Measurement of Persistent Current in a Gd123 Coil With a Superconducting Joint Fabricated by the CJMB Method

Recently, we have proposed the concept of a crystalline joint by melted bulk (CJMB) for making a superconducting connection between GdBa
₂
Cu
₃
O
_7-δ
(Gd123)-coated conductors (wire) using a wire-bulk-wire structure. In a model experiment, a joint between a Gd123-coated conductor and large piece of Y123 bulk (wire-bulk) as one-half of a joint was demonstrated, resulting in a superconducting joint with a critical current of 10 A at 77 K, and a high tensile strength greater than 100 MPa. In this study, a joint between coated conductors in a wire-bulk-wire structure was constructed using a Yb123 sheet fabricated from bulk material. As a result of using the CJMB method, we successfully fabricated a superconducting joint over the short time of less than 1 day (including joint formation and oxygen annealing). A persistent current coil having a superconducting joint was fabricated using the CJMB method. Its resistance was estimated from the current decay rate of the coil, to have a low value not exceeding 10
^-10
Ω after one day following the external power cutoff.