Spectroscopic diagnostic technique has been employed to investigate the characteristics of the unsteadiness of do plasma spraying jets for two types of plasma torches. The continuous transient signal of the arc voltages and the spectral line intensities of the jets have been obtained, and their frequency characteristics have been studied by means of fast Fourier transform method. Three factors to jet fluctuation have been represented and distinguished from each other. Digital high-speed photography technique has also been introduced to investigate the fluctuation of plasma jet. Snapshots of the jet and the spectrum analysis result of arc voltage and spectral line intensity have indicated that the effect of the power supply occupies dominant proportion on the jet fluctuation for the argon plasma jet. The influence of gas flow rate on the arc restrike characteristics has been studied. Distributions of the jet temperature and number densities of nitrogen atom in the argon plasma jet region have been obtained with the distributions of line intensities of argon and nitrogen atom. [References: 13]
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