Improvement of Critical Current in Superconducting Joint Between Multi-Filamentary Bi2223 Tapes

Self Cite

A superconducting joint for multi-filamentary Bi2Sr2Ca2Cu3O10+δ (Bi2223) tape, which has applications in nuclear magnetic resonance and magnetic resonance imaging, has been developed based on incongruent melting and multi-junction methods. In this study, the critical current limit, optimal oxygen annealing conditions, and reproducibility of this joint are experimentally evaluated. The results indicate that the critical current limit of the joint at 77 K is determined by that of the tape. The critical current limit was estimated to be about 40 A. Additional oxygen annealing after heat treatment below 1143 K. appears to have no effect on the critical current, and that above 1153 K slightly increases the critical current. It is found that the multi-junction method effectively increases the reproducibility of obtaining a high critical current. To obtain a high critical current at 77 K, the highest temperature in the joint creation process should be lowered to near the incongruent melting temperature of Bi2223 (about 1133 K in air). Two Bi2223 coils, each with one joint (four junctions), were prepared and their persistent current at 77 K was tested. A persistent current of above 20 A was measured with a resistance of about 10 pΩ.

Section: Principles Of Efficient Joint Creation Methodsmentioning

confidence: 99%

“…A low resistance of below 10 −12 Ω was obtained under a persistent current of several amperes in a small Bi2223 coil. A high critical current of above 50 A at 77 K was recently achieved in a self-magnetic field using multiple junctions [2]. Figure 1 shows the image of the multi-junction structure of joint.…”

Section: Introductionmentioning

confidence: 98%

Resistance at 77 K of two Bi-2223 coils with superconducting joints prepared by incongruent melting

Kanazawa,

Sekine

2024

Self Cite

“…However, this method cannot be simply applied for Bi2223, because Bi2223 crystals incongruently melt and Bi2212 crystal and other impurity grains remain after solidification. A modified partial melt-solidification method using small heaters has been attempted to connect Bi2223 tapes, where a part of Bi2223 melts and both Bi2223 and Bi2212 crystals exist around the joint interface [8]. Although this method can produce BB joints by heating for a short time, the joint I c is slightly lower than the target value of our program.…”

Section: Difficulties With Superconducting Joints Connecting Hts Tapesmentioning

confidence: 97%

Superconducting joints for the 1.3 GHz persistent NMR magnet under JST-Mirai Program

Shimoyama

2023

Superconducting joint technologies connecting high-T c superconducting (HTS) tapes, such as REBCO-coated conductors and Bi2223 silver-sheathed tapes, have been developed for the fabrication of superconducting magnets generating 30.5 T with persistent current operation at 4.2 K under the JST-Mirai Program since 2017. These are indirect joints using a superconducting intermediate layer to join highly crystallized HTS layers of tapes. Thus far, high I c values of above 100 A at 77 K in the self-field have been achieved by both joints. These performances are sufficient for installation to the 30.5 T magnet, while efforts to further improve the reproducibility of high I c for joints connecting long-length HTS tapes have been continuously made. The current status of HTS joint technologies is summarized in this paper partly from the view point of material science.

“…For magnet applications operated in the persistentmode, I cj characteristics should be improved further. A recent study revealed that a self-field I cj at 77 K can be improved by optimizing the heat treatment condition or joining multiple positions [101].…”

Section: Bi-2223 Superconducting Joint Through the Incongruent Meltin...mentioning

confidence: 99%

Review of the temporal stability of the magnetic field for ultra-high field superconducting magnets with a particular focus on superconducting joints between HTS conductors

Takeda¹,

Maeda²,

Ohki³

et al. 2022

Superconducting magnets used in applications such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) require significant temporal magnetic field stability, which can be achieved when the MRI and NMR magnets are operated in the persistent current mode (persistent-mode) using superconducting joints. However, the ultra-high field MRI and NMR magnets are sometimes operated in the driven mode. Herein, we present an analysis of the temporal magnetic field drift and fluctuations observed for MRI and NMR magnets operating in the driven mode and an exploration of effective methods for stabilizing the temporal magnetic field fluctuations. In the last decade, substantial improvements have been achieved in superconducting joints between high-temperature superconductors (HTS). These superconducting joints enable the development of persistent-mode ultra-high field magnets using HTS coils. Therefore, we herein review the superconducting joint technology for HTS conductors and describe the results of the persistent-mode operation achieved by a medium-field NMR magnet using an HTS coil. Particularly, the cutting-edge progress achieved concerning HTS superconducting joints, including joining methods, superconducting properties, and future prospects, is highlighted along with the issues that need to be addressed.