Plasma space potential measurements on ISX-B

The authors experimental program is focused on full documentation of the radial space potential in ISX-B. This includes ohmic discharges, up to l MW of neutral beam injection both co- and counter- with respect to the plasma current, and balanced neutral beam injection. The authors are also documenting the scaling with plasma current and density. The data are obtained with a full set of machine diagnostics, including multi-point Thomson scattering, ion temperature, and impurity rotation. As a secondary, but important, objective the authors are obtaining plasma fluctuation measurements. They are investigating both the turbulent background spectra observed with soft x-ray arrays, and MHD activity. Initial measurements indicate fluctuations on the secondary ion signal 2:1 to l00:1 above the background noise, and clear indications of low frequency oscillations (typically 6 KHz) during high MHD. Detailed spectral analysis of approximately phi and approximately n/sub e//σ(approximately T/sub e/) are not yet available, but should be reported at this meeting