Effect of Pressure in Fast-Front Lightning Discharges in Air

The effect of gas pressure on fast impulse discharges (70 ns) in a short point-plane gap was investigated. Fast-frame photography allowed the tracking of the development of the discharge with high temporal resolution. At low pressures, the gap is initially bridged by a bright glow that can carry significant amounts of current. At higher pressures, the gap is initially filled with numerous filaments that transport little current. In this case, the current takes off only when the arc bridges the gap. In the interval t = 1-10 mus, the arc exhibited a braided structure that rotated rapidly.