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Summary form only given, as follows. A test bed for producing low density plasmas of high fractional ionization and evaluating various plasma diagnostics has been constructed. At present, the system consists of a 10 cm. diameter, commercially-built ion beam system, vacuum chamber, scanning Langmuir probe system, microwave interferometer, and quadrupole mass spectrometer. The ion beam system is made up of an inductively coupled, rf excited (13.56 MHz) discharge region with a pair of molybdenum extraction grids for forming the beam. Ion beam currents of up to 2.5 mA per centimeter squared are possible with ion energies from 50-1500 eV. The Langmuir probe system can be scanned radially across the ion beam and moved to three positions along the beam axis. Microwave interferometer measurements of the line-integrated electron density can also be made at these axial positions. Initial measurements have been made in an argon ion beam plasma with a total density of less than 3e13 particles per cubic centimeter. Measurements of charged particle densities in the beam as a function of radial position will be compared with line-integrated interferometer data. In addition, measurements of the electron energy distribution functions in the beam plasma will also be presented.