The development of divertor high heat flux components is one of the critical issues to realize next generation fusion devices, such as ITER. Since the divertor is located across the magnetic field line, the components are subjected to a high heat/particle flux from the plasma. In ITER, the maximum surface heat load to the components is estimated to be 15 - 20 MW/m² in the normal operation period. The ITER divertor must be capable to withstanding such high heat flux. Recent progress on the development of new divertor high heat flux components in JAERI is presented in this paper.

High heat flux experiments of various divertor mock-ups have been carried out at JAERI. Small-scale divertor mock-up was tested in PBEF (Particle Beam Engineering Facility). The mock-up has armor tiles made of 3-D carbon-fiber-reinforced carbon composite (CFC) brazed with Cu-Mn material onto a cooling tube made of DS-Cu (dispersion strengthened copper), which meets ITER material requirements. In the thermal cycling experiment at a heat flux of 20 MW/m² for 1,000 cycles, the mock-up could survive the thermal cycle with no progressive degradation of the thermal performance while the armor tiles showed severe erosion due to sublimation.

For the development of real-scale divertor mock-ups, 1.3m-long vertical target mock-ups were successfully developed and tested. To simulate the geometry of the ITER vertical target, the mock-ups have curved surface and have stainless steel back plate. The armor tile was made of unidirectional CFC and the cooling tube was made of DS-Cu and pure copper. At a heat flux of 20 MW/m², the mock-up with DS-Cu cooling tube could withstand 1,000 thermal cycles without any evidence of thermal fatigue of the cooling tube. On the contrary, the mock-up with pure copper cooling tube showed coolant leakage from the cooling tube at around 400 thermal cycles due to thermal fatigue; the pure copper cooling tube proved to be highly vulnerable to thermal fatigue. The DS-Cu cooling tube was found to be one of the promising materials for the cooling tube of the divertor from the thermal fatigue point of view.