The development of breakdown in a homogeneous field at high overvoltages in helium-neon mixtures and nitrogen

The development of predisruptive processes up to breakdown can be visually displayed using high-speed cinematographic techniques. This study was carried out in helium-neon mixtures and in pure nitrogen. The primary electrons are released from the cathode by a powerful UV flash, and under those conditions the anode streamer is set off near the cathode. The propagation of the anode-directed streamer is observed in a homogeneous applied field for very high overvoltages (200-300%) and for E/p values of up to 55 V cm -1 Torr -1 for the helium-neon mixtures, and up to 190 V cm -1 Torr -1 for nitrogen. The velocities of the streamer's various stages are measured. The recordings show that, in its propagation from cathode to anode, the streamer proceeds into two distinct phases separated by a transition zone.