Radiation of nanosecond surface sliding discharge in a supersonic air flow

The radiation of a surface sliding discharge in supersonic air flows with an oblique shock wave has been experimentally studied at the flow Mach numbers of 1.20–1.60 and density of 0.01–0.50 kg/m$^3$. A discharge about 500 ns in duration was initiated in the shock tube test section at the pulsed voltage of 25 kV. The discharge radiation was analyzed based on streak images and 9-frame ICCD images with the nanosecond resolution. It has been established that the discharge channel radiation in supersonic flows undergoes a two-stage attenuation within 2–3 $\mu$s and then decays with a characteristic time of 800–1300 ns which significantly exceeds the decay time in still air.