Heating of a Local Region of a Branching Streamer as a Starting Point of a Space Leader and a Negative-Leader Step

Abstract

Localized plasma formations called space leaders are observed in streamer coronas of negative leaders of long laboratory sparks. The main leader completes a step when the space leader comes into contact with the head of the main leader. In the present work, we discuss the creation mechanism of local plasma formations (henceforth, generally, referred to as the hot spots) that are able to initiate a space leader. It is assumed that spontaneous increase in the conductivity in a local region of one of the streamers of the main leader corona initiates two secondary coronas from the ends of this region. The corona current warms up the region, leading to formation of the hot spot, provided that the magnitude of the field in the heated region is sufficiently high. Finally, hot spots grow into the space leader with further increase in the temperature and conductivity. The necessary condition for achieving the temperature of ≈2000 K in the hot spot within the observation time of tobs ≤ 1 µs is the magnitude of the ambient electric field strength E0 = 20 kV cm–1 that is almost twice higher than the average magnitude of the electric field strength of ≈11 kV cm–1 in a negative corona.