Stability and thermal equilibrium in cable-in-conduit conductors

The stability of modern superconductors depends not only on the cooling and the amount of copper in the cross section of the strands but also on the smoothness of the transition from the superconducting into the normal state. Frequently the latter factor is much more important than the cooling and the copper content. Superconductors with a broad transition are more stable and easier to control than the superconductors with a sharp transition, although the price for better stability might be somewhat lower operating current. The paper gives thermal equilibrium equations and stability criteria against small perturbations and determines the ultimate current that could be reached by a cable-in-conduit conductors depending on operating conditions. The effects of various factors (e.g., magnetic field profile, mass flow and smoothness of the transition to normal state) on the thermal equilibrium and ultimate current are studied and discussed