Investigation of Micro-arc Discharge in Deep Sea Water at High Pressure

In this work, micro-arc discharges generated in sea water at high pressure were investigated. For generation of micro-arc discharges, electrodes were introduced into a high-pressure chamber and a current pulse was supplied to the electrodes by a custom pulse current source. By using pin-to-pin electrodes system, micro-arc discharges were successfully generated in highly conductive sea water at high pressure up to 17.5 MPa for the first time. Analysis of current and voltage waveforms showed that micro-arc discharge process at high pressure was same to the atmospheric pressure case and could be divided into three phases: pre-heating, micro-arc discharge and subsequent oscillation. A difference to atmospheric pressure was increase of power consumption during pre-heating phase with increase of pressure. Use of pin-to-pin electrode system with insulation of sides allowed us to generate micro-arc discharges with relatively low energy even at high pressure due to concentration of strong electric field between the electrodes in a small volume. Repetition number of reproducible discharges using the same electrodes was limited below 30 due to erosion of the electrodes caused by a high current during the discharge. A rod-to-rod electrode system consisting of two parallel metal rods aligned with a small gap was developed instead. In the case of rod-to-rod electrode system, due to increase of the surface of the facing electrodes, local erosion caused by high current did not have significant impact on the reproducibility of the discharges while the energy consumption increased by 33% compared to the pin-to-pin electrode system owing to increased volume between the electrodes in the gap. By using the rod-to-rod electrode system, it was succeeded to generate reproducible micro-arcs at high pressures up to 17.5 MPa. Repetition number was increased to more than 100 owing to improved durability of the electrodes.