndose así una anisotropía de presión en las particulas, debido a la invarianza adiabatica de su momento magnetico. Esta anisotropía produce inestabilidades cinéticas en el plasma, las que propagan ondas en escalas del radio de Larmor de las partículas. Algunos ejemplos relevantes para nuestro estudio son las inestabilidades de whistler e ion-ciclotrón. Estas inestabilidades pueden resonar preferentemente con los electrones e iones, respectivamente, otorgando o quitando energía a las partículas. Realizamos simulaciones con moderadas razones de masa entre iones y electrones, para estudiar a los electrones en el régimen cinético. Consideramos consistentemente el régimen no-lineal y cuasi-estacionario de las inestabilidades. Estudiamos el calentamiento de los electrones, y se encontró que estos se calientan principalmente por viscosidad. Sin embargo, se encontró un calentamiento extra, el que es transferido desde los iones a los electrones debido a la interacción de estos últimos con las ondas ion-ciclotrón (las que a su vez son principalmente producidas por los iones). Este calentamiento extra aumenta con la magnetización y disminuye al aumentar la razón de masa y la temperatura de los iones. Además, la componente no térmica del espectro de energía de los electrones se ve fuertemente modificada cuando el radio de Larmor de estos es similar al de los iones. Esta componente no térmica se asemeja bastante a lo que se infiere de observaciones de sistemas como Sgr A*. Nuestro trabajo nos permitió entonces encontrar condiciones que facilitan el calentamiento y aceleración no térmica de electrones debido a la transferencia de energía entre iones y electrones en plasmas no colisionales.
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Bocoum, Maïmouna. "Harmonic and electron generation from laser-driven plasma mirrors." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX023/document.
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Dans cette thèse expérimentale, nous nous intéressons à la réponse non-linéaire d’un miroir plasma sous l’influence d’un laser d’intensité sous-relativiste (~10^18 W/cm^2), et de très courte durée (~30fs). Nous avons en particulier étudié la génération d’impulsions attosecondes (1as=10^(-18) s) et de faisceaux d’électrons en effectuant des expériences dites de « pompe-sonde » contrôlées. Un premier résultat important est l’observation d’une anti-corrélation entre l’émission X-UV attoseconde et l’accélération d’électron lorsque l’on change la longueur caractéristique du plasma, résultats confirmés par des simulations numériques. Un second résultat important concerne le diagnostique de l’expansion du plasma sous vide par « interférométrie en domaine spatial » (SDI), technique élaborée dans le cadre de cette thèse. Enfin nous discutons à deux reprises l’utilisation d’algorithmes de reconstruction de phase dans le domaine spatiale ou temporel.De manière plus générale, nous avons cherché à replacer ce travail de thèse dans un contexte scientifique plus général. En particulier, nous tentons de convaincre le lecteur qu’à travers l’intéraction laser-miroir plasma, il devient concevable de fournir un jour aux utilisateurs des sources peu onéreuses d’impulsions X-UV et de faisceaux d’électrons de résolutions temporelles inégaléesThe experimental work presented in this manuscript focuses on the non-linear response of plasma mirrors when driven by a sub-relativistic (~10^18 W/cm^2) ultra-short (~30fs) laser pulse. In particular, we studied the generation of attosecond pulses (1as=10^(-18) s) and electron beams from plasma mirror generated in controlled pump-probe experiment. One first important result exposed in this manuscript is the experimental observation of the anticorrelated emission behavior between high-order harmonics and electron beams with respect to plasma scale length. The second important result is the presentation of the « spatial domain interferometry » (SDI) diagnostic, developed during this PhD to measure the plasma expansion in vacuum. Finally, we will discuss the implementation of phase retrieval algorithms for both spatial and temporal phase reconstructions.From a more general point of view, we replace this PhD in its historical context. We hope to convince the reader that through laser-plasma mirror interaction schemes, we could tomorrow conceive cost-efficient X-UV and energetic electron sources with unprecedented temporal resolutions
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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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Alinder, Simon. "Electron cooling in a cometary coma." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-324842.
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The ESA Rosetta spacecraft investigated comet 67P/Churyumov-Gerasimenko duringtwo years from August 2014 to the end of September 2016. The dual Langmuir probewas used to measure plasma parameters including the thermal energy of theelectrons. The observed thermal energy (or temperature) of the electrons was ratherhigh, in the range 5-10 eV almost throughout the mission. However, near perihelionthe Langmuir probe measurements indicated the prevalence of two electronpopulations with distinct temperatures, one hot (5-10 eV) and one cold (less than 1eV). It has been hypothesized that the electrons of the colder population wereformed relatively close to the nucleus and that they subsequently cooled by inelasticcollisions with the neutral gas. In this project work we develop a model for studyingelectron cooling in a cometary coma. The model takes into account collisions withwater molecules as well as the influence of a radial ambipolar electric field.Rymdsonden Rosetta från ESA undersökte kometen 67P/Churyumov Gerasimenkounder mer än två år, från augusti 2014 till slutet av september 2016.En Langumirprob användes för att undersökta plasmamiljön runt kometen, tillexempel elektronernas termiska energi. Den observerade termiska energin förelektronerna (eller elektrontemperaturen) var ganska hög, ca 5-10 eV undernästan hela uppdraget, men när kometen var nära perihelium detekterade instrumentenäven kalla elektroner, med en energi under 1 eV, distinkta från devarma. En hypotes är att dessa kalla elektroner bildas nära kärnan av att varmaelektroner genomgår inelastiska kollisioner med den neutrala gasen och tapparsin energi. I detta projekt utvecklar vi en modell för att studera elektronernasbeteende i koman. Modellen tar hänsyn till kollisioner med neutrala vattenmolekylersåväl som påverkan av ett radiellt ambipolärt elektriskt fält.
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Löfgren, Torbjörn. "Numerical modeling of electron beam-plasma interactions." Doctoral thesis, KTH, Alfvén Laboratory, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2878.
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Merle, Antoine. "Stability and properties of electron-driven fi shbones in tokamaks." Palaiseau, Ecole polytechnique, 2012. https://pastel.hal.science/docs/00/77/31/03/PDF/Merle_PhD.pdf.
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In tokamaks, the stability of magneto-hydrodynamic modes can be modified by populations of energetic particles. In ITER-type fusion reactors, such populations can be generated by fusion reactions or auxiliary heating. The electron-driven fishbone mode belongs to this category of instabilities. It results from the resonant interaction of the internal kink mode with the slow toroidal precessional motion of energetic electrons and is frequently observed in present-day tokamaks with Electron Cyclotron Resonance Heating or Lower Hybrid Current Drive. These modes provide a good test bed for the linear theory of fast-particle driven instabilities as they exhibit a very high sensitivity to the details of both the equilibrium and the electronic distribution function. In Tore Supra, electron-driven fishbones are observed during LHCD-powered discharges in which a high-energy tail of the electronic distribution function is created. Although the destabilization of those modes is related to the existence of a fast particle population, the modes are observed at a frequency that is lower than expected. Indeed, the corresponding energy assuming resonance with the toroidal precession frequency of barely trapped electrons falls in the thermal range. The linear stability analysis of electron-driven fishbone modes is the main focus of this thesis. The fishbone dispersion relation is derived in a form that accounts for the contribution of the parallel motion of passing particles to the resonance condition. The MIKE code is developed to compute and solve the dispersion relation of electron-driven fishbones. The code is successfully benchmarked against theory using simple analytical distributions. When coupled to the relativistic Fokker-Planck code LUKE and to the integrated modeling platform CRONOS, it is used to compute the stability of electron-driven fishbones using reconstructed data from tokamak experiments. Using the code MIKE with parametric distributions and equilibria, we show that both barely trapped and barely passing electrons resonate with the mode and can drive it unstable. More deeply trapped and passing electrons have a non-resonant effect on the mode that is, respectively, stabilizing and destabilizing. MIKE simulations using complete ECRH-like distribution functions show that energetic barely passing electrons can contribute to drive a mode unstable at a relatively low frequency. This observation could provide some insight to the understanding of Tore Supra experimentsLa stabilité des modes magnéto-hydrodynamiques dans les plasmas de tokamaks est modifiée par la présence de particules rapides. Dans un tokamak tel qu'ITER ces particules rapides peuvent être soit les particules alpha créées par les réactions de fusion, soit les ions et électrons accélérés par les dispositifs de chauffage additionnel et de génération de courant. Les modes appelés fishbones électroniques correspondent à la déstabilisation du mode de kink interne due à la résonance avec le lent mouvement de précession toroidale des électrons rapides. Ces modes sont fréquemment observés dans les plasmas des tokamaks actuels en présence de chauffage par onde cyclotronique électronique (ECRH) ou de génération de courant par onde hybride basse (LHCD). La stabilité de ces modes est particulièrement sensible aux détails de la fonction de distribution électronique et du facteur de sécurité, ce qui fait des fishbones électroniques un excellent candidat pour tester la théorie linéaire des instabilités liées aux particules rapides. Dans le tokamak Tore Supra, des fishbones électroniques sont couramment observés lors de décharges où l'utilisation de l'onde hybride basse crée une importante queue de particules rapides dans la fonction de distribution électronique. Bien que ces modes soit clairement liés à la présence de particules rapides, la fréquence observée de ces modes est plus basse que celle prévue par la théorie. En effet, si on estime l'énergie des électrons résonants en faisant correspondre la fréquence du mode avec la fréquence de précession toroidale des électrons faiblement piégés, on obtient une valeur comparable à celle des électrons thermiques. L'objet principal de cette thèse est l'analyse linéaire de la stabilité des fishbones électroniques. La relation de dispersion de ces modes est dérivée et la forme obtenue prend en compte, dans la condition de résonance, la contribution du mouvement parallèle des particules passantes. Cette relation de dispersion est implémentée dans le code MIKE qui est ensuite testé avec succès en utilisant des fonctions de distributions analytiques. En le couplant au code Fokker-Planck relativiste LUKE et à la plate-forme de simulation intégrée CRONOS, MIKE peut estimer la stabilité des fishbones électroniques en utilisant les données reconstruites de l'expérience. En utilisant des fonctions de distributions et des équilibres analytiques dans le code MIKE nous montrons que les électrons faiblement piégés ou faiblement passants peuvent déstabiliser le mode de kink interne en résonant avec lui. Si l'on s'éloigne de la frontière entre électrons passants et piégés, les effets résonants s'affaiblissent. Cependant les électrons passants conservent une influence déstabilisante alors que les électrons piégées tendent à stabiliser le mode. D'autres simulations avec MIKE, utilisant cette fois des distributions complètes similaires à celles obtenues en présence de chauffage de type ECRH, montrent que l'interaction avec les électrons faiblement passants peut entraîner une déstabilisation du mode à une fréquence relativement basse ce qui pourrait permettre d'expliquer les observations sur le tokamak Tore Supra
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Reckenthäler, Peter. "Electron Pulses probing Plasma Dynamics and aligned Molecules." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-107542.
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Kennett, Eleanor. "Transmembrane Electron Transport Systems in Erythrocyte Plasma Membranes." University of Sydney. School of Molecular and Microbial Biosciences, 2005. http://hdl.handle.net/2123/620.
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Electron transport systems exist in the plasma membranes of all cells. Although not well characterised they play roles in cell growth and proliferation, hormone responses and other cell signalling events, but perhaps their most important role, especially in erythrocytes, is enabling the cell to respond to changes in both intra- and extracellular redox environments. Human erythrocytes possess a transmembrane electron transport capability that mediates the transfer of reducing equivalents from reduced intracellular species to oxidised extracellular species and is concomitant with proton extrusion. In the work for this thesis I showed that erythrocyte membranes contain a transmembrane WST-1 (water soluble tetrazolium-1) reductase activity that uses reducing equivalents from intracellular NADH to reduce extracellular WST-1. The rate of WST-1 reduction was increased by the presence of phenazine methosulfate and, although of low activity, it showed similar properties to a previously reported transmembrane NADH-oxidase activity. 1H NMR experiments showed that WST-1 was reversibly bound to the membrane and/or proteins in the membrane within the timeframe of the NMR experiment, confirming the location of the WST-1 reduction. Preliminary attempts to purify NADH:WST-1 reductase and NADH:ferricyanide reductase activities from the erythrocyte plasma membrane were inconclusive. The protein(s) responsible for the reduction of these oxidants appear to be of low abundance in the plasma membrane and may be part of a larger protein complex. Further work on the isolation of these redox activities is required before the protein(s) involved can be identified with any confidence. The ability of cells to export electrons suggests that an electron import mechanism might also exist to re-establish the cell�s redox-buffering equilibrium under conditions of oxidative stress. This hypothesis was tested in glucose-deprived erythrocytes using reduced glutathione and NADH as extracellular electron donors. It was shown that neither reduced glutathione nor NADH donated reducing equivalents through a transmembrane redox system. Extracellular NADH was, however, able to produce profound changes in starvation metabolism and methaemoglobin reduction rates. The addition of extracellular NADH caused a six-fold increase in the rate of lactate production above that observed in glucose-starved controls, together with a concomitant decrease in pyruvate production. In erythrocytes containing high levels of methaemoglobin, extracellular NADH increased the rate of methaemoglobin reduction in both the presence and absence of glucose. These results were explained by the leakage of lactate dehydrogenase from erythrocytes due to an admittedly low level of haemolysis. This caused the displacement of the intracellular pseudo-equilibrium of the lactate dehydrogenase reaction via transmembrane exchange of lactate, allowing the conversion of extracellular pyruvate to lactate and resulted in an increase in intracellular NADH concentrations. The latter increased the rate of methaemoglobin reduction. In conclusion, the work described in this thesis showed that erythrocyte membranes do not contain mechanisms for importing electrons or reducing equivalents from extracellular reduced glutathione or NADH. Erythrocytes do, however, contain an electron export system which can reduce extracellular oxidants such as WST-1 and the activity of this system depends on an intricate balance between intracellular antioxidants and enzyme activities. There is much still to be learnt about plasma membrane redox systems, little is known, for example, about the protein composition, mechanism of action, and the in vivo conditions under which these systems are most active.
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Lowe, Robert Edward. "Simulation of electron acceleration at collisionless plasma shocks." Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246324.
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Bansal, Parvinder S. "A pulsed electron cyclotron maser for plasma heating." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381504.
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Garner, R. C. (Richard Charles). "Electron microinstabilities in an ECRH, mirror-confined plasma." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15096.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Bibliography: leaves 198-201.
by Richard Charles Garner.
Ph.D.
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Haakonsen, Christian Bernt 1985. "Kinetic electron phenomena in dense magnetized plasma wakes." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103664.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.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 (pages 135-143).
Flow past an obstacle by dense magnetized plasma, having both Debye-length and gyroradii smaller than the obstacle, is explored using particle-in-cell (PIC) simulations. These simulations are relevant to a wide range of physical settings, ranging from the moon in the (supersonic) solar wind to Mach probes in (subsonic) tokamak plasmas. For supersonic flow, the evolution of the resulting elongated wake is captured with high-resolution 1D simulations, using kinetic electrons with realistic mass. This leads to the discovery of a novel wake phenomenon, where electron holes spawned from a narrow dimple in the velocity-distribution grow to large velocity extents, leading to disruption of the ion beams present in the wake. Those beams are the result of shadowing by the obstacle, which also occurs for electrons in what is a less elongated forewake, lying outside the traditional wake. This forewake is explored with 2D simulations, also using kinetic electrons with realistic mass, and it is found that drift-energization near the obstacle can significantly modify the electron distribution in some regions. Most significantly, drift-energization appears to quite robustly generate a slope-reversal of the electron velocity-distribution, which is expected to become unstable; this phenomenon thus provides a novel drive for forewake instability. 2D simulations at subsonic flow are used in an initial investigation of whether kinetic electron effects also impact the stability of wakes at slower flow. It is found that kinetic electrons do trigger disruption of the ion beams in the wake, as in the (supersonic) 1D simulations, but the hole-growth phenomenon cannot be conclusively implicated because a highly artificial electron mass needed to be used. In summary, the understanding of kinetic electron effects as dense magnetized plasma flows past an obstacle is greatly enhanced, uncovering a number of novel phenomena with implications for the stability of the resulting wake and forewake
by Christian Bernt Haakonsen.
Ph. D.
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Takahashi, Seiichi, Masatoshi Sato, and Yukiharu Ohsawa. "Parallel electric fields in nonlinear magnetosonic waves in an electron-positron-ion plasma." American Institite of Physics, 2008. http://hdl.handle.net/2237/12010.
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Keston, David Arthur. "Bernstein modes in weakly relativistic e'-e'+ plasma." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264260.
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Paro, Autumn D. "Modeling High Altitude Electron Density Plumes Using Direct Numerical Simulation." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/210.
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Electron densities form field-aligned structured regions in the natural ionosphere and after a high altitude nuclear explosion (HANE). These electron densities, known as plumes, are made up of many smaller individual field-aligned regions called striations. Striation modeling for systems effects has traditionally been done use a statistical approach. This statistical approach evolves different moments of the electron density. Due to lack of test data it has never been validated. The purpose of this project was to use a direct numerical simulation to solve equations governing the differential motion of individual striations. It was done in five steps: 1) Transport a single striation, 2) solve potential equation, 3) combine transport and potential equations, 4) optimize combined solver, and 4) simulate a fully-striated plume for comparison with the statistical model.
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Owen, J. A. "Effects of the relativistic correction to the electron mass on electron cyclotron current drive." Thesis, University of St Andrews, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370602.
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Laberge, Michel. "Electron acceleration in a plasma wave above a laser irradiated grating." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30725.
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The acceleration of electrons in a laser produced plasma wave was studied experimentally. A plasma with a modulated density was produced by illuminating a grating with a ruby laser at an intensity of 10¹⁰ W/cm². The plasma expanding above the surface of the grating was diagnosed using interferometry, shadowgraphy and Raman-Nath scattering. The plasma density was found to be modulated with an amplitude of [formula omitted]/n=8% for grating spacings ranging from 6 to 35 µm. A CO₂ laser of intensity 7xlO¹¹ W/cm2 then irradiated this modulated plasma and generated plasma waves. The phase speeds of the plasma waves are v[formula omitted] = ±[formula omitted]k[formula omitted], where k[formula omitted] is the wavenumber of the grating and [formula omitted] is the frequency of the CO₂ laser. Electrons were injected at an energy of 25 keV in one of the plasma waves. In order for the phase speed of the wave to synchronize with the accelerating electrons, a grating with constantly increasing line spacing was used.
No conclusive evidence of electron acceleration was obtained, even after the injection energy was increased to 92 keV. This lack of evidence was the result of a large electric field perpendicular to the surface of the grating, which deflected the electrons onto the grating. This detrimental electric field is produced when fast electrons are emitted by the plasma and leave it positively charged. At the low laser intensity used in this experiment, the origin of these electrons could not be identified. Some techniques to remedy this difficulty are proposed.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Spark, Stephen N. "Pulsed mm-wave electron cyclotron maser experiments." Thesis, University of Strathclyde, 1988. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21311.
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A pulsed Electron Cyclotron Maser (E. C. M.) was developed and used to generate high power mm-waves in the W-band (75-110GHz) and the G-band (150-220GHz) frequency ranges. The relativistic electron beam (R. E. B.) was produced from a field-immersed, field-emission, cold cathode. A shaped anode cavity was designed for the optimum cavity Q, resonant frequencies, relative mode density, reflection coefficients and mode conversion in the output coupler. Two pulsed conventional field coils were used; coil#1 (maximum B-field : 9T) produced the uniform intra-cavity magnetic field and coil#2 (maximum B-field : 1T) acted as a cathode field tuning coil. The addition of the cathode tuning coil increased the useful output energy in any pulse by a factor of =400. Four diagnostics were used to determine the characteristics of the maser; 1) direct uncalibrated power monitoring, 2) calibrated frequency measurements (made using a quasi-optical diffraction grating spectrometer), 3) near field radiation pattern measurements and 4) calibrated absolute power measurements (made using a thermopile calorimeter). The following characteristics of the maser oscillation were identified: in the W-band, single mode oscillation in the TE03 mode was observed, centred at 95.2GHz, with an output power of =50kW. The cavity was crudely step-tunable with the excitation of the TE13 mode at 81.4GHz and the TE12 mode at 88.OGHz. In the G-band, multi-mode oscillation was observed at all values of the intra-cavity magnetic field. With the increased mode density at these frequencies, the maser was quasi-continuously tunable and 200GHz oscillation was observed. These results proved to be self-consistent with the device-dependent calculations used to design the system and the general E. C. M. theory developed previously.
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Hammel, Benjamin Diethelm. "Study Of Intense Energetic Electron Beams In X-Pinch Experiments." Thesis, University of Nevada, Reno, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10161337.
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High-energy electron beams, with electron kinetic energies (∼1 MeV) much greater than the surrounding plasma temperature (<1 keV), are a common feature in Z-pinch pulsed power experiments. Their existence is indicated by non-thermal spectral signatures, such as high-energy Bremsstrahlung photons from the anode hardware and characteristic X-ray emission not representative of the pinch "hot-spot" temperatures. Despite their regular occurrence, the properties of these beams (kinetic energy, current) are not well known.
This dissertation describes an experimental study of X-pinch generated high-intensity electron beams, performed on the 1 MA pulsed power generator at the Nevada Terawatt Facility, and the feasibility of a novel method for inferring the total kinetic energy in the beam, through time-resolved measurements of the beam-induced shock that propagates through the anode.
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Önel, Hakan. "Electron acceleration in a flare plasma via coronal circuits." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2009/2903/.
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The Sun is a star, which due to its proximity has a tremendous influence on Earth. Since its very first days mankind tried to "understand the Sun", and especially in the 20th century science has uncovered many of the Sun's secrets by using high resolution observations and describing the Sun by means of models.
As an active star the Sun's activity, as expressed in its magnetic cycle, is closely related to the sunspot numbers. Flares play a special role, because they release large energies on very short time scales. They are correlated with enhanced electromagnetic emissions all over the spectrum. Furthermore, flares are sources of energetic particles. Hard X-ray observations (e.g., by NASA's RHESSI spacecraft) reveal that a large fraction of the energy released during a flare is transferred into the kinetic energy of electrons. However the mechanism that accelerates a large number of electrons to high energies (beyond 20 keV) within fractions of a second is not understood yet.
The thesis at hand presents a model for the generation of energetic electrons during flares that explains the electron acceleration based on real parameters obtained by real ground and space based observations.
According to this model photospheric plasma flows build up electric potentials in the active regions in the photosphere. Usually these electric potentials are associated with electric currents closed within the photosphere. However as a result of magnetic reconnection, a magnetic connection between the regions of different magnetic polarity on the photosphere can
establish through the corona. Due to the significantly higher electric conductivity in the corona, the photospheric electric power supply can be closed via the corona. Subsequently a high electric current is formed, which leads to the generation of hard X-ray radiation in the dense chromosphere.
The previously described idea is modelled and investigated by means of electric circuits. For this the microscopic plasma parameters, the magnetic field geometry and hard X-ray observations are used to obtain parameters for modelling macroscopic electric components, such as electric resistors, which are connected with each other. This model demonstrates that such a coronal electric current is correlated with large scale electric fields, which can accelerate the electrons quickly up to relativistic energies.
The results of these calculations are encouraging. The electron fluxes predicted by the model are in agreement with the electron fluxes deduced from the measured photon fluxes. Additionally the model developed in this thesis proposes a new way to understand the observed double footpoint hard X-ray sources.Die Sonne ist ein Stern, der aufgrund seiner räumlichen Nähe einen großen Einfluss auf die Erde hat. Seit jeher hat die Menschheit versucht die "Sonne zu verstehen" und besonders im 20. Jahrhundert gelang es der Wissenschaft viele der offenen Fragen mittels Beobachtungen zu beantworten und mit Modellen zu beschreiben. Die Sonne ist ein aktiver Stern, dessen Aktivität sich in seinem magnetischen Zyklus ausdrückt, welcher in enger Verbindung zu den Sonnenfleckenzahlen steht. Flares spielen dabei eine besondere Rolle, da sie hohe Energien auf kurzen Zeitskalen freisetzen. Sie werden begleitet von erhöhter Strahlungsemission über das gesamte Spektrum hinweg und setzen darüber hinaus auch energetische Teilchen frei. Beobachtungen von harter Röntgenstrahlung (z.B. mit der RHESSI Raumsonde der NASA) zeigen, dass ein großer Teil der freigesetzten Energie in die kinetische Energie von Elektronen transferiert wird. Allerdings ist nach wie vor nicht verstanden, wie die Beschleunigung der vielen Elektronen auf hohe Energien (jenseits von 20 keV) in Bruchteilen einer Sekunde erfolgt. Die vorliegende Arbeit präsentiert ein Model für die Erzeugung von energetischen Elektronen während solarer Flares, das auf mit realen Beobachtungen gewonnenen Parametern basiert. Danach bauen photosphärische Plasmaströmungen elektrische Spannungen in den aktiven Regionen der Photosphäre auf. Für gewöhnlich sind diese Potentiale mit elektrischen Strömen verbunden, die innerhalb der Photosphäre geschlossen sind. Allerdings kann infolge von magnetischer Rekonnektion eine magnetische Verbindung in der Korona aufgebaut werden, die die Regionen von magnetisch unterschiedlicher Polarität miteinander verbindet. Wegen der deutlich höheren koronalen elektrischen Leitfähigkeit, kann darauf die photosphärische Spannungsquelle über die Korona geschlossen werden. Das auf diese Weise generierte elektrische Feld führt nachfolgend zur Erzeugung eines hohen elektrischen Stromes, der in der dichten Chromosphäre harte Röntgenstrahlung generiert. Die zuvor erläuterte Idee wird mit elektrischen Schaltkreisen modelliert und untersucht. Dafür werden die mikroskopischen Plasmaparameter, die Geometrie des Magnetfeldes und Beobachtungen der harten Röntgenstrahlung verwendet, um makroskopische elektronische Komponenten, wie z.B. elektrische Widerstände zu modellieren und miteinander zu verbinden. Es wird gezeigt, dass der auftretende koronale Strom mit hohen elektrischen Feldern verbunden ist, welche Elektronen schnell auf hohe relativistische Energien beschleunigen können. Die Ergebnisse dieser Berechnungen sind ermutigend. Die vorhergesagten Elektronenflüsse stehen im Einklang mit aus gemessenen Photonenflüssen gewonnenen Elektronenflüssen. Zudem liefert das Model einen neuen Ansatz für das Verständnis der harten Röntgendoppelquellen in den Fußpunkten.
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Hasegawa, Hiroki, Shinsuke Irie, Shunsuke Usami, and Yukiharu Ohsawa. "Perpendicular nonlinear waves in an electron–positron–ion plasma." American Institute of Physics, 2002. http://hdl.handle.net/2237/7019.
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Cass, Ann C. "Experiments on vortex symmetrization in magnetized electron plasma columns /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9906488.
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Elahi, A. "Plasma electrochemistry : electron transfer at the solid/gas interface." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1427871/.
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The ability to control redox reactions at the solid/gas interface is demonstrated for the first time, by considering gaseous flame plasma as an electrolyte. An innovative method to perform potentio-dynamic experiments in a liquid-free electrochemical system using flame plasma is described. This novel approach can help apply the well-established foundations of electrochemistry developed almost exclusively in liquids, to the new context of gas plasma. There are limited examples using plasmas as media to study redox reactions but no examples of voltammetry in the gas phase at true solid/gas interfaces. Successful electrochemical measurements are illustrated by doping the flame plasma with both inorganic and organic species, and recording distinct faradaic peaks at defined potentials in cyclic voltammograms. The sensitivity of the system is highlighted by the ability to distinguish between several amino acids, pinpointing specific functional groups. The most significant innovation responsible for these measurements is the development of a reference electrode able to function at temperatures over 1300 K. Extensive assessment of several materials has enabled the development and optimisation of a reference electrode, allowing an extension of the potential window to 10 V; an unprecedented value in electrochemistry. After careful experimentation and appropriate control experiments, the features observed are confirmed as specific reduction processes at the solid/gas interface. Undoubtedly, and perhaps expectedly, there are significant departures from the analogous process in condensed phases. The physical origin of these electrochemical signals is discussed and a framework of interpretation upon which a full mechanistic understanding can be based is provided. The scope of commercial and academic impact is extensive. Liquid-free electrochemistry presents access to a plethora of redox reactions, which lie outside potential limits defined by liquids. The prospect of new redox chemistries will enable new technological applications such as electrodeposition and electroanalysis, which have significant economic and environmental benefits.
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Barroy, Pierre ReneÌ Jean. "Electron kinetics in non-equilibrium plasmas." Thesis, Open University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272394.
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Ouahioune, Nedjma. "Čerenkov emission of whistler waves by electron holes." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446395.
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Electron holes are positively charged nonlinear structures in which trapped electrons are supported by a positive electrostatic potential. These structure are regularly observed in space and laboratory plasmas by means of diverging bipolar electric field signatures. Recent observations and simulations have shown that fast moving electron holes can generate electromagnetic whistler waves via Čerenkov emission. The fast moving positive charge correspond to localised currents which can potentially excite waves. The aim of the project is to study both theoretically and numerically the properties leading to the Čerenkov emission of whistler waves by three-dimensional electron holes. In addition, efforts are dedicated to the derivation of a model providing the properties of emitted whistlers. The model is compared with the observational features of electromagnetic whistler waves generated by electron holes.
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Hughes, Ian G. "Electron ion and ion-ion collisions." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335410.
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Talaee, Omid. "Distribution of Electron Temperatures in Titan's Lower Ionosphere." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-194685.
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The report contained herein is a statistical analysis of electron temperatures withinTitan’s lower ionosphere. Electron temperatures in this altitudinal range are of greatimport for researchers. The main contributing factors are investigated to see whatphysical processes are the sources of variability in electron temperatures. Oneimportant result from this analysis lends itself to determining recombinationcoefficients thus determining organic process rates occurring within Titan’satmosphere. To accomplish this analysis, data from the Langmuir probe aboard the Cassini craft isutilized. The Langmuir probe is an instrument which can be used to measure currentdifferences in a plasma environment. From this, plasma properties such astemperature, density, and velocity can be calculated. It was named after IrvingLangmuir, whose theories became the basis for Orbit Motion Limited theory. Of the possible factors that determine the variation in electron temperatures, altitudewas the most evident and largest contributor. Once the data had been reduced toremove the effect of altitude on the temperature, other factors such as latitude, solarzenith angle, and ram angle were investigated to ascertain which, if any, wasresponsible for variations in temperature. Upon completion of the analysis, it waslearned that ram angle also had an identifiable effect upon electron temperatures. This effect was further investigated to ensure confidence in the results. Thecompletion of this part of the analysis showed that the effect shown with respect toram angle was indeed reproducible and that no other investigated factor had a majoreffect on electron temperatures. After the confidence procedure was completed,several previous studies findings were confirmed. These confirmed results include therelation of solar zenith angle with respect to both electron temperature distributionand density distribution, as well as a possible confirmation relating temperature anddensity for electrons.n/
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Wallace, Martin C. "Ion density fluctuations in plasma and their effects on hot electron generation /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FWallace.pdf.
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Duddy, Pamela E. "Electron scattering by molecular oxygen." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287611.
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Novotný, Oldřich. "Experimental Study of Electron-Ion Recombination Using Storage Ring and Afterglow Techniques." Doctoral thesis, Rennes 1, 2006. http://www.nusl.cz/ntk/nusl-266018.
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Kamperidis, Christos Antonios. "Investigation of Electron Laser Wakefield Acceleration in Novel Plasma Structures." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485616.
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This thesis presents experimental and simulation results on electron acceleration from the interaction of ultra-intense, ultra-short lasers with underdense plasmas, based on two schemes of the Laser Wakefield Acceleration (LWFA) mechanism. Using the 100 TW laser, in LUll, France, with pulse durations of 500 fsec and intensities' greater than 5.1018 W/cm2 , electron energies of up to 200 MeV,)Here observed. The spectra of the electron beams exhibit a maxwellian distribution, which together-with the recording of the Raman satellites of the laser spectrum suggest that we operate in the Self Modulated-LWFA, making these beams the highest energy observed to date, in that scheme. Total charge estimates suggest that a 1% energy transfer to the electron beam is possible. Occasional non-maxwellian features in the electron spectra, backed up by simulations, suggest that mechanisms other than SM-LWFA are also present in the interaction. Most importantly, self-guiding channels of - cm scales are observed adding a new perspective in achieving a commercially viable LWF accelerator. In the classical short pulse regime of LWFA, the ASTRA (0.6 J, < 50 fsec) laser is used to compare electron acceleration, with and without an external waveguide. Maximum electron energy results in the self-guided regime are only 2x lower compared to the externally guided case. The stability and reproducibility of the beam however, is improved when the external waveguide is used. Electron beams with 200 MeV maximum energy and narrow energy spread are consistently observed. The appearance of these beams is strongly linked with ionisation effects, either from high ion states of waveguide wall material, or recombined gas. A particle tracking code shows that electrons released from ionisation processes within the laser pulse, and hence within the plasma wake, are trapped by the wake and accelerated, pro.ducing a bunch with low energy spread. These lay the basis for future experiments, envisaging improved stability, wall-plug energy transfer efficiency and high brilliance electron beams.
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Kamperdis, Christos. "Investigation of Electron Laser Wakefield Accelaration in Novel Plasma Structures." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498528.
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Decker, Joan 1977. "Electron Bernstein wave current drive modeling in toroidal plasma confinement." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33937.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 333-340).
The steady-state confinement of tokamak plasmas in a fusion reactor requires non-inductively driven toroidal currents. Radio frequency waves in the electron cyclotron (EC) range of frequencies can drive localized currents and are thus particularly attractive for control of the current profile. In the high-[beta] regimes of spherical tokamaks (ST) such as NSTX and MAST, heating and current drive (CD) by conventional electron cyclotron waves is not possible. However, electron Bernstein waves (EBW) have been proposed as an alternative for CD in these overdense devices. Given the important role predicted for CD by EBWs in high-[beta] STs, a detailed study of EBWCD must be undertaken. In this thesis a systematic analysis of EBWCD is provided. In particular, the characteristics of EBWs, the physics of resonant wave-particle interaction, and the CD mechanisms are investigated in detail. The CD efficiency and the current deposition profile are calculated using the numerical code DKE, which solve the drift-kinetic equation. Two scenarios for EBWCD are identified. The first scenario consists of approaching a harmonic of the EC resonance from a lower B-field region and drives current in the plasma core using the Fisch-Boozer mechanism.
(cont.) The other scenario consists of approaching a harmonic of the EC resonance from a higher B-field region and drives current off-axis on the outboard side using the Ohkawa mechanism. Both schemes drive current in the toroidal direction opposite to the parallel wave vector. The EBWCI) efficiency is found to be higher than ECCD efficiency because the EBW power is deposited in the tail of the electron distribution function. The results of this thesis confirm the important role of EBWs for driving currents in high-[beta] plasmas. The analytical and numerical tools developed as part of this thesis can be used to design, predict, and analyze future EBWCD experiments. Among these tools is the kinetic solver DKE, which can be used for electron current drive calculations in toroidal plasmas for different types of radio-frequency waves, such as lower hybrid and electron cyclotron waves.
by Joan Decker.
Ph.D.
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Devine, Paul. "Simulations of electron whistler-mode waves in an anisotropic plasma." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260899.
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Rashid, Riyaz. "Low temperature electron cyclotron resonance plasma deposition of silicon dioxide." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620439.
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Buckner, A. J. F. "The theory of electron heating in collisonless plasma shock waves." Thesis, University of St Andrews, 1993. http://hdl.handle.net/10023/13973.
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Equations are derived to describe the evolution of an electron distribution function under the action of electromagnetic instabilities in a non-uniform plasma using an extension of the quasilinear theory of Kennel and Engelmann. Variations in both the electron density and temperature and the background magnetic field are taken into account. These equations are simplified in the limit of small electron beta so that an electrostatic approximation is justified. Methods are then presented which allow the solution of these equations (or, in principle, the more complex electromagnetic equations). In particular, a method of solving the kinetic dispersion relation for an arbitrary background (first-order) distribution function with the minimum of additional assumptions and approximations is described in detail. The electrostatic equations are solved for a number of different cases in order to study the action of the modified two stream instability on the electron distribution function. Throughout, realistic values of the ratios of electron to ion mass and electron plasma to cyclotron frequency ratio are used. The applications to collisionless plasma shock waves are discussed, and it is found that the modified two stream instability can produce the (relatively small) amounts of electron heating observed at quasi-perpendicular terrestrial bow shocks, and the flat-topped electron distribution functions seen to evolve. Extensions to the model which would greatly improve its applicability and accuracy, as well as the amount of computational effort required, are discussed.
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Green, James Simon. "Fast electron energy transport in high intensity laser-plasma interactions." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7688.
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This thesis presents experimental measurements of fast electron energy transport made using optical probing, x-ray and XUV imaging techniques. Hydrodynamic and hybrid particlein- cell (PIC) simulations were used to interpret the results. Measurements of fast electron heating patterns were made using the Vulcan 100 Terawatt (TW) and Petawatt (PW) lasers. For the first (100 TW) experiment the laser power was increased from 10 TW to 70 TW and a transition was observed between collimated electron flow and an annular transport pattern. Hybrid modelling showed that a form of beam hollowing accounted for this. Using the PW laser, a comparison was made of different diagnostic techniques for measuring the fast electron beam divergence. Cu K-alpha and optical probing measurements were found to be consistent, with both measuring a divergence angle significantly larger than that measured before at lower intensities. Several different target geometries were used to investigate how energy coupling from the laser into the fast electron beam is affected by the presence of a laser guide cone. Using the Vulcan PW laser, a significant decrease in energy coupling was observed when using metallic cone-slab targets. The addition of a cone assembly to plastic I AI sandwich targets acted to reduce the fast electron heating pattern. Novel cone-wire target geometries revealed that heating of a cone-guided wire plasma is maximised close to the wire surface. Computational modelling revealed that this is due to enhanced Ohmic heating. Finally, measurements were made of the dependence of laser intensity on the fast electron beam divergence. Data taken at intensities relevant to fast ignition was combined with previous published measurements. It was found that the divergence angle increased with laser intensity and had little dependence on pulse duration. PIC modelling was performed to analyse the data and possible explanations for the intensity dependence are discussed.
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Nagel, Sabrina Roswitha. "Studies of Electron Acceleration Mechanisms in Relativistic Laser-Plasma Interactions." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4639.
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Laser-plasma interactions have many potential applications, such as medical treatments,x-ray generation, particle acceleration and inertial confinement fusion (ICF).In all of these applications, understanding how laser energy is absorbed by the materialand converted into energetic electrons is very important. Therefore it is vitalto enhance the understanding of how these energetic electrons are created and whatmechanisms influence them. This Thesis comprises experimental studies of electron acceleration mechanismsin laser-plasma interactions, as well as simulations relevant to these experiments. The experiments described were conducted at the Rutherford Appleton Laboratoryutilising the VULCAN laser facility, and investigate laser interactions with both underdenseand overdense plasmas. In the underdense regime, the intensity dependence of the accelerated electronshas been studied experimentally, as well as the impact of the focusing geometry onthe generation of hot electrons. For high intensities, experimental measurementsshow a scaling of the temperature of the electrons with a0. Density and f-numberdependencies of the accelerated electrons are also observed. The effect of laser polarisation and target thickness on the escaping electronsis studied for laser interactions with solid targets, or overdense plasmas. It wasfound that the effective temperature of the electrons depends on both the laserpolarisation and the target thickness. The electron production from ultra-thin foils,and the effect of laser pre-pulse are also investigated.
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Bajlekov, Svetoslav. "Towards a free-electron laser driven by electrons from a laser-wakefield accelerator : simulations and bunch diagnostics." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:99f9f13a-d0c2-4dd8-a9a4-13926621c352.
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This thesis presents results from two strands of work towards realizing a free-electron laser (FEL) driven by electron bunches generated by a laser-wakefield accelerator (LWFA). The first strand focuses on selecting operating parameters for such a light source, on the basis of currently achievable bunch parameters as well as near-term projections. The viability of LWFA-driven incoherent undulator sources producing nanojoule-level pulses of femtosecond duration at wavelengths of 5 nm and 0.5 nm is demonstrated. A study on the prospective operation of an FEL at 32 nm is carried out, on the basis of scaling laws and full 3-D time-dependent simulations. A working point is selected, based on realistic bunch parameters. At that working point saturation is expected to occur within a length of 1.6 m with peak power at the 0.1 GW-level. This level, as well as the stability of the amplification process, can be improved significantly by seeding the FEL with an external radiation source. In the context of FEL seeding, we study the ability of conventional simulation codes to correctly handle seeds from high-harmonic generation (HHG) sources, which have a broad bandwidth and temporal structure on the attosecond scale. Namely, they violate the slowly-varying envelope approximation (SVEA) that underpins the governing equations in conventional codes. For this purpose we develop a 1-D simulation code that works outside the SVEA. We carry out a set of benchmarks that lead us to conclude that conventional codes are adequately capable of simulating seeding with broadband radiation, which is in line with an analytical treatment of the interaction. The second strand of work is experimental, and focuses on on the use of coherent transition radiation (CTR) as an electron bunch diagnostic. The thesis presents results from two experimental campaigns at the MPI für Quantenoptik in Garching, Germany. We present the first set of single-shot measurements of CTR over a continuous wavelength range from 420 nm to 7 μm. Data over such a broad spectral range allows for the first reconstruction of the longitudinal profiles of electron bunches from a laser-wakefield accelerator, indicating full-width at half-maximum bunch lengths around 1.4 μm (4.7 fs), corresponding to peak currents of several kiloampères. The bunch profiles are reconstructed through the application of phase reconstruction algorithms that were initially developed for studying x-ray diffraction data, and are adapted here for the first time to the analysis of CTR data. The measurements allow for an analysis of acceleration dynamics, and suggest that upon depletion of the driving laser the accelerated bunch can itself drive a wake in which electrons are injected. High levels of coherence at optical wavelengths indicate the presence of an interaction between the bunch and the driving laser pulse.
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Goldberg, Lars [Verfasser], and Bernhard [Akademischer Betreuer] Schmidt. "Spectroscopic Electron Density Determination of Plasma Targets for Plasma Wakefield Acceleration / Lars Goldberg ; Betreuer: Bernhard Schmidt." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1178672786/34.
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Svensson, Martin. "Electron heating in collisionless shocks observed by the MMS spacecraft." Thesis, Luleå tekniska universitet, Rymdteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67892.
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Shock waves are ubiquitous in space and astrophysics. Shocks transform directed particle flow energy into thermal energy. As the major part of space is a collisionless medium, shocks in space physics arises through wave-particle interactions with the magnetic field as the main contributor.The heating processes are scale dependent. The large scale processes governs the ion heating and is well described by magnetohydrodynamics. The small scale processes governs the electron heating lies within the field of kinetic plasma theory and is still today remained disputed. A step towards the answer for the small scale heating would be to measure the scale, in order to relate it to a known instability or other small scale processes.The multi-spacecraft NASA MMS spacecraft carries several high resolute particle and field instruments enabling almost instantaneous 3D particle measurements and accurate measurements of the magnetic field. Also the separation between the four MMS spacecraft is as small as < 8km for a certain mission phase. This allows for new approaches when determining the scale which for shocks has not been possible before when using data from previous multi-spacecraft missions with spacecraft separation much larger. The velocity of the shock is large compared to the spacecraft,thus the shock width cannot be directly measured by each spacecraft. Either a constant velocity has to be estimated or we could use gradients of a certain parameter between the spacecraft as the shock flows over them. The usage of gradients is only possible with MMS as all the spacecraft could for MMS be within the shock simultaneously. The change for a parameter within the shockis assumed to be linear between the spacecraft and measurements. It is also assumed that the gradient of the parameter maximizes in the shock normal direction. Using these assumptions two methods have been developed. They have the same working principles but are using two or four spacecraft for linear estimation at each measurement point. From the gradient and parametric data the shock ramp width could then be found. The parameter used in this thesis is the electron temperature. The methods using one, two and four spacecraft were tested using electron temperature data from different shock crossings. Two problems with the gradient methods were found from the results, giving false data for certain time spans. To avoid these problems, the scale of the electron temperature gradient was determined for roughly half the shock ramp. It was found using the two and four spacecraft methods that an assumption of constant velocity for the shock speed is an uncertain assumption. The shock speed varies over short time scales and in the shock crossings analysed the constant velocity estimations were generally overestimated. From the two and four spacecraft methods roughly half of the temperature rise in the shock ramp occurred over 10.8km or 12.4 lpe. This is almost a factor of two greater than previous scale estimates using Cluster data and a multi-spacecraft timing method for shock speed estimation.From the results it is concluded that the methods when using gradients between spacecraft has some restrictions. They can only be used for MMS data, requires quasi-perpendicular high Mach number and will give false results if the temperature is disturbed by interacting hot plasma clouds. However, even though we have these limitations for the tested gradient methods, they were found better and more reliable compared to previous methods for shock scaling.
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Touati, Michaël. "Fast Electron Transport Study for Inertial Confinement Fusion." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0076/document.
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Un nouveau mod`ele r´eduit pour le transport de faisceaux d’´electrons relativistes dans des solide ou des plasma denses est propos´e. Il est bas´e sur la r´esolution des deux premiers moments angulaires de l’´equation cin´etique relativiste, compl´et´es par une relation de fermeture d´eduite du principe de maximisation de l’entropie angulaire de Minerbo. Le mod`ele prend en compte aussi bien les effets collectifs du transport avec les champs ´electromagn´etiques auto g´en´er´es que les effets collisionnels li´es au ralentissement des ´electrons par collision sur les plasmons, les ´electrons li´es et les ´electrons libres du milieu ainsi que leur diffusion angulaire par collisions sur les ´electrons et les ions. Le mod`ele permet une r´esolution num´erique rapide des ´equations du transport de faisceau d’´electrons rapides tout en d´ecrivant l’´evolution cin´etique de leur fonction de distribution. Malgr´e le fait de travailler avec les grandeurs angulaires moyennes, le mod`ele a ´et´e valid´e par comparaison avec des solutions analytiques d´eriv´ees dans un cas acad´emique de transport de faisceau mono ´energ´etique et collimat´e dans un plasma dense et chaud d’Hydrog`ene ainsi qu’avec une simulation PIC hybride dans un cas r´ealiste de transport d’´electrons acc´el´er´es par laser dans une cible solide. Le mod`ele est appliqu´e `a l’´etude de l’´emission de photons Kα lors d’exp´eriences laser-plasma ainsi qu’a` la g´en´eration d’ondes de chocA new hybrid reduced model for relativistic electron beam transport in solids and dense plasmas is presented. It is based on the two first angular moments of the relativistic kinetic equation completed with the Minerbo maximum angular entropy closure. It takes into account collective effects with the self-generated electromagnetic fields as well as collisional effects with the slowing down of the elec- trons in collisions with plasmons, bound and free electrons and their angular scattering on both ions and electrons. This model allows for fast computations of relativistic electron beam transport while describing the kinetic distribution function evolution. Despite the loss of information concerning the angular distribution of the electron beam, the model reproduces analytical estimates in the academic case of a collimated and monoenergetic electron beam propagating through a warm and dense Hydro- gen plasma and hybrid PIC simulation results in a realistic laser-generated electron beam transport in a solid target. The model is applied to the study of the emission of Kα photons in laser-solid experiments and to the generation of shock waves
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Reid, Remington R. "Microwave Emission and Electron Temperature in the Maryland Centrifugal Experiment." Thesis, University of Maryland, College Park, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3590773.
Full textAbstract:
The use of two magnetised plasma waves as electron temperature diagnostics for the Maryland centrifugal ecperiment (MCX) are explored. First, microwave emission in the whistler mode is examined and ultimately found to be a poor candidate for diagnostic purposes owing to reflections from elsewhere in the plasma confusing the signal. Second, the electron Bernstein wave is found to offer promise as means to measure the radial electron temperature profile. Several numeric codes are developed to analyze the observed microwave emission and calculate the electron temperature profile. Measurements of electron Bernstein wave emission indicate that the electrons in the plasma attain temperatures close to 100 eV. Clear evidence is shown that the measurements are not influenced by reflections or emission from hot (Te > 1keV) superthermal electrons. The measured electron temperature is shown to be in reasonable agreement with recent measurements of the plasma ion temperature.
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Mollart, T. P. "Electron emission processes in cold cathode thermal arcs." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5546/.
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In this Thesis the processes of electron emission from cathode electrodes are studied theoretically, and the applicability of these mechanisms to the non refractory cathodes that can be used to sustain thermal arcs was examined. Apparatus that was used to generate and manipulate thermal arcs along rail electrodes is described in this thesis. Techniques for driving arcs over polished sample electrodes with magnetic or aerodynamic forces are outlined. Scanning electron microscopy was used to study emission site formation on highly polished electrodes with a natural 2.5 nm oxide layer. Theoretical maximum electron current densities that can be extracted by the arc were calculated and these were used, in conjunction with information from the experimental work, to make estimates of the lifetime of emission spots that are seen on the cathode electrodes of thermal arc devices. The lifetime was found to be dependent on the arc velocity over a range of velocity values from 3 to 80 ms(^-1). The lifetime measured ranged from 2.4 µs to 0.024 µs. Experiments on arcs driven at a constant velocity using a combination of aerodynamic and magnetic forces showed that the formation of emission spots was independent of die applied external magnetic field. The presence of artificially grown copper (11) oxide layers, 50 nm and 100 nm thick, were found to influence the lifetime. The effect of the oxide layer was predicted using a simple model accounting for the change of resistance that such an oxide layer would be expected to cause. Additional experiments showed that the resistance of the arc was independent of the oxide layer thickness, as predicted by the model.
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McKitterick, David. "Phonon probing of magnetically quantised 2D electron systems." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359910.
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Chen, Chen. "Electron Temperature Enhancement Effects on Plasma Irregularities Associated with Charged Dust in the Earth's Mesosphere." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/25937.
Full textAbstract:
Recently, experimental observations have shown that Polar Mesospheric Summer Echoes PMSE may be modulated by radio wave heating the irregularity source region with a ground-based ionospheric heating facilities. It is clear from these past
investigations that the temporal behavior of PMSE during ionospheric heating shows promise as a diagnostic for the associated dust layer. To investigate the temporal behavior of plasma irregularities thought to produce PMSE, this work describes a new model that incorporates both finite diffusion time effects as well as dust charging. The hybrid model utilizes fluid ions described by continuity and momentum equations, electrons whose behavior is determined from quasi-neutrality, and charged dust described by the standard Particle-In-Cell PIC method. The model has been used to investigate the temporal behavior of charged dust associated electron irregularities during electron temperature enhancement associated with radio wave heating. The model predicts that the temporal behavior of the irregularities depends on the ratio
of the electron-ion ambipolar diffusion time to the dust particle charging time Td/Tc. The results indicate that typically for Td/Tc << 1, an enhancement in electron irregularity amplitude occurs for a period after turn-off of the radio wave heating. The work also predicts that for Td/Tc >> 1, an enhancement in electron irregularity amplitude occurs for a time period after the turn-on of the radio wave heating. Due to the dependence of Td on irregularity scale-size, these results have important implications
for observations of PMSE modification at different radar frequencies. Both continuous and discrete charging model were embedded into this computational model, the results were compared and analyzed.
It is evident that significant diagnostic information may be available about the dust
layer from the temporal behavior of the electron irregularities during the heating process which modifies the background electron temperature. Particularly interesting and important periods of the temporal behavior are during the turn-on and turn-off of the radio wave heating. Although a number of past theoretical and experimental
investigations have considered both these on and off period, this dissertation considers further possibilities for diagnostic information available as well as the underlying physical processes. Approximate analytical models are developed and compared to a more accurate full computational model as a reference. Then from the temporal behavior of the electron irregularities during the turn-on and turn-off of the radio wave
heating, the analytical models are used to obtain possible diagnostic information for various charged dust and background plasma quantities.
Finally, two experiment campaigns have been performed at HAARP, Gakona, Alaska. Preliminary observation results look promising for the existence of PMSE turn-on overshoot. However, more careful experiments need to be done before firm conclusions can be drawn. The new designed Echotek digital receiver is ready for use now. It will be much superior to the experimental setup used for measurements in the previous campaign.Therefore, future experimental campaigns are planning next year to support the theoretical research.Ph. D.
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Ali, Safdar. "Electron - Ion Recombination Data for Plasma Applications : Results from Electron Beam Ion Trap and Ion Storage Ring." Doctoral thesis, Stockholms universitet, Fysikum, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75311.
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This thesis contains results of electron-ion recombination processes in atomic ions relevant for plasma applications. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. Dielectronic recombination (DR) cross sections, resonant strengths, rate coefficients and energy peak positions in H-like and He-like S are obtained for the first time from the EBIT measurements. Furthermore, the experimentally obtained DR resonant strengths are used to check the behaviour of a scaling formula for low Z, H-and He-like iso-electronic sequences and to update the fitting parameters. KLL DR peak positions for initially He- to B-like Ar ions are obtained experimentally from the EBIT measurements. Both the results from highly charged sulfur and argon are compared with the calculations performed with a distorted wave approximation. Absolute recombination rate coefficients of B-like C, B-like Ne and Be-like F ions are obtained for the first time with high energy resolution from storage ring measurements. The experimental results are compared with the intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients of each of these ions are obtained by convoluting the energy dependent recombination spectra with a Maxwell-Boltzmann energy distribution in the temperature range of 103-106 K. The resulting plasma rate coefficients are presented and compared with the calculated data available in literature.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 5: Accepted. Paper 6: Manuscript. Paper 7: Manuscript.