Measurements and kinetic modeling of energy coupling

Nanosecond pulse discharge plasma imaging, coupled pulse energy measurements, and kinetic modeling are used to analyze the mechanism of energy coupling in high repetition rate, spatially uniform, nanosecond pulse discharges in air in plane-to-plane geometry. Under these conditions, coupled pulse energy scales nearly linearly with pressure (number density), with energy coupled per molecule being nearly constant, in good agreement with the kinetic model predictions. In spite of high-peak reduced electric field reached before breakdown, E/N ∼ 500–700 Td, the reduced electric field in the plasma after breakdown is much lower, E/N ∼ 50–100 Td, predicting that a significant fraction of energy coupled to the air plasma, up to 30–40%, is loaded into nitrogen vibrational mode. A self-similar, local ionization kinetic model predicting energy coupling to the plasma in a surface ionization wave discharge produced by a nanosecond voltage pulse has been developed. The model predicts key discharge parameters such as ionization wave speed and propagation distance, electric field, electron density, plasma layer thickness, and pulse energy coupled to the plasma, demonstrating good qualitative agreement with experimental data and two-dimensional kinetic modeling calculations. The model allows an analytic solution and lends itself to incorporation into existing compressible flow codes, at very little computational cost, for in-depth analysis of the nanosecond discharge plasma flow control mechanism. The use of the model would place the main emphasis on coupling of localized thermal perturbations produced by the discharge with the flow via compression waves and would provide quantitative insight into the flow control mechanism on a long time scale. (Some figures may appear in colour only in the online journal)