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-selfsustained plasma discharge generated by a high E=n ( 300 Td) nanosecond-pulsed discharge, which provides ionization in combination with an orthogonal low E=n ( 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 Tv N2 of the order of 1100 K. Downstream injection of CO2, NO, and H2 results in vibrational relaxation, demonstrating the ability to further tailor the vibrational energy content of the flow. N2-NO vibration–vibration and N2-H2 vibration–translation rates inferred from these data agree well with previous literature results to within the uncertainty in rotational-translational temperature. I.