Comparative study of electron temperature in cascaded arc Ar/N2 plasma using laser Thomson scattering combined optical emission spectroscopy approach

The expanding cascaded arc Ar/N2 plasma has been investigated by both the active and passive optical diagnostic technologies. In the investigation, the laser Thomson scattering (LTS) and optical emission spectroscopy (OES) have been adopted to measure electron temperature (Te) and electron excitation temperature (Texc), respectively. The LTS measurements show that a remarkable nonlinear behavior of Te as a function of the N2/(Ar + N2) ratio is found, which is caused by the collective interaction between the superelastic collision and the electron-impact excitation. The superelastic collisions by the highly excited vibrational nitrogen molecules can effectively heat the free electrons, while the electron kinetic energy can be transferred to N2 molecular internal energy via the electron impact with N2 in the ground state. The difference between Texc and Te demonstrates that the cascaded arc Ar/N2 plasma significantly deviates from the local thermodynamic equilibrium. This would be useful for improving our further understanding of nonequilibrium plasma and extending applications of the cascaded arc Ar/N2 plasma.