Browsing by Subject "Sub-nanosecond"
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Item Experimental investigation of ultra-fast breakdown at subatmospheric pressures(2007-05) Justis, William Hugo; Krompholz, Hermann G.; Neuber, Andreas A.; Hatfield, Lynn L.Ultra-fast gaseous breakdown is an important area of research in the pulsed power field for applications such as: ultra wideband systems, fast breaking plasma limiters, and ultra fast switches. Using newly developed digitizers and pulsing technology it is possible to accurately investigate breakdown inducing pulses in the sub-nanosecond regime exhibiting rise times on the order of 200 ps with pulse widths under 300 ps. Breakdown is examined in a controlled environment with a pressure range of 10-5 - 600 torr using both argon and dry air as background gases. E/N values range from 103 to 106 Td, and are typically above the threshold for runaway electron generation. Diagnostics include capacitive voltage dividers on incident and transmitted side coaxial lines and X-Ray detection through a scintillator/PMT combination. Initial X-Ray data collected shows the occurrence of high energy runaway electrons during the breakdown event. Breakdown voltages, conduction currents, and formative delay times are also investigated for the full pressure range, with parameters established through both gap and transmission line modeling. Results show consistent breakdown for pressures above 50 torr in a radial gap configuration. A shift of breakdown voltage towards lower pressures for increasing voltage amplitude has been observed. X-ray measurements indicate the presence of fast, high energy electrons across the entire pressure range leading due to runaway electrons. Intensity ratios indicate that electron energies are nearly equivalent to the applied voltage for pressures approaching atmosphere, these results match closely with results obtained from previous testing in axial gap configurations.Item Ultra-fast breakdown at pressures below one atmosphere(2006-08) Chaparro, Jordan E.; Krompholz, Hermann G.; Neuber, Andreas A.; Hatfield, Lynn L.Ultra-fast gaseous breakdown is an important phenomenon in pulsed power related to ultra wideband systems, plasma limiters, and ultra fast switches. Recent advances in digitizers and pulser technology has allowed for pulses with sub-nanosecond properties to be examined in detail. This thesis examines voltage pulses in quasi homogenous fields with rise times less then 200 ps and pulse widths less then 300 ps. The breakdown is examined in pressures from high vacuum to 600 torr in argon and air. E/N values range from the order of 103 to 106 Td, and are typically above the threshold for the generation of runaway electrons. Also discussed is the design and characterization of a transmission line system including a pulse shaping lens intended to limit wave distortion at a coaxial to biconical geometry. Finite element numerical simulations have been used to explain the behavior of the system. Diagnostic methods include waveform analysis from fast capacitive voltage dividers, X-Ray detection through a scintillator photomultiplier combination, and optical analysis through fast streak camera imaging. Parameters for the breakdown are established through modeling of the gap. X Ray emissions point to the role of runaway electrons in the breakdown. Electron energy at the anode is roughly determined for various pressure ranges. Streak camera imaging is used to show channel distribution and structure and its dependence on pressure. Results show breakdowns with development times too fast to be explained by standard breakdown mechanics indicating the importance of fast electrons in the event.