Propagation of an atmospheric pressure plasma plume

Summary form only given. The fundamentals on the propagation of the atmospheric pressure plasma jets are not yet well understood. Teschke et al (2005), Lu et al (2006, 2008), Sands et al (2008), Shi et al (2008), and Ye et al (2008) studied the dynamics of the various plasma jets generated by different devices and sustained by different driving voltages. They all found that the plasma plumes are not a continuous volume of plasma; rather the plumes are more like a bullet formed by a small and well- confined plasma volume that travels from the exit aperture and terminates somewhere in the surrounding air. The speed of the "plasma bullets" varies from ~10⁴-10⁵ m/s, which is several orders of magnitude higher than the gas velocities. Further analysis shows that the C-APPJs are electrically driven, which is quite similar to positive streamer discharges. However, there are several significant differences between the bullet-like plasma plumes and the widely studied positive streamers (cathode-directed streamer). For a positive streamer, the streamer head is connected to the power electrode by a highly conducting channel, which acts as a metallic "needle" protruding from the power electrode: the field at the end of the streamer is greatly enhanced. Obviously, this is not the case for the "plasma bullet", which looks like isolated from the power electrode. Nevertheless, more studies are needed to have a better understanding of the plasma bullet behavior. In this paper, a special designed plasma jet device is used to study this phenomenon. It is found that a helium primary plasma can propagate through the wall of a dielectric tube, and keep propagating inside the dielectric tube (secondary plasma). High speed photographs show that the primary plasma disappears before the secondary plasma starts to propagate. Both plumes propagate at a hypersonic speed. Detailed studies on the dynamics of the plasma plumes show that the local electric field induced by th- charges on the surface of the dielectric tube plays an important role in the ignition of the secondary plasma. This indicates that the propagation of the plasma plumes may be attributed to the local electric field induced by the charges in the bullet like plasma volume.