The evolution of the discharge mechanism in a dielectric bounded cavity due to surface effects

Combined electrical/optical measurements were performed to study the evolution of the discharge mechanism in dielectric bounded cavities due to discharge by-products. A transition from a streamerlike mechanism (highly localized with large magnitude) to a Townsendlike mechanism (diffuse with small magnitude) is described. Important parameters influencing the transition are stress duration, type of dielectric, cavity dimensions, cavity surface resistivity, and test voltage. The effect of these parameters is described and illustrated by video pictures and time-resolved discharge pulse measurements. The transition is favored by small cavity height/cavity diameter ratios, by low values of dielectric surface resistance, and by a test voltage that is high if compared to the voltage needed for breakdown according to Paschen's law.<>