The continuous improvement of H-mode discharge performance with progressively increasing lithium coatings in NSTX

Lithium wall coatings have been shown to reduce recycling, improve energy confinement [1,2], and suppress edge localized modes [3,4] in the NSTX. Here we show that these effects depend nearly \textit{continuously} on the amount of pre-discharge lithium evaporation. We observed a nearly monotonic reduction in recycling and a decrease in edge electron transport [5] with increasing lithium. Moreover we see a reduction in the electron temperature and profile peaking factors, as well as an improvement in ELM stability [6] with increasing lithium. These correlations challenge basic expectations, given that even the smallest coatings provided a nominal minimum lithium coating thickness of 30 nm, and an average of 60 nm near the outer divertor strike point; the maximum coating thickness was 8x higher. In comparison, the nominal implantation range, which is the relevant scale length for recycling and pumping, was $<$ 10 nm. *Supported in part by U.S. DoE contracts DE-AC05-00OR22725 and DE-AC02-09CH11466. \\[0pt] [1] Kugel H. W.\textit{, et al.} \textit{PoP} \textbf{15,} 056118 (2008). [2] Bell M.G.\textit{, et al.} \textit{PPCF }\textbf{51,} 124054 (2009). [3] Maingi R.\textit{, et al.} \textit{PRL} \textbf{103,} 075001 (2009). [4] Mansfield D. K.\textit{, et al.} \textit{JNM} \textbf{390-391,} 764 (2009). [5] Canik J. M.\textit{, et al.} \textit{PoP} \textbf{18,} 056118 (2011). [6] Boyle D. P.\textit{, et al.} \textit{PPCF} submitted (2011).