Observation of surface discharge in nitrogen based on pockels effect

Surface discharge phenomena on dielectric materials in nitrogen are investigated by Pockels effect technique. A needle-plate electrode system is adopted, and one single cycle of 20-Hz sinusoidal HVac is applied with an amplitude of 5 kV. It is found that positive discharges have two distinct regions, i.e., surface charges appear uniformly in a core region, and then, they develop into streamer pattern away from the core. Negative charge distribution always extends uniformly, and when negative voltage returns to zero, back discharge phenomena can be seen clearly. Within pressure decreases from 101 to 21 kPa, the scale of discharge area, the branch width, and the numbers of streamers increase, but charge densities reduce. It is interesting that the products of core region's radius of positive discharges and corresponding pressure are all around 80 torr × cm.