Quench Characteristics of an NbTi CICC With Non-Uniform Current Distribution

The effect of non-uniform current distribution (NUCD) on stability and quench characteristics of an NbTi/Cu cable-in-conduit conductor (CICC) with non-insulated or bare strands has been investigated by artificially introducing NUCD among the strands using a sophisticated current feeder system with thin-film resistive heaters. The stability margin or minimum quench energy (MQE) has been found to decrease significantly, especially in the transition region between so-called well-cooled and ill-cooled regions, due to the introduction of NUCD. The experimental results of stability margin with uniform current distributions have been compared with numerical calculations using the 1-D finite element code GANDALF, whereas the non-uniform current distribution cases have been treated by another code developed by the authors, which models the last two twisting stage of the conductor with uniform contact resistances between sub-cables. The numerical calculation results also simulate the similar behaviors as found in experiments. The quench propagation velocities deduced from voltage tap signals are also discussed.