Model of Current Formation at the Initial Stage of Return Stroke

The experimental studies of the breakthrough phase of the leader spark discharge in 1.3 m gap are presented. A numerical model describing the dynamics of streamer zone parameters and the dynamics of leader current pulse during the breakthrough phase is developed. The dependences of leader velocity in the breakthrough phase on the reduced electric field E/N in the streamer zone are obtained. These dependences are compared with the measurement data; it is shown that the leader velocity VL ~ (E/N)3/2. Agreement between the calculated and measured time profiles of the leader current during the breakthrough phase is obtained. It is shown that the main origin of the sharp increase in the current at times of 1–2 μs is the growth of the reduced electric field in the streamer zone, associated with a decrease in the length of this zone as a result of the convergence of the leader heads. The growth of the field leads to an increase in the streamer velocity in the streamer zone, an increase in the leader current and the velocity of the leaders.