A program to Evaluate the Erosion on the CFC tiles of the ITER Divertor

The plasma-facing surfaces of the ITER divertor are armoured with tungsten in the upper part of the inner and outer vertical targets and carbon-fibre composite (CFC) in the lower part, the region where the scrape-off layer intercepts the divertor. The CFC in the form of a monoblock in the vertical target is the most loaded part of the plasma-facing surfaces, and hence it is subjected to high erosion and has a significant risk of failure. A program has been developed with the aim of understanding the impact on the erosion lifetime and on the probability of a critical heat flux event in the heat sink of a combination of two main effects: the material property variations (particularly pronounced in CFC) and the presence of joining defects. The software allows the evolution of the surface profile of the armour to be predicted and the margin on critical heat flux at the heat-sink-to-coolant interface to be estimated for a range of postulated defects, for start-of-life through to end-of-life of the component. In assessing erosion, the code takes account of geometry and sublimation, and physical and chemical erosion of the CFC armour. The code allows the computation of the effect of normal and off-normal (ELMs, etc.) operation. The incident angle (a glancing angle of a few degrees) of the particle and heat flux onto the target is taken into account. The program has been validated by comparison with analytical approximations and experimental data. The code has been developed in APDL language to operate inside a commercial and certificate finite element program such as ANSYS. (author)