Is an extended barrier-free discharge under nanosecond-pulse excitation really diffuse?

Abstract

A homogeneous discharge with a large volume is a desirable plasma source for many applications. Nanosecond-pulsed high-voltage (HV) excitation is believed to be a promising strategy for obtaining homogeneous or diffuse discharges at atmospheric pressure. In this paper, using a knife–plate geometry driven by a nanosecond-pulsed generator, a diffuse plasma sheet with a gap distance of 1 cm and a length of 12 cm is generated in atmospheric air, maintaining a low gas temperature of ∼330 K. However, time-resolved images reveal that the discharge, which appears diffuse to the naked eye, actually consists of multiple individual streamers that propagate from knife (HV) to plate (ground). The appearance of two processes, namely primary and secondary streamers, is consistently verified by discharge images, electric field evolution and fluid simulation. This further proves that the entire discharge belongs to an intermediate state between corona and spark. This work aids a deeper understanding of the intrinsic characters of similar diffuse discharges and optimizing parameters in practical applications.