Thermal dynamics of leader decay and reactivation in long air gap discharges

In this study, we present a comprehensive investigation of positive leader discharges, with the aim of enhancing our understanding of leader decay and reactivation. Our approach involved a detailed experimental and computational analysis of the phenomena. Specifically, we employed a time-resolved quantitative Schlieren platform, which provided us with high spatial resolution (60.0 & mu;m pixel(-1)) and short exposure times (0.37 & mu;s frame(-1)), allowing us to capture the 2D spatial-temporal evolution of gas temperature in positive leaders with a gap length of up to three meters. In addition, we employed a detailed thermal-hydrodynamic model coupled with a comprehensive kinetic scheme, consisting of 28 chemical species and 125 chemical reactions. Our simulations showed good agreement with the measured mean gas temperature and expansion rate of thermal radius. We conducted experiments under the same applied conditions to obtain both stable and decaying leaders. Our results show that once a positive leader starts to decay, the temperature drops below 3000 K. At the same time, both the electric field and conductivity decrease significantly compared to a stable leader. In addition, before the temperature drops below 2000 K and transforms into an aborted leader, a decaying leader might be reactivated.