Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) are essential for the proper design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer to the others. In the present work we have examined the critical surface for the current density, Jc(T,B,Theta), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd. (Japan), SuNAM Co., Ltd. (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 and 77 K and in magnetic field up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, θ = 0, 45 and 90°, in order to probe the angular anisotropy of Jc. In spite of the large variability of CCs’ performance, we show here that field and temperature dependences of Jc at a given angle can be reproduced using a scaling relation based only on three parameters. As a complement to this analysis, we present an overview of the electromechanical and thermal conduction properties of the CCs from the six manufacturers and we discuss the implications for the design of high field insert coils.

The authors acknowledge the financial support from the Swiss National Science Foundation (Grant N. PP00P2–14467 and 51NF40–144613). Research also supported by FP7 EuCARD-2 http://eucard2.web.cern.ch, Grant Agreement 312453.

Superconducting magnets are an essential part of achieving the goal of commercial fusion energy generation using a tokamak. The current state of the art fusion tokamaks use low temperature superconducting magnets. However, high temperature superconducting (RE)Ba₂Cu₃O_7-δ coated conductors show great promise as possible replacements for low temperature superconductors in future devices. We have used our bespoke probe for measuring the critical current versus strain and temperature [1] in our world-class 15 T split-pair horizontal magnet to assess the suitability of these conductors for use in fusion magnets. We will present our most recent results on the variation of critical current and upper critical field with temperature (4.2 K < T < 100 K), magnetic field (0 T < B < 15 T), angle (full 360⁰) and applied strain (-1.5 % < ε < +1 %).
References:

1. Sunwong, P., J.S. Higgins, and D.P. Hampshire, Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet. Review of Scientific Instruments, 2014. 85(6).
2. Sunwong, P., et al., The critical current density of grain boundary channels in polycrystalline HTS and LTS superconductors in magnetic fields. Superconductivity Science and Technology, 2013. 26: p. 095006.

This work is funded by EPSRC under grant EP/K504178/1.

It is well established that in-plane alignment is essential to realize high critical current density in coated conductors (CCs) because of grain connectivity. It is also relevant to realize thick film deposition for the superconducting layers to increase overall critical current. The value of in-plane alignment, Df, of the substrate template is typically around 3 to 4 degree. However, the requirement for the substrate alignment is not yet fully understood especially in thick film and its performance. In this study, we have investigated the influence of highly textured IBAD based template on the in-filed current transport properties in Gd₁Ba₂Cu₃O_7-d (GdBCO) CCs. As a result of improved selfepitaxy of the CeO₂ top layer, Df of the template can be reduced as low as 1.9 degree. We compared in-field critical currents of BaHfO₃ doped 1.5 um-thick PLD-GdBCO deposited on such highly textured substrate and standard one, i.e., Df is 3.5 degree. From the analysis of critical current as a function of external magnetic field and temperature, we found that normalized pinning force density curves are scaled on the same curve for both case, however, the maximum value has increased 15 to 20 % for the case of highly textured substrate. This indicates that the nano-structures of the GdBCO layer are hardly influenced by the substrates, whereas effective cross-section area can be improved because of the reduction of current blocking obstacles in the case of highly textured substrate. From SEM observation of the GdBCO surface, it has been also confirmed that outer-growth can be suppressed effectively by using the highly textured substrate. These results show that the improvement of substrate in-plane alignment is still important and effective even in the range of Df< 3 degree to enhance in-field current carrying capability of CCs. Note that, it is not originated from the well-known weak-link issue but the suppression of outer-growth in a thick film deposition for the superconducting layer.

This work is supported by the Ministry of Economy, Trade and Industry (METI) as the Project for Development of HTS Coiling Technology.

The research leading to these results have received funding from the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement n0. NMP-LA-2012-280432.

High critical current density (J_c) YBa₂Cu₃O₇ (YBCO) superconducting films have been grown on cube-textured metal tapes for the purpose of developing second generation (2G) superconducting wires for high temperature, high magnetic field applications. In the standard RABiTS approach, a biaxially crystal aligned YBCO layer is deposited on a Y₂O₃/YSZ/CeO₂ buffered Ni-W alloy tape.
2G superconducting wires become highly resistive when they are quenched, therefore, to manufacture reliable and safe HTS applications, it is necessary to use conducting (metal) layers with low resistivity such as Cu and Ag to attach to the 2G superconducting wires to stabilize and protect the wires from damage due to quenches. Presently, insulative oxides are used for the buffer layers, thus thick Ag and Cu layers are required to be deposited as the stabilizer layers on the YBCO layer. However, the high material and process costs for the Ag and Cu layers are one of the major obstacles for achieving low-cost 2G superconducting wires. Because the resistivity of pure Cu is much lower than that of the Ni-W alloy, use of a conductive buffer layer instead of the insulative ones combining with textured Cu tape, can release 2G superconducting wires from the expensive Ag and Cu stabilizer layers.
We prepared Nb-doped SrTiO₃ films on Ni-electroplated {100}<001> textured Cu tapes laminated with SUS316 and epitaxially grew YBCO layers on them. J_c of the YBCO layer on the Nb-STO/Ni/Cu/SUS316 was 2.6 MA/cm² at 77 K in self field. We believe that our new architecture will play an important role for realizing a low-cost 2G superconducting wire.

This research was supported by JST, ALCA.

It is important to reduce the effect of shielding current in the case of magnet applications of REBa₂Cu₃O_7-d (RE123) coated conductors (CCs) with high homogeneity and stability of magnetic field, such as Magnetic Resonance Imaging (MRI) and medical accelerator coils. For this purpose, it is well known in the low temperature superconducting magnet that the multi-filamentary structure is indispensable. In this study, we have been developing the laser scribing technique as a method of fabricating the multi-filamentary CCs and made up a reel-to-reel (RTR) laser scribing equipment using an excimer laser source (KrF 248 nm). This method is superior in controllability of a slot width and low damage to superconducting layer. By using this technique, we successfully produced multi-filamentary CCs having width less than 500 µm and achieved high uniformity ([standard deviation 𝜎 / Average of I_c] x 100 < 5%) of I_c distribution in the filaments. As a typical effect of the filamentary structure, it has confirmed that the time for reaching the steady state was drastically shortened. Concretely, it was shortened in 440 µm filament-specimens until 3 hours, whereas the period of finishing magnetic relaxation estimated about 116 days without partition. In the presentation, we will report the detail of fabricating process of multi-filamentary CCs and characterization results such as I-V curves, magneto-optical imaging, AC-losses and magnetic relaxations.

This work was supported by the Ministry of Economy, Trade and Industry (METI) as ‘Development of Fundamental Technologies for HTS Coils’.