Statistical time lags in air—pressure and polarity dependence

Abstract This paper investigates the influence of gas pressure on the polarity dependence of statistical time lags in air for a needle-plane gap. The needle-plane gap was stressed by a DC step voltage that lasted 10 s. The positive streamers were observed to have shorter time lags than negative at 1 bar absolute pressure. This polarity dependence was reversed at 3 bar and negligible at 5 bar. Simulations were performed to study this pressure dependence. These simulations support that detachment from negative ions is the main source to start electrons for positive streamers. For negative streamers, the conclusions are less clear. Based on the simulation results, detachment from negative ions inside the inception region was ruled out and field emission did not provide a consistent explanation across all pressure levels for negative streamers in these experiments. It is speculated that a field dependent surface effect, potentially related to secondary emission, dominates for negative streamers.