Abstract
We report results of an experiment in which lithium wall coatings were gradually
introduced into NSTX, resulting in a gradual improvement in energy confinement, alteration
of edge plasma profiles, and growing periods of ELM suppression. As a result of increasing
lithium wall coatings, recycling and edge fueling were reduced, which relaxed the edge
density profile gradients. In contrast, the edge Te profile was unaffected in the H-mode
pedestal steep gradient region at constant plasma stored energy; however, the region of steep
Te gradients extended radially inward by several cm following lithium coatings.
Consequently, the pressure profile width and pedestal height increased substantially, while the
ELM-free discharge peak pressure gradients were comparable to the pre-lithium ELMy
discharge gradients. The measured edge profiles in discharges with and without lithium were
simulated with the SOLPS code, which indicated that both a reduction in recycling and a drop
in the edge and SOL cross-field transport was required to match the post-lithium profiles.
Edge stability calculations showed that the discharges with lithium coatings were farther from
the low-n kink/peeling modes boundary than the pre-lithium discharges.