Guiding effect of runaway electrons in atmospheric pressure nanosecond pulsed discharge: mode transition from diffuse discharge to streamer

• Published in: Plasma sources science & technology Vol. 31; no. 11; pp. 114002 - 114011
• Main Authors: Huang, Bangdou, Zhang, Cheng, Ren, Chenhua, Shao, Tao
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.11.2022
• Subjects: ionization wave; nanosecond pulsed discharge; runaway electrons
• ISSN: 0963-0252; 1361-6595
• DOI: 10.1088/1361-6595/ac9c2c

Abstract In this study, the role of runaway electrons (RAEs) during the pulsed breakdown in the atmosphere is investigated. Nanosecond pulsed discharge (NPD) is driven by high-voltage pulses between blade-to-plate electrodes (with the blade as the cathode). RAEs with an energy higher than 10 keV are selected by a titanium foil with a thickness of 1  μ m and detected by a beam collector with a front of about 50 ps. The temporal-spatial evolution of the electric field over the NPD period is measured using electric field induced second harmonic method adopting a picosecond pulsed laser. It is verified that the current amplitude of RAEs decreases drastically with the voltage amplitude V p and the peak electric field at the front of the ionization wave formed during the breakdown of NPD plays a key role in maintaining the runaway state of electrons. With single-shot discharge imaging, it is observed that the discharge is initially in a diffuse mode near the cathode, while it branches and transits into streamers, which can be either synchronously propagating multi streamers (with a high V p ) or certain dominant streamers (with a low V p ). Using particle-in-cell Monte-Carlo collision simulation, a similar mode transition of diffuse to streamer is observed with RAEs emitted from the cathode and it is illustrated that the flux of RAEs controls the pre-ionization degree and further dictates branching and non-uniformity of discharge, which qualitatively explains the experimental observation. It is proposed that an enhanced RAEs emission would produce a large volume diffuse discharge at atmospheric pressure.