Superconducting joint fabrication for HTS second generation GdBCO/YBCO tapes

Superconducting joint is crucial for second generation high-temperature superconducting (2G HTS) closed-loop coils that work in persistent current mode (PCM) operation. Here, we report an efficient approach for superconducting joint of YBCO coated conductors (CCs). The YBCO layer was etched to from some microchannels, which serve as oxygen diffusion paths during oxygenation annealing, to accelerate the recovery of critical current (I c) of the joined two YBCO layers. The I c of the superconducting joint is 118 A at 77 K with an optimized joining temperature and a short oxygenation annealing time (10 h), which is about 82% I c of the joined YBCO CCs. The persistent field decay of the closed-loop coil shows a joint resistance (R j) of less than 2.2×10-13 Ω at 77 K. Two YBCO films epitaxially grown along the c-axis diffuse into each other at the interface and form a dense joining, enabling superconducting current path. This superconducting joint technique can promote the achievement of the PCM operation in 2G HTS magnet applications, such as magnetic resonance imaging and nuclear magnetic resonance.

Section: Methodsmentioning

confidence: 99%

An efficient approach for superconducting joint of YBCO coated conductors

Huang¹,

Shang²,

Xie³

et al. 2022

“…One is a non-superconducting joint, including a soldering joint using low-melting-point solder materials [8,9] and a diffusion joint by Ag diffusion at above 400 • C in O 2 atmosphere [10,11] as well as a welding joint by an ultrasonic weldsolder hybrid method [12,13]. The other is a superconducting joint represented by connecting REBCO superconducting layers directly through high-temperature melting diffusion [14,15] and joining via an intermediate layer deposited on a superconducting layer of virgin tape [16,17]. As a typical nonsuperconducting joint, soldering is the most commonly used welding technology for REBCO tapes due to its simple process, good reproducibility and convenient site construction.…”

Section: Introductionmentioning

confidence: 99%

Low-resistance joints for YBCO-coated conductors with Ag nanoparticle paste

Wentao

Ming

Han

et al. 2023

Due to the limited available piece length of YBCO coated conductors (i.e., tapes or wires) and the different requirements for magnetic field, joint is inevitable for manufacturing high temperature superconducting magnets. In this work, a sintering nano silver process was developed and used to connect YBCO tapes stabilized by silver layer by low temperature and short time sintering of Ag nanoparticle paste. The thermodynamic characteristics of Ag nanoparticle paste were explored by a TG/DSC setup. The effect of sintering temperature, mechanical pressure and lapped length on microstructures and electrical properties of joint were comprehensively investigated. It is found that the pre-volatilization of low boiling point solvent in the paste is beneficial to improve the densification of sintered structure, thus contribute to increasing the critical current Ic of joint. With increasing the sintering temperature, Ic of joint is close to that of the virgin tape and joint resistance experiences a small fluctuation, but joint connectivity is enhanced. As the temperature reaches 205℃, Ic decreases to 84% of the virgin tape and joint resistance increases obviously. In addition, axial tension strength at room temperature has been improved with the increase of mechanical pressure, while the resistance has not demonstrated distinct variation. Considering electromechanical properties, the optimal joining process is determined as sintering at 180℃ and 30 MPa for 10 min. The joint by this technology possesses closely connected interface and well sintered nano silver microstructure with pores. By further extending lapped length, YBCO joint resistivity as low as ~10.56 nΩ.cm2 has been obtained, which is around a quarter of that of soldering joint, and the process is much easier than that of silver diffusion joint.

“…Superconducting magnets with the persistent current mode (PCM) are essential for magnetic resonance imaging (MRI) 2G-HTS CC superconducting joint technology for real commercial high-temperature superconducting closed coils [7]. In order to circumvent the intricacies associated with fabricating superconducting joints, researchers have embarked upon an exploration for an alternative structural configuration that obviates the necessity for such joints, thereby ensuring reliable PCM operation of HTS magnets [6].…”

Section: Introductionmentioning

confidence: 99%

A novel joint-less coil: promising unprecedented magnetic field stability to solve the persistent current mode issue in 2G-HTS magnet application

Dong,

Huang,

Wang

et al. 2023

Closed coils fabricated using second generation high temperature superconducting (2G-HTS) coated conductors (CCs) are promising for superconducting magnets, which operating in persistent current mode (PCM) such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems. However, the fabrication and application of superconducting joints for 2G-HTS CCs still pose a significant challenge. This paper reports a PCM joint-less 2G-HTS coil for capturing magnetic fields, which is called ‘Four Pancake Coil (FPC)’. A novel winding method was developed to form four pancake structure and effectively solved the closed-loop problem of 2G-HTS magnets. Meanwhile, the FPCs generated a 70.4 mT central magnetic field at 77 K and lasted for 57 d with a magnetic field drift rate of only 0.065 ppm h−1, which can satisfy the requirements of MRI magnets. In addition to the closed-loop characteristics of the FPC, the stacked magnet also provides expandability and ease of maintenance exchange. These advantages make it highly promising for the development of closed-loop 2G-HTS magnets.