Shock wave generated by negative pulsed discharge in supercritical carbon dioxide

A shock wave generated by negative pulsed discharge in pressurized carbon dioxide including supercritical (SC) phase was observed by means of Schlieren method. A negative pulsed voltage with a rise time of 90 ns and half-width of 410 ns was applied to a point electrode. The resulting shock wave, seemingly a multi-layered structure, was able to be confirmed despite the single pulsed voltage. Shock wave velocities and Mach number were calculated by Schlieren images at gas, SC and liquid phases. The largest Mach number was in the SC phase, though shock wave velocity strength was, from weakest to strongest, in the order of gas, SC and liquid phases. Additionally, Mach-Zehnder and Schlieren methods were used in combination to confirm the detailed structure of shock wave in supercritical carbon dioxide (SC-CO₂). On the ground of fringe shift, we considered that shock wave in SC-CO₂ does not have a multi-layered structure; however, a general shock wave may form with negative pressure.