Negative DC Prebreakdown Phenomena and Breakdown-Voltage Characteristics of Pressurized Carbon Dioxide up to Supercritical Conditions

This paper deals with the experimental results on prebreakdown phenomena and breakdown voltage characteristics of a negative dc point-to-plane gap in-compressed carbon dioxide up to the supercritical pressure as the first step to develop a plasma reactor with supercritical carbon dioxide. The gap length and the curvature radius of the point tip were 200 and around 35 mum, respectively. The experimental results show the following: 1) corona discharge preceding complete breakdown is observed more clearly in liquid and supercritical fluid than in gas; 2) the estimated discharge onset voltage according to the streamer theory is in fairly good agreement with the measured breakdown voltage in the gas density region of 0.1-30 kg ldr m^-3; 3) the breakdown mechanism in liquid can be classified into two categories: bubble-triggered breakdown at lower pressure and non bubble-triggered breakdown at higher pressure; 4) the breakdown mechanism in supercritical fluid is similar to that in higher pressured liquid; and 5) the density and temperature dependences of breakdown voltage in liquid and supercritical fluid are related closely with the breakdown mechanism.