Stability criteria for cable-in-conduit superconducting cables for steady or slow pulse operation

In the design of CIC conductors using NbTi or Nb₃Sn strands cooled with supercritical He, the choice of stability criteria for near steady state operation presents a problem. The disturbances are small, under 10 mJ/cm³of cable material, too small for design significance. The main parameters affected by the choice of stability criteria are temperature margin and Cu:nonCu ratio, both of which strongly affect cable cost and overall current density. Methods quantifying the copper required for stability have been elementary, mostly using cryogenic stability (the well-cooled condition). Recent experimental and analytical work on the electric field achieved before quench Eq suggest a more exact method. Cable quench is modeled by a simple stability simulation, including copper conduction and the superconducting transition. A heat transfer coefficient is derived from ITER model coil data. As an example it is applied to conductor design for the ITER fusion reactor magnets.