Laboratory experiments on the interaction of streamers ∗

Pictures show that streamer or sprite discharge channels emerging from the same electrode or position sometimes seem to reconnect or merge even though their heads carry electric charge of the same polarity; one might therefore suspect that reconnections are an artifact of the two-dimensional projection in the pictures. We have used stereo-photography of laboratory scale streamer discharges to investigate the full three-dimensional structure of such events. We analyze reconnection, possibly an electrostatic effect in which a late thin streamer reconnects to an earlier thick streamer channel, and merging, a suggested photo-ionization effect in which two simultaneously propagating streamer heads merge into one new streamer. We also investigate the branching lengths and angles in the 3D streamer tree structures.