Effect of Voltage Rise Rate on Streamer Branching and Shock Wave Characteristics in Supercritical Carbon Dioxide

This paper reports on the dependence of voltage rise rate on positive streamer branching and shock waves in supercritical carbon dioxide. Voltages with rise rates of 0.21 and 4.5 kV/ns were applied to a needle-to-plane electrode. Prebreakdown phenomena involving streamer growth and shock wave propagation were observed by means of a shadowgraph method. The results show that the spread angle of the streamer at the needle tip under 4.5 kV/ns was nearly twice as large as that under 0.21 kV/ns. The discharge may initiate without density reduction due to electrostrictive force. While shock wave Mach number was little affected by the voltage rise rate, it increased by increasing the negative voltage peak. Consequently, the velocity of shock wave is presumed to be influenced by the population of the vibrational state of carbon dioxide.