A recent article in Nuclear Materials and Energy presents an integrated modeling framework for studying boron powder injection as a method for real-time conditioning of plasma-facing components in tokamaks. The work combines three established simulation tools to describe how injected boron particles move through the plasma, how they are ionized and transported, and how they interact with material surfaces through erosion and deposition.

The study builds on earlier work that used three-dimensional plasma edge modeling to describe boron transport from localized sources in the scrape-off layer. In that earlier approach, transport and deposition were analyzed without explicitly treating dust particle dynamics or surface evolution.  The new framework extends this by including the ablation and transport of boron powder particles and by coupling these results to a surface evolution model that accounts for erosion, redeposition, and material mixing.

The simulations are based on a DIII-D tokamak scenario and consider injection of solid boron powder at rates corresponding to milligrams per second. The modeling couples the EMC3-EIRENE code for plasma and impurity transport with the Dust Injection Simulator, which describes particle motion, heating, and ablation. These results are then linked to the WallDYN3D model, which calculates how material accumulates and evolves on plasma-facing surfaces over time.

The results show that injected boron particles evaporate near the plasma edge once they reach sufficiently high temperatures. After ionization, the transport of boron is largely determined by the background plasma flow, which in the simulated conditions directs most of the initial impurity flux toward the inboard divertor according to the impurity fluid modeling. Particle size in the range from a few micrometers to a few hundred micrometers has little effect on this transport behavior.

When only this initial transport is considered, deposition appears localized and asymmetric. Including erosion and redeposition processes alters this picture. Material that reaches the wall is partially re-eroded and redistributed through the plasma edge. Over time, this leads to a different flux distribution and increased deposition on the outboard divertor compared to the first-pass prediction. The simulations reach a quasi-steady state in which erosion and deposition balance. The modeling further shows that boron and carbon undergo continuous recycling near divertor surfaces. The resulting surface composition depends on the balance between incoming boron flux and erosion. At lower injection rates, the model produces mixed boron and carbon layers, while higher injection rates lead to stronger boron enrichment.

The authors also compare fluid and kinetic treatments of impurity transport. The kinetic approach, which includes finite particle acceleration and thermalization, results in more localized transport than the fluid approximation. The simulation domain is limited to a portion of the divertor, where plasma-material interactions are most intense. Extending the modeling to the full wall geometry is identified as a next step, leveraging EMC3-EIRENE's wide-grid capability.

The integrated framework is intended to support further studies of real-time wall conditioning with boron and lithium powders and pellets. It will furthermore be used in ongoing work to assess solid boron injection for ITER, where similar modeling approaches are planned to evaluate coating distribution and lifetime.

F. Effenberg et al, 'Integrated modeling of boron powder injection for real-time plasma-facing component conditioning', Nuclear Materials and Energy 42, 101832, 2025, https://doi.org/10.1016/j.nme.2024.101832; arXiv:2407.00821