DC performance of subsize NbTi cable-in-conduit conductors

Five subsize NbTi cable-in-conduit conductors with parametric variations were fabricated and their DC performance was tested in the SULTAN facility. A comparison of the measured strand data and the cable performances clearly indicates that the current carrying capacity of the conductors is considerably reduced due to the self-field effect. This result reflects that because of the high transverse resistance the interstrand current sharing is not very efficient. Furthermore, the take-off electric field was found to decrease monotonously with increasing quench currents. In the case of large overall current densities, sudden take-offs occur before the critical current criterion (0.1 muV/cm) has been reached. The observed quench behavior is a consequence of the large contribution of the self-field to the total magnetic field, which leads to strongly enhanced electric fields in the strands on the high field side of the conductor. As soon as the heat generated in the peak field region exceeds the locally available cooling power a quench is initiated. Considering insulated strands and a uniform current distribution the quench behavior has been reproduced by simulations.