The high- poloidal scattering system for NSTX-U.

An 8-channel, high- poloidal far-infrared (FIR) scattering system is under development for the National Spherical Torus eXperiment Upgrade (NSTX-U). The 693 GHz poloidal scattering system replaces a 5-channel, 280 GHz high- toroidal scattering system to study high-k electron density fluctuations on NSTX-U. The FIR probe beam launched from Bay G is aimed toward Bay L, where large aperture optics collect radiation at 8 simultaneous scattering angles ranging from 2° to 15°.

Far-infrared tangential interferometer/polarimeter design and installation for NSTX-U.

The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system has been refurbished and is being reinstalled on the National Spherical Torus Experiment-Upgrade (NSTX-U) to supply real-time line-integrated core electron density measurements for use in the NSTX-U plasma control system (PCS) to facilitate real-time density feedback control of the NSTX-U plasma. Inclusion of a visible light heterodyne interferometer in the FIReTIP system allows for real-time vibration compensation due to movement of an internally mounted retroreflector and the FIReTIP front-end optics. Real-time signal correction is achieved through use of a National Instruments CompactRIO field-programmable gate array.