Development of a 5T 2G HTS Magnet With a 20-cm-Diameter Bore

REBCO coated conductors known as second-generation (2G) high-temperature superconductor are expected to show high performance in superconducting applications because of their high mechanical strength and high current density in a magnetic field. Recently, there have been reports about fabricating impregnated REBCO coils. However, more characteristic data of REBCO coils with larger diameters are required in order to apply these conductors to practical superconducting applications. In this work, we fabricated a cryo-cooled high-temperature superconducting magnet, which was composed of 24 pancake coils with an inner diameter of 260 mm, using REBCO coated conductors. The total length of REBCO coated conductors was approximately 7.2 km. These conductors were laminated with a copper stabilizer and were fabricated by Fujikura Ltd. using ion-beam-assisted deposition and pulsed laser deposition methods. Before fabricating the magnet, all pancake coils were evaluated their V - I characteristics in liquid nitrogen, in order to confirm the characteristics without degradation. After the fabrication, the magnet was cooled down to 24 K by a Gifford-McMahon cryocooler. We excited the magnet up to 5 T, successfully.