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An original DC double anode plasma torch has been devised and tested, which generates a long-time and highly stable argon plasma jet at atmospheric pressure. The arc unsteadiness and dynamic behaviour are investigated through the fluctuations of electrical signals combined with the classical tools, such as the statistic method, fast Fourier transform (FFT) and correlation analysis. The current–voltage characteristics of the argon plasma jet show an increasing tendency. The takeover mode is identified as the typical fluctuation behaviour of the double arc argon plasma jet in our experiment. The FFT and correlation calculation results of electrical signals exhibit the only characteristic frequency of 150 Hz, whereas the high frequency fluctuations are totally disappeared. Such low frequency fluctuation (150 Hz) can be attributed to the inherent characteristic of the torch power source and is independent of any change in the operating parameters. These results indicate that the nature of fluctuation in an argon plasma jet is mainly induced by the undulation of tri-phase rectified power supply. In addition, both arcs are characterized as the one and only system, and each arc root attachment is rather evenly diffused than located at a fixed position on the anode surface. The time shift derived from the cross correlation between the arc voltage and current intensity can be used as an independent parameter to reflect the fluctuating behaviour in the plasma jet. |
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