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Title: Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes

Abstract

A sequence of H-mode discharges with increasing levels of pre-discharge lithium evaporation (‘dose’) was conducted in high triangularity and elongation boundary shape in NSTX. Energy confinement increased, and recycling decreased with increasing lithium dose, similar to a previous lithium dose scan in medium triangularity and elongation plasmas. Data-constrained SOLPS interpretive modeling quantified the edge transport change: the electron particle diffusivity decreased by 10-30x. The electron thermal diffusivity decreased by 4x just inside the top of the pedestal, but increased by up to 5x very near the separatrix. These results provide a baseline expectation for lithium benefits in NSTX-U, which is optimized for a boundary shape similar to the one in this experiment.

Authors:
 [1];  [2];  [1];  [3];  [1];  [1];  [1];  [1];  [4];  [5];  [5]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Princeton Univ., NJ (United States)
  4. Columbia Univ., New York, NY (United States)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1358036
Report Number(s):
PPPL-5278
Journal ID: ISSN 0920-3796; PII: S0920379616304550
Grant/Contract Number:
AC02-09CH11466; AC05-00OR22725; FC02-04ER54698; FC02-99ER54512; AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Fusion Engineering and Design
Additional Journal Information:
Journal Volume: 117; Journal ID: ISSN 0920-3796
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; NSTX; Lithium; Recyling; Pedestal; Energy confinement

Citation Formats

Maingi, R., Canik, J. M., Bell, R. E., Boyle, D. P., Diallo, A., Kaita, R., Kaye, S. M., LeBlanc, B. P., Sabbagh, S. A., Scotti, F., and Soukhanovskii, V. A. Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes. United States: N. p., 2016. Web. doi:10.1016/j.fusengdes.2016.06.058.
Maingi, R., Canik, J. M., Bell, R. E., Boyle, D. P., Diallo, A., Kaita, R., Kaye, S. M., LeBlanc, B. P., Sabbagh, S. A., Scotti, F., & Soukhanovskii, V. A. Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes. United States. doi:10.1016/j.fusengdes.2016.06.058.
Maingi, R., Canik, J. M., Bell, R. E., Boyle, D. P., Diallo, A., Kaita, R., Kaye, S. M., LeBlanc, B. P., Sabbagh, S. A., Scotti, F., and Soukhanovskii, V. A. 2016. "Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes". United States. doi:10.1016/j.fusengdes.2016.06.058. https://www.osti.gov/servlets/purl/1358036.
@article{osti_1358036,
title = {Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes},
author = {Maingi, R. and Canik, J. M. and Bell, R. E. and Boyle, D. P. and Diallo, A. and Kaita, R. and Kaye, S. M. and LeBlanc, B. P. and Sabbagh, S. A. and Scotti, F. and Soukhanovskii, V. A.},
abstractNote = {A sequence of H-mode discharges with increasing levels of pre-discharge lithium evaporation (‘dose’) was conducted in high triangularity and elongation boundary shape in NSTX. Energy confinement increased, and recycling decreased with increasing lithium dose, similar to a previous lithium dose scan in medium triangularity and elongation plasmas. Data-constrained SOLPS interpretive modeling quantified the edge transport change: the electron particle diffusivity decreased by 10-30x. The electron thermal diffusivity decreased by 4x just inside the top of the pedestal, but increased by up to 5x very near the separatrix. These results provide a baseline expectation for lithium benefits in NSTX-U, which is optimized for a boundary shape similar to the one in this experiment.},
doi = {10.1016/j.fusengdes.2016.06.058},
journal = {Fusion Engineering and Design},
number = ,
volume = 117,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
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  • 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 themore » 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.« less
  • 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 inmore » divertor recycling coefficient from similar to 98% to similar to 90%. The reduction in recycling and fuelling, coupled with a drop in the edge particle transport rate, reduced the average edge density profile gradient, and shifted it radially inwards from the separatrix location. In contrast, the edge electron temperature (T-e) profile was unaffected in the H-mode pedestal steep gradient region within the last 5% of normalized poloidal flux, psi(N); however, the T-e gradient became steeper at the top of the H-mode pedestal for 0.8 < psi(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.« less
  • In this paper, the effects of a pre-discharge lithium evaporation variation 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 D α 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 τ E and H-factor normalized to scalings, with increasing lithium dose was also observed. At the highest doses, wemore » 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. As a result, this indicates that the benefits of lithium conditioning should apply to the highly shaped plasmas planned in NSTX-U.« less
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