Modeling Thermal Charge Exchange Neutrals Originating from the Divertor on DIII-D

Neutral and main-ion measurements in the plasma edge are essential in understanding pedestal formation and sustainment. Charge exchange is one of the dominant atomic physics interactions that determines pedestal structure and plays a crucial role in plasma fueling, wall sputtering, and particle transport. Neutrals originating along the midplane have a shorter path but have a lower density while neutrals originating from the divertor have a longer path but have a higher density. The spectroscopic diagnostic presently installed on DIII-D directly measures thermal neutral profiles in the midplane, but is constrained to the neutral beam injection path. A new, proposed spectroscopic diagnostic will measure the cold neturals profile above the divertor region where it is believed that the recycling neutral flux is greater. Synthetic spectra that simulates the new diagnostic’s line of sight yields the expected neutral energy distribution originating from the divertor region. Finally, the profiles derived from the divertor’s synthetic spectra are compared to the spectrally resolved measurements along the midplane. The impact on fueling and sputtering from the two regions are compared and discussed.