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.

This paper describes a series of experiments designed to examine the antenna characteristics of probes which are used as detectors in ion-acoustic wave experiments. Reception patterns are measured which are in qualitative agreement with theoretical predictions. The near-field antenna pattern of the wave-launching grid is found to be important.

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