Spectroscopic determination of H, He, and H2 temperatures in a large-scale microwave plasma source

Abstract

Emission spectroscopy was used for the diagnostic of a large-scale, slot antenna excited microwave plasma source operating in pure hydrogen and in helium-hydrogen and argon-hydrogen mixtures at low pressures (p=0.3mbar) and microwave power ranging from 600to900W. No evidence was found for excessive broadening of the Hα line under the present operating conditions, even though this line was found to be broader than the helium singlet line at 667.8nm. The Doppler temperatures corresponding to this helium line (400–900K) are close to the rotational temperatures (300–800K) determined from the Q branch of the Fulcher-α band under the same conditions. The kinetic temperature of H atoms corresponding to the Doppler broadening of the Hα line varies spatially between 3100 and 3400K (95% He–5% H2, p=0.3mbar, and P=900W) and between 3350 and 3900K (95% Ar–5% H2, p=0.3mbar, and P=600W) keeping constant the mixture composition, pressure, and microwave power. The rotational H2 temperature in argon-hydrogen mixtures varies from 330to400K under the same conditions. Therefore, the results presented here indicate that the kinetic temperature of H atoms is higher than the background gas temperature.