Effect of Nanosecond Pulse Parameters on Plasma Characteristics and Radical Concentrations in Water Cathodes

Abstract

Nanosecond pulsed plasma is a potential technology for wastewater treatment due to its high efficiency in driving plasma. In this article, a miniature needle water cathodes discharge structure based on the printed circuit board (PCB) technology is designed to achieve efficient plasma generation. The development process of plasma under nanosecond pulses was investigated, and the effects of pulse parameters on radical concentration, plasma temperature, and electron density were analyzed. In short-gap water cathode configurations, the initial tens of nanoseconds of the pulse dominate the optical signals. Initial secondary streamers span the entire gas gap. The absence of the $\mathrm{H}_{\alpha }$ emission and the delayed appearance of OH(A-X) indicate that OH is primarily generated through molecular reactions rather than electron impact dissociation. Short pulse widths and short rise times facilitate efficient generation of radical concentrations and electron density. Increasing the voltage amplitude and repetition frequency enhances the inhomogeneity of the electron density but reduces the mean electron density due to plasma volume expansion. High-voltage amplitudes also elevate radical concentrations and plasma temperature. The increase of repetition frequency promotes energy deposition in the background gas, which raises the plasma temperature, leading to a stronger discharge and an increase in the yield of radicals.