Experiments on the propagation of ion acoustic solitons that propagate in a positive ion–negative ion plasma are described. The solitons are launched from a solid metal disk to which a small negative step voltage [Δφ≊−2(Te/e) V] is applied. The mechanism for the excitation of the soliton, the identification of the fast and the slow modes in such a plasma, and the observation of a transient sheath are presented.

Experiments on the propagation and collision of a Korteweg-deVries soliton in a positive ionnegative ion plasma are described. Both a one-dimensional overtaking collision and a twodimensional resonant collision are examined. Soliton propagation into a steady-state plasma sheath created by an additional biased metal plate in such a plasma is large enough that the detailed soliton motion in the locally inhomogeneous plasma can be easily studied. A partial reflection and partial transmission of the soliton at a critical density within the sheath is observed and interpreted.

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Reflection of modified Korteweg–de Vries solitons from the sheath in front of a negatively biased metal disk is experimentally investigated in a negative ion plasma. Both rarefactive and compressive solitons are reflected and the polarity of the reflected solitons is the same as that of the incident solitons. The points of reflection for the rarefactive and compressive solitons are at different locations. As the magnitude of the negative bias potential that is applied to the reflector is increased, the two reflection points move away from the reflector. An interpretation in terms of the sheath characteristics is presented.

Experimental observations that may have general interest are presented concerning a low micrometre size dust panicles pressure plasma ("lo-' Torr) that consists of three components: positively charged ions, negatively charged ions and electrons ('negative ion plasmas'). These ObSeNatiOnS include Langmuir probe characteristics and sheaths that are germane to such a plasma. Properties of plasma waves in a negative ion plasma such as phase velocity, dispersion and soliton propagation are described.