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Electrical resistance of gases in explosive magnetic flux compression generator environments
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Gases that are electrical insulators at STP can become conductors when subjected to the high pressure and temperature environment in explosive magnetic flux compression generators (FCGs). This thesis describes experiments performed to determine the electrical properties of several gases in the FCG environment. The hydrodynamics in a helical explosive magnetic flux compression generator (FCG) are modeled using the Gurney method and a shock physics code, CTH, developed at Sandia National Laboratory. The armature in a typical FCG is calculated to approach the stator at approximately 3 km/s. To simulate FCG operating conditions in the volume between the armature and stator, expendable, stagnated shock, explosively driven shock tubes are designed to propel aluminum flyer plates towards dense stainless steel plugs. Two opposing copper probes are inserted into the shock tube walls and charged to 2 kV by an external capacitor bank. The voltage across these probes is tracked by oscilloscope and the current is measured with a Pearson transformer at the capacitor bank. The current and voltage measurements are used to calculate a bulk resistance for the gas between the probes. Current limited experiments with series resistors have also been conducted. Experiments were performed using argon, helium, sulfur hexafluoride, and synthetic air (20% oxygen/80% nitrogen) as the shock tube fill gas. Argon readily ionizes throughout its volume in the shock tube. This effect is believed to be due to photo-ionization from radiation emitted in the shocked region. Helium only becomes ionized when the initial shock wave reflects off the stainless steel plug and stagnates. Air ionizes in the shock wave and maintains a resistance near 3 Ohms when the initially shocked region is measured. SF6 is ionized and becomes less resistive as the shocked region crosses the probes. The SF6 resistance measurement is 200 Ohms for the initial shock wave. In all cases, the reflected shock wave is expected to have sufficient energy to begin disassembling the shock tube, and calculations based on measurements made after the reflected shock wave reaches the voltage probes are unreliable.
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Includes bibliographical references (leaves 52-55).
Issued also on microfiche from Lange Micrographics.
Dorsey, Daniel John (2000). Electrical resistance of gases in explosive magnetic flux compression generator environments. Master's thesis, Texas A&M University. Available electronically from
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