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Description
Gas recirculation effects have been modeled following a nanosecond-pulse high-voltage discharge across a pin-to-pin air gap, where subsequent pulses in a burst have been found to couple very efficiently if the repetitive pulses occur above a critical frequency. Previous data from the same pulse discharge system indicated that the inter-electrode gas temperature increased rapidly following the first pulse up to several thousand Kelvin, but the inter-electrode region was rapidly cooling by 4 $\mu$s after the first pulse, presumably due to recirculating fresh gas. For this system, repetitive pulses at frequencies of 20 kHz and above exhibited strong thermal coupling, indicating that fresh gas recirculation does not cause a de-coupling of the following discharge until about 50 $\mu$s after the first pulse. The model developed is a computational fluid dynamics code that simulates the pulse energy deposited by the initial 10 ns arc into the inter-electrode gas and then computes the evolution of the resulting gas density and temperature profile after the pulse. The grid is set up to be two-dimensional and axially symmetric about the inter-electrode axis with the shape of the electrodes accurately represented. The simulated density profiles as a function of time are compared to experimental measurements which used Rayleigh laser scattering to determine the gas density along several different radial lines through the inter-electrode space. The Rayleigh scattering technique employed a pulsed 532 nm laser and gated intensified CCD camera that allowed both temporal and spatial resolution of the gas density after the pulse discharge.
