Optical Emission Spectroscopic Studies on Atmospheric Electrodeless Microwave Plasma in Carbon Dioxide-Hydrogen Mixture

Optical emission spectroscopic measurements were performed on atmospheric pressure electrodeless microwave plasmas produced in a 95% carbon dioxide-5% hydrogen mixture. The rotational and vibrational temperatures of the plasma were determined by measuring the C₂ Swan band spectra at wavelengths in the ranges of 500-517 and 548-565 nm. The electron number density of the plasma was deduced by measuring the Stark broadening of the hydrogen Balmer-β line shape at 486.13 nm. The microwave power was fixed at 2 kW, and the flow rate was varied from 5 to 20 standard liter per minute. The difference between the rotational and vibrational temperatures was found to be negligible. The temperatures reached 6200 (±200) K and were independent of the flow rate. The electron number densities of the plasmas were estimated to be approximately 2.06 (±0.12) × 10¹⁴cm^-3. Thermodynamic-equilibrium calculations indicated that the temperature corresponding to the measured electron density was 6221 (±200) K, which is almost the same as the temperatures measured according to the C₂ Swan band spectra. Therefore, the electron temperature was nearly the same as the gas temperature, and the plasma was in local thermal equilibrium.