Lateral mapping of hydrogen isotopes in the carbon-based materials exposed in tokamak TEXTOR using focused ion beams

Primoz, Pelicon1; Cadez, Iztok1; Simcic, Jurij1; Markelj, Sabina1; Brezinsek, Sebastijan2; Kreter, Arkadi2; Litnovsky, Andrey M.2; Philipps, Volker2; Rubel, Marek3 1Slovenia; 2Germany; 3Sweden

The interaction of the tokamak plasma with plasma-facing components results in erosion, transport, re-deposition of wall materials as well as fuel retention in the vessel wall. Fuel retention in deuterium-fueled fusion experiments is currently intensively studied to allow predictions for the tritium retention in ITER. Tritium retention in ITER may lead to a forced cleaning intervention due to excess safety limits in the vessel.
The evaluation of retention processes rely mostly on fuel quantification in the tokamak plasma-exposed wall materials like graphite limiters with millimeter lateral resolution. However, the fuel retention patterns exhibit in many cases strongly structured patterns at the micrometer scale. Measurement methods able to measure the distribution of hydrogen with isotopic mass resolution and lateral resolution at micrometer scale are therefore required to improve the understanding of the retention mechanisms.
The techniques of hydrogen isotope-resolving lateral micromapping based on the high-energy focused ion beams are presented. Elastic Recoil Detection Analysis (ERDA) with 3 MeV 7Li microbeam as well as Nuclear Reaction Analysis (NRA) with 2.5 MeV 3He microbeam are discussed. Strong influence of surface topography on the ERDA method favors the NRA technique for the analysis of the real materials used in fusion devices. Hydrogen isotope distribution maps obtained during the ex-situ analyses of wall materials exposed in the deuterium plasma of the tokamak TEXTOR are presented including graphite (EK98) and Carbon Fibre Composits (DMS780 and NB31).

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