Initiation process and propagation mechanism of positive streamer discharge in water

Abstract

The aim of this study was to clarify the initiation process and the propagation mechanism of positive underwater streamers under the application of pulsed voltage with a duration of 10 μs, focusing on two different theories of electrical discharges in liquids: the bubble theory and the direct ionization theory. The initiation process, which is the time lag from the beginning of voltage application to streamer inception, was found to be related to the bubble theory. In this process, Joule heating resulted in the formation of a bubble cluster at the tip of a needle electrode. Streamer inception was observed from the tip of a protrusion on the surface of this bubble cluster, which acted as a virtual sharp electrode to enhance the local electric field to a level greater than 10 MV/cm. Streak imaging of secondary streamer propagation showed that luminescence preceded gas channel generation, suggesting a mechanism of direct ionization in water. Streak imaging of primary streamer propagation revealed intermittent propagation, synchronized with repetitive pulsed currents. Shadowgraph imaging of streamers synchronized with the light emission signal indicated the possibility of direct ionization in water for primary streamer propagation as well as for secondary streamer propagation.

Pulsed Discharge Plasmas in Contact with Water and their Applications

“…The figure also shows an intense light emission (called the secondary streamer), which develops from the tip of one of the PS toward the lower anode electrode and the upper cathode electrode (not shown). Figure 5 shows the initiation of the PS processes [30]. Joule heating causes fluctuations and micro-bubbles at the tip of the needle anode electrode.…”

“…5. Initiation of bushlike process [30] probably appears because of the distribution of positive electrical charges. When the local electric field in the protrusion exceeds a certain threshold, the PS process initiates.…”

“…Figure 5 shows the initiation of the PS processes [30]. Joule heating causes fluctuations and micro‐bubbles at the tip of the needle anode electrode.…”

“…E-mail: akiyama@fusiontech.jp *Fusiontech Corporation, 2-39-1, Toyooka, koushi-shi, Kumamoto 861-1115, Japan **Faculty of Engineering, Iwate University, 3-18-8, Ueda, Morioka-shi, Iwate 020-8550, Japan reports related to the phenomena of large-volume discharges in water have been published. These reports include the initiation of discharges in water, specifically the transition from the bush-like streamer (primary streamer) to the filamentary streamer (secondary streamer); propagation and extinction of filamentary streamers; the behavior of bubbles produced by filamentary streamers; the generation of shock waves resulting from the collapse of bubbles gathered at the tip of an electrode; the measurement of temperature, density, electric field, and radicals produced by filamentary streamers [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”

Formation mechanism of streamer discharges in liquids: a review

“…A lot of effort has been spent to understand the underlying physics of streamers in various liquids and many reviews have been attempted [15,[33][34][35][36][37][38]. 'Direct impact ionisation' and 'gas bubble' are two classical mechanisms that has been proposed for almost a century [17] and are being frequently used currently to explain some experimental pre-breakdown phenomena in liquids [39][40][41][42][43]. However so far, a comprehensive theory of the breakdown in liquid does not exist yet and sometimes one possible mechanism proposed in one experiment is inconsistent with observations in another set of devices.…”