Modelling the sputtering and reflection from a beryllium surface: atomistic analysis

Abstract

Sputtering from plasma-facing surfaces upon particle impact can limit the lifetime of components in fusion devices, especially in the diverter region. Atomistic simulations of the processes associated with plasma–wall interactions allow for a detailed analysis of sputtering, reflection and adsorption. Most former works of beryllium sputtering by hydrogen isotopes were aimed mostly on the sputtering yield. We investigate the influence of impact energy and angle on sputtering, and analyze these quantities also for the outgoing particle. We model the sputtering by non-cumulative molecular dynamics simulations with a large number of trajectories for the various parameters. The underlying forces and energies are obtained from high-dimensional neural networks fitted to density functional calculations. We find a good agreement with the previously reported sputtering yields for perpendicular impact and a qualitative accordance with experimental data. In detail, the sputtering yield increases with increasing impact energy for angles of incidence larger than 45° with respect to the surface normal, while smaller angles show a maximal yield up to 100 eV. In cases where D reflection rather than sputtering occurs, a similar pattern is found for all angles, with the maximal reflection rate at 80°.

Modelling the impact of argon atoms on a tungsten surface

“…The mechanisms governing sputtering seem to be different for the Ar case, compared to light atom irradiation [45]. This is not unexpected, due to the mass and size of Ar which leads to negligible penetration at low energies and low penetration at higher energies.…”

Sputtering and reflection from a beryllium surface: effects of hydrogen isotope mass, impact position and surface binding energy

“…The MD simulations were performed using a neural network potential energy function. The parameters and computational details of the simulations were the same as described previously [12]. For the new simulations on sputtering with T we simulated perpendicular impacts with energies of 10 and 20 eV (5000 trajectories each) and, 30, 50, 75 and 100 eV (2000 trajectories each).…”

“…In figure 1 we compare the sputtering yields from H and T impacts at various energies with the results from deuterium [12]. We include also the yields computed with the Eckstein and Yamamura formulas [13,14].…”

“…Concerning the other differences between our simulated and the yields predicted by analytical expressions, they arise partially because our sputtering events are resolved with respect to the impact angles while one input to the Eckstein formula is an average over a rough surface. (More detail is given in [12]).…”

Effect of 14.7 MeV Protons on Beryllium Micro Brush / Copper ITER First Wall using SRIM

“…Then, the small amounts of T liberated when Be Since 1994, the first reason for the selection of Be is its acceptable effect on plasma performance and as the first wall due to its erosion lifetime, fuel retention and its performance in ITER [5], [6], [7], [8], [9]. Its life time depends on the erosion and deposition processes and the incidence angle effects were included by an enhancement of self-sputtering yield [10], [11]. To keep the plasma away from the walls, then the strong magnetic fields are used as shown in figure 1.…”