Characterization of an atmospheric double arc argon-nitrogen plasma source

Abstract

In the framework of studies devoted to hazardous waste destruction, an original dc double anode plasma torch has been designed and tested, which produces an elongated, weak fluctuation and reproducible plasma jet at atmospheric pressure. The arc instabilities and dynamic behavior of the double arc argon-nitrogen plasma jet are investigated through the oscillations of electrical signals by combined means of fast Fourier transform and Wigner distribution. In our experiment, the restrike mode is identified as the typical fluctuation behavior in an argon-nitrogen plasma jet. The Fourier spectra and Wigner distributions exhibit two characteristic frequencies of 150 Hz and 4.1 kHz, which reveals that the nature of fluctuations in the double arc argon-nitrogen plasma can be ascribed to the undulation of the power supply and both arc roots motion on the anode channels. In addition, the microscopic properties of the plasma jet inside and outside the arc chamber are investigated by means of optical emission spectroscopy, which yields excitation, electronic, rotational, and vibrational temperatures, as well as the electron number density. The results allow us to examine the validity criteria of a local thermodynamic equilibrium (LTE) state in the plasma arc. The measured electron densities are in good agreement with those calculated from the LTE model, which indicates that the atmospheric double arc argon-nitrogen plasma in the core region is close to the LTE state under our experimental conditions.