Aerothermodynamic Characterization of Inductively Generated Carbon Dioxide Plasma by Laser Absorption Spectroscopy

Abstract

This paper describes the application of tunable diode laser absorption spectroscopy to a high-power supersonic carbon dioxide plasma, which is relevant for Mars entry. The measurements are complemented by optical emission spectroscopy and intrusive probe diagnostics. The experiments are performed in the PWK3 plasma wind tunnel, powered by the IPG4 inductive plasma generator. An infrared diode laser is tuned by a frequency generator targeting the atomic oxygen triplet at 844 nm. Radial measurements of the plasma jet are conducted at an axial distance of 105 mm from the nozzle exit. The absorption data are corrected for the laser baseline and for oscillations induced by the vacuum pumps. On the plasma jet centerline, a temperature of Ttr=3240±552 K and an excited state number density of nO*=2.9±0.3⋅1015 m−3 are determined by analyzing the isolated S13−P13 absorption profile. A centerline mass-specific enthalpy of 41.67−23.7+14.0 MJ/kg is estimated by assuming thermochemical equilibrium inside the plasma generator, followed by isentropic expansion of the flow. In consideration of the uncertainties, this agrees well with the value of 34.46±1.4 MJ/kg determined based on intrusive probe measurements.