Experimental study of polarity dependence in repetitive nanosecond-pulse breakdown

Pulsed breakdown of dry air at ambient pressure has been investigatedin the point-plane geometry, using repetitive nanosecond pulses with10 ns risetime, 20--30 ns duration, and up to 100 kV amplitude. Amajor concern in this paper is to study the dependence of breakdownstrength on the point-electrode polarity. Applied voltage, breakdowncurrent and repetitive stressing time are measured under theexperimental conditions of some variables including pulse voltagepeak, gap spacing and repetition rate. The results show thatincreasing the E-field strength can decrease breakdown time lag,repetitive stressing time and the number of applied pulses asexpected. However, compared with the traditional polarity dependenceit is weakened and not significant in the repetitive nanosecond-pulsebreakdown. The ambiguous polarity dependence in the experimentalstudy is involved with an accumulation effect of residual charges andmetastable states. Moreover, it is suggested that the reactionsassociated with the detachment of negative ions and impactdeactivation of metastable species could provide a source of primaryinitiating electrons for breakdown.