Streamer Breakdown with Runaway Electrons Forming Diffuse Discharges in an Inhomogeneous Electric Field

Abstract

The results of experimental investigations of formation of diffuse nanosecond discharges in a nonuniform electric field in air and other gases at the pressures within 12.5–400 kPa are presented. The experiments were performed using a four-channel ICCD-camera, an ultra-fast streak-camera, and wideband oscilloscopes. It is found out that spherical streamers are formed in a sharply nonuniform electrical fields under high voltages in a pre-breakdown stage of the discharge, irrespective of the gas used (air, nitrogen, hydrogen, methane, neon, or helium). The data are obtained on the instantaneous streamer velocity in air at different voltages and on the displacement current caused by the electric field re-distribution in the gap during the streamer formation. Beams of runaway electrons are recorded. The mechanism of formation of anode- and cathode-directed streamers at high voltages is discussed.