Scientists used a heavy‑ion beam in a time‑of‑flight elastic recoil detection setup to trace material migration on plasma‑facing tiles from the TEXTOR tokamak. A 36 MeV iodine ion beam was directed at carbon composite limiter tiles that had been exposed to nitrogen‑15 and molybdenum hexafluoride during experiments. The recoil technique measured the distribution of elements within the first 400 nm of the surface. The analysis revealed that molybdenum, a high‑atomic‑number element, had eroded from one part of the wall and redeposited elsewhere, carrying trapped nitrogen‑15 along with it.

The method provides depth profiles for both light isotope tracers and heavier species in situ, showing where high‑Z material has moved. However, the roughness of the limiter tiles limited the depth resolution, so absolute concentrations could not be precisely quantified. Relative amounts of different elements were still reliable, allowing conclusions about migration patterns.

This study demonstrates that heavy‑ion elastic recoil detection can successfully characterise the very top layers of fusion‑device walls and trace both metal migration and light‐element retention, albeit with caution about absolute numbers due to surface roughness.