Parametric studies of subsize NbTi cable-in-conduit superconductors for ITER-FEAT

A parametric study of the ac loss behavior and the stability of 3 NbTi subsize cable-in-conduit conductors has been performed in the SULTAN test facility. Two of the conductors are distinguished only by the SnAg and the Ni coating of the strands. The effective transverse resistance in the SnAg conductor is considerably lower than that found for the conductor with Ni coated strands. Hence, the coupling loss in the SnAg coated conductor is considerably higher than that in the Ni coated conductor. Cyclic loading of the conductor reduces the coupling loss in the SnAg coated conductor, whereas the ac loss of the Ni coated conductor is unchanged. The stability of the conductors has been found to be closely related to the ac loss. Due to the smaller ac loss in the Ni coated conductor the minimum field integral of (dB/dt)²dt required to initiate a quench is considerably larger than that for the SnAg coated conductor.