L-H Threshold Studies in NSTX
Authors: S.M. Kaye, R. Maingi, D. Battaglia, R.E. Bell, C.S. Chang, J. Hosea, H. Kugel, B.P. LeBlanc, H. Meyer, G.Y. Park, and J.R. Wilson
Abstract: Recent experiments in the low aspect ratio National Spherical Torus Experiment (NSTX)
have been run in support of the high priority ITER and ITPA issue of access to the H-mode.
Speci cally, a series of experiments showed reduced power threshold values for deuterium vs
helium plasmas, and for plasmas with lower current, lower triangularity and with lithium
conditioning. Application of n=3 fi elds at the plasma edge resulted in higher power thresholds. To within the constraints of temporal and spatial resolutions, no systematic difference
in Te, ne, pe, Ti, v or their derivatives was found in discharges that transitioned into the
H-mode versus those at slightly lower power that did not. Finally, H98y;2 1 confi nement
quality could be achieved for powers just above the threshold power in ELM-free conditions.
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Submitted to: Nuclear Fusion (June 2011)
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Download PPPL-4635 (pdf 720 KB 29 pp)
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