Time Resolved Plasma Characterization by Optical Emission Spectroscopy in a Nanosecond Pulsed Plasma Gas-Liquid Reactor*

Time resolved optical emission spectroscopy (OES) was used to determine electron density and excitation temperature as functions of pulse width and pulse frequency in a nanosecond pulsed plasma gas-liquid flow reactor with argon (Ar) and deionized liquid water. The plasma characteristics were obtained by analysis of H-Balmer lines. The pulse frequency was varied between 5kHz – 100kHz using a custom-made power supply (Airity Technologies, LLC). The peak electron density in a single pulse varies between 1.8×10¹⁷ cm^-3 - 4.8×10¹⁷ cm^-3 with frequency. The peak electron density was observed at 20kHz. After voltage breakdown and the increase in current, the electron density rises quickly and exponentially decays over a single pulse. The electron decay is longer than the current decay (40 ns), and the decay time constant for electron density varies between 110ns^-1 – 140ns^-1 with frequency and these results will be used to analyze the recombination mechanisms in our plasma.