STREAMER BREAKDOWN OF LONG AIR GAPS

Streamer breakdown of long (> 10 cm) air gaps under normal conditions is studied numerically. It is shown that streamer breakdown requires a n average electric field of 25 kV/cm. The time during which streamer b reakdown develops is primarily determined by the stage of quasi-unifor m heating of a streamer channel, which begins after the gap is bridged by the streamer and the return wave of the enhanced electric field is damped. This time is less than a hundred nanoseconds; and, for stream er breakdown to develop in a gap with a strongly nonuniform electric f ield, the voltage pulse should have a sufficiently sharp front. It is shown that such breakdowns can occur only in the submicrosecond range. The main microscopic processes responsible for the composition and te mporal evolution of a streamer plasma at different stages of the disch arge are revealed. The results of calculations agree qualitatively wit h experimental data on nanosecond breakdown.