In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection

F. Effenberg, S. Abe, G. Sinclair, T. Abrams, A. Bortolon, W. R. Wampler, F. M. Laggner, D. L. Rudakov, I. Bykov, C. J. Lasnier, D. Mauzey, A. Nagy, R. Nazikian, F. Scotti, H. Q. Wang, R. S. Wilcox

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Abstract

Experiments have been conducted in the DIII-D tokamak to explore the in-situ growth of silicon-rich layers as a potential technique for real-time replenishment of surface coatings on plasma-facing components (PFCs) during steady-state long-pulse reactor operation. Silicon (Si) pellets of 1 mm diameter were injected into low- and high-confinement (L-mode and H-mode) plasma discharges with densities ranging from 3.9- 7.5×1019 m-3 and input powers ranging from 5.5 to 9 MW. The small Si pellets were delivered with the impurity granule injector at frequencies ranging from 4 to 16 Hz corresponding to mass flow rates of 5-19 mg s-1 (1- 4.2×1020 Si s-1) at cumulative amounts of up to 34 mg of Si per five-second discharge. Graphite samples were exposed to the scrape-off layer and private flux region plasmas through the divertor material evaluation system to evaluate the Si deposition on the divertor targets. The Si II emission at the sample correlates with silicon injection and suggests net surface Si-deposition in measurable amounts. Post-mortem analysis showed Si-rich coatings containing silicon oxides, of which SiO2 is the dominant component. No evidence of SiC was found, which is attributed to low divertor surface temperatures. The in-situ and ex-situ analysis found that Si-rich coatings of at least 0.4-1.2 nm thickness have been deposited at 0.4-0.7 nm s-1. The technique is estimated to coat a surface area of at least 0.94 m2 on the outer divertor. These results demonstrate the potential of using real-time material injection to form Si-enriched layers on divertor PFCs during reactor operation.

Original languageEnglish
Article number106004
JournalNuclear Fusion
Volume63
Issue number10
DOIs
StatePublished - Oct 2023

Funding

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-AC02-09CH11466 (PPPL), DE-FC02-04ER54698 (DIII-D), DE-FG02-07ER54917 (UCSD), DE-NA0003525 (SNL), DE-AC52-07NA27344 (LLNL) and DE-AC05-00OR22725 (ORNL). The authors acknowledge the use of Princeton’s Imaging and Analysis Center, which is partially supported through the Princeton Center for Complex Materials (PCCM), a National Science Foundation (NSF)-MRSEC Program (DMR-2011750). The DIII-D data shown in this paper can be obtained in digital format by following the links at https://fusion.gat.com/global/D3D_DMP . The author Florian Effenberg gratefully acknowledges discussions with Stefan Bringuier, Anthony Leonard, Nikolas Logan, Adam Mclean, Shawn Zamperini, and Žana Popović. The United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

Keywords

  • divertor
  • erosion
  • material migration
  • plasma-facing components
  • real-time coating
  • silicon oxide
  • siliconization

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