Study of negative pulsed breakdown phenomena in supercritical carbon dioxide

Summary form only given. The authors studied the initiation mechanism of negative pulsed discharge in supercritical carbon dioxide (SCCO₂) in a point-to-plane gap¹. The generation mechanism of the initial electron under supercritical and liquid phases suggested field emission and the primary streamer grew in the form of bush from the cathode point. Although a negative pulsed voltage with a peak voltage of 50 kV and half width of 410 ns was applied to the 1 mm gap, streamer growth was limited to within a quite narrow region. This study provides the negative pulsed breakdown process in SCCO₂. In order to apply higher stress to the cathode point, the curvature radius of the needle was set at a few μm to a few hundred μm, while the gap distance was set at less than 1 mm. Tungsten was adopted as the needle material due to its high melting point; it was shaped by electro chemical polishing. The experimental setup consists of a high pressure chamber with point-to-plane electrode, a magnetic pulse compression module and pulsed Nd: YAG laser for Shadowgraph image. Negative breakdown in SCCO2 was enabled by adjusting the gap distance to a few hundred μm. Several bush-like streamers observed using the Shadowgraph method grew from the needle tip, causing breakdown. This breakdown process is discussed using Shadowgraph images and breakdown voltages.