Erosion/redeposition analysis of lithium-based liquid surface divertors

Abstract

A sputtering erosion/redeposition analysis was performed for three candidate tokamak fusion reactor liquid divertor surfaces–lithium, tin–lithium (Sn 80Li 20), and flibe (LiF+BeF 2 salt). The analysis uses coupled edge-plasma, impurity-transport, and sputtering codes (UEDGE/WBC/VFTRIM), and available sputtering data. A pure-lithium surface strongly absorbs impinging D–T ions-this results in a high temperature, low density, (∼200 eV, ∼ 1×10 19 m −3) low-recycle plasma edge regime. Lithium appears to perform well in this regime. Although overall sputtering is high, self-sputtering is finite. Most (∼95%) of the sputtered lithium is confined to the near-surface region and redeposited on the divertor with the remainder (∼5%) also being redeposited after transport in the scrape-off layer. Lithium core plasma contamination is low (∼10 −4 Li/ D– T) . Tin–lithium and flibe would likely operate in a high-recycle regime (e.g., 30 eV, 3×10 20 m −3 ). Erosion/redeposition performance of these materials is also good, with finite self-sputtering and negligible core plasma contamination predicted, but with some concern about changing surface composition due to different constituent element redeposition distances.