Diagnostics for initial plasma operations on the National Spherical Torus Experiment

The goals of the diagnostic set for initial plasma operations on the Nation al Spherical Torus Experiment (NSTX) are to provide information on the fund amental discharge parameters necessary to characterize NSTX plasmas, and gu ide NSTX operations for optimized performance. While most of these diagnost ics involve relatively straightforward techniques requiring little or no re search and development, and rely heavily on reusing existing equipment, a f ew pose considerable challenges due to the NSTX geometry. Magnetic diagnost ics and visible discharge imaging will be the primary systems for plasma co ntrol and equilibrium. Confinement and transport studies will be supported by electron temperature, density, and impurity profile diagnostics. Scrapeo ff layer and divertor physics will be investigated with spectroscopic and b olometric diagnostics, thermocouples, and edge Langmuir probes. X-ray fluct uation diagnostics and magnetic pickup coils will be provided for MHD stabi lity analysis. The latter impose special difficulties for NSTX, because of the high temperature environment and the very limited space on the center s tack. This article provides an overview of the diagnostics planned for the first phase of NSTX, and highlights the design features needed to satisfy t he difficult constraints the device imposes on magnetic diagnostics. (C) 19 99 American Institute of Physics. [S0034-6748(99)52301- 0].