Poloidal High-k Scattering on NSTX-U

A poloidal high-k scattering system is under development by UC Davis and PPPL to study high-k electron density fluctuations on NSTX-U. The 8-channel diagnostic system, which operates at 693 GHz, replaces a 280 GHz, 5-channel toroidal high-k scattering system on NSTX. The probe beam is launched from Bay G towards Bay L where large aperture optics collect radiation at 8 simultaneous scattering angles ranging from 2 to 15°, corresponding to poloidal wavenumbers from 7 cm^-1 to >40 cm^-1. The receiver optics and subharmonic mixer array are mounted on a 5-axis receiver carriage which is translated and rotated as a whole to position the scattering region as desired between r/a= 0.1 and the plasma edge (r/a = 0.99). Upwards and downwards scattering options are available, and can be easily switched from one mode to another between discharges. Details of the diagnostic, including installation and commissioning schedules, will be presented.