The accurate description of boron (B) material properties and boron-plasma interactions is crucial for high-fidelity modeling of boron powder injection and ablation. The first critical analysis of the B thermophysical, evaporative, optical and plasma-surface interaction properties is presented. Simulations of B powder ablation in Scrape-Off-Layer (SOL) plasmas with the SPIDER dust dynamics code are reported focusing on the charge and energy balance. Charging is dominated by electron-induced electron emission, mainly of secondary electron nature with an important contribution from electron backscattering, while thermionic emission remains subdominant due to recollection in the electrostatic potential. This behavior differs significantly from tungsten (W) grains, for which charging is dominated by the onset of thermionic emission at high surface temperatures. Nevertheless, B and W grains of the same size exhibit comparable lifetimes in near-SOL plasma parameters. The analysis of sensitivity of the SPIDER predictions to estimated B property uncertainties revealed robustness of the results.
In order to reduce the edge plasma temperature in fusion reactor divertors such as ITER’s, the introduction of radiating elements (i.e., impurity gas seeding) may be necessary. Nitrogen has been proposed for that purpose due to its good radiation characteristics in the edge plasma temperature range; however, it has the added complication that it will interact chemically with both the hydrogenic fuel and any metal surfaces.The current study looks at the influence of nitrogen co-bombardment on deuterium retention in tungsten by comparing deuterium only and combined deuterium–nitrogen implantation in tungsten with 1% to 10% N at 300–700 K and with energies of 500 eV/D + and 1000 eV/N+. After implantation, thermal desorption spectroscopy (TDS) is used to measure the amount of deuterium retained, and X-ray photoelectron spectroscopy (XPS) is used to investigate nitride formation on the surface.We observe an order-of-magnitude increase in deuterium retention in the temperature range ∼ 500–600 K. This increase occurs for N+/D+ ratios as low as 1% and is accompanied by large-scale blistering of the surface.XPS analysis of the co-bombarded surfaces indicate the formation of a tungsten-nitride layer from room temperature to 700 K. We believe that a change in the nature of the tungsten-nitride layer around 500 K creates a permeation barrier affecting the ability of deuterium to diffuse to the surface and increasing deuterium retention.
Boron (B) is used in magnetic confinement experiments for wall conditioning to achieve a clean, oxygen-free plasma. Continuously renewable rods made of boron nitride–boron (BN-B) pebbles were recently proposed as a candidate plasma-facing material capable of surviving the extreme plasma heat flux environment in future reactors. The present work presents interpretative modelling using the ERO2.0 code aiming at reproducing sputtering behaviour of solid B and BN-B pebble rods under deuterium (D) irradiation experiments in the linear plasma device PISCES-A, where B erosion was inferred from passive spectroscopy. The SDTrimSP sputtering yields for B underlying ERO2.0 simulations are discussed in view of experimental results from PISCES-A and other devices. ERO2.0 modelling shows that BN-B pebbles have similar effective erosion rates as reference solid B targets. Sputtering yields are higher on inclined surfaces of the pebbles, but the increased gross erosion is balanced out by simultaneously increased redeposition on the sides of the pebbles.
