Comparison of fueling efficiency from different fueling locations on DIII-D

Fueling with gas and pellet injection from several different locations has been used on the DIII-D tokamak to study core fueling and transport in H-mode and L-mode plasmas. Specific experiments have been carried out to examine the fueling efficiency into DIII-D H-mode plasmas that have periodic edge localized modes (ELMs). The fueling efficiency, defined as the total increase in number of plasma electrons divided by the number of input fuel atoms, is determined by measurements of plasma electron density profiles before and after a fueling pulse. We have found previously that there is a significantly higher fueling efficiency for pellets injected from the inner wall [J. Nucl. Mater. 290 (2001) 398] versus outside midplane pellet injection or gas puffing. In this study we extend this work to include the investigation of gas puffing from the same inner wall injection locations as the pellets to determine if a similar effect may exist. The mechanism for the improved pellet fueling from the inner wall is hypothesized to be a ∇B induced polarization of the pellet cloud leading to an E×B drift [Phys. Plasmas 7 (2000) 1968] in the major radius direction. The possibility of similar physics playing a role in gas puff fueling is examined in these experiments and does not appear to be a significant effect.