In this paper, a multi-structure needle-ring electrode argon plasma jet device was designed to investigate the influence of reactor structure parameters and discharge parameters on the length of atmospheric pressure non-equilibrium plasma jet. Specifically, the effects of the discharge voltage, the electrode gap, the distance between the end of the high-voltage electrode and the ground electrode, and the volume flow of argon on the jet length were explored. The results demonstrate that the maximum length of the plasma jet in the external environment can reach 80mm when the inner diameter of the tube is 15 mm; the jet length first increases and then tends to be stable with the increase in the discharge voltage; the jet length presents two peaks with the increasing voltage; the end of jet appears the unstable phenomenon of "beating" when the discharge voltage is high. Besides, the longer the distance between the end of the high-voltage electrode and the ground electrode, the longer the jet length. Nevertheless, the relationship between the distance and the jet length is non-linear. The jet length first increases and then decreases with the increase in the electrode gap. The phenomenon of "particle countercurrent" is observed when the electrode gap and discharge voltage are relatively large. With the increase in the argon volume flow, the plasma jet length also exhibits a trend of first increasing and then decreasing. To sum up, the main factors affecting the length of the plasma jet is transport mode during the plasma transport process.

In order to better analyze the characteristics of particle distribution and its influencing factors in the ionized space during the process of coaxial dielectric barrier discharge, the self-designed two-dimensional axisymmetric structure exciter was used to carry out optical diagnosis, with the electron temperature calculated through Gaussian fitting. Also, the plasma model was applied to conduct research on the discharge process through numerical simulation, with the electron density and electron temperature changes analyzed by using different discharge parameters. The research results show that with the increase of discharge voltage, pressure inside reactor and relative permittivity, the discharge process is promoted. In addition, the rise of current density leads to an increase in the number of charged particles on the surface of the medium during the discharge process, while the rise of discharge intensity causes an increase of the electron density. Electron temperature decreases due to the increased loss of collision energy between particles. These results are confirmed by the comparison of experimental data with simulation results.

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