Speaker
Description
Tungsten (W) is the main candidate for plasma-facing materials in tokamaks, as it features, among other properties, low sputter yield and low retention of hydrogen isotopes. However, W lacks intrinsic gettering properties for mid-Z impurities, which are necessary to reduce the presence of impurities that are otherwise capable of degrading the plasma. ITER plans to use boronization as a wall conditioning process that coats the walls with a thin layer of boron (B) to reduce the partial pressure of oxygen and water. This procedure may lead to formation of W–B compounds through redeposition. Such modifications can significantly affect sputtering, fuel retention, and interaction with seeding gases.
In this contribution, we will summarize recent comprehensive experimental and computational efforts to understand the behavior of tungsten and boron containing mixed materials and their consequences in fusion devices. Layers with integral composition of W1B(1-x) with x in the range from 0 to 1 were prepared, mimicking layers expected to form in ITER. Experiments, often performed in-situ, investigated sputter yields, surface morphology evolution (surface enrichment, crack formation) after ion irradiation, hydrogen isotope retention and neon incorporation across a range of irradiation temperatures. Finally, detailed atomic-scale modeling, including sputtering simulations based on molecular dynamics as a function of surface composition, were conducted and show good agreement with the observed experimental trends.
Our results highlight the critical impact of boron incorporation on key surface properties of tungsten, with direct relevance for plasma-facing component performance and lifetime in future fusion reactors.