Speaker
Description
In a future fusion reactor, energetic ions and neutrals escaping from the plasma will interact with plasma facing materials (PFM) on the first wall of the reactor. The impact of these particles will lead to modifications of the PFM, which in turn affects the performance, durability and safety of the reactor. Reliable modelling is therefore necessary to accurately predict these interaction and material modifications. One fundamental quantity of ion-solid interaction is the interatomic potential, which describes the force field between atoms. It plays a crucial role in predicting collision cascades and thus sputter yields, implantation profiles and near-surface modification under ion bombardment. However, the commonly employed screened Coulomb potentials are known to be inaccurate for fusion relevant energies, and experimental attempts of a quantitative assessment are scarce [1]. Time-of-Flight Low Energy Ion Scattering (ToF-LEIS) allows the assessment of interatomic potentials at energies or interaction distances relevant for the plasma surface interactions in fusion reactors.
In this work, we experimentally investigate the interatomic potential of He and Cr, with complementary measurements using deuterium (D) planned to assess isotope effects for fusion plasmas. Cr is of particular interest as it is a component of steel (i.e. EUROFER97 [2]), considered as structural material for future fusion reactors, while also being explored as a constituent of SMART (self-passivating metal alloys with reduced thermo-oxidation) materials for use as PFM [3]. Specifically, we performed angular scans of the scattering yield on a Cr(100) single crystal, using a beam of 3keV He+ ions. By adjusting the screening length with a correction factor in Molecular Dynamics (MD) simulations, we were able to reproduce the width and intensity of the minima and maxima in the experimental angular scans. The resulting improved potentials were subsequently compared to commonly used interatomic potential models as well as earlier studies on Fe and Cu, elements with similar atomic number in order to identify potential trends on the interatomic potential strength. Furthermore, the effect of the ion energy on the observed interatomic potential was investigated to assess how the interaction strength evolves with ion velocity and thereby improve the predictability across an extended range.