Laboratory study of the bi-leader process from an electrically floating conductor. I. General results

In-flight experiments have shown that in most cases the aircraft striking process is initiated by the bidirectional propagation of two leaders of opposite polarities. A laboratory experiment has been designed to analyse in detail the development of such a `bi-leader´ from an electrically floating conductor suspended in a 10.5 m plane-to-plane gap, submitted to an impulse voltage. The shape of the floating object, the electrode configuration and the voltage waveshape have been optimised to allow the observation of the simultaneous development of both discharges before their junction with the planes. Current and electric field probes have been installed at both ends of the floating object, and synchronised with time-resolved optical diagnostics. The authors give a detailed description of the observed phenomena and compare the characteristics of the positive and negative discharges with those already studied in classical rod-to-plane gaps