Study On The Spectral Property Of Plasma Jet Generated By Gaseous Discharge

Plasma jet provided a new method for synthesis of new materials; it was applied in surface treatment of metals and surface coating. Gaseous discharge, as a mean path of obtaining plasma, played a more important role in both civil and industrial applications.The N₂ plasma jet was generated from a nozzle using an AC discharge of about 15KV. The emission spectra were obtained by using the concentration modulation spectroscopic technique. Usually it was thought the molecular concentration was in direct ratio of the absolute value of discharge current for concentration modulation technique—twice the discharge frequency f. However, in our experiment the signal could be detected using both 1f and 2f. The reason was the discharge was not continuous, but occurred as a pulse only once in every negative half cycle. Fourier transform analysis was operated on the signal pulse, it was found that besides the original frequency, there were a large amount of frequencies of odd and even multiple of the original frequency. So the signal could be demodulated using both 1f and 2f. The phenomena that the pulsed discharge presented with continuous AC voltage was discussed.It was found that the vibrational temperature decreased first and then increased along the downstream from the nozzle by measuring the emission spectrum from the different axial position in the jet. A phenomenological model was presented to fitting with experimental data, explaining the vibrational temperature variation with the different axial position Z. The N₂⁺/ N₂ ratio variated along the axis and the property of discharge in the experimental system was studied.