Streamer and leader breakdown in air at atmospheric pressure in strongly non-uniform fields in gaps less than one metre

The breakdown in synthetic air at 100 kPa in rod-plane arrangements at 50 mm gap and in atmospheric air in the range of a few centimeters to some ten centimeters was investigated at positive polarity. Different shapes of the rods (spherical and sharp cut) were used to investigate the influence of the details of the electric field at the tips. Optical diagnostics using an image intensifier and a photomultiplier tube was applied to determine the relevant breakdown mechanisms. Streamer crossing was observed at typical average fields of about 4 to 5 kV/cm. Breakdown occurred at significantly higher fields via leader propagation or streamer-to-spark transition. The experimental results are compared to a simple 1D leader model and to breakdown data from literature. A reasonable description of experimental values by the leader model is seen.