Effects of Applied Voltage on Branching of Positive Leaders in Laboratory Long Sparks

Positive leaders branch less frequently than negative counterpart, and the physical processes and properties of positive leader branching remain a mystery. We investigated 10 m laboratory discharges under four positive voltages using a high‐speed video camera. Positive leaders differ from negative leaders by either directly splitting or connecting with floating bidirectional leaders to form branching, and the number of leader branches shows a positive correlation with the applied voltage, that is, the branched channels increased from 1 to 4 when the voltage increased by a factor of 1.5. Grounding points are positioned beneath the electrode and are more concentrated with lower voltage. During the stable progression of the leader, there is a slight increase in its development speed as the applied voltage rises. When the voltage is increased by 70%, the average breakdown time decreases by 40%. These characteristics provide insights into the branching mechanism of positive leaders. Plain Language Summary The discharge mechanisms in natural and laboratory discharges are highly complex. This study aims to unravel the branching mechanism of positive leaders through laboratory experiments. A specific 10 m rod‐to‐plate discharge gap was designed to vary the maximum applied voltage, making it possible to examine the effects of applied voltage on the leader discharging trunk and branched channels. The statistical results indicate that as the peak voltage increases, the number of leader channels during the discharging process also increases. In natural lightning, positive leader channels generally exhibit low bifurcation rates, whereas in our study, the maximum number of discharging channels reached four with a sufficiently high applied voltage. The strike ground points of the trunk channel tend to be more dispersed when the applied voltage increases. Additionally, as the voltage rises, the average propagation speed of the leader trunk channel also increases. Our study presents the first systematic findings in this field, with crucial implications for a comprehensive understanding on the leader branching process and the development of discharge models. Key Points The positive correlation between the number of positive leader branches and applied voltage is demonstrated for the first time As the applied voltage increased, the strike ground points of the discharge channel became more dispersed The average 3‐D speed of the positive leader trunk channel exhibits a slight