Colored Diffuse Mini Jets in Runaway Electrons Preionized Diffuse Discharges

Abstract

Optical emission of the nanosecond diffuse discharge initiated by runaway electrons in an inhomogeneous electric field was investigated in a single-pulse and pulse-periodic modes in different gases (air, nitrogen, and argon). The amplitude of voltage pulses, pulse rise time, and interelectrode distance were, respectively, 200 kV, 0.5 ns, and 13 mm for single-pulse mode, and 13 kV, 4 ns, and 2 mm for pulse-periodic mode. In the single-pulse mode, the diffuse mini jets (DMJs) of different colors with lengths up to 7 mm appear near electrodes. Blue DMJs were observed near electrodes with a small radius of curvature made of a stainless steel. Red DMJs were observed near the grounded flat electrode made of aluminum and in the center of discharge gap near a spark channel. It was shown that radiation intensity of DMJs increased with the increase in nitrogen pressure up to 0.4 MPa, but subsequent increase in pressure up to 0.7 MPa led to the decrease in radiation intensity. In the pulse-periodic mode, colored DMJs are observed as well, the size of which was $\sim 1$ mm. In this mode, the spectral and amplitude-temporal parameters of the radiation of DMJs have been studied. It was shown that the color of DMJs is determined by the radiation of electrode metal vapors. It was shown that the DMJs originate from the bright spots (explosive centers) on electrodes.