Improved material mixing model in ERO2.0: Nonlinear effect of boron concentration on tungsten sputtering and influx from mixed tungsten-boron surfaces

An upgraded homogeneous mixing model for plasma-facing surfaces in ERO2.0 has been developed using a database of SDTrimSP mixed-material simulations, replacing earlier linear interpolation between pure-material sputtering yields. The SDTrimSP simulations predict nonlinear relationships between tungsten sputtering yield and low-Z surface concentration, in particular increased tungsten erosion by deuterium from tungsten-boron surfaces at low impact energies (<300 eV). The updated model features parameterised analytic fit formulas for the sputtered energy and angular distributions, offering higher sampling resolution, significantly reduced memory requirements, and improved robustness against Monte Carlo noise compared to tabulated SDTrimSP outputs. As the first application of the model in an inter-ELM H-mode JET plasma scenario, ERO2.0 simulations predict that introducing a 10% B surface concentration on W divertor components reduces total W erosion by 7%, primarily due to B ions, but increases W erosion and influx from D atom impact by 5% at the outer divertor entrance.