Observations of pulsed discharge phenomena in supercritical carbon dioxide by means of shadowgraph method

This paper describes the temporal development of pulsed discharges in supercritical carbon dioxide (SCCO₂). A magnetic pulsed compression generator with a step-up transformer was used to deliver high voltage pulses to a 5 mm-gap needle-to-plate electrode in SCCO₂ (9.4 MPa and 313 K). A time-resolved shadowgraph method was employed to observe pre- and postbreakdown phenomena. A continuous wave Ar laser (488 nm) was used as light source and a gated ICCD camera was synchronized with the pulsed discharge. The observation shows that the sequence of pulsed discharge phenomena in SCCO₂ including branched streamer in the pre-breakdown phase, shock wave propagation and density fluctuation in the post-breakdown phase. Rayleigh-Taylor instability was observed in the boundary between gaseous and SC regions.