Preliminary assessment of possible carbide formation on Be and T contaminated CFC tiles from JET

The fusion plasma is far too hot to be brought into direct contact with a physical wall. It would degrade the wall and the debris would extinguish the plasma. Schemes are developed to cool down the plasma locally before it impacts on a physical surface. The resulting plasma wall-interaction in ITER is facing several challenges including surface erosion, material redeposition and tritium retention. In the JET facility both Be and C are used together as plasma facing materials (PFM), and the resultant surfaces show considerable mixing between the two elements. In this work a first XPS characterisation has been performed on the surface of several PFM samples obtained from various JET tiles from the Mk II GB divertor. The substrates of the tiles are CFC, and the deposited films have various D/C ratios depending on the position in the tokamak. Ion beam analysis shows that the D/C ratio is ~1 in the shadowed areas and Be/C ~1–2 in the plasma-exposed regions of the inner divertor. These values could give rise to the formation of BeC. Indications of carbide components are found in the XPS spectra. The processes for material migration and the morphology of deposits are discussed.