Study on the Magnetic Properties of Metal Substrates at Low Temperature by Fabricated Compact SST

In recent years, a development of a high magnetic field magnet using a high temperature superconducting (HTS) wire has been advanced. On the other hand, we are planning to use the HTS wires for superconducting applications cooled by cryocooler. So, it is necessary to measure the temperature dependence of the magnetic properties of the metal substrates (Hastelloy, stainless steel and NiW) for HTS wire under conduction cooling conditions. We have been developing a single sheet tester (SST) that can evaluate the magnetic properties of electromagnetic steel sheets and other materials. However, since the size of an excitation coil in the conventional SST is large, it is difficult to install them in the conduction cooling system. In this study, we fabricated the compact SST and its measurement accuracy was compared with the conventional SST. The magnetic properties of metal substrates were measured at room temperature and liquid nitrogen temperature (77 K). As a result, although the measurement accuracy of the compact SST was slightly reduced by decreasing the coil size, we found that the error of the magnetic field homogeneity of the compact SST was within 2% at the center region of the 5 mm length. The magnetic properties of Hastelloy and stainless steel were almost unchanged at both room temperature and liquid nitrogen temperature. However, the magnetic properties of the NiW substrate changed significantly at liquid nitrogen temperature. The
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characteristics of the NiW substrate in the rolling and transverse directions were clearly different, and the iron loss increased significantly at liquid nitrogen temperature.