Core Transport of Lithium and Carbon in ELM-free Discharges with Lithium Wall Conditioning in NSTX
Authors: F. Scotti, et. al.
Abstract:
Core transport of intrinsic carbon and lithium impurities is analyzed in
H-mode discharges in NSTX. The application of lithium coatings on graphite plasma
facing components led to high performance H-mode discharges with edge localized
mode (ELM) suppression and resulted in core carbon accumulation. Lithium ions did
not accumulate and had densities less than 1% of carbon densities. Core transport
codes NCLASS, NEO and MIST are used to assess the impact of lithium evaporative
coatings on impurity transport. The disappearance of ELMs, due to changes in the
electron pressure profiles, together with modifications in neoclassical transport, due
to changes in main ion temperature and density profiles, explains the core carbon
accumulation in discharges with lithium coatings. Residual anomalous transport in
the pedestal region is needed to explain the experimental carbon density profile shape
and evolution. The enhancement in neoclassical lithium particle diffusivities due to
the high carbon concentration can be partially responsible for the low lithium core
concentration.
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Submitted to: Nuclear Fusion, (June 2013)
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