Examination of material damage on components of future fusion reactors

Nowadays materials based on beryllium, carbon or tungsten are those most favored for use as wall components which will be heat loaded by the plasma in future fusion reactors. These materials are subjected to extreme heat loads (up to 20 MWm-2) during normal operation. In order to carry the heat away safely, the above materials are joined to metallic heat sinks (molybdenum or copper alloys) by an appropriate joining technique. As the components and the joints are thermally cycled by the heat load, thermal fatigue will cause material damage. Additionally, in the case of an unsteady plasma the materials will be extremely thermoshocked by energy densities up to 140 MJm-2. Under these conditions the materials facing the plasma (Be, C, W) will be strongly eroded. At the same time local melting, recrystallisation and cracking will cause extensive material damage. The thermal load on materials normally observed in fusion reactors will be simulated by means of appropriate testing equipment (electron-beam for instance). The material damage thus caused will be examined by metallography, scanning electron microscopy using energy dispersive analysis, quantitative microstructure analysis and non-contact profilometry. Based on these results appropriate materials as well as joining techniques will be designed for use in future fusion facilities such as ITER. (orig.)