Characteristics of O₂-ar inductively coupled plasma test flow during catalytic recombination processes

The flowfield characterization in an inductively coupled plasma generator is conducted by optical emission spectroscopy and laser absorption spectroscopy as well as direct simulation Monte Carlo computation. A silicon carbide test piece is exposed to a 1-kilowatt oxygen-argon inductively coupled plasma test flow, and the emission intensity profiles of an atomic oxygen spectral line at 844.636 nm and an argon spectral line at 842.4648 nm along the central axis of the quartz tube are first obtained by optical emission spectroscopy with the surface temperature of 300, 1280, and 1430 K. By comparing the measured emission intensity profiles with the computed number density profiles, qualitative agreement is found for the case with the surface temperature of 300 K, while the difference becomes evident for the other two cases. Because the emission intensity obtained by the spectrometer is generally the integrated value along the line of sight, the measured emission intensity profile can be different from the true emission intensity profile along the central axis. Measure of the emission intensity profiles of atomic oxygen and argon in the radial direction by applying the inverse Abel transform to characterize the entire flowfield in the test chamber is attempted. It is found that the emission intensity near the quartz tube is significantly strong around the test piece not depending on the surface temperature of the test piece. Moreover, the electronic excitation temperature is evaluated through a Boltzmann plot, and it is found that it increases toward the test piece. In the direct simulation Monte Carlo computation, the measured emission intensity profiles of atomic oxygen and argon along the central axis for heating cases are qualitatively reproduced when the measured electronic excitation temperature at the exit boundary is assumed. These results show that the emission intensity profiles of atomic oxygen and argon in the entire flowfield around the test piece should be estimated by applying the inverse Abel transform for evaluating the catalytic efficiency of atomic oxygen recombination accurately.