Temporal evolution characteristics of the excited species in a pulsed needle-water discharge: effect of voltage and frequency

Abstract

Transient spark discharge has broad application prospects due to its excellent performance in generating reactive oxygen species, but there is currently limited research on transient excited species, which are important precursors for the formation of these species. In this paper, we obtained a transient spark discharge with a needle-water electrode configuration, and then developed an optical detection system based on a photomultiplier to measure the temporal evolution of four excited species. It is observed that N2 (C) is produced mainly in the streamer phase, while H (n = 3), O (3p), and OH (A) are produced mainly in the spark phase, which results from the difference in threshold energy and pathway for generating different species. To investigate the variation mechanism of peak time and peak intensity during the evolution process, the gas temperature T g, electron density n e, and electron excitation temperature T exc were calculated by using the optical emission spectroscopy under different pulse voltage and pulse repetition frequency conditions. The results indicate that the discharge conditions influence the physical parameters of T g, n e, and T exc as well as the output voltage waveform, and then they jointly determine the evolution characteristics of excited species. These insights contribute to understanding the characteristics of excited species which affect the formation of reactive species by influencing the chemical chain reaction in the transient spark discharge.