Approaching the Best Wire for Non-Destructive Pulsed Magnet
Kindo Group
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 the coil-wire strong. Cu-Ag wire has been 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 copper. By using the wire, we succeeded in generating a field of 85.8 T in 2011. The best wire, unfortunately, was an accidental success. The wire was not reproduced though we continued to produce wires with similar physical properties. There were many wires having the same strength and conductivity but nothing could generate the field exceeding 80 T. This would be a mystery because the maximum field depends on the tensile strength of the wire mainly. Our efforts to reproduce the best wire were in vain. 10 years have passed since it became mystery.
To solve the mystery, we firstly classified the wire 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. Figure 1 shows the waveform of the magnetic field generated using this wire. There was no distortion of the waveform from the start to the end of the magnetic field generation, and we succeeded in generating a magnetic field of 85.97 T completely non-destructively, breaking the previous record.
Fig. 1. The shape of completely non-destructive magnetic field of 85.97 Tesla.
The mystery of Cu-Ag wire was solved. The mystery lay in the manufacturing process, especially drawing one. Based on these results, we will develop wires that have undergone the ideal manufacturing process to generate even higher magnetic fields, and will provide a 100 T fields non-destructively contributing the joint research program.