Spectroscopic Characteristics of Atmospheric Pressure Plasma Plume in a Rod-Ring Electrode Geometry

A novel argon plasma jet driven by an alternating current voltage is developed to generate atmospheric pressure non-equilibrium plasma plumes in the upstream and downstream regions of the rod electrode. The novel jet is neither similar to a linear-field jet, nor a cross-field jet. The angle between the electric field and the gas flow direction can be changed easily in this novel jet. By increasing the applied voltage or the angle, the upstream plume length increases and the downstream plume length decreases. With optical and electrical methods, the discharge aspects are investigated and it is found that the discharge pulse number increases with increasing the applied voltage for every voltage cycle. With optical emission spectroscopy, it is found that the spectral lines of Ar and OH can be observed in both of the upstream and downstream plumes. Besides, the spectral lines of N-2 can be only observed in the downstream plume. Moreover, the spectral intensity of the downstream plume is slightly higher than that of the upstream plume. Based on the collision-radiation model, the intensity ratio of two spectral lines is investigated to obtain the electron density and the excited electron temperature for the upstream and downstream plumes. Results indicate that the electron densities increase with increasing the applied voltage for the upstream and downstream plumes. The excited electron temperatures of the two plumes also increase with increasing the applied voltage. Moreover, the electron density and the excited electron temperature of the downstream plume are higher than those of the upstream plume under the same applied voltage. Additionally, the gas temperature is also investigated by fitting the spectra of OH radicals for the upstream and downstream plumes. It is also found that the gas temperature of the downstream plume is slightly higher than that of the upstream plume.