Upgrade of the FIDA Spectroscopy system at the NSTX-U Tokamak

Fast-ion transport studies in spherical tokamaks such as NSTX-U are of particular interest due to the presence of large trapped particle fraction and super-Alfvenic ions thanks to low field operation. One method to study the fast-ion distribution function is Fast-Ion D-Alpha (FIDA) spectroscopy which measures the Doppler shifted Balmer-Alpha emission emitted by neutralized fast-ions following charge-exchange reactions. Here we present the design and first test results of two different FIDA spectrometers to be employed at NSTX-U. First, an existing double slit spectrometer has been refurbished by installing a novel scientific CMOS camera and replacing lenses that have been found to introduce scattered light. The spectrometer is now able to handle 32 channels and utilizes significant demagnification of the entrance slit to allow for camera operation with 10ms time resolution. Secondly, a novel Czerny Turner type spectrometer which uses custom made aspherical lenses instead of mirrors has been designed and commissioned. The spectrometer is based on a design developed for DIII-D¹ and has been optimized for measurements with kHz time resolution. Expected synthetic spectra predicted with the TRANSP² and FIDASIM³ codes will be presented together with an estimate of the signal to noise ratio for the two spectrometers to be installed at NSTX-U.