Dependence of Recycling and Edge Profiles on Lithium Evaporation in High Triangularity, High Performance NSTX H-mode Discharges
Authors: R. Maingi, T.H. Osborne, M.G. Bell, R.E. Bell, D.P. Boyle, J.M. Canik, A. Dialla,R. Kaita, S.M. Kaye, H.W. Kugel, B.P. LeBlanc, S.A. Sabbagh, C.H. Skinner, V.A.Soukhanovskii, and the NSTX team
Abstract: In this paper, the effects of a pre-discharge lithium evaporation scan on highly shaped discharges in the National Spherical Torus Experiment (NSTX) are documented. Lithium wall conditioning ('dose') was routinely applied onto graphite plasma facing components between discharges in NSTX, partly to reduce recycling. Reduced Dα emission from the lower and upper divertor and center stack was observed, as well as reduced midplane neutral pressure; the magnitude of reduction increased with the pre-discharge lithium dose. Improved energy confinement, both raw τE and H-factor normalized to scalings, with increasing lithium dose was also observed. At the highest doses, we also observed elimination of edge-localized modes. The midplane edge plasma profiles were dramatically altered, comparable to lithium dose scans at lower shaping, where the strike point was farther from the lithium deposition centroid. This indicates that the benefits of lithium conditioning should apply to the highly shaped plasmas planned in NSTX-U.
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Presented at: the 21st International Conference on Plasma Surface Interactions in Controlled Fusion Devices (21st PSI), May 26-30, 2014, Kanazawa City, Japan.
Accepted for publication in: Journal of Nuclear Materials
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Download PPPL-5039 (pdf 2.06 MB; 14 pp)
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