Characteristics of ELM activity and fueling efficiency of pellet injection from different locations on DIII-D

Pellet injection from several different locations has been used on the DIII-D tokamak to study con fueling and transport in H-mode and L-mode plasmas. These experiments have provided a variety of conditions in which to examine the fueling efficiency and edge localized mode (ELM) interaction with pellets injected into DIII-D plasmas. The fueling efficiency, defined as the total increase in number of plasma electrons divided by the number of pellet fuel atoms, is determined by measurements of density profiles before and just after pellet injection. New injection ports on the DIII-D inner wall enable high field side (HFS) pellet injection from both the midplane and 30 cm above the midplane, These ports, in addition to the previously existing top vertical ports and outside midplane port, enable a comparison of the effect of injection location on fueling efficiency and ELM activity, We find that the ELMs triggered from HFS injected pellets and vertical HFS injected pellets are similar to the nominal background ELMs in ELMing H-mode plasmas. In contrast, the low field side (LFS) injected pellets trigger large-magnitude ELMs that lead to a strong reduction in fueling efficiency. The fueling efficiency of the HFS injected pellets is found to be significantly higher than with the LFS injected pellets and remains high even with significant heating power. (C) 2001 Elsevier Science B.V. All rights reserved.