The paper titled “In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection” by Florian Effenberg et al, was published in Nuclear Fusion. In this work, silicon-rich films were grown in situ on tokamak plasma-facing components (PFCs) using real-time small Si pellet injection. The research was conducted in the DIII-D tokamak using high confinement (H-mode) plasmas.

In the detailed experiments, silicon (Si) pellets of 1 mm diameter were injected into plasma discharges of various densities and input powers. The impurity granule injector (IGI) introduced these pellets at 4-16 Hz frequencies.

Using the divertor material evaluation system (DiMES), graphite samples were exposed to plasma to gauge the Si deposition on the divertor targets - the observed Si II emission at the sample correlated with the silicon injection, indicating surface Si deposition.

Post-experiment analysis revealed Si-rich coatings primarily composed of silicon oxides, with SiO2 being the most prominent component. Notably, SiC was absent, which was determined to be due to too low divertor surface temperatures. Both in-situ and ex-situ analyses measured Si-rich coating thicknesses between 0.4-1.2 nm, depositing at rates of 0.4-0.7 nm/s. This method is estimated to have the capacity to coat a surface area of at least 0.94 m2 on the outer divertor.

The research indicates the potential of real-time material injection to create Si-enriched layers on divertor PFCs during reactor operation, providing valuable insights for further advancements in the field.

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