Streamers in pulsed positive corona: low and high current regimes

Streamers are observed with a CCD camera in point-plane and wire-plane configurations. Two pulsed power supplies are compared: a spark-gap switched capacitor (C-supply) and a system with a transmission line transformer (TLT-supply). At 40 kV the C-supply gives ~1 A current and the TLT-supply 60 A, due to better impedance matching in the second case. At low currents the streamers are thin (~0.3 mm) and show a lot of branching. At high current the streamers are thick (~5 mm), nevertheless in both cases the current density is the same in both regimes, ~1 A/mm2. The influence of dielectric layers and a layer of water above the cathode is also shown