Study of negative pulsed breakdown phenomena in supercritical carbon dioxide

Phenomena caused by negative pulsed breakdown in supercritical carbon dioxide with a 100 μm needle gap distance were observed by means of Shadowgraph method. The tip curvature of the needle corresponded to r = 8 and 490 μm. The appearance of streamer at pre-breakdown varied greatly by changing the needle tip curvature, although the breakdown voltage, approximately 60 kV, remained somewhat constant. A large bushlike streamer and several individual small bushlike streamers grew from the cathode at r = 8 and 490 μm. Several small subsequent streamers grew from the side of the needle with a tip curvature of 8 μm, and one of the subsequent streamers infrequently grew by the approximately the same length as the gap distance. This infrequent phenomenon may be similar to the breakdown mechanism of that with a large tip curvature. The reflection shock wave from the plane electrode at pre-breakdown was observed, suggesting no influence to breakdown occurrence.