Effects of gas recirculation on the coupling of repetitive ns pulse discharges: laser Rayleigh scattering and CFD modeling results

The effects of gas recirculation following a nanosecond-pulse high-voltage discharge across a pin-to-pin quiescent air gap have been experimentally measured and modelled. The results of a computational fluid dynamics code complemented experimental laser Rayleigh scattering measurements of spatially and temporally resolved absolute gas density. Of particular interest was the evolution of the low-density hot gas region formed immediately after the discharge and shockwave, followed by the eventual onset of recirculation of fresh gas back into the central discharge region. The trends of the data provide an explanation of previously observed energy coupling in repetitive pulses occurring above a critical repetition frequency. Ultraviolet images of the discharge path of a subsequent nanosecond pulse at various times after the initial pulse support the concept that energy coupling between pulses diminishes below this critical frequency.