Nitrogen Vibrational Population Measurements in the Plenum of a Hypersonic Wind Tunnel

Picosecond coherent anti-Stokes Raman scattering is used for measurement of nitrogen vibrational distribution function in the plenum of a highly nonequilibrium Mach 5 wind-tunnel incorporating a high-pressure pulser-sustainer discharge. First-level vibrational temperatures of the order of 2000 K are achieved in the 300 torr non-self-sustained plasma discharge generated by a high E/n (similar to 300 Td) nanosecond-pulsed discharge, which provides ionization in combination with an orthogonal low E/n (similar to 10 Td) dc sustainer discharge, which efficiently loads the nitrogen vibrational mode. It is also shown that operation with the nanosecond-pulsed plasma alone results in significant vibrational energy loading, with T-nu (N-2) of the order of 1100 K. Downstream injection of CO2, NO, and H-2 results in vibrational relaxation, demonstrating the ability to further tailor the vibrational energy content of the flow. N-2-NO vibration vibration and N-2-H-2 vibration-translation rates inferred from these data agree well with previous literature results to within the uncertainty in rotational-translational temperature.