Ion beam analysis of tungsten layers in EUROFER model systems and carbon plasma facing components

• Deuterium sputtered model samples for EUROFER studied by ToF-MEIS.
• Tungsten enrichment by preferential sputtering quantified and depth profiled.
• Iodine and chlorine beams compared for tungsten analysis.

The tungsten enriched surface layers in two fusion-relevant EUROFER steel model samples, consisting of an iron–tungsten mixture exposed to sputtering by deuterium ions, were studied by Rutherford backscattering spectrometry and medium energy ion scattering. Exposure conditions were the same for the two samples and the total amount of tungsten atoms per unit area in the enriched layers were similar (2 · 1015 and 2.4 · 1015 atoms/cm2 respectively), despite slightly different initial atomic compositions. A depth profile featuring exponential decrease in tungsten content towards higher depths with 10–20 at.% of tungsten at the surface and a decay constant between 0.05 and 0.08 Å−1 was indicated in one sample, whereas only the total areal density of tungsten atoms was measured in the other. In addition, two different beams, iodine and chlorine, were employed for elastic recoil detection analysis of the deposited layer on a polished graphite plate from a test limiter in the TEXTOR tokamak following experiments with tungsten hexafluoride injection. The chlorine beam was preferred for tungsten analysis, mainly because it (as opposed to the iodine beam) does not give rise to problems with overlap of forward scattered beam particles and recoiled tungsten in the spectrum.