Speaker
Description
We present ERO2.0 simulations that reproduce the experimentally observed similarity in erosion rates between boron nitride–boron (B-BN) pebbles and solid boron (B). Low-Z plasma-facing materials like B are attractive for fusion reactors due to their low core plasma radiation compared to high-Z materials such as tungsten. However, pure B erodes and evaporates rapidly, limiting component lifetime and causing significant tritium co-deposition. A recent solution embeds B pebbles in a boron nitride matrix [1], forming sacrificial B-BN rods extruded into the divertor. The pebbles detach under plasma loading to be transported away for reconditioning and re-extruded in a closed loop. This renewable divertor concept is being considered for Thea Energy's planar-coil stellarator [2]. Laser-heating experiments simulating high heat fluxes showed acceptable B-BN recession rates. In PISCES-A linear plasma tests, B-BN and solid B samples exhibited similar erosion rates, but B-BN demonstrated a two-order-of-magnitude reduction in deuterium retention.
We apply the ERO2.0 impurity transport and erosion code [3] to these PISCES-A experiments to validate the code and prepare for extrapolation to reactor conditions. Additional comparisons are made with B exposure experiments at DIII-D [4], PSI-2 linear plasmas [5], and ion-beam data. The simulations qualitatively confirm the experimental observation that B-BN and solid B experience similar net erosion. The more oblique incidence of deuterium projectiles on the curved pebble surfaces increases gross erosion, which is compensated by enhanced redeposition of sputtered B within the pebble structure. Simulations also predict a modest shift in the angular distribution of sputtered B toward more oblique angles for the pebble geometry. For quantitative comparison with experimental erosion rates, we examine sputtering yields from the SDTrimSP code [6]. Initial simulations underestimated erosion by about a factor of four, but agreement improves significantly by adopting a lower surface binding energy for B. We also discuss experimental uncertainties, including the deuterium ion energy distribution and factors affecting sputtering yields, such as nitrogen from the BN binder. Finally, we assess the contribution of chemical erosion and compare it with BD A–X molecular band emission measured during the PISCES-A experiments.
[1] E. Martinez-Loran et al., Nucl. Mater. Energy 2025
[2] D.A. Gates et al., Nuclear Fusion 2025
[3] J. Romazanov et al., Phys. Scripta 2017
[4] A. Ottaviano et al., presented at APS-DPP 2025
[5] M. Sackers et al., Nucl. Mater. Energy 2025
[6] A. Mutzke et al., IPP Report 2024-06