Investigation of pulsed breakdown characteristics in high-pressure CO2 including supercritical phase under non-uniform electric field

In this paper, dependence of positive polarity nanosecond pulsed breakdown voltage on CO₂ density was examined from gas to supercritical (SC) phases. The pulsed voltage with equivalent voltage rise rate (0.75 kV/ns) was applied to needle-to-plane electrode in all experimental conditions. In addition, the time lag of spark at high pressure gas and SC phases were investigated with Laue plots. The obtained results were as follows: 1) the breakdown voltage increased in gas phase and saturated in SC phase; 2) the local reduction of breakdown voltage specifically appeared at medium density of 90.8 kg/m³ (gas phase); 3) in the high pressure gas phase (82.1-103.1 kg/m³), the statistical time lag was extremely small at 90.8 kg/m³ irrespective of constant formative time lag; 4) it was difficult to quantify the formative and the statistical time lags in SC phase.