Wall Forum 2022

Helium transport in tungsten during fuzz growth was investigated to provide insight into the helium-induced nanostructuring process which adversely affects the near-surface properties of plasma-facing tungsten components. Fuzz layers with thicknesses of 1.0 or 1.7 µm were initially formed with pure ⁴He plasma at 1100 K, then sequentially exposed to a mixed ³He-⁴He plasma at a range of sample temperatures (i.e., 316-1053 K). ³He retained in the fuzzy layer and in the bulk substrate after plasma exposure were measured by nuclear reaction analysis. An increase in ³He retention was observed at 1053 K in the bulk, but no comparable decrease was observed the fuzz layer, suggesting more efficient trapping of helium in the bulk at this temperature, and no diffusion of helium from the fuzz layer to the bulk. An analytical model of helium transport in vacuum within the fuzz layer was developed for comparison. Model results were found to compare well with experimental results of retention in the bulk when considering helium reflection from the fibers sides and when considering that only ~10^-3% of helium incident on bulk tungsten is retained. Using model results for helium implantation in the bulk, the helium fluence-fuzz thickness relation was derived, which matched well with experimental data. Hence it was determined that fuzz growth is governed by helium content in the bulk, which occurs by implantation and not diffusion. [mehr]

The WallDYN code has been used in the past to make prediction about Be erosion and deposition in ITER and the resulting fuel retention by co-deposition. These calculations were done in 2D assuming a flat toroidally symmetric frist wall. Recently the calculations were re-done in 3D taking the geometric details of the shaped Be first wall of ITER into account. The presentation will show how the 3D plasma was "obtained" from a 2D SolPS/OSM solution and how the shaped first wall affects Be erosion/deposition and the resulting fuel retention. The new 3D results are also compared to the old 2D calculation and to ERO2.0 predictions. [mehr]

The Helmholtz-Zentrum Dresden-Rossendorf (HZDR) operates several user facilities for materials research and defect characterization employing positron annihilation spectroscopy. In this talk, you will obtain an overview of positron basics, the Monoenergetic Positron Source (MePS) as well as the other source-based positron beams and setups at the HZDR. [mehr]