Picosecond CARS Measurements of Vibrational Distribution Functions in a High Pressure Non-Self-Sustained Discharge

Picosecond Coherent Anti-Stokes Raman Scattering (CARS) is used for measurement of nitrogen Vibrational Distribution Function (VDF) 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 ($\sim $300 Td) nanosecond pulsed discharge, which provides ionization, in combination with an orthogonal low E/n ($\sim $10 Td) DC sustainer discharge, which efficiently loads the nitrogen vibrational mode. It is also shown that operation with the nanosecond pulsed plasma alone results in significant vibrational energy loading, with T$_{v}$(N$_{2})$ of the order of 1100 K. Downstream injection of CO$_{2}$, NO, and H$_{2}$ results in vibrational relaxation, demonstrating the ability to further tailor the vibrational energy content of the flow. N$_{2}$ -- NO V-V and N$_{2}$ -- H$_{2}$ V-T rates inferred from this data agree well with previous literature results, to within the uncertainty in rotational-translational temperature.