Valery Petrykin

REBa₂Cu₃O_7-δ (REBCO, RE: rare earth element) coated conductors (CCs) have superior in-field performance compared to low-temperature superconductors and Bi-based superconductors, however, due to its crystal structure, REBCO CCs exhibit significant anisotropy, i.e., critical current density (J_c) is generally high for B // a-b and low for B // c-axis. Isotropic angular dependence would be ideal for such applications as magnets and coils, because anisotropic angular dependence will hinder current carrying capability in the winding and also make it more difficult for quench protection. To realize an isotropic angular dependence, artificial pinning centers (APCs), such as BaMO₃ (M: Metal), have been introduced to enhance J_c for B // c-axis. However, it is still challenging to enhance pinning over all angles. In this study, we investigated a possible way to improve the angular dependence of REBCO CCs by applying face-to-face double-stacked (FFDS) configuration. Our previous study showed that FFDS interface resistivity is around 50 nΩcm² at 77 K, enabling sufficient current sharing with small enough dissipation in cases of local J_c degradation in one side of the REBCO CC. In addition, Based on this finding, we examined whether to compensate for the angular dependence of the REBCO CCs. We made a FFDS CC by combining two REBCO CCs with different angular dependences, i.e., YBa₂Cu₃O_7-δ (YBCO) CC with low J_c for B // c-axis and EuBa₂Cu₃O_7-δ (EuBCO) with BaHfO₃ (BHO) doping CC which has high J_c for B // c-axis. Current–voltage (I-V) measurements at various angles confirmed that FFDS CCs facilitate current sharing under applied fields. As a result, we analyze the I-V characteristics by applying an equivalent circuit model and confirmed the more isotropic angle dependence of I_c properties as designed. In conclusion, the FFDS configuration provides a practical means to current-carrying performance compared to the original CC strands and presents a practical method for tailoring REBCO CCs angular dependence with flexibility.

During the fabrication of commercial REBa₂Cu₃O_7-x (REBCO; RE: rare-earth element)-coated conductors (CCs), inhomogeneities with low critical current (I_c) are occasionally introduced, which may result in electromagnetic instability, particularly at low temperatures. To mitigate the degradation of the current carrying capabiity caused by these defects, we developed long face-to-face double-stacked (FFDS) CCs via reel-to-reel solder bonding process. Previously, we successfully fabricated 400-m-long FFDS CCs via this process and investigated their mechanical properties. However, the current transport properties are still unclear. In this study, we investigated the interfacial resistivity of the FFDS CCs made by the continuous soldering process, and it was confirmed that the joint resistivity is consistently between 40 to 50 nΩcm² where the joint distances were changed to 3.5, 5.0, and 11.6 cm. In addition, the effect on the current carrying capability was also examined by using model samples in which we introduced artificial defects with almost 50% drop of local I_c. It has been demonstrated demonstrated that the transport current can be recovered at almost 85 to 90% of a defect-free CCs, with I_c nearly two times of the strand, thanks to the current sharing effect through the solder joints. Namely, the interface resistivity of 40–50 nΩcm² by our process was sufficiently small to obtain a current sharing effect and suppress the influence of the local inhomogeneity effectively.

In order to improve the mechanical and electromagnetic robustness of REBCO coated conductors (CCs) for their application in superconducting equipment, we have developed and characterized Face-to-Face Double Stack (FFDS) CCs by stacking the superconducting surfaces of two single superconducting CCs together. In this work, we were able to produce FFDS CCs with a single length of over 400 m. I _c characteristics were measured at different temperatures and magnetic fields, and 128.8 A/4 mm-w (70 K, 3 T) was achieved for FFDS with artificially pinned CCs. Furthermore, mechanical strength with critical bending diameter of 5 mm such as flatwise strength and twisting are also reported.

We investigate the field, angle and temperature dependence of the full-width critical current, I _c, of pulsed laser deposition-grown GdBa₂Cu₃O₇ coated conductors with and without additional 6 mol% BaSnO₃ (BSO) nanoparticles fabricated by SuperOx. The transport characteristics measured from 7 to 77 K and in applied magnetic fields of up to 6 T are complemented by scanning transmission electron microscopy. This combined approach allows for further insight into the vortex pinning mechanism and helps with understanding the enhancement in I _c. An exemplary scaling of the pinning force curves versus field at different temperatures confirms the additional contribution to pinning by the BSO nanoparticles. Through the temperature dependence of I _c, the weak and strong pinning contributions are determined: strong pinning dominates over almost the entire temperature range especially near the matching field of 1 T, where the largest enhancement in I _c is achieved.

Superconducting joints have been demanded to lengthen REBa ₂ Cu ₃ O _y -coated conductors for electrical power applications. In this study, we propose a new joint method for GdBa ₂ Cu ₃ O _y -coated conductors via crystallizing precursor films additionally deposited on the conductors. Two GdBa ₂ Cu ₃ O _y -coated conductors with precursor films were placed in a face-to-face manner in a furnace, then they were crystallized under mechanical pressure to joint them. A superconducting joint was achieved with a high critical temperature of 90.8 K. Microstructural observation by a transmission electron microscope revealed that there were only a few pores at the joint boundary without a secondary phase having c -axis-oriented GdBa ₂ Cu ₃ O _y .

There has been demand to lengthen superconducting joints of REBa ₂ Cu ₃ O _y coated conductors to realize magnet applications. In this work, jointed samples of GdBa ₂ Cu ₃ O _y coated conductors were prepared by crystallizing precursor films deposited by a pulsed laser deposition method under mechanical pressures, and influence of the pressures on superconducting and mechanical properties were investigated. While areal fraction and shearing stress of the joints were increased by increasing the pressure, superconducting properties were degraded. X-ray diffraction analysis indicated that the degradation was due to the formation of a secondary phase and decrease of oxygen contents in GdBa ₂ Cu ₃ O _y .

We present the preparation of a new architecture of coated conductor by Inkjet printing of low fluorine YBa2Cu3O7-x on top of SuperOx tape: CGO/LMO/IBAD-MgO/Y2O3/Al2O3/Hastelloy. A 5-layered multi-deposited, 475 nm thick YBCO film was structurally and magnetically characterized. A good texture was achieved using this combination of buffer layers, requiring only a 30 nm thin IBAD-MgO layer. The LF-YBCO CC reaches self-field critical current density values of JcGB~15.9 MA/cm2 (5 K), ~1.23 MA/cm2 (77 K) corresponding to an Ic(77K)=58.4 A/cm-width. Inkjet printing offers a flexible and cost effective method for YBCO deposition, allowing patterning of structures.

An industrial R&D programme is ongoing at SuperOx, aimed at improving 2G HTS wire performance in magnetic field. We introduce perovskite artificial pinning centres (APC) into the HTS layer matrix. In contrast to most studies described in the literature, we use the high rate production processing parameters and PLD equipment at SuperOx. This paper reports the results of Phase I of this programme. We fabricated 2G HTS wires by pulsed laser deposition of GdBCO films doped with 6%, 12% and 18% (molar) of BaSnO ₃ and 6% (molar) of BaZrO ₃ , and compared their performance with an undoped reference sample. The depositions were carried out at production growth rates of 375, 560 and 750 nm min ⁻¹ by varying laser pulse frequency. BaZrO ₃ and BaSnO ₃ formed columnar semi-coherent nanoinclusions in the GdBCO film matrix. The average transverse size of the nanocolumns was about 5 nm, and their volume density correlated with the dopant concentration. All doped samples exhibited much lower angular anisotropy of in-field critical current and higher lift-factors than the undoped sample. Samples containing 6% BaSnO ₃ and deposited at the lower growth rates, had higher I _c than the undoped sample in the entire temperature range, in a wide range of magnetic field ( B // c ). The sample containing 6% BaZrO ₃ had higher I _c than the undoped sample at 20 and 4.2 K. These results are an encouraging start of our programme, as they show a positive impact of APC introduced into 2G HTS wires fabricated at production throughput. Phase II work will be focussed on maximising the improvements in specific temperature and field conditions, as well as on the verification of reproducibility of the improvements in production wires.