Observation of the Space Leader During the Attachment Process in Positive Laboratory Sparks

A long-standing but fundamental question in lightning and laboratory spark researches is how the positive and negative leader attach with each other. Here we report optical images and discharge current waveforms during the breakthrough phase of attachment process in positive laboratory sparks. The space leader inside the common streamer zone was observed for the first time. The recorded electric current as well as the calculated impedance of the common streamer zone reveal the evolution process of the space leader. Finally, a new scenario including three subsequent stages is proposed for leaders’ attachment process.