How boronization alters tungsten erosion: Insights from ion-beam studies of W-B mixed layers

Abstract

Tungsten is the prime candidate for plasma-facing components in ITER and future fusion reactors, yet erosion of tungsten surfaces remains a critical source of high-Z impurities in fusion plasmas. In present-day devices, boronization is widely used as a wall conditioning technique that deposits boron onto plasma-facing surfaces and thereby modifies their erosion behavior. Here we investigate the sputtering response of tungsten-boron (W-B) mixed layers under fusion-relevant ion bombardment. Thin films with systematically varied W:B composition, from pure tungsten to pure boron, were irradiated with 2 keV Ar+ and 2 keV D2+ ions, representing typical impurity and fuel species in magnetically confined fusion plasmas. Elemental compositions were determined by time-of-flight elastic recoil detection analysis (ToF-ERDA) and high-resolution Rutherford backscattering spectrometry (HR-RBS), while total sputter yields were measured in situ using a highly sensitive quartz crystal microbalance. A clear and systematic trend emerges: the total eroded mass decreases strongly with increasing boron concentration, particularly for Ar+ irradiation. Boron enrichment significantly suppresses tungsten sputtering while shifting the composition of the eroded flux toward low-Z species. These results demonstrate that boronization can substantially mitigate tungsten erosion and thus reduce high-Z impurity sources in fusion plasmas, providing important quantitative input 50 for plasma-wall interaction modelling and impurity control strategies in ITER-relevant operating regimes.