High-voltage pulse discharge in water is a promising technology to enhance the permeability of coal seam and rock mass by generating fractures within them. With the aim of improving the stability and efficiency of this technology, a high voltage electric pulse experiment system was constructed. The discharge electrodes in the experiment was hemispherical. The positive and negative electrodes were arranged on the same axis with adjustable spacing. Five sets of experiments were undertaken with

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... electrode spacing of 1mm, 2mm, 3mm, 4mm, and 5mm, respectively. In the experiments, an oscilloscope was used to analyze the voltage, current, and pressure wave signals. The experimental results of two typical voltage-current curves indicate that the peak pressure of plasma shock wave follows a parabolic trend with the electrode spacing, and there is an optimal electrode spacing for a given discharge voltage. The peak pressure of plasma shock wave tends to increase linearly with the increase of discharge voltage. The greater the electrode spacing, the greater the sensitivity of shock wave peak pressure to the discharge voltage. The shock wave peak pressure sensitivity of 5 mm discharge spacing is 4.7 times that of 1 mm discharge spacing. The experimental results for the voltages of 9 kV, 12 kV, and 24 kV with the optimal electrode spacing show that a power function is the best fit for the attenuation of the peak pressure of shock wave with its propagation distance. INDEX TERMS Electrodes spacing, plasma shock wave, peak pressure, pressure attenuation, high-voltage discharge in water, hemispherical electrode. VOLUME 9, 2021 This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. For more information, see https://creativecommons.org/licenses/by-nc-nd/4.0/