Determination of gas temperature in an open-air atmospheric pressure plasma torch from resolved plasma emission

The resolved emission spectrum of an open-air atmospheric pressure plasma torch was recorded with a 0.5 m spectrometer and CCD camera. The plasma emission under these conditions was found to be dominated by continuum radiation and emission from species, which obscured large portions of the N2 second positive emission spectrum. Despite these difficulties, the gas temperature of the torch could be determined from a fit of partially resolved N2+ first negative vibrational transitions and a blackbody fit to the continuum radiation. The vibrational temperature, determined from a Boltzmann plot, was 4300±900 K while the blackbody radiation temperature was 4400±400 K. To check these gas temperature determinations, measured spectra over selected spectral regions were compared with spectral simulations using N2+ first negative emission, N2 second positive emission, and a blackbody. Best agreement between measured and simulated spectra was with blackbody temperature, rotational temperature, and vibrational temperature set to 4400 K.