Surface science in hell: understanding plasma-surface processes in a fusion reactor

In a fusion reactor, power from the core plasma is exhausted by the surrounding plasma-facing materials which are bombarded by high fluxes of energetic neutral and charged energetic particles. Study of the plasma-surface interface is very challenging as surface analysis techniques are often impossible to apply in-situ. Understanding of the plasma-surface processes is only possible by supporting experiments in large devices by dedicated small-scale experiments mimicking some specific conditions. 2 specific illustrations of this approach will be detailed. The systematic study of the co-deposition of beryllium with tritium using NRA, TDS, SEM and XPS allowed derivation of scaling laws able to reconcile discrepancies between different research groups and to identify the role of beryllium hydride formation as an important process. A novel experimental setup has been developed at FOM to study the response of a plasma-immersed surface to intense heat loads expected during plasma instabilities. Fast spectroscopic and infrared measurements allow in-situ diagnosing while high-resolution microscopy is routinely used to investigate the induced surface changes. An unexpected outcome of the system is its ability, by tuning the experimental conditions, to produce nano-particles with very narrow size distribution, bridging the gap with fundamental surface science.