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

Journal Article · 23 August 2023 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/acee98 · OSTI ID:1996585

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

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– $7.5\times {10}^{19}$ 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– $4.2\times {10}^{20}$ 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 SiO ₂ 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 m ² 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.

• Research Organization: General Atomics, San Diego, CA (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Contributing Organization: DIII-D Team
• Grant/Contract Number: AC02-09CH11466; AC05-00OR22725; AC52-07NA27344; FC02-04ER54698; FG02-07ER54917; NA0003525
• OSTI ID: 1996585
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 10 Vol. 63; ISSN 0029-5515
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: IAEA
• Language: English