Stability and design criterion for cable-in-conduit-conductors with a broad transition to normal state

Stability criterion in cable-in-conduit conductors (CICC) is often associated with heat removal rate higher than heat generated in the normal zone, which requires low current density in the strands. We show that this criterion is not a mandatory requirement for serviceability of CICC and that CICC may work reliably at higher current densities. In conditions of limited and well defined perturbations, sufficient stability is provided not by a large amount of copper and high transient heat transfer, but by a smooth transition to the normal state and easy current redistribution. A strand parameter space in terms of Ic and N-value meeting CICC requirements for stability, limited heat generation, and minimum temperature margin is proposed and discussed. The theory predictions are compared with known experimental data on CICC.