Real-time Si Material Injection for In-Situ Coating in the DIII-D Tokamak: Paper Published in Nuclear Fusion Journal

The paper by Florian Effenberg et al, "In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection, " was published in Nuclear Fusion. This study investigated the in-situ formation of silicon-rich layers on tokamak plasma-facing components with real-time Si material injection.

Silicon (Si) pellets with a diameter of 1 mm were injected into DIII-D H-mode plasma discharges. The impurity granule injector (IGI), developed by PPPL, enabled this, operating at frequencies between 4-16 Hz. The divertor material evaluation system (DiMES) was employed to expose graphite samples to plasma to determine the Si deposition rate on divertor targets. Results indicated a correlation between Si II emission and the frequency of silicon injection, pointing to surface Si-deposition. Subsequent analysis revealed the presence of Si-rich coatings, primarily composed of silicon oxides, notably SiO2. The absence of SiC was noted, likely due to low divertor surface temperatures. Evaluations showed these Si-rich coatings to have thickness values between 0.4-1.2 nm and deposition rates of 0.4-0.7 nm/s. The method appears capable of addressing a surface area of approximately 0.94 m2 on the outer divertor. Extrapolations for a fusion power plant (FPP) setting show that injecting a few hundred kg per year would be necessary to replenish and maintain millimeter-thick low-Z claddings, while less would be required for surface conditioning. The study concludes that using Si or SiC powder injection and a heated divertor could optimize the method and promote in situ SiC formation in future experiments.

F. Effenberg et al 2023 Nucl. Fusion 63 106004 DOI 10.1088/1741-4326/acee98

https://iopscience.iop.org/article/10.1088/1741-4326/acee98

Find preprint on arXiv:2304.03923 [physics.plasm-ph]