Plasma characteristics and mode transitions of needle-to-needle discharge in ambient air

Abstract Needle-to-needle discharge plasma in atmospheric pressure air environments has been proven to have applications in different fields depending on its kinds of discharge modes, which in turn lead to the importance of investigating the characteristics and mode transitions of the discharge plasma. In this paper, AC high-voltage is employed to generate a needle-to-needle bare electrodes discharge plasma in the air. The modulation of the discharge mode can be achieved by adjusting key factors such as electrode gap, capacitance and voltage, and can be categorized into four modes: streamer discharge, streamer glow mixed discharge, glow discharge, and arc discharge. The discharge images, waveforms of voltage and discharge current, discharge dynamic evolution processes, and optical emission spectra of the four discharge modes are diagnosed. It is found that, with discharge modes transiting from streamer to arc, both the duration time and gas temperature of discharge increase, while the peak current decreases. Correspondingly, the discharge morphology, current waveform and reactive species generation also undergo significant changes, which are critical for understanding the mode transition.