Validation of NUBEAM with Prompt Torque Measurements in DIII-D

The NUBEAM calculation of prompt torque is validated against experimental measurements of angular acceleration for several DIII-D discharges. NUBEAM calculates the heat and momentum sources of neutral beam injection, so its accuracy is important for many transport studies, particularly for intrinsic rotation and momentum transport. We compare measurements of prompt torque from Charge Exchange Recombination Spectroscopy (CER) to prompt torque calculations from NUBEAM. This comparison is done to validate NUBEAM's momentum source calculation, though the accuracy of the prompt torque calculation has implications for the model as a whole. We find that NUBEAM prompt torque generally agrees with measurements in the core (0.2<ρ<0.7), while the model deviates from the measurements at the edge (0.7<ρ<1.0). Measurements show co-Ip prompt torque at the edge, and NUBEAM calculates counter-Ip torque at the edge due to beam loss. Agreement at the edge occurs at low densities and high safety factor where little to no prompt torque is measured or predicted. These results suggest NUBEAM predicts too much fast ion loss at the edge.