Observation of the Streamer–Leader Propagation Processes of Long Air-Gap Positive Discharges

A novel observation method is proposed to study the streamer-leader propagation processes of long air-gap positive discharges. Experiments of 3-12 m air-gap discharges have been conducted in this paper. The observed images could clearly and particularly describe the characteristics of the positive streamer-leader propagation processes. Some important phenomena of the propagation processes are indicated and discussed, such as the leader's velocity that varied with the time, the different lengths of inception leaders, the leader's branching phenomena, the continuous streamer-leader propagation processes simultaneously with the voltage's descent, and the upward leader's propagation processes.