An efficient approach for superconducting joint of YBCO coated conductors

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.

Section: Introductionmentioning

confidence: 99%

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

Wentao

Ming

Han

et al. 2023

“…Both high joint I c (I cj ) and low joint resistance (R j ) are required for a superconducting joint. Over the past decade, significant progress has been made in superconducting joint technology for HTS tapes/wires [11][12][13][14][15][16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Angular dependence of resistance and critical current of a Bi-2223 superconducting joint

Takeda,

Nishijima,

Nakai

et al. 2023

Low resistance and high critical current are prerequisites for superconducting joints used in persistent-mode magnets. Herein, we use a joint resistance evaluation system, previously developed by us, to systematically evaluate the angular dependence of resistance and critical current of a Bi-2223 superconducting joint in a closed-loop sample. The current decay is measured by rotating the sample incrementally. The time dependence of the loop current is evaluated at 4 K, 0.15–0.28 T, and magnetic field angles ranging from 90° to 0, wherein 90° corresponds to the direction parallel to the tape surface. The results suggest that the resistance and critical current of the joint depend on the angle of the magnetic field. The evaluated critical current increases as the angle increases. The angular dependence of resistance can be divided into three regions: low-resistance, transition, and high-resistance regions. The low-resistance region exists at high angles close to 90°. In this region, the decay of the loop current is small, and the persistent current continues to flow. Furthermore, the joint resistance is less than 1.4 × 10−13 Ω. In the transition region, the joint resistance significantly increases by three orders of magnitude with sample rotation. This significant increase is attributed to an increase in the perpendicular component of the magnetic field, which decreases the critical current of the joint. At lower angles, the joint resistance remains high, ranging from 10−11 to 10−10 Ω. A significant decay in the loop current is observed in the high-resistance region. Based on these findings, we conclude that the design of a persistent-mode magnet must consider not only the magnitude but also the direction of the magnetic field applied to superconducting joints.

“…Researchers have reported various joint techniques for REBCO CC tapes, broadly categorized as superconducting or non-superconducting (resistive) joints. Superconducting joints involve the direct connection of REBCO superconducting layers at high temperatures in a vacuum environment, resulting in almost zero joint resistance (R j ), making it ideal for superconducting device applications [4][5][6][7][8][9]. The diffusion bonding of non-superconducting Ag layers in CC tapes can be created through high-temperature heat treatment and additional oxygenation annealing to restore critical current (I c ).…”

Section: Introductionmentioning

confidence: 99%

Performance characteristics of REBCO coated conductor joints fabricated by flux-free hybrid welding

Nisay,

Shin

2023

Recently, the joining of rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes using ultrasonic welding (UW) has demonstrated outstanding potential in the in-line fabrication of longer tapes required for superconducting device applications. The UW method can produce CC joints by applying ultrasonic vibration in less than one second, and hybrid welding (HW) has been adopted to improve further the joint resistance (Rj) and electromechanical properties of the UW CC joints. However, conventional methods for preparing the HW and soldered CC joints involve applying solder flux to remove the oxide film, which can cause corrosion to the surface of the CC tapes and affect the joint's lifespan during device operation. Therefore, this study aims to fabricate a robust HW CC joint of pre-solder insertion without solder flux and compare its joint strength and electromechanical properties with the traditional cases with the solder flux. While similar Rj can be obtained from both cases of HW CC joints, the flux-free HW CC joint has slightly higher joint strength and superior adhesive characteristics than those with flux. The difference in fracture mechanisms after lap-shear and T-peel tests between flux-free HW and with flux was extensively discussed. Additionally, the study investigates the correlation between a decrease in Rj with longer joint length in differently stabilized and processed CC tapes for flux-free HW. Overall, this study demonstrated that the flux-free HW method could efficiently produce robust CC joints with a lesser risk of corrosion and enhanced joint characteristics.