Ambipolar Plasma Potential Measurement in a Minimum -b Magnetic Well.

A heavy neutral beam probe diagnostic technique for magnetically contained plasmas is developed and used in an environment with three dimensional field gradients. With the newly developed neutral beam probe, the effects of the magnetic field are eliminated from the primary beam and reduced on the secondary without jeopardizing the good spatial and temporal resolutions characteristic of beam probes. Consequently complex field geometries are now accessible for beam probing and further studies. The space potential of a Hollow Cathode Arc in a Baseball generated minimum-B well is measured. Measurements of electron temperature and density are shown feasible. Also, the need for and the design of a detector with two dimensional sensitivity is outlined.