Simulation of tungsten armour cracking due to small ELMs in ITER

Simulations of tungsten armour cracking under small ELM-like plasma heat load, which does not cause surface melting, have been performed using the PEGASUS-3D code. A dedicated series of experiments have been performed in the QSPA-Kh50 facility for measurements of the unknown tungsten thermophysical properties and for verification of the PEGASUS-3D simulation results. The simulations revealed that a cellular crack network with average mesh size Lambda similar to 0.5mm formed after first ELMs and the pattern does not change further. With increasing number of repetitive ELMs loads, the average crack width Delta(n) has a maximum value Delta(m). The ratio of Delta(m)/Lambda is equal to the tungsten thermal expansion at the maximum surface temperature. Delta(n) tends to this value exponentially. The number of ELMs n(m) needed for Delta stabilization depends on the ELMs energy density and time duration, n(m) similar to 300 for the simulated ELMs of 0.45 MJ/m(2) and 0.25 ms duration. The PEGASUS-3D code is prepared for simulations of tungsten armour damage under action of ELMs of various energy deposition and time duration. These parameters of ELMs depend on ITER regimes of operation and on how successful will be the efforts on ELMs mitigation. (C) 2010 Elsevier B.V. All rights reserved.