FEM Modeling of Current Sharing in Tape Stack Cables; Influence of ICR, ITR, Defect Number, and Thermal Boundary Conditions

This research explored current sharing and quench evolution in rare-earth barium copper oxide (ReBCO) based superconducting cables intended for use in the High Energy Physics (HEP) accelerator magnets. We used 3D finite element simulation studies of three-tape stack (carpet stack) cables. A given number of defects per tape length was assumed, along with specified electrical and thermal resistance values within and between tapes. Previous studies with a single defect in a three-tape stack cable showed that in addition to intra and inter-tape electrical resistivity, values of thermal resistivity and thermal boundary conditions were needed to determine a current sharing level. Here we defined the current sharing level as CSR = $I_{{cable}\_{defect}}$/$I_{{cable}\_{no}\_{defect}}$ just before thermal runaway. The current sharing level varied with inter-strand contact resistance (ICR), inter-strand thermal resistance (ITR), and thermal boundary conditions. As one example a three-tape stack cable with an interlayer electrical contact efficiency, η = 5400 μΩ*cm², an interlayer thermal contact efficiency, ω = 5.54 K*m²/W, liquid helium cooling on the outer surface of the cable, and one defect (set at 10% ${I}_{{c}}$) in the central tape had a current sharing value of 0.91 (i.e., the ability to achieve 95% of nominal {defect free} ${I}_{{c,cable}}$ before a quench). Increasing the number of defects per unit length in the central tape reduced the achievable I/${I\neg}_{{c,cable}}\,$from 0.95 to 0.87.