Electromechanical Performance Study on Silver Diffusion Joints of REBCO Coated Conductors under Axial Tensile Stress

Developing closed-loop magnets that operate in persistent current mode (PCM) is crucial for achieving higher resolution and sensitivity in NMR and MRI devices. Here, we reported a new closed-loop multi-pancake (MP) HTS magnet operated in PCM based on a novel jointless winding method and superconducting joint of REBCO coated conductors (CCs), to the best of our knowledge. The in-field characteristics of the CC and the joint were investigated to determine the operating parameters of the magnet. A steady central field of the magnet reached ~408.4 mT at 77 K with an operating current of 16.5 A. The joint resistance was inferred from a higher excitation current of 17 A to be at least less than 2.5x10-10 Ω. Furthermore, although the Ic value of the joint was considerably lower than that of the CC at self-field, it could maintain similar comparable or even higher in-field Ic compared to the CC, which is immensely beneficial for magnet applications. This study provided some insights into the design and construction of the closed-loop MP magnets operating in PCM.

Section: Introductionmentioning

confidence: 99%

Development of a multi-pancake HTS magnet operated in persistent current mode based on superconducting joint of REBCO coated conductors

Huang,

Dong,

Wang

et al. 2024

“…By optimizing the connection process [11,24], the minimum R sj of the YBCO joint prepared by Ag diffusion welding can be as low as ∼10 nΩ cm 2 , which is much lower than that of the soldering joint. Wu et al [25] reported that the axial tensile stress of the joint was improved to that of the virgin level by alleviating the local stress concentration through a lamination process. In addition to soldering and Ag diffusion, ultrasonic welding can also be used to join REBCO tapes.…”

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.

“…Furthermore, the resistance at the Ag/REBCO interface was identified as the predominant source of the total joint resistivity [19]. Thus, the absence of resistive layers within the joint minimizes the metal resistance and interface contact resistance through the direct connection of Ag-protecting layers of CC tapes via diffusion joints, which can have an R j range of 4.9-10 nΩ cm 2 for YBCO CC joints and 23-60 nΩ cm 2 for GdBCO CC joints [5][6][7][20][21][22][23][24][25]. Watanabe et al have reported that higher R j in GdBCO CC than YBCO CC joint was caused by the reduction of oxygen at the GdBCO layer and the diffusion of Gd to the Ag layer [20].…”

Section: Introductionmentioning

confidence: 99%

“…The bending deformation of the coil windings also affected the properties of the CC joints. However, the electromechanical properties of Ag-stabilized REBCO CC joints under axial tension and bending have rarely been reported [24,25]; therefore, the electromechanical performance of these Ag-stabilized REBCO CC joints is necessary to be investigated.…”

Section: Introductionmentioning

confidence: 99%

Applicability of ultrasonic welding to Ag-stabilized REBCO CC joints and evaluation of their electromechanical properties

Nisay¹,

Diaz²

2022

Manufacturing a single long-length rare-earth barium copper oxide (REBCO) coated conductor (CC) tape with uniform critical current (Ic) is still a challenge; therefore, joining between multiple-length CC tapes is needed in the production of longer CC tapes for superconducting cables, coils, and magnets. Various joining techniques have been developed to achieve acceptably low joint resistance (Rj) with no Ic degradation and good electromechanical properties. The authors established ultrasonic welding (UW) and hybrid welding (HW) methods for joining Cu-stabilized CC tapes with different configurations. However, these methods have yet to be applied to Ag-stabilized CC tapes to produce compact joints and longer tapes during in-line production. This study used the UW and HW methods to fabricate Ag-stabilized CC joints to have low Rj without Ic degradation through a direct connection at the overlapped Ag layers between both CC tapes. Two CC tape samples with different thicknesses of ~2 µm and ~6 µm Ag stabilizers were supplied to produce UW and HW Ag-stabilized CC joints. These were compared with soldered CC joints fabricated by a mechanically controlled soldering method. In the case of UW, the design of experiment (DOE) using the Taguchi method was used to systematically determine the optimized weld parameter combination that yields a lower Rj without any Ic degradation. This study is a systematic attempt to evaluate the applicability of UW for solid-state joining between thin Ag layers, unlike the conventional joining of thick Cu stabilizers. Moreover, the electromechanical properties of differently processed Ag-stabilized REBCO CC joints were evaluated using both lap-shear and double-bending tests. As a result, the optimum UW parameter combinations were obtained to achieve Ag-stabilized CC joints. However, some variations were probably due to the differences in the production batch and thickness of the Ag layers. The UW Ag-stabilized CC joints showed superior joint characteristics and electromechanical properties compared to soldered CC joints. Good solid-state bonding of the Ag layers was observed through microscopic observation of the cross-section at the joint region of the UW CC joint. The joint characteristics and electromechanical properties of the UW Ag-stabilized CC joints can be further improved using the HW method.