Experiments on Surface Wave Propagation along Annular Plasma Columns

Abstract

The propagation of surface waves along a plasma column of annular cross section was investigated experimentally. The laboratory plasma used for the experiment was a mercury‐vapor dc discharge. The properties of the experimental discharge tube were examined to show some basic differences between the laboratory plasma and the idealized model of the plasma used for the analysis. In particular, a radially non‐uniform density distribution and the variation of the distribution with the applied magnetic field was noted. In spite of the radial‐density inhomogeneity, the experimentally determined phase constants of the backward‐surface wave are in good agreement with values predicted from the uniform density theory. The attenuation in the absence of the magnetic field is consistent with collisional losses, predominantly with the walls of the container. The effect of an axial magnetic field on the surface‐wave characteristics is examined. Experimental results show that in the presence of a magnetic field the attenuation of the backward wave is markedly increased; this enhancement of the damping is not consistent with simple collision theory within the framework of the uniform‐density model.