Effect of External Heat Input on Stability of Conduction Cooled HTS Coils

Stability crisis develops in conduction cooled magnets (CCM) if the cooling length exceeds a critical value L*, brought by the strong temperature dependence of the index loss. In practical cases, windings are often subject to an additional thermal input (e.g., from joints, suspension etc.) superimposed on the index loss, which reduces stable parametric space and affects the design criteria. Analysis is presented of the effect of external heat on coil stability for the cases of uniform and localized heat sources. Dimensionless limiting criteria are obtained which define the design margin for CCM with an external thermal input; influence of the input location within the coil is analyzed. Minimum quench energies for conduction-cooled windings are determined by numerical modeling. The specifics of quench development from a localized disturbance in CCM are described.