Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xiv, 93 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 85-88). WVU users: Also available in print for a fee.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 22, 2009) Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2009. / Includes bibliographical references (p. 112-116).

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiv, 170 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 159-164).

Zugl.: Aachen, Techn. Hochsch., Diss., 2009

Regensburg, Univ., Diss., 2009.

Techn. Hochsch., Diss., 2004--Aachen.

Compréhension et maîtrise des phénomènes intervenant sous haute tension à l'interface entre un gaz et un isolant solide.Dans le cadre du remplacement du SF6 dans les appareils moyenne tension, une étude de l’isolation électrique mixte (gaz (air) / solide isolant) a été réalisée. L’objectif étant de déterminer l’influence de la nature du solide sur la tenue au claquage. Pour cela plusieurs matériaux ont été sélectionnés tel que l’époxy / silice (matériau de référence chez Schneider Electric), le PA6T/66.GF50 (nouveau matériau pour cette application) ainsi que plusieurs autre matériaux permettant une meilleure compréhension du phénomène (PTFE, PC, PP, …). Les caractérisations diélectriques ont permis de mesurer des déclins de potentiel, des courants volumiques ainsi que des permittivités en fonction de la nature des matériaux. A partir de ces données, des mesures de claquage ont été effectuées. Deux configurations de champ électrique ont été testées (parallèle et perpendiculaire au solide). La géométrie « pointe-plan » a été sélectionnée, permettant l’observation de décharges partielles avant le claquage et donc une étude de la propagation de la décharge et non de l’initiation de celle-ci. Ces mesures ont permis de déterminer l’influence du solide sur la tension de claquage, avec une influence indirecte de la nature du matériau et sa teneur en eau. Dans notre configuration, la présence d’un isolant solide dégrade la tenue diélectrique. La permittivité est le paramètre influençant la tension de claquage, avec une réduction de celle-ci en présence de matériaux à forte permittivité (comme l’alumine). Aucun lien n’a pu être mis en évidence entre les mesures de déclin de potentiel et les tensions de claquage. Pour caractériser le développement de la décharge électrique le long de l’isolant solide, des visualisations et des mesures de courant ont été réalisés. Les visualisations ont permis d’observer deux types de décharges menant avant le claquage. Dans un premier temps le développement d’une décharge en surface « streamer de surface », puis celui d’une décharge dans le gaz « streamer de volume ». Ces observations ont permis de conclure que le streamer menant au claquage se développe majoritairement dans l’air en configuration de champ parallèle. Les mesures de courant ont apporté des informations sur l’initiation de la décharge, en montrant une réduction de la tension et du temps d’initiation de la décharge en présence d’un solide. Des résultats semblables ont été obtenus pour une large gamme de matériaux. Cependant certains matériaux de faible permittivité (PP, PTFE) se distinguent avec des tensions et des temps d’initiation retardés et aléatoires, semblables à ceux obtenus dans l’air sans solide. Il a été montré que l’initiation et la propagation n’influencent pas la tension de claquage en géométrie pointe-plan. Celle-ci est déterminée par la transition au claquage.Mots-clés : appareillages moyenne tension, tension de claquage, caractérisation diélectriques, streamers, courant transitoires, visualisations. / Comprehension and control of phenomena occurring under high voltage at the interface between a gas and a solid insulator.In the context of SF6 replacement in medium-voltage apparatus, a study of mixed electrical insulation (gas (air) / insulating solid) was carried out. The aim is to determine the influence of the nature of the solid on breakdown voltage. For this purpose several materials have been selected such as epoxy / silica (reference material of Schneider Electric), PA6T / 66.GF50 (new material for this application) and several other materials allowing a better understanding of the phenomenon (PTFE, PC, PP, ...). The dielectric characterizations allowed us to measure potential decay, currents and permittivities according to the nature of the materials. From this data, breakdown measurements have been carried out. Two configurations of electric field were tested (parallel and perpendicular to the solid). The "point-to-plane" geometry was selected, allowing the observation of partial discharges before breakdown and therefore a study of the propagation of the discharge and not of the initiation. These measurements show the influence of the solid on the breakdown voltage, with an indirect influence of the nature of the material and its water content. In our configuration, the presence of a solid insulator lowers the dielectric strength. The relative permittivity is the main parameter influencing the breakdown voltage, with a reduction of it in the presence of materials with high permittivity (alumina). It was not possible to establish a link between surface potential decay measurements and breakdown voltages. In order to characterize the development of the electric discharge along the solid insulation, visualizations and transient current measurements were achieved. The visualizations allowed the observation two types of discharges before the breakdown. First, the development of a surface discharge "surface streamer", followed by a discharge in the gas "volume streamer". These observations lead us concluding that streamers leading to breakdown develop predominantly in air above the surface in the parallel field configuration. Current measurements provide information on the initiation of the discharge. There exists a reduction of voltage and initiation time of the discharge in the presence of a solid. Similar results have been obtained for a wide range of materials. However, several low permittivity materials (PTFE, PP) show a different behaviour, with higher and scattered time delay and initiation voltage, similar to those obtain in air without solid. It has been shown that initiation and propagation do not influence the breakdown voltage in poi nt-plane geometry. The transition to breakdown mainly determines the breakdown voltage.Key words: medium voltage apparatus, breakdown voltage, dielectric characterization, streamers, transient currents, visualizations.

Nanopores have emerged as a simple but effective tool to investigate the behavior of polymers in solution. They have shown great potential to simplify expensive and time consuming procedures like DNA sequencing, protein detection, and disease biomarker detection. With the development of in situ fabrication of solid-state nanopores by controlled breakdown (CBD) of a dielectric material, nanomanufacturing of nanopore-based technologies became feasible. However, there are still a lot of challenges to overcome for these applications to become reality. One of the major problems with solid-state nanopores is the rapid passage time of analytes going through the pore, complicating detection and reliable identification of molecules. In this thesis molecular structures are proposed that increase passage times due to increased interactions between analyte and pore wall, and at the same time increase signal amplitude due to increased blockage of the pore. These structures are short, branched DNA molecules that were assembled with built-in modifications and matching sequences to assume their structure. Nanopore experiments reveal that these structurally defined DNA produce higher detection rates than their linear DNA counterparts, making them better candidates for labels in single-molecule sensing experiments.

The compact linear collider (CLIC) is a leading candidate for the next generation high energy linear collider. As any breakdown would result in a partial or full loss of luminosity for the pulse in which it occurs, obtaining a low breakdown rate in CLIC accelerating structures is a critical requirement for the successful operation of the proposed collider. This thesis presents investigations into the breakdown phenomenon primarily in the low breakdown rate regime of interest to CLIC, performed using the CERN DC spark systems between 2011 and 2014.The design, construction and commissioning of several new pieces of hardware, as well as the development of improved techniques to measuring the inter-electrode gap distance are detailed. These hardware improvements were fundamental in enabling the exciting new experiments mentioned below, which in turn have provided significant additional insight into the phenomenon of breakdown. Experiments were performed o measure fundamental parameters of individual breakdowns, including, the turn-on time and the delay before breakdown in order to gain an improved understanding of how breakdowns are triggered and the underlying process behind them. The turn-on time measurements are the highest bandwidth measurements made to date with the CERN DC systems and are closer than ever before to the value which is expected from the present understanding of breakdown simulations. Another key measurement was that of the breakdown rate scaling with electric field. Previous investigations of this relationship in the DC systems were unable to investigate breakdown rates below 10^3 breakdowns per pulse. These new results are able to investigate this relationship down to a breakdown rate of 10^-8 and are hence a considerable improvement. Thanks to these improved results a remarkable similarity to the scaling of the breakdown rate with electric field in RF cavities was discovered. The conditioning, or change in breakdown rate over time was also studied for the first time in the CERN DC spark systems as well as the newly built fixed gap system. The qualitative conditioning behaviour of the Fixed Gap System again showed interesting similarities to that observed in RF structures. Preliminary studies into the effect of pulse length and magnetic field on the breakdown rate were conducted as well. This is the first time the effect of a DC magnetic field was studied in a DC spark system and in contrast to experiments in RF cavities no statistically significant effect was observed. The dependence of the breakdown rate on pulse length, again the first measurement of its kind in a DC system also revealed a similar scaling law to that observed in RF accelerating structures. Both of these preliminary measurements would need to be repeated to confirm the results.