Erosion and core contamination of boron pebble aggregates exposed to DIII-D divertor conditions

A boron pebble aggregate was exposed in DIII-D via DiMES for the first time to investigate erosion mechanisms, core contamination, pre/post structural and chemical resilience, fuel retention, and overall feasibility. Low-Z renewable divertor concepts are a promising solution for mitigating high heat and particle fluxes in magnetic confinement fusion devices while maintaining good core performance. Thea Energy Inc., in collaboration with UCSD, is investigating the use of a boron pebble rod for future stellarator divertor designs. Measurements from L-mode, H-mode, and VDE shots (with > 40 MW/m² parallel heat fluxes) reveal evidence of boron released via macroscopic pebbles. Filtered imaging indicates that eroded boron ions are affected by divertor flow patterns, demonstrating cross-field directionality of ejected boron. Core DIII-D boron uptakes coinciding with strike points traversing the pebble target were more prominent than carbon, suggesting that boron transport to the core may be more significant than the carbon-based binder contribution. The sputtering yield and trajectory of emitted neutral boron is compared to recent experiments conducted in a D+ PISCES-A plasma and molecular dynamics simulations showing yields of up to 0.03 atoms/ion.