Investigation of positive streamers by double pulse experiments

We have studied the effects of a previous streamer discharge on a subsequent discharge by applying two near-identical consecutive voltage pulses with pulse-to-pulse intervals ¿t between 200 ns and 40 ms. Images from both discharges where superimposed to study and compare their morphology. The experiments have been performed on positive streamer discharges in a 103 mm point-plane gap in 133 mbar artificial air, pure nitrogen and pure argon. We have found that for short ¿t (below 1 µs for air and nitrogen and below 15 µs for argon) the second-pulse streamers continue the paths formed during the first pulse. At higher ¿t this stops and later new streamer paths are formed. These new (thin) streamer paths initially move on the edge of the old channels. For again higher ¿t they start to overlap with the old channels and, finally (with ¿t in the milliseconds range), they become independent of the old paths.