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Experiments have been conducted in the DIII-D tokamak to explore the in-situgrowth of silicon-rich layers as a potential technique for real-timereplenishment of surface coatings on plasma-facing components (PFCs) duringsteady-state long-pulse reactor operation. Silicon (Si) pellets of 1 mmdiameter were injected into low- and high-confinement (L-mode and H-mode)plasma discharges with densities ranging from $3.9-7.5\times10^{19}$ m$^{-3}$and input powers ranging from $5.5-9$ MW. The small Si pellets were deliveredwith the impurity granule injector (IGI) at frequencies ranging from 4-16 Hzcorresponding to mass flow rates of $5-19$ mg/s ($1-4.2\times10^{20}$ Si/s) atcumulative amounts of up to 34 mg of Si per five-second discharge. Graphitesamples were exposed to the scrape-off layer and private flux region plasmasthrough the divertor material evaluation system (DiMES) to evaluate the Sideposition on the divertor targets. The Si II emission at the sample correlateswith silicon injection and suggests net surface Si-deposition in measurableamounts. Post-mortem analysis showed Si-rich coatings containing siliconoxides, of which SiO$_2$ is the dominant component. No evidence of SiC wasfound, which is attributed to low divertor surface temperatures. The in-situand ex-situ analysis found that Si-rich coatings of at least $0.4-1.2$ nmthickness have been deposited at $0.4-0.7$ nm/s. The technique is estimated tocoat a surface area of at least 0.94 m$^2$ on the outer divertor. These resultsdemonstrate the potential of using real-time material injection to formSi-enriched layers on divertor PFCs during reactor operation.

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