Abstract
Plasma discharges in liquids, initiated by 7 kV DC microsecond pulses, were studied using deionized water, saline, and potassium bromide solutions at varying concentrations. The discharge process includes a high-potential resistive phase and a subsequent arc phase characterized by bright emissions. While a time calculation model accurately predicts the resistive phase in ionic solutions, it fails to do so for deionized water, indicating unpredictable behaviour. Imaging with an ICCD camera revealed discharge dynamic, microbubble formation, and arc-phase emissions. Optical spectroscopy confirmed the presence of hydrogen and oxygen atoms across all discharges, indicated by H𝛼, H𝛽, and O I 777 nm spectral lines, with black body radiation observed initially. A broad emission band around 500 nm suggested 𝐻2𝑂+ (A-X) emission. Stark broadening analysis of H𝛼 and H𝛽 provided electron density measurements, found to be consistent across different liquids, decreasing significantly over the discharge duration. The analysis also showed a considerable drop in collisional van der Waals broadening, reflected in the 𝑃/𝑇^0.7 values. These electron density values, alongside red shifts and widths of the H𝛼 peak, corroborated the data from line broadening, and were used alongside H𝛼 and H𝛽 intensities to estimate stable electron temperatures near 2 eV throughout the pulse. Adding an inductor to the discharge circuit in deionized water increased discharge duration significantly and seemed to stabilize the plasma, suggesting controlled behaviour with lower average electron densities and temperatures. This modification hints at the potential for inductance adjustments to manipulate plasma chemistry in deionized water.This thesis is embargoed until 31 Dec 2026.
| Date of Award | Dec 2024 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Sponsors | Ministry of Higher Education |
| Supervisor | David Riley (Supervisor) & Thomas Field (Supervisor) |
Keywords
- Plasmas
- Spectroscopy
- Deionized water