Role of ExB drift in impurity transport in radiative divertors

In DIII-D puff-and-pump experiments, argon impurities are injected into the private flux region (PFR) in the upper single-null configuration for heat flux mitigation. Previous results show that the argon core accumulation is reduced, when the ion grad-B drift is directed away from the upper divertor, with the ExB drift across the PFR towards the outer strike point. This indicates that the ExB drift across the PFR plays an important role in preventing impurity leakage from the outer divertor. Further experiments show that, as the impurity injection rate increases, the electron temperature gradient in the PFR decreases near the target, thereby weakening Er as well as the Er x B drift. Such a decrease in grad-Te is also associated with enhanced argon accumulation in core plasmas. These findings suggest that the effect of ExB drift on seeded impurity trapping may be diminished at larger argon impurity injection rates due to the reduced grad-Te in the PFR. Modeling with the SOLPS-ITER code has been employed to investigate the role of the ExB drift in confining argon seed impurity in divertors.