Improvements to a Fast-ion D$_\alpha$ Simulation Code

FIDASIM is a code that models fast-ion D$_\alpha$ (FIDA) light that is produced by charge-exchange reactions between fast ions and injected neutral beams in tokamak plasmas. Reactions with both the primary injected neutrals and with the cloud of secondary ``halo'' neutrals that surround the beam are treated. Accurate calculation of the fraction of neutrals that occupy excited atomic states (the collisional-radiative transition equations) is an important element of the code. Judicious selection of grid size and other parameters facilitate efficient solutions. D$_\alpha$ light from beam emission, direct charge-exchange with protons, and the beam halo are also calculated. For greater speed, conversions to FORTRAN and GPU are underway. FIDASIM has been applied to data from DIII-D, NSTX, ASDEX Upgrade, and MAST.