Test results on the first 50 kA NbTi full size sample for the International Thermonuclear Experimental Reactor

Within the framework of the R&D studies for the International Thermonuclear Experimental Reactor (ITER) project, the first full size NbTi conductor sample was fabricated industrially and tested in the SULTAN facility (Villigen, Switzerland). This sample (PF-FSJS), which is relevant to the poloidal field coils of ITER, is composed of two parallel straight bars of conductor, connected at the bottom through a joint designed according to the CEA twin-box concept. The two conductor legs are identical except for the use of different strands: a nickel plated NbTi strand with a pure copper matrix in one leg, and a bare NbTi strand with a copper matrix and internal CuNi barrier in the other leg. The two conductors and the joint were extensively tested as regards DC and AC properties. This paper reports on the test results and analysis, stressing the differences between the two conductor legs and discussing the impact of the test results on the ITER design criteria for the conductor and joint. While joint DC resistance, conductors and joint AC losses fulfilled the ITER requirements, neither conductor could reach its current sharing temperature at relevant ITER currents, due to instabilities. Although the drop in temperature is slight for the CuNi strand cable, it is more significant for the Ni plated strand cable.