Polarity effect of applied pulse voltage on the development of uniform nanosecond gas breakdown

The spatio-temporal evolution of electric parameters of plasma and emission produced by high-voltage periodic pulsed discharge has been studied. The discharge was initiated by voltage pulses of 13.5 kV amplitude, 25 ns duration and 6 ns rise time with a repetition frequency of 40 Hz in molecular nitrogen at a pressure of 5 Torr. Differences between discharge characteristics for positive and negative polarities of the pulse has been investigated. The net electrical charge was measured by a calibrated capacitive gauge moving along the discharge tube. Time-resolved electric fields and electron densities at different distances from the high-voltage electrode were obtained. On the other hand, the electric field was derived from relative time-resolved emissions of second positive and first negative systems of molecular nitrogen. The spatial and temporal behaviour of the emission correlates with the behaviour of the electric field obtained from electrical measurements. A comparison of electric field values determined by different methods demonstrates a significant dependence of the results on the voltage polarity and leads to the conclusion that their differences, when working with positive polarity of voltage, is due to the non-local character of the discharge development.