Experimental study of the dynamics of leader initiation with a long dark period

Abstract

Abstract Leader discharge plays a key role in the breakdown of long air gap and the evolution of natural lightning discharges. Prior to the formation of continuous leaders, streamer corona bursts with dark periods in between generally appear. To attain a better physical understanding of the dynamics of discharge during dark periods, experimental studies with a specially designed electrode based on an improved quantitative schlieren system were performed. The experiments measured gas density and temperature changes of the leader discharge channel within the dark period for the first time. Temperature changes in a single discharge channel and corresponding current were obtained simultaneously. Measurements show that at the axis of the streamer stem and the unstable leader within the dark period the gas temperature is below 2000 K and decreases monotonically with time. These measurements confirmed the prediction of a previous theoretical study. To analyse the properties of discharge during the dark period, the measurements were compared with simulation results based on a detailed 1D thermo-hydrodynamic model. The measured temperature drop was less significant than that computed from simulation. This discrepancy is believed to be caused by heating from the ionic current, which was neglected in the previous studies. The ionic current helps to maintain the gas temperature during the long dark period but cannot reverse its decline. From a comparison and analysis, several suggestions are proposed to improve both the measurement system and the numerical model for further quantitative investigations of the dynamics of leader initiation.