Test results of a Nb₃Al/Nb₃Sn subscale magnet for accelerator application

The High Energy Accelerator Research Organization (KEK) has been developing a Nb₃Al and Nb₃Sn subscale magnet to establish the technology for a high-field accelerator magnet. The development goals are a feasibility demonstration for a Nb₃Al cable and the technology acquisition of magnet fabrication with Nb₃Al superconductors. KEK developed two double-pancake racetrack coils with Rutherford-type cables composed of 28 Nb₃Al wires processed by rapid heating, quenching, and transformation in collaboration with the National Institute for Materials Science and the Fermi National Accelerator Laboratory. The magnet was fabricated to efficiently generate a high magnetic field in a minimum-gap common-coil configuration with two Nb₃Al coils sandwiched between two Nb₃Sn coils produced by the Lawrence Berkeley National Laboratory. A shell-based structure and a 'bladder and key' technique have been used for adjusting coil prestress during both the magnet assembly and the cool down. In the first excitation test of the magnet at 4.5 K performed in June 2014, the highest quench current of the Nb₃Sn coil, i.e., 9667 A, was reached at 40 A/s corresponding to 9.0 T in the Nb₃Sn coil and 8.2 T in the Nb₃Al coil. The quench characteristics of the magnet were studied