Japanese developments of fusion reactor plasma facing components

For ITER and fusion reactors, evaluation studies on plasma facing materials and low activation materials, and developments of plasma facing components have achieved significant advances in Japan. Plasma material interactions of in-vessel materials such as carbon-tungsten mixed material, carbon dust, ferritic steel, vanadium alloy and SiC have been investigated. In particular, gas desorption, fuel hydrogen retention and hydrogen absorption which causes hydrogen embrittlement have been examined, and the suitability as an in-vessel material has been discussed. For the plasma facing components of ITER, new materials and technologies have been developed. 3-D-CFC with high thermal conductivity (500 W/m per K), CVD technique for tungsten coating with 5-mm thickness, oxygen free copper clad dispersion strengthened copper cooling tube (OFCu clad DS Cu), and joining technique between carbon fiber reinforced carbon composite (CFC) and copper alloy with silver-free braze have been developed. A component of CFC brazed onto OFCu clad DS Cu with silver-free braze withstood a heat flux of 20 MW/m2. For fusion reactors, a cooling structure made of low activation ferritic steel has been developed.