Quasi-Elastic Light Scattering Diagnostics for a High Voltage Spark Discharge
Lovik, Mark Alan
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Permalink
https://hdl.handle.net/2142/70414
Description
Title
Quasi-Elastic Light Scattering Diagnostics for a High Voltage Spark Discharge
Author(s)
Lovik, Mark Alan
Issue Date
1988
Doctoral Committee Chair(s)
Scheeline, Alexander
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Abstract
Quasi-elastic light scattering was used as a diagnostic probe into analyte material transport processes in a unipolar, positionally stable, high voltage spark discharge. The material transport by particulate intermediates was studied. Instrumentation was constructed to allow spatially-, temporally-, and angularly-resolved scattering measurements on the positionally stable spark discharge. Active polarization control on the light scattering instrument was characterized using ellipsometry and Mueller calculus. Mie scattering theory was used in the determination of particle size in an aluminum cathode model system.
Two possible production mechanisms were expected to be able to account for the observed spark-generated particulates. Particle production could be a result of Joule heating of the electrode, followed by shock wave ejection of the molten cathodic material. Condensation of analyte vapor in the spark discharge could also account for spark-generated particulates. From crude velocity measurements made on the particle system, an upper velocity range of 8 meters/second was calculated for the observed particle. This velocity was calculated to be inconsistent with a cathodically ejected particle model.
Particulates were observed to remain within the spark environment for about 0.5 seconds, and comparison of experimental data with Mie scattering calculations provided a mean size estimate of 4.4$\mu$m for the particle system. Temporally-resolved measurements of particle scattering showed the point of condensation of analyte to particulates to occur from 300-400$\mu$s after spark initiation.
Cross-correlation between scattering by particulates and spark sampling phenomena, seen as analyte emission, indicated partial correlation between particle production and sampling variation in the spark. The temporal interdependence between particle scattering and analyte emission variation was inconclusive. Statistical variability due to low particle counts in scattering measurements may have been the limiting aspect in correlation measurements.
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