Time-resolved diagnostics of a pin-to-pin pulsed discharge in water: pre-breakdown and breakdown analysis

Abstract

This paper presents an experimental study of an underwater pulsed plasma discharge in pin-to-pin electrode configuration. Time resolved refractive index-based techniques and electrical measurements have been performed in order to study the pre-breakdown and breakdown phenomena in water. A single high voltage pulse with amplitude of a dozen of kV and duration of [0.1-1] ms is applied between two 100 µm diameter platinum tips separated by 2 mm. This novel experimental work reports that different cases of electrical discharge in water occurs for a unique set of experimental conditions such as (i) bush-like channels from the cathode that do not span the electrode gap, (ii) bush-like channels from the cathode leading to breakdown and (iii) filamentary structures from the anode leading to a stronger breakdown. Two breakdown mechanisms, anode and cathode regimes, have been clearly identified and related to the two principal schools of thoughts to explain discharge propagation in liquid.

Influence of applied voltage and electrical conductivity on underwater pin-to-pin pulsed discharge

“…Higher conductivity of the solution leads to faster current dissipation as already mentioned, and also higher current flow (as shown in Fig.2) which facilitates the vaporization process by ohmic heating. If Joule effect plays a significant role in discharge initiation, the increase of the conductivity facilitates the discharge formation, as observed for Case (1). However the non-dependence of Case (2) duration in conductivity confirms that the gas phase production does not only depend on Joule effect as already mentioned in [1].…”

“…However the value of the intercept E decreases when the conductivity increases, being equal to E 50 =1.75 kV, E 100 = 1.3 kV and E 500 = 0.65 kV, which confirms that this parameter is a characteristic of the liquid properties [1].…”

“…A single high voltage of duration between 100 µS and 1 ms is applied between two 100 µm diameter platinum tips separated by 2 mm and immersed in the aqueous solution. This work, which provides valuable complementary results of paper [1], is of great interest to better understand the mechanisms of initiation and propagation of pin-to-pin discharge in water. For low conductivity (from 50 to 100 µS/cm) results have confirmed two regimes of discharge (cathode and anode) and the increase of the applied voltage first makes the breakdown more achievable and then favors the apparition of the anode regime.…”

“…As defined in [1], the delay time corresponds to the time needed for the appearance of the gas phase at the cathode and those of the transient current, whereas the duration corresponds to the duration of the transient current and those of the gas phase expansion. Results obtained in the cathode regime (each measurement is based on a dozen of experiments) are reported on The influence of the conductivity on the delay time is not significant since the dispersion of the measurements is important.…”

“…Most of these works have used the pin-to-plane electrodes system for underwater pulsed discharge experiment but few studies concern symmetric pin-to-pin configuration. Recently, the authors have reported the analysis of pre-breakdown and breakdown phenomena for underwater pin-to-pin discharge [1]. Keeping all the experimental parameters constant, two regimes of discharge have been identified regarding its structure, its velocity and its propagation way.…”