Varying the Pre-discharge Lithium Wall Coatings to Alter the Characteristics of the ELM-free H-mode Pedestal in NSTX
Authors: D.P. Boyle, J.M. Canik, R. Maing, P.B. Snyder, T.H. Osborne, and the NSTX Team
Abstract:
A previous experiment in the National Spherical Torus Experiment (NSTX) showed
pre-discharge lithium deposition gradually suppresed edge-localized modes (ELMs) and had
nearly continuous relationships with reduced recycling and transport. In this paper, additional
data filled gaps in the earlier experiment, and demonstrates that recycling, confinement, and
pedestal structure continued to improve with additional lithium, even after ELMs were
completely suppressed. New analysis shows that toroidal rotation and ion temperature also
increased continuously with additional lithium. Besides its evolution with additional lithium,
we also characterize the time evolution of the ELM-free H-mode pedestal as average density
rose and impurities accumulated. We find that the pedestal structure, divertor heat flux and Dalpha
profiles, and inferred recycling coefficient did not change significantly, at least until
radiative losses become dominant. This suggests that the low-recycling properties of lithium
were not significantly degraded over the duration of the discharge.
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Submitted to: Journal of Nuclear Materials/Elsevier
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