Influence of pulse parameters on the spatial density distribution and yield characteristics of ozone in nanosecond pulsed plasma with a water cathode

Abstract Atmospheric cold plasma is a promising technology for wastewater treatment, in which ozone (O 3 ), as a long-lived and highly oxidizing reactive species, plays a key role. In this study, nanosecond pulsed plasma was generated using a water cathode structure, and the spatial density distribution, yield rate, and energy yield of O 3 were measured using ultraviolet absorption spectroscopy. The spatial distribution of O 3 resembled the shape of the plasma channel, forming a cylindrical profile with the maximum density located at the channel center. Due to diffusion, the O 3 distribution extended to a radius of approximately 8 mm, exceeding the optical radius of the plasma (∼4 mm). After the discharge, the rapid decomposition of O 3 by metastable species led to the lowest O 3 density at the channel center, in contrast to the stable spatial distribution during the discharge. The power, which significantly influenced both O 3 density and yield rate, was effectively controlled by tuning the pulse parameters. Compared to high-frequency, low-voltage conditions, low-frequency, high-voltage operation resulted in a significantly higher energy yield of O 3 . In addition, short pulse widths (<100 ns) were found to enhance the energy yield of O 3 . Due to the localized high temperature and the abundant H 2 O supply from the water cathode, the H 2 O concentration in the discharge region greatly exceeded that in the feed gas. As a result, atomic O was significantly consumed, ultimately leading to a reduction in O 3 formation via three-body collisions.