Radial constraints and the polarity mechanism of plasma plume

Plasma plumes have found a wide range of applications over the recent decade, stimulating studies of characteristics of plasma plumes generated under different conditions. Regardless of whether they propagate within a dielectric tube or different shielding gases, the behavior of these plumes will be affected by the boundary condition of the plume. Yet, at present, little is known about the behavior of plasma plumes of different polarities, especially negative plasma plumes, when propagating under different boundary conditions. To bridge this gap, in this paper, the characteristics of positive and negative plasma plumes propagating within a quartz tube, ambient Ar, and air are studied. The results reveal that the behavior of the positive plasma plume is similar under three different boundary conditions. However, this is not the case for the negative plasma plume, the behavior of which differs significantly between the three cases. Numerical simulation suggests that electron loss due to the drift in the radial direction impacts significantly the characteristics of the negative plasma plume.