Correlating Plasma Properties to Liquid Chemistry in a Nanosecond Pulsed Helium Gas-Liquid Water Discharge

To develop nonthermal plasma gas-liquid chemical reactors it is important to understand how the plasma properties such as electron density and electron temperature affect the chemical reactions. Therefore, we determine electron density and energy as functions of pulse width and pulse frequency with nanosecond pulsed discharges in a continuous flow gas-liquid film reactor with helium and deionized liquid water. The electron density was determined by the Stark broadening of H_α and H_β. The excitation temperature was found from the intensity ratio of the H-Balmer lines. The pulse frequency was varied between 1 – 10 kHz and the pulse width from 40 – 200 ns using a commercial power supply (Eagle Harbor Technologies, NSP-120-20, Seattle, WA). A custom-made power supply (Airity Technologies, Palo Alto, CA) was used to vary the pulse frequency from 5 – 100 kHz. The temporal variation of electron density for a single pulse is compared with our previous work with argon where the electron densities were found to reach maximums at specific resonant frequencies. With argon, the results correlated with chemical reactions of perfluorinated organic compounds but not hydrogen peroxide formation.