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Analysis of a laser induced plasma in high pressure SF6 gas for high-voltage, high-current switching

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Please use this identifier to cite or link to this item: http://hdl.handle.net/1928/3231

Analysis of a laser induced plasma in high pressure SF6 gas for high-voltage, high-current switching

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Title: Analysis of a laser induced plasma in high pressure SF6 gas for high-voltage, high-current switching
Author: Clark, Waylon
Advisor(s): Gilmore, Mark
Committee Member(s): Savage, Mark
Lynn, Alan
Department: University of New Mexico. Dept. of Electrical and Computer Engineering
Subject: Laser induced breakdown
Sulfer Hexafluoride
Laser Plasma
Laser Triggered Gas Switch
High pressure SF6
SF6
LC Subject(s): Laser plasmas.
Degree Level: Masters
Abstract: The Laser Triggered Switch Program at Sandia National Laboratories is an intensive development study to understand and optimize the laser triggered gas switch (LTGS) for the Z-Refurbishment (ZR) project. The laser triggered gas switch is the final command-triggered switch in the machine, and reliability and performance of the switch is crucial. A modified LTGS trigger section with optical viewing windows perpendicular to the laser propagation is used to analyze a laser induced plasma spark in SF6 gas in order to quantify parameters such as spark length and plasma temperature. The laser spark is created through a focusing lens by the fourth-harmonic (266nm) of a 5ns FWHM pulsed Nd:YAG laser with 30mJ maximum energy output. Several diagnostic methods are used to analyze the laser spark. Visible spark length measurements are made using a lens system mounted to a CCD camera at gas pressures ranging from sub-atmosphere to four atmospheres. Differing focal length lenses are compared to determine an optimal focal length for a given gas pressure and laser energy. The visible length of the laser induced plasma channel is used as an indicator of the ability of a spark to trigger a switch at a given gas pressure and charge voltage. As a rule of thumb, the visible spark length must be at least 30% of the electrode gap spacing to produce acceptable switch run-time and jitter. Schlieren imaging and electrical length measurements using a capacitive probe are also used to obtain laser induced spark lengths. Spectroscopy is used to estimate laser plasma temperature from which plasma resistivity is calculated.
Graduation Date: May 2007
URI: http://hdl.handle.net/1928/3231


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