DC performances of ITER NbTi conductors: Models vs. measurements

Within the R&D program on the International Thermonuclear Experimental Reactor (ITER) Poloidal Field (PF) coils, a full size conductor sample was tested in the SULTAN facility (CRPP Villigen, Switzerland). This sample is composed of two straight ITER-like cable-in-conduit conductors, using the same NbTi strand. The two conductors are identical except that one leg has a cable containing steel wraps around the main subcables as in the ITER design, while the other has no wraps inside. The paper presents conductor DC test results compared to predictions given by various models developed within ITER-associated laboratories. These models aim to predict the DC behavior of the cable from the experimental performances of the single strand. They have to explain the observed voltage-current (V-I) or voltage-temperature (V-T) characteristics, including the thermal runaways. The lower experimental performances compared to all expectations have shown the necessity to revise the models and to introduce a possible uneven current distribution among the strands of the cables.