Heat treatment of CuCrZr cooling tubes for JT-60SA monoblock-type divertor targets

The JT-60SA divertor has to withstand a maximum heat flux of ∼15 MW/m2 for 100 s, and JAEA has developed the monoblock-type CFC divertor target for JT-60SA. To boost production yield of the targets, CFC cracking due to thermal expansion and contraction of the CuCrZr cooling tubes must be suppressed. CuCrZr properties depend strongly on the heat treatment, and the target is heat-treated during the manufacturing processes of brazing, solution treatment, and annealing. CuCrZr test specimens were heat-treated with the targets, and the strength and hardness of the specimens were almost the same for the quenching cooling rates of ∼0.65 °C/s and ∼1.5 °C/s around 800 °C. This indicates that the slower quenching cooling rate is acceptable, and consequently at least half of the mock-ups could remove the required high heat flux of 15 MW/m2.