Pellet Fueling Research on DIII-D

Core fueling by pellet injection will be an essential technique for sustaining burning plasma scenarios in ITER and in a fusion pilot plant. The physics of core pellet fueling is an area of active study on DIII-D, with current emphasis on understanding the interaction of the core fueling process with edge and boundary phenomena that are also essential for a high-performance plasma scenario. Interactions of concern include the possible return or onset of edge-localized modes due to perturbation of the edge pedestal, and the effects on stability of the divertor plasma detachment. Modeling of the magnetohydrodynamic stability of the pedestal under the pellet particle source, and a series of upgrades to the DIII-D pellet injection system to enable experimental study of such interactions, are underway. The ability to vary pellet mass and delivery location, with absolutely calibrated mass measurements, allows for flexible variation and quantitative analysis of the pellet particle source. These capabilities and future upgrades to increase pellet injection rates to levels relevant for divertor detachment studies, along with planned approaches for modeling the detachment response to the dynamics of the pellet particle source, are described.