Summary, assessment and implications of the ITER Model Coil test results

Abstract: Testing of the five International Thermonuclear Experimental Reactor (ITER) model coils is nearly complete and it is possible to produce an overall summary of the conductor performance assessment. The interpretation is supported by a large database of tests on components (especially strand) and by analysis of the two main phenomena that influence the strand performance in the cable (current non-uniformity and mechanical loads). Individually, interpretation of individual coils is difficult but taken together the results enable conclusions to be drawn about the expected behaviour of conductors in the ITER coils. The conductor design has successfully resolved many of the problems of stability and pulsed current behaviour associated with large multi-strand cables, and the performance is better than expected in these areas. The current sharing behaviour is below expectations, probably due to an extra unexpected strain effect in the Nb3Sn strands arising from the local magnetic loads, and the paper concentrates on this issue. Design modifications are required to recover the performance and updated design criteria to implement these are proposed.