Initial studies of plasma facing component surface conditioning in the national spherical tokamak experiment upgrade with the materials analysis particle probe

F. Bedoya, J. P. Allain, R. Kaita, C. H. Skinner, Bruce E. Koel, F. Scotti

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

An innovative PFC diagnostic, the Materials Analysis Particle Probe (MAPP) was used to study the chemistry of Plasma Facing Components (PFCs) in the National Spherical Tokamak Experiment Upgrade (NSTX-U). NSTX-U used boronization as conditioning strategy during the 2015–2016 experimental campaign. Deposition with ∼9.1 g of deuterated tri-methyl boron (d-TMB) in a helium glow discharge resulted in coatings with an equivalent thickness of 7.0 nm at the lower outer divertor region. MAPP was used to capture for the first time the in-vacuo evolution of the chemical state of ATJ graphite PFCs after boronization and plasma exposure via X-ray Photoelectron Spectroscopy (XPS) on a day-to-day basis. The XPS data shows the formation of B4C on the PFCs surface during boronization. We observed the gradual increase of the B2O3 fraction in the coatings with plasma exposures. In contrast, we measured the formation of non-stoichiometric oxides when the samples were only exposed to residual gases and an argon vent. MAPP data revealed erosion and oxidation of deposited boron coatings over the course of tens of shots (a time resolution improved several orders-of-magnitude compared to post-campaign PFC characterization) that is correlated with the transitory nature of plasma performance enhancement with boron conditioning.

Original languageEnglish (US)
Pages (from-to)1248-1252
Number of pages5
JournalNuclear Materials and Energy
Volume12
DOIs
StatePublished - Aug 2017

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Materials Science (miscellaneous)
  • Nuclear Energy and Engineering

Keywords

  • Boronized graphite
  • Conditioning
  • NSTX-U
  • Plasma facing components
  • XPS

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