Superconducting joint of REBCO wires for MRI magnet

Abstract

A high temperature superconducting wire (HTS wire) is promising for various superconducting magnet applications because it operates at a higher temperature than a low temperature superconducting wire (LTS wire) is. Particularly, a MRI magnet using the HTS wires (HTS-MRI magnet) is expected to obtain light-weight, compact and low operating cost compared to a LTS-MRI magnet. The MRI magnets are generally operated by a persistent current mode. A magnet of the persistent current mode consists of multiple superconducting magnets and persistent current switch (PCS) that connects with superconducting joints. However, the superconducting joint of the HTS wires has not been realized stably at this time. We have developed a superconducting joint by using a commercial REBCO wire. The HTS-MRI magnet requires that resistivity of less than 10−12 ohm and current capacity of more than 100 A is achieved by a direct-joint between superconducting layers of the two REBCO wires. Moreover, measurement equipment for low joint resistivity was prepared as measuring the decay of the magnetic field in the one-turn loop. In our R&D, the joint resistance and the critical current were achieved with 155 A and 5.3×10−13Ω.