THE EFFECT OF TIP CURVATURE ON THE PREBREAKDOWN STREAMER STRUCTURE INCYCLOHEXANE

In this paper, the effect of tip curvature on the generation and propa gation of prebreakdown density change streamer in cyclohexane was inve stigated. The streamer inception voltage increased with tip curvature, which was higher for a positive point than a negative one. The initia l structure of the streamer was a single filament for both polarities in cyclohexane. For a negative point, the streamer structure changed f rom sphere to hemisphere, pagoda and bush-like form with increasing ti p curvature and applied voltage. A slim channel connecting the streame r with needle tip was clearly observed for tip radii > 5 mu m, while i t was not for those < 3 mu m. For positive streamers, on the other han d, it changed from slow bush-like form to fast filamentary with increa sing tip curvature and applied voltage. Both magnitude and propagating speed of the streamer at its inception voltage increased with a tip c urvature. After the growth stopped, they broke up into small bubbles a nd contracted with damped oscillation. From the spatial distribution o f the field strength between the point and plane calculated by the fin ite element method, it was found that there exists a specific distance from the tip where the field strength is equal under any tip radii us ed in this study for both polarities. This distance and field strength may considered to be the minimum length and field for an electron ava lanche in liquid.