Development of High Strength and High RRR Aluminum-Stabilizer for Superconducting Cable in CEPC Detector Magnet

For the development of a large-aperture superconducting detector magnet in circular electron-positron collider (CEPC), super-conducting cables consisting of Nb-Ti/Cu wires and aluminum stabilizer are essential in both handling large electromagnetic forces during normal operation and redistributing the operation current of tens of kiloampere in case of a quench. High-purity aluminum stabilizer offers extremely high residual resistivity ratio (RRR) for quench protections, however, is too ductile to withstand huge Lorentz forces. Doping technology have been studied in detail in this paper to improve the yield strength of 4N8-aluminium (99.998%) while minimizing the reduction of RRR. All aluminum-alloy samples are characterized by a GM cryocooler for the measurement of RRR and by the standard tensile test facility for the measurement of 0.2% yield strength. It is found that by doping in Ni-0.025% Be-0.025%, annealing at 430 °C, cold-working hardening (∼21%), and curing at 130 °C for 15 h, the resultant aluminum alloy obtains an Rp0.2 of 75 MPa at room temperature and a RRR of 417, meeting the basic design requirements of the superconducting detector magnet for CEPC.