Homogeneous dielectric barrier discharge in nitrogen at atmospheric pressure

A dielectric barrier discharge in nitrogen at atmospheric pressure was investigated by means of the electrical measurement, the fast photography and the time-resolved spectroscopy. By addition of a nitrogen flow, a stable homogeneous discharge was produced in a gap not longer than 3 mm and it was identified with a Townsend discharge. It was found that the discharge was extinguished while the voltage of the gas gap continued to increase. This extraordinary manner of discharge extinction was explained by the limited number of trapped electrons on the dielectric surface that could not provide a long-lasting Townsend discharge with sufficient secondary electrons. Due to the 'memory effects' the lowest breakdown voltage for a Townsend discharge in a 2 mm gap is only 4.9 kV in contrast to the streamer breakdown voltage of 8.2 kV. The working domain of the Townsend discharge is dependent on the frequency and the amplitude of the applied voltage. When the flow velocity increases from 0 to 140 cm s(-1), the discharge current decreases from 2.9 to 2.3 mA and the breakdown voltage increases from 5.3 to 5.9 kV, which is attributed to the nitrogen pressure in the gap increasing with the flow velocity. With the gas flow, the intensities of the spectral lines from the second positive system of N-2 are almost unchanged, whereas those from NO gamma systems are significantly reduced. From this phenomenon, it may be inferred that the density of oxygen as impurity in the discharge gap decreases with the gas flow. This result is in agreement with the existing theory that less oxygen leads to more metastables N-2(A) surviving to produce more seed electrons for initiating a Townsend discharge in nitrogen at atmospheric pressure.