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Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U

Journal Article · · Nuclear Materials and Energy
 [1];  [2];  [3];  [1];  [4];  [5]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Univ. of Illinois, Urbana, IL (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. Stony Brook Univ., Stony Brook, NY (United States)
+ Show Author Affiliations
Boronization is a Plasma Facing Component (PFC) conditioning technique widely used in tokamak machines. The National Spherical Torus Experiment-Upgrade (NSTX-U) applied this conditioning, using a plasma glow with a deuterated Trimethyl-boron (d-TMB) and He mixture. The use of boronization during the campaign improved the plasma performance, allowing longer plasma discharges and H-mode access. The chemical state of an ATJ graphite sample, used as a proxy for the NSTX-U PFCs, was monitored in-situ using the Materials Analysis Particle Probe (MAPP) diagnostic and X-ray Photoelectron Spectroscopy (XPS). The XPS data showed a progressive rise (from < 5% to 23%) in the oxygen concentration of the boronized ATJ sample as the D+ fluence increased. Filterscopes were used to measure the light emitted by oxygen impurities in the plasma near the surface of the PFC. An increase in the registered magnitude of the OII line, normalized to the Dγ intensity, was observed as the concentration of O on the ATJ surface increased. The plasma performance was found to be strongly correlated to oxygen impurity concentrations at the plasma edge and on the PFC surface, as measured by the discharge length and access to the H-mode regime. In this work, we present a quantitative analysis of the evolution of the chemistry of the ATJ surface, and the oxygen presence in the plasma-material interface, and report relevant plasma parameters observed during the same period of time.
Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE; USDOE National Nuclear Security Administration (NNSA)
Contributing Organization:
The authors would like to thank the whole NSTX-U team for their technical and scientific support. This work was supported by USDOE BES/FES Grant No. DE-SC0010717, USDOE Contracts DE-AC02-09CH11466 and DE-AC52-07NA27344 and USDOE cooperative agreement DE-SC0014264. The digital data for this paper can be found in: http://arks.princeton.edu/ark:/88435/dsp011v53k0334.
Grant/Contract Number:
AC02-09CH11466; AC52-07NA27344; SC0010717; SC0014264
OSTI ID:
1513535
Alternate ID(s):
OSTI ID: 1548392
OSTI ID: 22834750
Report Number(s):
LLNL-JRNL--774765
Journal Information:
Nuclear Materials and Energy, Journal Name: Nuclear Materials and Energy Journal Issue: C Vol. 17; ISSN 2352-1791
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Boronization
NSTX-U
PFC conditioning
Plasma diagnostics
XPS