Propagation and diagnostic of ion acoustic waves in a low pressure argon discharge

In a dc argon discharge column of pressure 5 x 10-4 torr, ion acoustic waves are studied experimentally. Plasma parameters obtained from the phase velocity of waves are compared with Langmuir probe measurements. The wave diagnostic method yields the electron temperature lower than the probe method by a factor of 3 to 5, if the atomic argon ion is assumed as a dominant ion species. The axial profiles of ion drift velocity show the presence of ions flowing toward the anode along the potential drop in front of it. Furthermore it is found that the surface condition of the cathode sensitively affects the propagation of ion acoustic waves through the changes in discharge parameters. (author)