The effect of low direct voltage on streamer breakdown in long non-uniform air gaps

A kinetic model for the ionization processes in high-temperature air in a strong electric field is used to simulate numerically the effect of a low direct voltage on streamer breakdown in a long air gap between a spherical anode and a plane cathode. It is shown that the application of a low direct voltage strongly affects the discharge process after bridging the gap provided that the channel has been heated up to 3000 K by the completion of the high-voltage impulse. In this case a sudden voltage reduction does not lead to plasma decay; instead, the channel is slowly heated under the action of a low direct voltage and transforms into an arc channel for times lying in the microsecond range. The voltage required for the breakdown is noticeably less than the threshold of the leader process. The breakdown time strongly depends on the internal resistance of a voltage source.