Effects of various parameters on the length OFA cold plasma plume

Atmospheric pressure nonequilibrium plasmas have recently obtained considerable attention for several emerging applications such as surface modification and materials processing, biological and chemical decontaminations of media, thin film deposition, synthesis of nano materials, and water decontamination. On the other hand, because atmospheric pressure plasma jet devices can generate plasmas that are not spatially bound or confined by electrodes, they have obvious advantages over the traditional electrodes configuration. Because of these advantages, they are very desirable in many situations such as biomedical applications. Some of these plasma jet devices can generate plasma plumes with several centimeters long, while the gas temperature of the plasma is close to room-temperature and the plasmas are touchable by a human hand. High-speed photographs show that some of the plasma plumes, which look like continuous plasma volumes are actually bullet-like volumes of plasmas with propagation velocities within the range of 10⁴-10⁵ m/s. However, the fundamentals of these relative long cold plasma plumes are not yet well understood. In this paper, to have a better understanding of the mechanism of the generation of the plasma plumes, the effects of various parameters, including the applied voltage, the pulse width, the pulse frequency, the gas flow rate, and the diameter of the nozzle on the length of the plasma are studied. It is found that the applied voltage and the pulse width have significant effects on the length of the plasma. Detailed analysis shows that the integrated total charges of the primary discharge current may be directly related to the propagation of the plasma.