Philosophiae Doctor - PhD / In this thesis, using multispecies fluid plasma models, nonlinear electrostatic solitary wave fluctuations will be investigated in magnetized plasmas. The different models used for the investigation will be guided by the satellite observations in different regions of the Earth magnetosphere. These investigations will enable us to attempt theoretical explanations for the nonlinear potential structures observed in the satellite data. Multispecies plasma consisting of cool and hot electrons with Maxwellian distributions and fluid ions will be considered to study low frequency solitons. The ions will be considered as magnetized. The study will be extended to include magnetized oxygen ions. The model will be modified for regions of the magnetosphere consisting of two ions having Maxwellian distributions and magnetized electrons. The nonthermal distributions of energetic hot electrons and the Maxwellian distributions of cool electrons with magnetized cold ions fluid will also be considered. For all the models, the effect of ion and electron densities, temperatures, magnetic field strength and propagation angle will be studied during the investigation of soliton structures. In all the above mentioned studies, arbitrary amplitude theory is carried out by the Sagdeev pseudo-potential method. Further investigations on the charateristics and existence domains of the solitons is found both analytically and numerically, using satellite data where applicable

Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 124-131). Available also in a digital version from Dissertation Abstracts.

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).

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 96-100).

The electrodynamic interaction of Ganymede’s mini-magnetosphere with Jupiter’s corotating magnetospheric plasma has been shown to give rise to strong current systems closing through the moon and its ionosphere as well as through its magnetopause and magnetotail current sheet. This interaction is strongly evidenced by the presence of aurorae at Ganymede and of a bright Ganymede footprint on Jupiter’s ionosphere. This footprint is located equatorward of the main auroral emissions, at the magnetic longitude of the field line threading Ganymede. The brightness of Ganymede’s auroral footprint at Jupiter along with its latitudinal position have been shown to depend on the position of Ganymede relative to the center of the Jovian plasma sheet. Additionally, observations using the Hubble Space Telescope showed that Ganymede’s auroral footprint brightness is characterized by variations of three different timescales: 5 hours, 10-40 minutes, and ~100 seconds. The goal of the present study is to examine the relationship between the longest and the shortest timescale periodicities of Ganymede’s auroral footprint brightness and the local processes occurring at Ganymede. This is done by coupling a specifically developed brightness model to a three-dimensional multifluid model which tracks the energies and fluxes of the various sources of charged particles that precipitate into Ganymede’s ionosphere to generate the aurora. It is shown that the predicted auroral brightnesses and morphologies agree well with observations of Ganymede’s aurora from the Hubble Space Telescope. Our results also suggest the presence of short- and long-period variabilities in the auroral emissions at Ganymede due to magnetic reconnections on the magnetopause and in the magnetotail, and support the hypothesis of a correlation between the variability of Ganymede’s auroral footprint on Jupiter’s ionosphere and the variability in the brightness and morphology of the aurora at Ganymede. Finally, the modeled aurora at Ganymede reveals that the periodicities in the morphology and brightness of the auroral emissions are produced by two different dynamic reconnection mechanisms. The Jovian flow facing side aurora is generated by electrons sourced in the Jovian plasma and penetrating into Ganymede’s ionosphere through the cusps above the separatrix region. In this case, the reconnection processes responsible for the auroral emissions occur on Ganymede’s magnetopause between the Jovian magnetic field lines and the open magnetic field lines threading Ganymede’s Polar Regions. As for the magnetotail side aurora, it is generated by electrons originating from Ganymede’s magnetospheric flow. These electrons are accelerated along closed magnetic field lines created by magnetic reconnection in Ganymede’s magnetotail, and precipitate into Ganymede’s ionosphere at much lower latitudes, below the separatrix region.

La reconnexion magnétique est un processus fondamental de conversion d'énergie qui se produit dans les plasmas spatiaux ainsi que dans les plasmas de laboratoire. La reconnexion a lieu dans des couches de courant très fines et a comme conséquence la reconfiguration de la topologie magnétique et la conversion d'énergie magnétique dans l'accélération et le réchauffement des particules. Actuellement, le rôle de la reconnexion magnétique est reconnue comme un processus majeur dans l’environnement Soleil-Terre, depuis la couronne solaire jusque dans vent solaire, dans la magnétogaine ainsi qu'à la magnétopause et dans la queue magnétique. La reconnexion se déclenche dans la région de diffusion électronique. Dans cette région, les électrons se démagnétisent et sont accélérés par les champs électriques de reconnexion. Malgré les progrès déterminants dans la compréhension du processus de la reconnexion magnétique qui ont été accomplis grâce à l'utilisation des mesures in-situ en synergie avec les simulations numériques, la physique de la région de diffusion aux échelles électroniques est encore largement inconnue. Ce n'est que dans les dernières années, avec le lancement de la mission Magnetospheric MultiScale (MMS) et l'impressionnant augmentation des capacités de calcul des superordinateurs, que la dynamique de la région de diffusion électronique a commencée à être comprise. Une des questions fondamentales - qui reste encore sans réponse - est de comprendre si la structure de la région de diffusion électronique est homogène ou hétérogène aux échelles électroniques et même au-dessous de ces échelles.La finalité de ma recherche est d’avancer dans la compréhension de la structure de la région de diffusion des électrons avec deux approches diffèrent : les observations par satellites et simulations numériques complètement cinétique de type Vlasov.La première partie de ce mémoire présente les observations issus des satellites MMS en traversant la magnétopause en proximité du point sub-solaire et avec une séparation très petite entre les satellites ($sim 6$ km) i.e. comparable à la longueur d'inertie des électrons $d_e sim 2$ km.L’analyse des donnée montre que la région de diffusion électronique n'est pas homogène en terme de courant électrique et de champ électrique aux échelles électroniques et que la distribution spatiale de la conversion d'énergie est irrégulière aux échelles électroniques. Ces observations indiquent que la structure de la région de diffusion électronique peut être bien plus compliquée que ce qu'indiquent des études expérimentales antérieures et les simulations numériques de type PIC.La présente analyse des données MMS a souligné la nécessité de réaliser des simulations avec une résolution spatiale plus élevée et un bruit numérique négligeable - en particulier pour le champ électrique - pour progresser dans la compréhension des processus cinétiques qui interviennent aux échelles électroniques. En poursuivant cette motivation, la deuxième partie du mémoire est consacrée à l'étude de la région de diffusion électronique en utilisant un nouveaux modèle Eulérien Vlasov-Darwin complètement cinétique qui nous avons implémenté dans le code numérique ViDA. Le code ViDA a été spécifiquement conçu pour perfectionner notre compréhension de la dynamique des plasmas non collisionnels aux échelles cinétiques en donnant accès aux détails de la fonction de distribution électronique dans l’espace de phase. Une première partie est consacrée aux tests du code avec une simulation 2D de la reconnexion magnétique symétrique. Les données de simulation avec bruit négligeable ont été utilisées par la suite pour étudier la contribution des différents termes qui forment la loi d’Ohm dans la région de diffusion électronique. Nous avons traité en particulier la contribution du terme d’inertie électronique qui est responsable de la démagnétisation des électrons. / Magnetic reconnection is a fundamental energy conversion process occurring in space and laboratory plasmas. Reconnection takes place in thin current sheets leading to thereconfiguration of magnetic field topology and to conversion of magnetic energy into acceleration and heating of particles. Today reconnection is recognized to play a key role in the Earth-solar environment, from the solar corona to the solar wind, to magnetosheath, at the Earth's magnetopause, and in the magnetotail. Reconnection is initiated in the Electron Diffusion Region (EDR), where electrons decouple from the magnetic field and are energized by electric fields. Despite the very significant advances that have been made in the understanding of the magnetic reconnection process by means of in-situ measurements (notably provided by the Cluster mission) and by numerical simulations, the small electron scale physics of the dissipation region remains basically unsolved.It is only in the last years, with the launch of the Magnetospheric MultiScale mission (MMS) together with the recent impressive increasing of computational capabilities of supercomputers, that the dynamics of the Electron Diffusion Region has started to be enlightened. One of the key, yet still open questions, is whether the EDR has a preferred homogeneous or inhomogeneous structure at electron scales and below.The purpose of this Thesis is to advance in the understanding of the structure of the Electron Diffusion Region using two different approaches, notably MMS spacecraft observations and kinetic full Vlasov simulations. The first part presents MMS observations of an EDR encounter at the subsolar magnetopause when the four MMS probes were located at the smallest interspacecraft separationof $sim 6 $ km, which is comparable to a few electron inertial length ($d_e sim 2$ km).We find that the EDR is rather inhomogeneous at electron scales in terms of current density and electric field which appear to be different at different spacecraft. In addition, the pattern of the energy conversion is patchy, showing that the structure of the EDR at the magnetopause can be much more complex than it has been found in other MMS events and than it is usually depicted by kinetic PIC simulations.Our MMS data analysis has pointed out the need of simulations with better spatial resolution and low noise on the electron scales, in particular on the electric field, in order to better understand the kinetic physics at play at electron scales. Following this motivation, the second part of the Thesis aims at studying the EDR by using a novel fully-kinetic Eulerian Vlasov-Darwin model which we have implemented in the numerical ViDA code.The ViDA code is specifically designed to improve our understanding of the kinetic dynamics of collisionless plasma at electron scales by giving access to the fine phase space details of the electron distribution function. A first part is devoted to the testing of the code by performing 2D symmetric magnetic reconnection simulations. Then, low-noise simulation data have been used to investigate the contribution of the different terms in the Ohm's law in the EDR, focusing on the contribution of the electron inertia term which is responsible for the decoupling of the electron dynamics from the magnetic field.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21769号 / 工博第4586号 / 新制||工||1715(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 小嶋 浩嗣, 准教授 海老原 祐輔, 准教授 三谷 友彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / by Thomas Marshall Eubanks. / M.S.

The Turning Point Method (TPM) for the evaluation of ion scattering in a sheath of a biased probe immersed in an unmagnetized plasma is reviewed. The TPM implemented originally in a computer program for spherical probes is expanded to include cylindrical probes as well as the evaluation of the turning angle of the charged particle (repelled or attracted) around the probe. TPM results have the potential to provide a standard against which to compare more complicated current collection simulations. TPM results are validated by comparing with Laframboise's earlier work for current collection in the Orbital Motion Limited regime. Calculations of the turning angle of a charged particle with specific energy and angular momentum revealed that higher plasma shielding limits the range of impact parameters that experience significant scattering, and that attracted particles entering tangent to the sheath experience increased scattering. The TPM results also show that there are significant changes in orbital trajectories between different space charges within the Orbital Motion Limited limit.