Temperature measurements in microwave argon plasma source by using overlapped molecular emission spectra

The electron excitation temperature T-exc, vibrational T-vib, and rotational T-rot temperatures were measured in a high-pressure line-shaped microwave plasma source in argon over a wide range of gas pressure and microwave power, by using optical emission spectra. The selected ArI transition lines 5p-4s and 4p-4s were chosen to calculate electron excitation temperature using Boltzmann's plot method. Meanwhile, the emission spectra of hydroxyl OH molecular (A2 Sigma(+) -X-2 Pi(i), Delta nu = 0) band and the nitrogen N-2 second positive system (C-3 Pi(u) - B-3 Pi(g), Delta nu = +1), both second diffraction order, were used to evaluate the vibrational T-vib and rotational T-rot temperatures using the method of comparing the measured and calculated spectra with a chi-squared minimization procedure. The components of the overlapped spectrum are greatly influenced by the gas pressure; however, they are independent on microwave power. For temperatures, it was found that the T-exc dramatically decreases from 2.5 to 0.75 eV, which qualitatively agrees with T-e deduced from zeroglobal model. Both of T-vib and T-rot significantly decrease with as gas pressure increase from 0.4 to 50 Torr. Yet, they behave differently with microwave power. (c) 2015 AIP Publishing LLC.