Fabrication, microstructure and persistent current measurement of an intermediate grown superconducting (iGS) joint between REBCO-coated conductors

Abstract

A superconducting joint technology used for high-temperature superconductors (HTS) is the key for enabling persistent operation of HTS magnets. In the present work, we have succeeded in developing a superconducting joint between REBCO-coated conductors (CCs) using a joint strap with a microcrystalline GdBCO precursor intermediate layer. Heat treatment and oxygen annealing, with a total processing time of less than 1 d, grows a biaxially-textured intermediate layer to connect the GdBCO layers in the CCs. Microstructure observation of a part of the joint cross-section with SEM and TEM showed that the intermediate layer and the GdBCO layers in the conductors were atomically connected. An electron backscatter diffraction result showed that both the c- and a-axis misorientations among the GdBCO layers of the joined conductor and the GdBCO layer of the joint strap were about less than 5°. This intermediate grown superconducting joint gives a critical current of >100 A at 77 K in a self-field. A critical current of a joint at 4.2 K in a self-field is seven times higher than that at 77 K. The persistent field decay of a small double pancake coil, terminated with this joint, showed a joint resistance in the range of <3 × 10−12 Ω to <5 × 10−13 Ω at 77 K in a self-field over three days, with an operating current of ∼10 A (∼14% of the calculated coil critical current). The results show a promising prospect of the joint to be used for persistent magnets such as NMR and MRI.

Sintering Nano-Silver Paste by Resistive Joule Heating Process for 2G HTS Tape Joints

“…The diffusion joint method requires a relatively high temperature and compression pressure to cause inter-diffusion at the joint, such as Cu or Ag of the protective layer of 2G HTS tape, with the specific resistance of about 0.067 µΩ•cm 2 [13,14]. The superconducting joint method uses superconductive material to join the 2G HTS tapes, with specific resistance of <10 −6 µΩ•cm 2 [15][16][17][18][19]. Even though the superconducting joint method shows the lowest specific resistance at the joint, the retention superconducting properties are unstable after the high treatment temperature (>600 • C), which may cause damage of the epitaxy microstructure and oxygen stoichiometry [20,21].…”

Thermal Cycling of (RE)BCO-Based Superconducting Tapes Joined by Lead-Free Solders

“…As there is no joint concept meeting all the requirements at the same time, multiple solutions are currently developed in parallel. Examples of concepts are variations of (1) different geometries: overlapped ( Table 1 ), butt [ 3 ], and bridged [ 4 ]; (2) different joining techniques: soldered joint ( Table 1 ), ultrasonic welded joint ([ 2 , 5 ]), inserted mechanical lap joint [ 5 , 6 ], diffusion joints [ 7 ], and (3) different resistivity: resistive or superconducting [ 8 , 9 ].…”

The Underlying Mechanism of Faster Current Attenuation of HTS Magnet in Persistent Current Mode Subject to the Traveling Magnetic Fields

“…Although the current will gradually decrease in the closed-loop circuit under the static condition due to the joint resistance, the decay rate is within the permitted range [7]. Furthermore, with the development of the technology of superconducting joint, the HTS magnet in persistent current mode will present superior performance [8].…”