A discharge in water with a long gap was realized at low voltage. The main feature of this discharge was the assistance of a high pressure gas jet. For a gap length of 5 cm in tap water, the discharge or breakdown voltage was as low as 32 kV, which is five times lower than that of air- gap breakdown. The breakdown voltage increased linearly with the gap distance. Helium, nitrogen, argon and air were used as injection gases. The discharge characteristics were investigated as a functions of the injection gas species, the gap distance and the back pressure of the injection gas. Comparison of the discharge voltage with water surface discharge suggested that the gas jet assisted water discharge is a kind of surface discharge. The long gap discharge in water can be utilized for many environmental applications, such as wastewater treatment.
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