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 (FN) in the range of 0-1 m3/h,the plasma optical emission spectra (OES) were measured and studied.The vibration (Tvib) and rotation temperature (Trot) of nitrogen were obtained,by fitting the rovibronic bands of N2(C3Πu-B3Πg,0-1),and by the Boltzmann plot method for purposes of comparison.Tvib increased up to 2481 K with increasing nitrogen flow till 0.2 m3/h,and then decreased with further increasing FN,while Trot decreased monotonously and approached to ～350 K for FN ≥ 0.6 m3/h.The intensity of N2(C3Πu-B3Πg,0-0,1-0,0-3) and N2+(B2Σu+-X2Σg+,0-0) exhibited similar evolution with increasing FN to those of the Tvib and Trot,respectively.The discharge photos revealed that the discharge filaments gradually decreased with increasing FN,and eventually disappeared,which implied that a discharge mode transition emerged with increasing FN.The possible mechanism for the discharge mode transition is studied in detail according to the vibration (Tvib) and rotation temperature (Trot) of nitrogen.