Damage in Carbon Fibre Composite Armours of Actively Cooled Plasma Facing Components

J. Schlosser (Sp), CEA-Cadarache, Saint Paul lez Durance (France); E. Martin, University of Bordeaux 1 (France); D. Leguillon, University of P. & M. Curie, Paris (France); G. Camus, University of Bordeaux 1 (France); F. Escourbiac, M. Missirlian, R. Mitteau, CEA-Cadarache, Saint Paul lez Durance (France) 
The understanding of damage mechanisms of carbon fibre composite (CFC) armours for actively cooled plasma facing components (PFC’s) are an important challenge for controlled fusion devices. A reliable mechanical and thermal bond must be achieved despite of the thermal expansion mismatch between the composite tile and the metallic heat sink.
Flat tile water cooled concepts, designed for heat flux up to 10 MW/m2, were studied, developed, and finally successfully experienced in the Tore Supra (TS) tokamak. The bond is obtained thanks to a structuring of the CFC surface and a casting of copper, which allows a gradient layer to be built. During the validation phase, prototypes were fatigue tested in a high heat flux (HHF) facility and observations show some initiation of damage within the CFC in the vicinity of the bond. For the ITER machine a different tube-in-tile concept was developed. This new component was designed to sustain a heat flux of 20 MW/m2.
In order to predict the lifetime of a PFC, it is necessary to analyse the damage mechanisms and to model the damage propagation when the component is submitted to cyclic operative conditions (taking into account the stress field existing in the component after manufacture).
The paper deals with the fatigue behaviours observed during HHF tests of the components for TS and the prototypes for ITER, the final aim being to provide a tile damage ratio depending on the history of the heat loading (number of cycles, values of the heat load). The paper also includes modelling analyses performed at the microscopic and the macroscopic scales (damaging law for the CFC, geometric parameters of the bond) in order to investigate the fatigue mechanisms.

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