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

Abstract

Within the framework of the R&D studies for the International Thermonuclear ExperimentalReactor (ITER) project, the first full size NbTi conductor sample was fabricatedindustrially 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 parallelstraight bars of conductor, connected at the bottom through a joint designedaccording to the CEA twin-box concept. The two conductor legs are identical exceptfor the use of different strands: a nickel plated NbTi strand with a pure coppermatrix in one leg, and a bare NbTi strand with a copper matrix and internal CuNibarrier in the other leg. The two conductors and the joint were extensively testedas regards DC and AC properties. This paper reports on the test results andanalysis, stressing the differences between the two conductor legs and discussing theimpact 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 ITERrequirements, neither conductor could reach its current sharing temperature at relevantITER currents, due to instabilities. Although the drop in temperature is slightfor the CuNi strand cable, it is more significant for the Ni plated strand cable.