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 (A 2 Σ + - X 2 Π i, Δ ν = 0) band and the nitrogen N₂ second positive system (C 3 Π u - B 3 Π g, Δ ν = + 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 0.75eV, which qualitatively agrees with T e deduced from zero-global model. Both of T_vib and T_rot significantly decrease with as gas pressure increase from 0.4 to 50Torr. Yet, they behave differently with microwave power.