High-Speed Imaging of High-Frequency Effects of a CO2 Plasma Flow

This work presents the results of the investigation into the high-frequency behavior of a CO2 plasma flow. A highspeed imaging system is used in conjunction with narrow-bandwidth filters to measure spatially, spectrally, and highly temporally resolved data. The filters are selected to target individual transitions of atomic oxygen and carbon. The data sets are processed using an Abel transform algorithm allowing the extraction of the emission coefficient, upper-state number densities, and electronic excitation temperatures. The results show a distinct 300 Hz pulsing, which is spatially consistent across the entire flowfield. The two oxygen emission measurements are spatially similar; however, the carbon emission measurements show distinct differences in spatial distribution. The variations in emission coefficient and upper-state number density, both spatially and temporally, are attributed to the varying electron properties produced in the plasma generator, which is caused by the cyclic power supply. The electronic excitation temperatures increase downstream from the plasma generator, showing the effect of the highly energetic electrons equilibrating with the atoms. The temporal electron property fluctuations will have an important effect on flow characteristics that are affected by electrons, for example some chemical reactions. Other macroscopic flow properties, for example pressure, should not be affected by the high-frequency electron fluctuations.