Synthetic Diagnostic Development to Calculate Spatial Resolution of Beam Emission Spectroscopy and Charge Exchange Imaging

Beam Emission Spectroscopy (BES) and Charge eXchange Imaging (CXI) enables fast, spatially resolved density measurements by targeting the beam activated component of main ion or impurity line radiation. These measurements allow low-k to mid-k turbulence (0.5-1.5 cm^-1) to be characterized. The light is spatially localized to the crossing between the neutral beam and the line-of-sight of a fiber imaged in the plasma. The extent of the finite volume defined by this crossing determines maximum channel packing and therefore the spatial resolution of the diagnostic. The spatial extent has several main sources: finite spot size of an imaged fiber, finite beam width, optics etendue, finite lifetime effect, and transformation to field aligned geometry. The Point Spread Function (PSF) and Spatial Transfer Function (STF) of the diagnostic were calculated and integrated into pyFIDASIM, a synthetic diagnostic for the BES and CXI systems at DIII-D. The calculated PSF and STF were validated against pre-existing codes with good agreement. Using varied sightlines and fiber arrangements, an optimal configuration was determined for high resolution BES operation. Additionally, various density profiles were considered to identify an optimal plasma condition for studying core turbulence using BES.