Introduction of passive signals and 3D geometry to FIDASIM*

FIDASIM is a synthetic diagnostic code that simulates fast ion D-alpha (FIDA) and neutral particle analyzer (NPA) signals. The code accepts a theoretical fast-ion distribution function as input and predicts the FIDA and NPA spectra. Originally, FIDASIM assumed axisymmetry and included active signals produced only by charge exchange (CX) with injected neutrals. However, passive signals produced by CX with cold neutrals can also be important. For example, passive-FIDA signals of comparable magnitude with active signals were experimentally measured on NSTX-U [1]. Therefore, FIDASIM has been improved to predict passive signals for a given edge-cold neutral population. The time series passive spectra output by FIDASIM have been successfully cross checked with 2D passive-FIDA modeling done on NSTX-U. The effect of 3D fields on fast ion confinement is an ongoing field of study, e.g. toroidal field ripple, stellerators, etc. Thus, the functionality of FIDASIM has been enhanced to simulate signals produced in 3D geometry.