Observations of the Channel Illuminations During Dark Periods in Long Positive Sparks

摘要

No observations show evidence of ionization in long air gap discharge during dark periods. However, for the first time, weak channel illuminations are observed during the so-called dark periods in this paper. The length of these faint bright channels is almost constant during each dark period and is nearly equal to that of the remaining low-density channels created by the previous discharge. The phenomenon, that is, the dark period is not really dark, is more likely to occur at the time when there is a greater change rate of the applied voltage. These findings are based on the high-speed direct imaging and Schlieren photography together, in which the former is used to visualize the bright channels and the latter to detect the low-density area.