Surface chemistry analysis of lithium conditioned NSTX graphite tiles correlated to plasma performance

C. N. Taylor, K. E. Luitjohan, B. Heim, L. Kollar, J. P. Allain, C. H. Skinner, H. W. Kugel, R. Kaita, A. L. Roquemore, R. Maingi

Research output: Contribution to journalArticle

Abstract

Lithium wall conditioning in NSTX has resulted in reduced divertor recycling, improved energy confinement, and reduced frequency of edge-localized modes (ELMs), up to the point of complete ELM suppression. NSTX tiles were removed from the vessel following the 2008 campaign and subsequently analyzed using X-ray photoelectron spectroscopy as well as nuclear reaction ion beam analysis. In this paper we relate surface chemistry to deuterium retention/recycling, develop methods for cleaning of passivated NSTX tiles, and explore a method to effectively extract bound deuterium from lithiated graphite. Li-O-D and Li-C-D complexes characteristic of deuterium retention that form during NSTX operations are revealed by sputter cleaning and heating. Heating to ∼850 C desorbed all deuterium complexes observed in the O 1s and C 1s photoelectron energy ranges. Tile locations within approximately ±2.5 cm of the lower vertical/horizontal divertor corner appear to have unused LiO bonds that are not saturated with deuterium, whereas locations immediately outboard of this region indicate high deuterium recycling. X-ray photo electron spectra of a specific NSTX tile with wide ranging lithium coverage indicate that a minimum lithium dose, 100-500 nm equivalent thickness, is required for effective deuterium retention. This threshold is suspected to be highly sensitive to surface morphology. The present analysis may explain why plasma discharges in NSTX continue to benefit from lithium coating thickness beyond the divertor deuterium ion implantation depth, which is nominally <10 nm.

Original languageEnglish (US)
Pages (from-to)3157-3164
Number of pages8
JournalFusion Engineering and Design
Volume88
Issue number12
DOIs
StatePublished - Dec 2013
Externally publishedYes

Fingerprint

Deuterium
Tile
Lithium
Custodial Care
Recycling
Surface chemistry
Cleaning
Graphite
Plasmas
Heating
Callosities
Alcohol Drinking
Nuclear reactions
Photoelectrons
Ion implantation
Ion beams
Surface morphology
X ray photoelectron spectroscopy
X rays
Coatings

Keywords

  • Carbon-facing components
  • Deuterium
  • Divertor
  • Lithium
  • Plasma-surface interactions
  • Retention
  • X-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Nuclear Energy and Engineering
  • Materials Science(all)
  • Civil and Structural Engineering
  • Mechanical Engineering

Cite this

Taylor, C. N., Luitjohan, K. E., Heim, B., Kollar, L., Allain, J. P., Skinner, C. H., ... Maingi, R. (2013). Surface chemistry analysis of lithium conditioned NSTX graphite tiles correlated to plasma performance. Fusion Engineering and Design, 88(12), 3157-3164. DOI: 10.1016/j.fusengdes.2013.09.007

Surface chemistry analysis of lithium conditioned NSTX graphite tiles correlated to plasma performance. / Taylor, C. N.; Luitjohan, K. E.; Heim, B.; Kollar, L.; Allain, J. P.; Skinner, C. H.; Kugel, H. W.; Kaita, R.; Roquemore, A. L.; Maingi, R.

In: Fusion Engineering and Design, Vol. 88, No. 12, 12.2013, p. 3157-3164.

Research output: Contribution to journalArticle

Taylor, CN, Luitjohan, KE, Heim, B, Kollar, L, Allain, JP, Skinner, CH, Kugel, HW, Kaita, R, Roquemore, AL & Maingi, R 2013, 'Surface chemistry analysis of lithium conditioned NSTX graphite tiles correlated to plasma performance' Fusion Engineering and Design, vol 88, no. 12, pp. 3157-3164. DOI: 10.1016/j.fusengdes.2013.09.007

Taylor, C. N.; Luitjohan, K. E.; Heim, B.; Kollar, L.; Allain, J. P.; Skinner, C. H.; Kugel, H. W.; Kaita, R.; Roquemore, A. L.; Maingi, R. / Surface chemistry analysis of lithium conditioned NSTX graphite tiles correlated to plasma performance.

In: Fusion Engineering and Design, Vol. 88, No. 12, 12.2013, p. 3157-3164.

Research output: Contribution to journalArticle

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