Optical Science and Engineering ETDs

Waylon Clark

Publication Date

7-10-2007

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.

Degree Name

Optical Science and Engineering

Level of Degree

Masters

Department Name

Optical Science and Engineering

First Committee Member (Chair)

Savage, Mark

Second Committee Member

Lynn, Alan

Keywords

Laser plasmas.

Sponsors

Sandia National Laboratories

Document Type

Thesis

Language

English

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