New Findings on Cu-Ag Wire for the Pulsed High Field Magnet

Non-destructive pulsed magnet is the most important tool for a precise measurement under very high magnetic field. Generating high magnetic field, however, has been hard task because the magnet is destroyed due to considerable Maxwell stress. The stress reaches about 2 GPa in the field of 70 Tesla(T). The simplest solution for generating high field non-destructively is making a coil by use of the wire having higher strength. The Cu-Ag wire has been one of the best candidate for the coil-wire because the wire has the tensile strength of about 1.1 GPa and the conductivity of about 80% of pure copper. By using the wire, we succeeded in generating a field of 85.8 T in 2011 by mono coil system. The coil-wire of the same bobbin generated the 85 T-class field many times, but the wire of another bobbin could not reach to the same class field. The best wire could not be reproduced although we continued to produce wires with similar physical properties. There were many wires having the same strength and conductivity as to the best wire but nothing could generate the field exceeding 80 T. This would be a mystery because the maximum field mainly depends on the tensile strength of the wire. Our efforts to reproduce the best wire were in vain. 10 years have passed since it became mystery.<br/>To solve the mystery, we firstly classified the wires into good ones and bad ones. This classification indicated clearly that the quality of the wire depends on the manufacturing process, especially drawing one. In November 2021, we tested a wire regarded as an ideal combination of manufacturing process. The result was satisfactory. We succeeded in generating a magnetic field of 85.97 T completely non-destructively, breaking the previous record in 2011. The mystery of Cu-Ag wire was solved. The key for solving the mystery lays in the manufacturing process, especially drawing one. Based on these results, we are producing wires that have undergone the ideal manufacturing process to generate the 85 T-class magnetic fields stably. After reproducing the best wire, we have succeeded in making the 85 T-class fields repeatedely. Our progress in the wire production will be presented.