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

Abstract

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 D γ 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. Here in this work, we presentmore » 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.« less

Authors:
 [1];  [2];  [3]; ORCiD logo [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)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
Contributing Org.:
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.
OSTI Identifier:
1513535
Alternate Identifier(s):
OSTI ID: 1548392
Report Number(s):
LLNL-JRNL-774765
Journal ID: ISSN 2352-1791
Grant/Contract Number:  
SC0010717; AC02-09CH11466; AC52-07NA27344; SC0014264
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Materials and Energy
Additional Journal Information:
Journal Volume: 17; Journal Issue: C; Journal ID: ISSN 2352-1791
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
XPS; Boronization; NSTX-U; PFC conditioning; Plasma diagnostics; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Bedoya, F., Allain, J. P., Scotti, F., LaBombard, B., Kaita, R., and Krstic, P. S. Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U. United States: N. p., 2018. Web. doi:10.1016/j.nme.2018.10.010.
Bedoya, F., Allain, J. P., Scotti, F., LaBombard, B., Kaita, R., & Krstic, P. S. Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U. United States. doi:10.1016/j.nme.2018.10.010.
Bedoya, F., Allain, J. P., Scotti, F., LaBombard, B., Kaita, R., and Krstic, P. S. Tue . "Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U". United States. doi:10.1016/j.nme.2018.10.010. https://www.osti.gov/servlets/purl/1513535.
@article{osti_1513535,
title = {Effect of boronization on plasma-facing graphite surfaces and its correlation with the plasma behavior in NSTX-U},
author = {Bedoya, F. and Allain, J. P. and Scotti, F. and LaBombard, B. and Kaita, R. and Krstic, P. S.},
abstractNote = {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. Here 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.},
doi = {10.1016/j.nme.2018.10.010},
journal = {Nuclear Materials and Energy},
number = C,
volume = 17,
place = {United States},
year = {2018},
month = {11}
}

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