Fuel accumulation in co-deposited layers on plasma facing components

Abstract

The work is focused on the determination of the distribution and the total content of deuterium in co-deposits formed in the TEXTOR tokamak on a toroidal belt limiter which is the machine's major plasma facing component (PFC). Limiter tiles in use for 14 100 s of plasma operation were dismounted for examination with surface analysis and microscopy methods. Mapping of the deuterium distribution by means of nuclear reaction analysis (NRA) revealed the presence of deposition zones covering about 35% of the tiles'surface area. Besides C and D, other constituents of the layers were boron, silicon and inconel components. The co-deposit, with a stratified structure and a thickness of up to 50 μm , could be detached from the tiles. Deuterium depth profiling on both sides of the detached flakes and in the underlying graphite substrate enabled the D content in the deposition zones to be estimated at a level of 3.5×10 19 cm −2 . Adding the fuel content found in the erosion zone (3–7×10 17 cm −2) and on the back side of the tile (0.9–1.8×10 17 cm −2) , the total amount of D atoms trapped in all the limiter tiles was assessed to be about 2×10 23 atoms. D content in the co-deposits accounted for approximately 10 at.% ( C D/ C C∼0.1) which was considered to be low in comparison to much greater values observed in other devices. The results of the ion beam analyses (IBA) agree well with the determination by thermal desorption spectrometry (TDS).