Temperature-dependent in-situ LEIS measurement of W surface enrichment by 250 eV D sputtering of EUROFER

Highlights: • In-situ LEIS is utilised to detect W surface enrichment by preferential sputtering. • EUROFER steel is irradiated with 250 eV D atoms at various temperatures up to 800 K. • W surface enrichment is detected at room temperature but vanishes at 800 K. • An upper limit for the diffusion activation energy of W in EUROFER is 1.6 eV. - Abstract: Tungsten surface enrichment of EUROFER steel by 250 eV deuterium sputtering is in-situ measured using low energy He${}^{+}$ ion scattering spectroscopy. The samples are irradiated at various temperatures between 300 K and 800 K with a deuterium atom flux of 2 × 10¹⁸ m${}^{-2}$s${}^{-1}$ and maximum fluence up to 1.1 × 10²³ m${}^{-2}$. The measurements at room temperature show a clear increase of tungsten surface density, but already at 520 K the observed enrichment is only half as large. At a temperature of 800 K no tungsten surface enrichment is detectable. The obtained data yield an upper limit of 1.6 eV for the diffusion activation energy of tungsten in EUROFER.