Investigation of the Dynamics of a Microstructured Spark Channel in Air in the 'Tip (Anode)–Plane' Geometry at the Stage of Radial Expansion

The results of investigations of a spark discharge in air in the gap between the tip (anode) and a 1.5‑mm-long plane are presented. It is shown that, after breakdown, the discharge develops in the form of a beam of individual microchannels that close the discharge gap, then, after 20–30 ns, a continuous outer boundary of the channel forms and its radial expansion begins. The electron concentration at this moment reaches its maximum value at the level of 2 × 1019 cm—3. It was found that, starting from 60 ns, a cylindrical shock wave departs from the channel boundary. With time, the difference in the radii of the shock wave and the channel increases, resulting in the formation of a radial structure in the form of a highly conductive internal channel, separated from the shock wave by an intermediate shell. A computational and theoretical model is proposed to describe the dynamics of the spark channel expansion from the moment of the formation of a solid outer boundary, and a satisfactory agreement between the calculations and experimental data is obtained.