抄録
The ITER Central Solenoid (CS) model coil, CS Insert and Nb3Al Insert were developed and tested from 2000 to 2002. The AC loss performances of these coils were investigated in various experiments. In addition, the AC losses of the CS and Nb3Al Insert conductors were measured using short CS and Nb3Al Insert conductors before the coil tests. The coupling time constants of these conductors were estimated to be 30 and 120 ms, respectively. On the other hand, the test results of the CS and Nb3Al Inserts show that the coupling currents induced in these conductors had multiple decay time constants. In fact, the existence of the coupling currents with long decay time constants, the order of which was in the thousands of seconds, was directly observed with hall sensors and voltage taps. Moreover, the AC loss test results show that electromagnetic force decreases coupling losses with exponential decay constants. This is because the weak sinter among the strands, which originated during heat treatment, was broken due to the electromagnetic force, and then the contact resistance among strands increased. It was found that this exponential decay constant was the function of a gap (i.e., a mechanical property of the cable) created between the cable and conduit due to electromagnetic force. The gap can be estimated by pressure drop, measured under the electromagnetic force. The pressure drop can easily be measured at an initial trial charge, and then it is possible to estimate the exponential decay constant before normal coil operation. Accordingly, it is possible to predict promptly how many times the trial operations are necessary to decrease the coupling losses to the designed value by measuring the coupling losses and the pressure drop during the initial coil operation trial.
