ITER-CS インサート・コイルの分流開始温度特性

抄録

The performance of the ITER central solenoid insert (CSI) conductor was tested in 2015. The current-sharing temperatures (T_cs) were measured over 16,000 electromagnetic cycles, including three thermal cycles between 4.2 K and room temperature. T_cs under the initial magnetization (IM) condition (13 T, 40 kA) of the CSI conductor not only increased, but also decreased between 6.71 and 6.84 K against cycling; then T_cs became almost constant at 6.74 K. Thus T_cs under the IM condition, was approximately 1.5 K higher than the specification of 5.2 K throughout the test. The slope of the hoop strain (ε_hoop) on the CSI conductor against the electromagnetic force was 1.55×10^-4 % m/kN (in ε_hoop > 0) and 1.39×10^-4 % m/kN (in ε_hoop < 0). Taking the effect of ε_hoop into account, the T_cs of the CSI under the SULTAN simulated condition (11.5 T, 45.1 kA) was equivalent to that of the SULTAN test after around 10,000 cycles. Before around 10,000 cycles, especially at the initial charge, the T_cs of the SULTAN test was lower than that of the CSI test. It is assumed that the hoop strain in the CSI test accelerated a strain relaxation, which increased the T_cs from the initial charge. When the strain fully relaxed and T_cs stopped increasing after around 10,000 cycles, the T_cs of the SULTAN test became equivalent to that of the CSI test. Given this perspective, the CSI test and SULTAN test were consistent. In ε_hoop > 0, the absolute value of the effective strain (ε_eff) of the CSI test decreased (i.e., T_cs increased) against the electromagnetic force (F_r) because the effect of the positive ε_hoop on the increase in T_cs exceeded the effect of the F_r on the decrease in T_cs. The line of ε_eff −ε_hoop of the CSI test against F_r was nearly symmetric about the y-axis (F_r=0). Comparing the ε_eff −ε_hoop of the CSI test and the ε_eff of the SULTAN test, the slopes of the strain against F_r were almost the same between the CSI test and SULTAN test before cycling. The ε_eff of the SULTAN test became close to the ε_eff−ε_hoop of the CSI test after cycling. This CSI test demonstrated that mass-produced CS conductors are highly capable of being used in the ITER.