La reconnexion magnétique est un mécanisme fondamental de conversion d'énergie dans le plasma. Il se déroule dans les régions minces de fort courant appelées couches de courants, et produit le chauffage et l accélération des particules. Dans un milieu turbulent, la reconnexion magnétique a été observée dans de petites structures qui se forment dans celui-ci, et on a postulé que cela contribue de façon importante la dissipation de l'énergie turbulente l'échelle cinétique. Pour ce travail, nous examinons les données des satellites Custer dans la magnétogaine de la Terre, en aval du choc quasi-parallèle. La détection des couches de courant d'échelle ionique a été réalisé par l'application de la méthode de la variance partielle des incréments (PVI) pour des satellites multiples. Les proprietées des couches de courant observées étaient différentes pour des valeurs de l'indice PVI élevées(PV I > 3) et bas (PV I < 3). Nous avons observé une population distincte de haut indice PVI (> 3) structures qui représentaient ~ 20% du total. Ces couches de courant ont une rotation du champ magnétique élevée (> 90o). Afin d'estimer le chauffage local survenant dans ces couches de courant, une estimation de la température des électrons a été obtenue à haute résolution temporelle (125ms) parles distributions d'électrons partielles mesurées par Cluster. Cela a permis pour la première fois d'étudier le chauffage d'électrons localisés dans les couches de courant d'échelle ionique. L'augmentation observée de la température des électrons estimée dans les couches de courant aux PVI élevées suggèrent qu'ils sont importants pour le chauffage local d'électrons et de dissipation d'énergie. Nous avons également examiné les mesures l'intérieur de la région de diffusion d'une couche de courant o la reconnexion magnétique est en cours. Les observations simultanées par des satellites multiples permettent aussi d'étudier les distributions d'électrons et l'activité des ondes à des distances différentes de la ligne x. Des différences significatives ont été observées dans les populations d'électrons comme ils ont été chauffés en passant par la couche de courant. En particulier, les électrons sont chauffés dans la direction parallèle au champ magnétique proximité de la ligne x, alors qu'aucune variation significative n'a été observée dans la direction perpendiculaire. Cependant,la distribution est plus isotrope en aval de la ligne x, chauffées par des électrons dans la direction perpendiculaire. / Magnetic reconnection is a fundamental energy conversion process in plasma. It occurs in thin regions of strong current known as current sheets and results in particle heating and acceleration. In turbulence, which is ubiquitous in space plasma, magnetic reconnection has been observed to occur in small scale structures that form therein, and is thought to contribute to dissipation of turbulent energy at kinetic scales. For this work we examine data from the Cluster spacecraft in the Earth's magnetosheath, downstream of the quasi-parallel shock. The detection of ion-scale current sheets was performed by implementing the PartialVariance of Increments (PVI) method for multiple spacecraft. The properties of the observed current sheets were different for high (> 3) and low (< 3) values of the PVI index. We observed a distinct population of high PVI (> 3) structures that accounted for ~ 20% of the total. Those current sheets have high magneticshear (> 90degrees). In order to estimate the local heating occurring within those current sheets, a proxy of the electron temperature was obtained at high time resolution(125ms) from the partial distributions measured by Cluster. This allowed for the first time to study the localized electron heating within ion-scale currentsheets. The observed enhancement of the estimated electron temperature withinthe high PVI current sheets suggest that they are important for local electron heating and energy dissipation. We also examined measurements inside the diffusion region of a thin reconnecting current sheet. Multi-spacecraft observationsallow as to study electron distributions and wave activity at different distances from the x-line. Significant differences were observed in the electron populations as they were heated going through the current sheet. In particular electrons were heated in the direction parallel to the magnetic field in close proximity to thex-line, whereas no significant variation was observed in the perpendicular direction. However, the distribution was more isotropic downstream of the x-line with electrons heated in the perpendicular direction.

An artificially structured boundary (ASB) produces a short-range, static electromagnetic field that can reflect charged particles. In the work presented, an ASB is considered to consist of a spatially periodic arrangement of electrostatically plugged magnetic cusps. When used to create an enclosed volume, an ASB may confine a non-neutral plasma that is effectively free of applied electromagnetic fields, provided the spatial period of the ASB-applied field is much smaller than any one dimension of the confinement volume. As envisioned, a non-neutral positron plasma could be confined by an ASB along its edge, and the space-charge of the positron plasma would serve to confine an antiproton plasma. If the conditions of the two-species plasma are suitable, production of antihydrogen via three-body recombination for antimatter gravity studies may be possible. A classical trajectory Monte Carlo (CTMC) simulation suite has been developed in C++ to efficiently simulate charged particle interactions with user defined electromagnetic fields. The code has been used to explore several ASB configurations, and a concept for a cylindrically symmetric ASB trap that employs a picket-fence magnetic field has been developed. Particle-in-cell (PIC) modeling has been utilized to investigate the confinement of non-neutral and partially neutralized positron plasmas in the trap.

<pre>Bridging the gap between the classical and quantum regimes has consequences not only for fundamental tests of quantum theory, but for the relation between quantum mechanics and gravity. The field of levito-dynamics provides a promising platform for testing the hypotheses of the works investigating these ideas. By manipulating a macroscopic particle's motion to the scale of its ground state wavefunction, levito-dynamics offers insight into the macroscopic-quantum regime.</pre><pre><br></pre><pre>Ardent and promising research has brought the field of levito-dynamics to a state in which these tests are available. Recent work has brought a mesoscopic particle's motion to near the ground state. Several factors of decoherence are limiting efficient testing of these fundamental theories which implies the need for alternative strategies for achieving the same goal. This thesis is concerned with investigating alternative methods that may enable a mesoscopic particle to reach the quantum regime. </pre><pre><br></pre><pre><pre>In this thesis, three theoretical proposals are studied as a means for a mesoscopic particle to reach the quantum regime as well as a detailed study into one of the most important factors of heating and decoherence for optical trapping. The first study of cooling a particle's motion highlights that the rotational degrees of freedom of a levitated symmetric-top particle leads to large harmonic frequencies compared to the translational motion, offering a more accessible ground state temperature after feedback cooling is applied. An analysis of a recent experiment under similar conditions is compared with the theoretical findings and found to be consistent. <br></pre> <pre>The second method of cooling takes advantage of the decades long knowledge of atom trapping and cooling. By coupling a spin-polarized, continuously Doppler cooled atomic gas to a magnetic nanoparticle through the dipole-dipole interaction, motional energy is able to be removed from the nanoparticle. Through this method, the particle is able to reach near its quantum ground state provided the atoms are at a temperature below the nanoparticle ground state temperature and the atom number is sufficiently large.</pre> <pre>The final investigation presents the dynamics of an optically levitated dielectric disk in a Gaussian standing wave. Though few studies have been performed on disks both theoretically and experimentally, our findings show that the stable couplings between the translational and rotational degrees of freedom offer a possibility for cooling several degrees of freedom simultaneously by actively cooling a single degree freedom.</pre></pre>

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