Discharge Modes Suggested by Emission Spectra of Nitrogen Dielectric Barrier Discharge with Wire-Cylinder Electrodes

In this paper, nitrogen dielectric barrier discharge (DBD) plasma was generated in a quartz tube with coaxial wire-cylinder electrodes at atmospheric pressure. By varying the nitrogen gas flow (F_N ) in the range of 0-1m ³/h, the plasma optical emission spectra (OES) were measured and studied. The vibration (T_vib) and rotation temperature (T_rot) of nitrogen were obtained, by fitting the rovibronic bands of N₂(C³Π_u -B³Π _g, 0-1), and by the Boltzmann plot method for purposes of comparison. T_vib increased up to 2481 K with increasing nitrogen flow till 0.2 m³/h, and then decreased with further increasing F_N, while T_rot decreased monotonously and approached to ∼350 K for F_N ≥0.6m³/h. The intensity of N₂(C³Π_u-B³Π_g, 0-0, 1-0, 0-3) and N₂⁺(B²Σ_u⁺ -X²Σ⁺_g, 0-0) exhibited similar evolution with increasing F_N to those of the T_vib and T_rot, respectively. The discharge photos revealed that the discharge filaments gradually decreased with increasing F_N, and eventually disappeared, which implied that a discharge mode transition emerged with increasing F_N . The possible mechanism for the discharge mode transition is studied in detail according to the vibration (T_vib) and rotation temperature (T_rot) of nitrogen.