Expansion of Initial High-Current Spark Channels

Abstract

High-density short-gap sparks of nanosecond duration are triggered with a time jitter <1 nsec when charged up by a powerful 50-nsec, 7-kV pulse. This permits exact time coordination between the pulsed spark breakdown and a gated Kerr cell of 2–8 nsec exposure which is used for the photography of the initial channel. Development of the channel is observed by sequences of exposures at different gate settings. Maximum expansion velocities of 1.6 × 106 cm/sec in 1-atm air are determined 2.6 nsec after zero time of the breakdown, of a 1.3-nHy nanolite which value is in agreement with earlier observations by Demidov. The expansion velocity appears to follow the current. Development of erosion clouds from the anode are observed and jetlike flares appear to form after the current has ceased.