Electrical breakdown of water in microgaps

Abstract

Experimental and modeling studies on electrical breakdown in water in submillimeter gaps between pin and plane electrodes have been performed. Prebreakdown, breakdown and recovery of the water gaps were studied experimentally by using optical and electrical diagnostics with a temporal resolution on the order of one nanosecond. By using Mach-Zehnder interferometry, the electric field distribution in the prebreakdown phase was determined by means of the Kerr effect. Electric fields values in excess of the computed electric fields, which reach >4 MV cm −1 for applied electrical pulses of 20 ns duration, were recorded at the tip of the pin electrode, an effect which can be explained by a reduced permittivity of water at high electric fields. Breakdown of the gaps, streamer-to-arc transition, was recorded by means of high-speed electrical diagnostics, and through high-speed photography. It was shown, through simulations, that breakdown is initiated by field emission at the interface of preexisting microbubbles. Impact ionization within the micro-bubble's gas then contributes to plasma development. Experiments using pulse-probe methods and Schlieren diagnostics allowed us to follow the development of the disturbance caused by the breakdown over a time of more than milliseconds and to determine the recovery time of a water switch. In order to trigger water switches a trigger electrode with a triple point has been utilized. The results of this research have found application in the construction of compact pulse power generators for bioelectric applications.

Time-resolved Optical Emission Spectroscopy in Water Electrical Discharges

“…High voltage electrical discharges in water have been shown to produce chemically active species, such as hydrogen, ozone, oxygen, hydroxyl radicals and UV radiation which efficiently decompose molecules [2]. Different types of discharges utilizing high pulse voltage and electrodes immersed in water, arranged in a rod-plate [5][6][7][8] or two pin configuration [9,10], have been investigated. However, the fundamental properties of the liquid-phase plasma have not been yet completely understood, including its state or the chemical species produced in plasma.…”

In-liquid plasma: a novel tool in the fabrication of nanomaterials and in the treatment of wastewaters

“…An underwater streamer discharge occurs in liquid at a rate of 30 to 100 mm ms À1 while the liquid is being vaporized at the liquid/air interface. 14, 15 The occurrence of an underwater streamer discharge in the liquid phase generates ultraviolet rays, shock waves, and localized heat, together with chemically active species formed by the resulting plasma. 16 The second key method is to generate bubbles by heating, by shock waves, and by gas introduction (or the like) in the liquid to create in-liquid plasma.…”

Microdischarge Ignition in Liquid Heptane

“…Schoenbach et al [4] made the calculation of the electric field distribution, with an electrode arrangement and experimental conditions similar to ours, in water. Results show that the high field region is localized near the pin electrode and keeps high values, up to ∼100 μm.…”