Spectral Investigation on the Direct-Current Uniform Discharge Ignited by a Dielectric Barrier Discharge at Atmospheric Pressure

Atmosphere pressure uniform plasma has the broad application prospect in the industrial field. In order to get a atmosphere pressure uniform plasma in large scale, a large gap uniform discharge (up to 5 cm) was initiated between a needle anode and a plate cathode, which was ignited under a low sustaining voltage by a coaxial dielectric barrier discharge in ambient air with argon used as working gas. The characteristics of the discharge were investigated. The coaxial dielectric barrier discharge can lower the voltage for gas breakdown effectively. The results showed that the atmospheric pressure uniform discharge included a plasma column near the anode, a plasma plume, a dark space and a cathode glow. The plasma column and the cathode glow were continuous discharges, while in the plasma plume region the discharges at different positions initiated at different time. In fact, the plasma plume behaved like a "plasma bullet" which traveled from the cathode to the plasma column. Through electrical method, the voltage-current characteristic was investigated. The voltage-current curve had a negative slope, whichwas similar with the normal glow discharge at low pressure. By analyzing the optical emission spectrum from the discharge, the optical emission spectrum was composed of the second positive system of nitrogen molecules, the spectral lines from argon atom and oxygen atom. By Boltzmann plot method, the spatially-resolved excited electron temperature was obtained. It was found that the excited electron temperature of the plasma column was lower than that of the plasma plume. These experimental phenomena were explained qualitatively. These results are of great importance to the development of atmospheric pressure uniform discharge plasma source and its application in industrial field.