Breakdown of gas liquid composite in divergent fields

A point electrode of a 0.1-mm-diam. tungsten wire was enclosed by a of about ~1-mm diam. gas bubble. After a voltage pulse application the bubble was deformed and then pushed to the plane electrode in the tested liquid. At the negative point, the bubble surface was rather smooth, although its shape was far from a sphere. Regular current and photocurrent pulses were observed when the bubble was attached to the point cathode. After the departure of the bubble from the point, the period of the pulses became long and random. When the bubble came close to the plane, light was emitted between the bubble and plane just before breakdown. At the positive point, a treelike surface was observed at the plane side of the bubble. Current and photocurrent pulses were not regular. When the tip of the treelike bubble went down to a point some distance from the plane, breakdown occurred. He, O₂, and SF6 affected the breakdown voltage of the bubble liquid composite for both polarities. Shortening the width of applied voltage pulse increased the breakdown voltage