Thermal conductivity and contraction of single and fifty-stacked 2G HTS tapes for the design of a superconducting fusion magnet

Abstract

We measured the thermal conductivity, $\kappa \left(T\right)$, of the single GdBa₂Cu₃O${}_{7-\delta }$ coated conductor (GdBCO-CC) tape and a bundled sample prepared by soldering fifty GdBCO-CC tapes, to design the thermal stability of a next high-temperature superconducting fusion magnet. A low-temperature peak for $\kappa \left(T\right)$ was observed for the single GdBCO-CC tape at 28.6 K. A simple heat-flow model for the layered sample demonstrated that the applied heat flowed mainly through the high purity metal such as the Cu and Ag-stabilizing layers. The $\kappa \left(T\right)$ of the bundled sample was similar to that of the single tape, suggesting that the contribution of the soldering layers to the heat flow was negligible and the $\kappa \left(T\right)$ of fifty or more bundled samples can be estimated using the $\kappa \left(T\right)$ of the single tape. We also measured the thermal contraction of the single tape along the length and of the fifty-stacked tape along the stacking direction, and then found that the stacking structure caused the large shrinkage along the stacking direction, which should be useful to optimize the structure of magnet at the operating low-temperature.