Ion-acoustic waves in a multicomponent plasma with negative ions

Propagation of ion-acoustic waves has been investigated experimentally in an argon plasma mixed with sulfur hexafluoride using a multidipole double-plasma device. The device is separated into a driver and a target section with a magnetic filter. Waves are transmitted by a circular mesh grid placed in the target. Both the fast and the slow modes were observed to propagate downstream in the wide range of the density ratio of negative ions to positive ions. The measured phase velocities are in agreement with theoretical ones calculated from a plasma dispersion relation taking the drift of the plasma into consideration. The out-of-phase oscillation between positive ions and electrons, which is predicted by a fluid model of the multicomponent plasma, has been observed.