The Effect of Progressively Increasing Lithium Coatings on Plasma Discharge Characteristics, Transport, Edge Profiles, and ELM Stability in the National Spherical Torus Experiment

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/52/8/083001· OSTI ID:1055015

Maingi, Rajesh ^[1]; Boyle, D. P. ^[2]; Canik, John ^[1]; Kaye, S. M. ^[3]; Skinner, C. H. ^[3]; Allain, J. P. ^[4]; Bell, M. G. ^[3]; Bell, R. E. ^[3]; Gray, Travis K ^[1]; Jaworski, M. A. ^[3]; Kaita, R. ^[3]; Kugel, H. ^[3]; LeBlanc, B. P. ^[3]; Mansfield, D. K. ^[3]; Osborne, T. H. ^[5]; Raman, R. ^[6]; Sabbagh, S. A. ^[7]; Soukhanovskii, V. A. ^[8]

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1. ORNL
2. Princeton University
3. Princeton Plasma Physics Laboratory (PPPL)
4. Purdue University
5. General Atomics
6. University of Washington, Seattle
7. Columbia University
8. Lawrence Livermore National Laboratory (LLNL)

Lithium wall coatings have been shown to reduce recycling, suppress edge localized modes (ELMs), and improve energy confinement in the National Spherical Torus Experiment (NSTX). Here we document the effect of gradually increasing lithium wall coatings on the discharge characteristics, with the reference ELMy discharges obtained in boronized, i.e. non-lithiated, conditions. We observed a continuous but not quite monotonic reduction in recycling and improvement in energy confinement, a gradual alteration of edge plasma profiles, and slowly increasing periods of ELM quiescence. The measured edge plasma profiles during the lithium coating scan were simulated with the SOLPS code, which quantified the reduction in divertor recycling coefficient from ~98% to ~90%. The reduction in recycling and core fueling, coupled with a drop in the edge particle transport rate, reduced the average edge density profile gradient, and shifted it radially inward from the separatrix location. In contrast, the edge electron temperature (Te) profile was unaffected in the H-mode pedestal steep gradient region within the last 5% of normalized poloidal flux, N; however, the region of steep Te gradients extended radially inward from the top of the H-mode pedestal for 0.8< N <0.94 with lithium coatings. The peak pressure gradients were comparable during ELMy and ELM-free phases, but were shifted away from the separatrix in the ELM-free discharges, which is stabilizing to the current driven instabilities thought to be responsible for ELMs in NSTX.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1055015
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 52; ISSN 0029-5515
• Country of Publication: United States
• Language: English