3-D simulation of macroscopic erosion of CFC under ITER off-normal heat loads

Carbon fiber composites, CFC, newly developed for the divertor armor of the future tokamak ITER, have a rather complex structure of fiber framework and carbon matrix, allowing CFC to match the thermal conductivity requirements for the tokamak stationary regimes. But for the ITER off-normal events, their behavior is still not investigated in detail. Recent experiments on electron beam facilities simulating the slow transient loads of 20 MW/m2 have shown unusually high erosion rates of CFC in the temperature range of 3000–4500 K. To understand the mechanism of the enhanced erosion, numerical simulations for the new CFC are carried out using the Pegasus code that has been generalized to describe three-dimensional effects of brittle destruction and heat transport in the carbon composites. A new erosion mechanism is discovered. The enhanced erosion is caused by local overheating in CFC materials due to preferential cracking on the fiber surface and thermal isolation of the fibers from matrix. A large difference of fiber and matrix coefficients of thermal expansion is essential for the mechanism.