Masashi Haraguchi

Characteristics of Impregnated Pancake Coils Fabricated Using REBCO Coated Conductors

REBCO coated conductors are expected high performance in superconducting applications because of their high current density and high mechanical strength. However, in order to use these conductors in superconducting applications, a technique is required for fabricating impregnated REBCO coils without degradation.In this work, we fabricated six pancake coils without degradation using wounded REBCO coated conductors. These conductors were laminated with a copper tape as a stabilizer, and were fabricated by the IBAD/PLD method. In addition, we evaluated the V-I characteristics and n-values of the coils in liquid nitrogen and compared the calculated and measured values for the critical current (Tc) of the REBCO coated conductors. The measured Tc of the coils were in good agreement with the calculated ones. Furthermore, we fabricated a stacked coil using an approximately 190 m long REBCO coated conductor and evaluated the stability of the stacked coil at 77, 60 and 50 K under conduction-cooled condition. The thermal runaway current of the stacked coil was 166.4 A, and the central magnetic field was 1.27 T at 50 K.

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.

Evaluation of the Normal-Zone Propagation Characteristics of REBCO Coated Conductors With Laminated Cu Tape

The quench characteristics, particularly the normal-zone propagation and increase in hot-spot temperature, of REBa2Cu3Ox (REBCO) coated conductors are important issues for safe operation in the superconducting applications. Although experimental data on the quench characteristics of REBCO coated conductors have been reported only limited data is available specifically on REBCO coated conductors laminated with Cu tape of thickness no less than 0.1 mm, which are expected to be used for high-current operation in future superconducting applications. Here we reported experimental measurements of the normal-zone propagation velocity (NZPV) in REBCO coated conductors laminated with Cu tape of 0.1 mm thickness at 77, 65 and 50 K in a background magnetic field. We also compared these results with the NZPV at 77 K of REBCO coated conductors laminated with Cu stabilizer tape of thickness 0.05 and 0.3 mm.

Evaluation of a 426 kJ Cryocooled Magnet and a Model Magnet With REBCO Coated Conductors

REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors are expected to show high performance for superconducting applications because of their high current density and high mechanical strength. Fujikura has developed REBCO coated conductor over 570 A/cm width at 77 K, self field with over 800 m length. In addition, we have succeeded in developing a 5 T cryocooled REBCO magnet with a stored energy of 426 kJ. The magnet is composed of 24 pancake coils with an inner diameter of 260 mm, and the total length of the REBCO coated conductors is approximately 7.2 km. We confirmed that the REBCO magnet could be excited up to 5 T for 720 min 9 months after the fabrication of the magnet. It is important to validate the long-term operation test results of the REBCO magnets with larger diameters in order to use these conductors in practical superconducting applications. On the other hand, we have fabricated and evaluated a model magnet before we fabricated a 426 kJ cryocooled magnet. The model magnet is composed of 6 REBCO pancake coils and 18 “dummy coils” with an inner diameter of 260 mm and an outer diameter of 515 mm. The model magnet is about the same size and shape as the 426 kJ cryocooled magnet. We have confirmed that the calculated critical current (Ic) of the top pancake coil of the model magnet was in good agreement with the measured coil Ic from 30 to 77 K under the conduction-cooled conditions. In addition, we have evaluated the thermal runaway behavior of the model magnet under the conduction-cooled conditions. As a result, we have confirmed that the model magnet with a 0.3-mm-thick copper stabilizer had sufficient time to ramp down without degradation at 361 A transport current after the detected normal transition.