Spatial nonuniformity of electron energy in a microwave atmospheric-pressure microplasma

The characteristics of the electron energy in a microwave atmospheric-pressure argon microplasma are investigated by a spatially resolved optical emission spectroscopy. By adding tiny amount of xenon (< 1 ppm) as tracer gas into the argon discharge, it is found that the spatial distribution of the electrons with energy >8.3 eV is quite different from that of the electrons with energy >11.5 eV. Spatial distribution of the population ratio between 4p and 5p levels of Ar atom is also determined. Furthermore, with a collisional-radiative model, it is found that the spatial variation of this population ratio is mainly attributed to the spatial nonuniformity of the effective electron temperature.