Measurement of gas-density variation in pulsed streamer discharge at atmospheric pressure by Mach-Zehnder interferometry

In this study, gas-density variations occurring in pulsed streamer discharge at atmospheric pressure were quantitatively measured using a Mach-Zehnder interferometer. Experiments were performed using different gas compositions involving N2 or air in humid or dry conditions. Spatiotemporal variations in the gas density after the discharge were characterised in terms of the energy relaxation process of the molecules. The measured gas-density variations were well reproduced by a zero-dimensional simulation model of vibrational-to-translational energy transfer in humid-air and humid-N2 conditions. This indicated that the vibrational energy relaxation of N2 through water molecules has a major effect on the gas density. However, the gas-density variations in dry-air and dry-N2 conditions were not reproduced by the model; the corresponding etiology is outlined and discussed.