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Propagation of nonlinear ion-acoustic waves in a multi-component plasma with negative ions is investigated experimentally. At a critical concentration of negative ions, both compressive and rarefactive solitons are observed. The velocities and widths of the solitons are measured and compared with the soliton solutions of the modified Korteweg–de Vries equation and of the pseudopotential method. The modified Korteweg–de Vries equation is solved numerically to investigate overtaking collisions of a positive and a negative soliton. Fluid equations together with Poisson's equation are numerically integrated to simulate their head-on collisions.

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.

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