To reduce the material cost in REBa₂Cu₃O_y (RE: rare earth elements, REBCO) coated conductors, we attempted to exchange the relatively high-cost metal substrate into iron of a common metal. The biaxially textured iron metal tape is generally {110} <001>. This texture is considered to be unsuitable for the (001) orientation growth of the buffer layers with a cubic structure to promote the growth of the biaxially-aligned REBCO because the surface lattice structure is a rectangle. We attempted to fabricate a calcia-stabilized zirconia (CSZ) buffer layer on the {110} <001> textured-iron tapes as a new-buffer layer. Then, the biaxially-aligned CSZ was first successful fabricated through the mismatched interface for iron tapes in the world. The YBa₂Cu₃O_y film deposited on the CeO₂ coated CSZ buffer later indicated superconductivity with T_C onset of 90K. However, the mechanism of the CSZ crystal alignment through the mismatched iron surface was not simple. Therefore, the crystal orientation and microstructure of the CSZ were analyzed using the X-ray diffraction and the transmission electron microscopy. As a result, it was found that the rigid relationship between CSZ and Fe at the interface was only one direction of CSZ<110> // Fe<100>. According to microstructure analyses, (111) oriented and (001) oriented grains were existed at the vicinity of interface at the beginning of CSZ growth. However, dominant orientation became (001) orientation as far distance from the interface. The almost orientation of CSZ surface became (001) orientation in 400nm thickness. Furthermore, anisotropic distortion of CSZ was observed, and it was considered that this distortion was due to rectangular atomic arrangement of Fe(110). We will discuss the biaxial alignment of CSZ on the basis of the results of the X-ray measurement and the microstructure analysis using a transmission electron microscopy.

A part of this work is supported by JST-ALCA, JAPAN.

Toyo Kohan Co., Ltd and Sumitomo Electric Industries, Ltd. have developed a complex metal substrate for YBCO oxide superconducting wire, which consists of a nickel (Ni) plating layer, a cold-rolled copper (Cu) foil and an austenitic stainless steel (ASS) thin plate.
First of all, Cu foil and ASS thin plate are bonded by the surface activated bonding method developed originally by Toyo Kohan. After cladding, the substrate is annealed in order to direct the crystal orientation of Cu surface to {001}<100>, and then a Ni layer is epitaxially formed on the biaxially textured Cu layer by electric plating.
So far, we have reported that we could obtain the clad substrate with a full width at the half maximum (FWHM) of Ni(111) phi scan of 4.5 degrees and successfully fabricated a more than 500 m long and 200mm width strip of the clad substrate.
Moreover, we tried to form CeO₂ film as the first buffer layer on the substrate by the sputter deposition method and could obtain CeO₂ layer having an improved crystal orientation. Furthermore, we especially focused upon investigating influence of configuration between a target and the Ni/Cu/SUS316L clad substrate on the crystal orientation. As a result, according to locations on the substrate, the CeO₂ film we obtained showed considerable improvement of the crystal orientation and the value of out-of-plane texture (Δω) showed around 2.5 degrees. On the other hand, the in-plane texture was not improved.
In addition to it, in order to elucidate the mechanism of CeO₂ film growth, we observed the interface of the CeO₂/Ni by TEM. At the interface, diffraction patterns of CeO₂ and Ni did not coincide exactly but showed a slight tilt. The difference was an angle of about 3.0 degrees and corresponded to the angle of out-of-plane texture in the CeO₂ film. In other words, it was assumed that the improvement caused at the initial sputtering stage.

La₂Zr₂O₇ (LZO) film grown by chemical solution deposition (CSD) technique is a widely studied buffer layer for YBa₂Cu₃O_7-x (YBCO) film growth on rolling-assisted biaxially textured (RABiT) substrate. Biaxially textured LZO film is epitaxially grown on a cube-textured metal substrate. In RABiT substrate, cube texture is obtained as primary recrystallization of heavily cold-rolled fcc metals and it is normally developed before CSD film deposition to obtain an oriented film growth. In the present contribution, we show that biaxially textured LZO film can be grown directly on cold-rolled fcc metal substrate with a single heat treatment. In fact, we show that if the recrystallization temperature of the metallic substrate is lower than the nucleation temperature of the film, a biaxially textured film is obtained as a result of transient cube texture transfer. Biaxially textured LZO films grown on cold-rolled substrates are compared with films grown on recrystallized substrates. In particular, the growth of LZO on either pure Cu or Ni-based substrate was studied. Compared with LZO film grown on cube textured substrate, LZO grown on cold-rolled substrate show a similar morphology. Moreover, films are well adherent without cracks or delamination, suggesting that grain boundary migration in the metallic substrate has no detrimental influence on the film. In some cases, secondary recrystallization of the substrate occurs, without affecting the quality of LZO film.

This work was supported by MIUR in the framework of the FIRB-Futuro in Ricerca project “SURE:ARTYST” on chemical coated-conductor.

Epitaxial MgO/TiN buffer layer structure has been developed on different cube textured substrates using Pulsed Laser Deposition (PLD) technique. The behaviour of the architecture as barrier against diffusion of oxygen and cations has been investigated in order to assess the employment for physical and chemical subsequent deposition of buffer layer or YBCO film and to enabling the use of Cu-based alloy as cube textured substrates. The architecture shows a texture sharpening with respect to that of the substrate, indicating a good epitaxial growth even if the deposition temperature relatively low of 500°C has been used. The superconductive sample YBCO/SrTiO₃/MgO/TiN deposited by PLD on Cu-based cube texture substrate has been studied by TEM analysis of the cross section. No oxygen contamination in the substrate and no cation diffusion through the architecture can be appreciated. The TiN and MgO interfaces are characterized by a low roughness value that is even better with respect to the one of the substrate. Besides, the MgO/TiN buffer layer structure turns out robust enough that enable the development of YBCO coated conductor with two buffer-layer. The Thermal co-evaporation method was adopted to deposit YBCO films on the top of the MgO layer. Critical temperature T_C(R=0) of about 87K was been obtained, quite similar to critical temperature measured for YBCO films deposited on single crystal MgO substrate.

Acknowledgements: Authors acknowledge financial support by EUROTAPES project (EU-FP7 NMP-LA-2012-280432)

In the manufacture of coated conductors, having a high degree of flatness of the initial metallic tape is required. Usually, this is made by expensive and time-consuming mechanical polishing and/or electropolishing from as-rolled tapes, which also entails the disposal of the related waste.
One strategy to avoid these polishing procedures consists in depositing an oxide planarization layer on the rough substrates by cost-effective chemical solution deposition. In particular, piezoelectric inkjet printing is a suitable technique for long length deposition since it has closed reservoir, works on a drop-on-demand basis, shows high yield and it integrates easily in longer lengths and widths by assembling printhead arrays.
In particular, R2R single-pass inkjet printing of suitable precursor inks of Y₂O₃ was performed on 4-mm wide unpolished stainless steel tapes, adjusting printing parameters for obtaining uniform layers after thermal decomposition. Typically, Y₂O₃ thickness was around 100 nm. Afterwards, ABAD was used to deposit biaxially-textured YSZ on top of the Y₂O₃^MOD. X-ray diffraction analysis of in-plane alignment shows an enhanced YSZ texture for thickness of 800-1000 nm in the planarized samples in comparison to both unpolished and even standard polished stainless steel tapes.
Following ABAD texturing, epitaxial CeO₂ buffer and YBCO layers were successfully grown by PLD. Then end-to-end critical current (I_c) was measured at 77 K and self field. Compared to standard polished substrates, 50% of I_c was found, which accounts for ca. 100 A/cm·width.
Further data will be provided regarding these thin film arquitectures and future directions in scale-up will be discussed towards significant cost reduction in the overall manufacture of ABAD-based coated conductors.

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.

A new approach to deposit layers for coated conductors has been developed. High frequency surface acoustic waves (SAWs) were applied for atomization of precursor solutions into an ultra-fine aerosol. The deposition via aerosol droplet condensation offers several advantages over existing deposition methods including ink-jet printing and dip coating, e.g. a variable droplet size and the possibility of solvent evaporation in the aerosol phase. Perceptively, a combination of two or several SAW-atomizers could enable the simultaneous deposition of separate solutions and even nanoparticle dispersions.

First experiments were performed using water based as well as propionic acid based mixed Lanthanum and Zirconium precursor solutions having different metal concentrations. These solutions were supplied to a surface acoustic wave device via a stainless steel capillary, leading to a continuous aerosol production. The aerosol droplets containing the precursor solution were deposited on biaxial textured Ni5%W tapes on an area of 1 cm width and about 5 cm length and subsequently crystallized into a continuous thin La₂Zr₂O₇ buffer layer in a tube furnace. X-ray diffraction studies showed that the La₂Zr₂O₇ films have a high crystalline quality with a strong (00l)-orientation. Furthermore, results of SEM and FIB analysis on the deposited films will be presented.

In recent years, the novel Ni-W alloy composite substrates with high content of W element (the content of W in outer layer of the composite substrate is more than 7 at.%) are considered to be the most promising substrate material for the second generation of high-temperature superconducting tapes with high performance, because they are characterized by much higher mechanical strength and lower ferromagnetism than that of the more commonly used Ni-based substrates (such as Ni-5at.%W and Ni-7at.%W single alloy substrates). However how to develop sharp cube texture and to understand the mechanism of recrystallization texture evolution in these composite substrates are still challengeable missions so far and these difficulties are also the major factors in restricting their industrial applications. In this paper, a novel model of solute diffusion has been proposed for the first time. Through a precise design of the appropriate material structure and elemental component, the diffusion typed Ni-8at.%W/Ni-12at.%W/Ni-8at.%W alloy composite substrates with high content of W, high strength, non-ferromagnetism as well as sharp texture will be fabricated using this processing model. The evolution of deformation texture and elements diffusion behavior will be investigated, which influence the cube texture formation to a great extent. The Ni-8at.%W/Ni-12at.%W/Ni-8at.%W alloy composite substrates consist of three layers with different thickness ratios of 1:1:1, 1:2:1, 1:3:1, respectively. In addition, the effect of the substrate thickness, interbedded ration as well as the elemental diffusion on the shear structure in the different depth of the cross section will be investigated in order to understand the relevant relationship between the cube texture formation and the diffusion in the outer and inner layers of the composite substrate. Furthermore, the theoretical model of texture evolution and elemental diffusion will be established. Consequently, the mechanism of recrystallization texture evolution and cube texture formation in diffusion-typed composite substrates with high W content will be systematically elaborated and proposed.

This work is financially supported by the National Natural Science Foundation of China (51171002), by Beijing Municipal Natural Science Foundation (2132011)，by Special Funds from the Central Finance to Support the Construction of Local University, and by 211 Program of Beijing City and Beijing University of Technology.

Evolution of the microstructure and crystallographic texture during annealing have been investigated in a Cu–45 at.%Ni alloy cold-rolled to a von Mises strain of 5.7. Such a high strain resulted in a lamellar structure with an average boundary spacing along the normal direction of 67 nm as determined using the EBSD technique. The fraction of rolling texture components in the cold-rolled condition was 91% and fraction of high angle boundaries was measured to be 71%. Annealing at temperatures £ 450°C for 1 h caused structural coarsening accompanied by a slight strengthening of the rolling texture. A pronounced discontinuous recrystallization and the development of the cube texture were observed during annealing at temperatures above 450°C. Recrystallized cube-oriented grains were found to be larger than grains of other orientations. Changes in the recrystallized microstructure and texture during annealing at 1000°C were monitored by EBSD in one region after different periods of time. The cube texture was observed to strengthen significantly during grain growth, which led to a dramatic loss of high angle grain boundaries. In the microstructure annealed at 1000°C for 1 h the fraction of high angle boundaries was only 12%.

The authors gratefully acknowledge the support from the National Science Foundation of China (51171002), China Postdoctoral Science Foundation funded project (2014M560030) as well as the Project Supported by Beijing Postdoctoral Research Foundation (2014ZZ-38).

For high performance and low cost of coated conductors, optimized buffer layer stacks must be developed. Among the manufacturing efforts worldwide, IBAD-MgO is one of the dominant processes for the commercial production. However, preparation of the intermediated layers between IBAD-MgO and metal substrates should be taken into account. Initial nucleation, coalescence, texture growth of IBAD-MgO on Y2O3 and other materials grown by chemical solution methods were studied by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Ultra-smooth (RMS roughness < 0.9 nm) Y2O3 layers were obtained by repetition of multiple coating and annealing. For growth of MgO, we controlled flux rate of MgO and Ar+ ion radiation rate simultaneously. The crystallinity of the initial MgO was observed by reflection high-energy electron diffraction (RHEED) during the deposition. Correlation between the thickness and the growth rate of MgO layer is studied and the best azimuthal width in the phi-scan of the IBAD-MgO layer is recorded as 4 degree. In addition, the IBAD-MgO and SDP-Y2O3 buffer stacks were utilized for growth of high quality coated conductors.

For an enhancement of critical current density (J_c) of multifilamentary Nb₃Sn-based superconducting composites it is required to increase Sn concentration in the Nb₃Sn layers, to decrease the average grain size of equiaxed Nb₃Sn grains and to reduce the zone of columnar grains (in which Sn concentration is lower than in the equiaxed ones). In the present study the structure and morphology of the Nb₃Sn layers in the internal-tin wires have been studied by TEM (in longitudinal sections) and SEM (in the transverse sections and fractures). The composites under study were fabricated and tested by the value of J_c (non-Cu, 12 T, 4.2 K) at Bochvar High-Technology Research Institute of Inorganic Materials (VNIINM, Moscow, Russia) [1, 2] and differed in the initial Sn concentration, the presence of strengthening Cu-Nb inserts, the various regimes of the diffusion annealing, the number of Nb filaments and their diameter in the final wire. In all the internal-tin wires studied the zones of columnar grains are always present, contrary to, for example, the bronze-processed composites with tubular filaments [3], and the average grain size and grain size scattering of equiaxed Nb₃Sn grains are in genaral higher than in the traditional bronze-processed wires [4], but J_c in some of them is as high as 2276 A/mm². One of the reasons for such high J_c is the reduction of the zones of columnar grains in the Nb₃Sn layers. Much lower critical current density (850 A/mm²) in a internal-tin wire with smaller diameter of Nb filaments and lower Sn concentration in the matrix is not only because of the lower Sn concentration in the matrix, but also due to worse structure and morphology of the superconducting Nb₃Sn layers, namely, larger average grain size and grain size scattering of equiaxed grains, wider zones of columnar grains and higher aspect ratio of the latter.
References:
[1] V. Pantsyrny, A. Shikov, A. Vorobieva. Cryogenics. 2008;48:354–70
[2] V. Pantsyrnyi, A. Shikov, A. Vorobieva, S. Soudiev, V. Sergeev, E. Dergunova, I. Sinitsyn, N. Belyakov, S. Kukin. IEEE Trans. Appl. Supercond. 2004;14(2):996–9
[3] I.L. Deryagina, E.N. Popova, E.I. Patrakov. Phys Met. Metallogr. 2015;116(3):235–41
[4] E.N. Popova, I.L. Deryagina, E.G. Valova-Zaharevskaya. Cryogenics. 2014;63:63-8

The authors are thankful to E. Dergunova and A. Vorobyova (VNIINM) for the samples for these studies. The work has been done in the Collective Use Center of IMP within the State Program “Crystal” No 01201463333 with partial support of UB of RAS (project No. 15-17-2-11).

Nb-rod-method Cu-Nb reinforced Nb₃Sn (Cu-Nb/Nb₃Sn) wires have been successfully developed for commercialization of the React-and-Wind (R&W) processed Nb₃Sn coils. Superconducting performance of the Cu-Nb/Nb₃Sn wires are improved by applying the pre-bending treatment at room temperature, because of releasing the residual stress of Nb₃Sn filaments (pre-bending strain effects). The purpose of this study is to obtain information of the efficient use of the pre-bending strain effects for optimizing critical current (I_c) characteristics under pure bending strain on the R&W coil design. The Cu-Nb/Nb₃Sn strands of diameter 0.8 mm were heat-treated at 670 ˚C for 96 hours on stainless steel grooved cylindrical holders of different diameter 32, 40 and 50 mm, and some strands were applied repeating pre-bending strain ±0.5%. Each of the pre-bent strands and without pre-bent strands was transferred to a Ti-6Al-4V alloy grooved cylindrical holder of diameter 32 mm, and those Ic measurements were carried out under applied pure bending strains 0%, +0.5% and +0.9% at 11-17 T, 4.2 K. As a result, the pre-bent strand showed no deterioration of I_c in the applied pure bending strain of +0.5% and had larger I_c than that of without pre-bent strand. In this paper, the I_c enhancements of the pre-bent Cu-Nb/Nb₃Sn strands under pure bending strains are analyzed by the I_c characteristics under axial strains and considering the internal strain distribution.

Multifilamentary Nb₃Sn wire fabricated by the Powder-In-Tube (PIT) process can provide both high critical current densities, J_c, and small effective filament diameters, d_eff, at the magnetic fields required by the next generation of accelerator magnets. Currently, PIT wires obtain a maximum J_c (12 T, 4.2 K) of about 2500 A/mm² by converting up to 60% of the non-Cu cross section into superconducting Nb₃Sn A15 phase. However, as much as a quarter of this volume fraction is made up of A15 grains which are too large or are otherwise disconnected and cannot contribute to transport current, wasting both real estate and Sn that would be better used to make small grain A15. Our recent heat treatment studies of accelerator quality internal-Sn RRP wires suggests that there are important parallels in the phase evolution of both PIT and RRP strands that can be exploited to push critical currents in PIT strands closer to the levels found in the best internal Sn strands without compromising the low d_eff characteristic of PIT wires. We demonstrate these observations using quantitative measurements of the phase evolution during reaction obtained by image analysis of backscattered electron images of samples quenched from multiple steps in the heat treatment, combined with differential thermal analysis.

Work carried out in collaboration with the groups of A. Ballarino at CERN and B. Sailer at BEST. This work was supported by the US Department of Energy (DOE) Office of High Energy Physics under award number DE-SC0012083, by CERN under KE1920/TE , by the NHMFL (supported by the National Science Foundation under NSF/DMR-1157490) and by the State of Florida.

Internal tin (IT) Nb3Sn strands are remaining to be the most promising option that could attain the challenging requirements of high field magnets for new generation of particles accelerators. The overview on the superconducting properties of the IT Nb3Sn strands is presented. The limitations on the volume fraction of superconducting phase, critical current density (Jc) of Nb3Sn , residual resistivity ratio (RRR), hysteresis losses (effective filament’s diameter) are discussed. The design features of IT strands with enhanced mechanical strength are presented. The possible approaches to the optimization of the IT strands design that lead to simultaneous attainment of high Jc and low Hysteresis losses are proposed and analyzed.

Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to visualize internal structure of the body in detail. Due to its high copper-to-superconductor ratio, low cost and high stability, as is known, wire-in-channel NbTi/Cu superconducting wire occupies about 70% of the superconducting wire used in MRI system. In present paper, NbTi/Cu core wire with the copper-to-superconductor ratio of 1.3 and with the diameter of 0.72mm used for fabricating high copper-to-superconductor ratio wire-in-channel superconductor was prepared firstly. Furthermore, the effect of greatly heat treatment time, heat treatment number, the strain space between heat treatments, final drawing strain, as well as different NbTi bars was investigated for optimizing a process to obtaining high critical current density (Jc). Measurement results show that the acquired maximum Jc can reach about 3208A/mm2 at 4.2 K and 5 T. The obtained high Jc core wire was then put into an appropriate copper channel and these two parts were soldered by Tin alloy. Thus, wire-in-channel superconductor with copper-to-superconductor ratio of 11.5 and with the size of 1.96*1.12mm was fabricated. Critical current density of wire-in-channel superconductor decreases to 3125A/mm2 at 4.2 K and 5 T due to the process of soldering.

The correction busbar (CB) conductors fortheITER projectare being produced in China.The second China CB conductor sample (CBCN2, Phase II of conductor testing), and the third CB conductor sample (CBCN3, Phase III testing) were made of the WST strands, cabled by Changtong, jacketed at ASIPP, prepared by CRPP following the IO-approved procedure and tested in the SULTAN facility.
The current sharing (Tcs) test results show that the conductor sections of CBCN2 and CBCN3 have high Tcs performance. Using the electrical method, the Tcs of both CBCN2 and CBCN3 samples was 7.50 K at10 kA /2.9T (maximum operating field) before and after electromagnetic loading.
AC loss measurement was performed before any electromagnetic loading of the sample, and the measurements were repeated after 1000 cyclic loads. The measurements were performed at 2 T background field, without transport current, and at2.63 T background field with sample current of 10 kA. The AC loss performance of the CBCN2 and CBCN3 conductors differs slightly at ±0.2T AC filed and various frequencies.
According to the SULTAN test result, Tcs of CBCN2 and CBCN3 conductor samples meet the ITER acceptance criteria of 7.0 K.

The preparation and experimental testing of CBCN2 and CBCN3 conductor sample was due to the cooperation with CRPP and ITER Organization. We are thankful to ITER Organization for coordination work, and CRPP crew for sample preparation and test.

Roebel cables made from coated conductors have many desirable properties such as full transposition of strands and high current capacity which make them candidates for use in high field magnets. In high field the cable will experience significant transverse stress and the geometry of the Roebel assembly concentrates this stress in non-trivial patterns. For real cables the relative position of strands will be different from the idealised architecture due to errors in the manufactured transposition lengths of the strands and inaccuracy in positioning strands at commencement of cable assembly. We investigate using simple models how the accumulated random errors along the length of a cable may affect the transverse properties of Roebel cables. We measure experimentally the effect on critical currents of exposing the cables to high transverse stresses with strands in non-ideal positions to validate these models. We show that impregnation of cables can greatly mitigate the effects of transverse stress concentration caused by random shifts and the Roebel geometry.

Roebel assembled coated conductors are high-current and fully transposed cables which find applications in rotating machinery and high-field inserts for accelerator magnets, such as the EuCARD-2 HTS insert magnet. In such applications, Lorentz forces can lead to considerable mechanical loads on the cable. Roebel cables are particularly sensitive to transverse compressive loading, as the uneven thickness of the cable results in the force being concentrated on a relatively small area. In the EUCARD-2 HTS insert magnet, transverse stresses levels will be as high as 110 MPa, exceeding the tolerance of bare Roebel cables. Additional reinforcement by impregnation or adaptations of the cable geometry are therefore necessary. In this work, the transverse stress tolerance of several Roebel cables is analyzed in a mechanical press set-up which is capable of forces up 250 kN and currents up to 50 kA. The measurements are done in 10.5 T magnetic field and at liquid helium temperature. Bare cables are tested as well as cables impregnated with a silica-filled epoxy resin. A filling ratio of 50% was chosen to reduce the thermal expansion mismatch between resin and the conductor while keeping the viscosity low enough to impregnate without voids. The first results show a marked increase in the point of onset of critical current degradation for impregnated cables of 170 MPa compared to 40 MPa for the bare cable.

The work is part of EuCARD-2, partly funded by the European Commission, GA 312453

MgB2 has several intrinsic properties which make this compound a reliable material in a variety of commercial applications. Its remarkably high critical temperature is one of its most important benefits. Since this material is used in large-scale applications, knowledge regarding its mechanical properties becomes a relevant issue for design purposes. In this work, a 36-filament wires of MgB2 superconductor sheathed by a Ni alloy was studied. In situ compression tests were performed in order to investigate its mechanical properties and to observe the damage along the wire. In order to do this, the tests were periodically interrupted to obtain 3D images of the wires, analyzing the damage evolution. Furthermore, a finite element model was created to analyze the stress state in the wires.

The development of the power transmission lines based on long-length high temperature superconducting (HTS) tapes requires the high production quality of these tapes. That results in high homogeneity along the length of the tape as well as across its width, meaning that significant local damages of superconducting core should be avoided. Some other applications of HTS tapes will require stacked tape configurations. Therefore the study of the quality of HTS tapes in stacks is of high importance as well as the study of single long-length tapes quality. The current distribution along and across the tape provides us with the sufficient information about the quality of the tape performance in different current feeding regimes. In present work we develop the non-destructive characterization techniques to examine the current density distribution in the variety of HTS tapes. In order to obtain the current distribution we use a Hall probe to scan the self-magnetic field above the tape and then this dataset is used to solve the inverse problem for calculating the current density. The crucial point of our study is the fact that we use the minimum possible data of the magnetic field scan in order to solve the inverse problem for different HTS tape configuration, i.e. for single tapes and for the stacked tapes. To solve the inverse problem we developed several MATLAB codes. In these codes two mathematical methods are combined: one is based on solution of set of linear equations, and the other is based on the method of least squares. This developed technique is applied to a series of measurements for single commercial YBCO and BSCCO tapes and stacked BSCCO tapes. The calculation results for the stacked tapes show the flattening of current density profile in the tapes during various current feeding modes that is expected to be followed by increasing of critical current.

Acknowledgement: The authors thank Prof. Dr. Atsuo Iiyoshi, the President of Chubu University for his continuous encouragement and Prof. Dr. Igor A. Girka, the head of School of Physics and Technology at V.N. Karazin Kharkiv National University for his support of this research.

Metal organic deposition (MOD) method is widely used to fabricate the YBCO superconducting films of second generation high temperature superconducting (2G HTS) wires, due to its low-cost advantage. In this study, Pb addition was utilized to modify the MOD method, and significant improvements of YBCO film’s properties were observed. Using the precursor solutions prepared with or without lead acetate, YBCO films with the thickness of 600 nm were obtained for comparative study. It was found that the a/b-axis orientated grains could be efficiently suppressed by Pb addition, thus the critical current density was enhanced from 0.96 to 2.80 MA/cm² (77 K, self-field). Pb did not exist in the final YBCO films. By analyzing the film samples quenched in the crystallization process of heat treatment, it was supposed that the Pb compounds could help to optimize the nucleation of YBCO films and then evaporated because of the volatile behavior of Pb. The Pb-modified MOD method could own potential for the fabrication of high performance YBCO thick films in 2G HTS wires.

This study was supported by National Natural Science Foundation of China (51402165), Guangdong Natural Science Foundation (S2013040014199), and Fundamental Research Program of Shenzhen (JCYJ20140827160129762).

During the fabrication of YBCO superconducting films via MOD method, the crystallization temperature (T) is an important parameter for the YBCO formation reaction. The evaluations of standard entropy change (ΔS) and standard enthalpy change (ΔH) of the reaction could help to understand the mechanism of MOD-YBCO process. In this study, in situ resistance measurements were performed to investigate the influence of T on the growth rate (R) of YBCO film. Based on the reaction-diffusion model proposed by Huan Chen, the specific equation of R as a function of T was established. Diffusion coefficient, volume gas flow rate, and standard Gibbs free energy change (ΔG) were considered as T-dependent factors. The equation was fitting to the measured R-T data, and ΔS and ΔH were obtained. ΔG at different T could be obtained using ΔG=ΔH-TΔS, and they could be verified by the in situ resistance measurements with changing the gas flow or water vapor partial pressure.

This study was supported by National Natural Science Foundation of China (51402165), Guangdong Natural Science Foundation (S2013040014199), and Fundamental Research Program of Shenzhen (JCYJ20140827160129762).

REBa₂Cu₃O_y (REBCO, RE = rare earth elements) coated conductors have been considered as prime materials for the electric power applications towards the next generation. There are several processes available for fabricating REBCOs such as metal organic deposition (MOD), pulsed laser deposition and chemical vapor deposition. Among these processes, MOD is the best process due to its inexpensiveness, high material yield and facileness. Furthermore, it is easy to introduce artificial pinning centers (APC) into the films by controlling the starting solution to enhance critical current density (Jc) in magnetic fields. In this work, YBCO films with BaHfO₃ (BHO) as APC were fabricated by MOD and the effect of additional heating process was investigated. Two samples were fabricated with and without the additional heating process. The mean size of BHO particle in YBCO with and in YBCO without were measured about 15 nm and about 19 nm, respectively. Also, it was recognized clearly that the size distribution of BHO particles became small in the case of the sample with additional heating process. Consequently, number density of BHO was maximized from 4.0 x 10²¹ m^-3 to 9.0 x 10²¹ m^-3 and in-field Jc of the film was improved from 1.1 × 10⁵ A/cm² to 1.4 × 10⁵ A/cm² at 77.3 K in 3T by introducing the additional heating temperature.


This work is supported by the Ministry of Economy, Trade and Industry (METI) as “Development of Fundamental Technologies for HTS Coils”.

A simple tape-self-heating method has been realized in the development of coated conductor process. Because of the high resistance of the Hastlloy or other Nicole alloy, the heating current density in the metal tape is only 25A/mm2 to reach 800oC substrate temperature. With this technique, the energy for directly heating the thin tape had been decreased down to less than one third of the conventional indirect heating method. The brush type electrode feed the current into the tape from its narrow side, so it suitable for reel-to-reel and double-sided deposition. Without of the heater of the indirect heating method close to the tape, the arrangement of deposition source is much free. This method could be used into any deposition process that needs high temperature in coated conductor. Using this heating method, a double-sided structure coated conductors, which could double the engineering critical current density, had been prepared with MOCVD. The critical current density of the 500 nm thick superconducting film reached 3 MA/cm2. Especially, a very high deposition rate, which is comparable to that of the laser-assisted MOCVD, has been obtained in our MOCVD of superconductivity thin film for each side.

This work was supported by the 863 projects of Department of Science and Technology of China (program number 2014AA032702), and the Sichuan Youth Science and Technology Innovation Research Team Funding (No.2011JTD0006).

For coated conductor manufacture, quality control tools are required to ensure that each constituent layer is made within specifications. Regarding thickness control, reflectometric analysis of thin film arquitectures is a fast, cost-effective and non-destructive optical measurement, which could be eventually integrated in-line during continuous production.
In this work, reflectometry was applied in coated conductors arquitectures of the generic type YBCO^TFA/Ce_0.9Zr_0.1O₂^MOD/YSZ^ABAD/Y₂O₃^MOD/SS. Optical models for thickness determination of planarizing layer, yttrium-doped zirconia, buffer ceria and YBCO superconductor layer were established in order to have suitable n and k values as a function of light wavelength ranging between 200 and 1100 nm. In the particular case of YBCO layer, the thickness can only be measured after thermal decomposition from YBCO-TFA precursor solutions and before epitaxial crystal growth takes place, due to the metallic nature of the final superconductor layer at room temperature.
Details of the reflectometric analysis of each layer in the above-mentioned arquitecture will be presented and discussed. Furthermore, the potential implementation of this technique during the continuous reel-to-reel manufacture of coated conductors will be also considered.

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.

For most of the electric applications of REBCO coated conductors (CC) a copper shunt with a thickness of 20 – 50 µm is indispensable. Suitable copper layers have been produced by cathodic electrodeposition. We investigate and propose CC architecture with a Cu shunt thickness and geometry to handle 100% overcurrent capacity, preventing sharp edges and facilitate winding work. With a new chemistry both for the copper sulfate Cu SO4 solution and the cyan – free alkaline electrolytic solution we deposited a shiny, ductile and non-porous copper layer. Due to current load- controlled pulse plating technology both Ni based Hastelloy and NiW substrates could be Cu plated up to an electrolyte current density of 100 mA/cm². Fabricated hybrid Cu – REBCO tapes reveals that continuous electrodeposition in reel-to-reel technique bring the CC production to perfection. With less than 20 Eurocent /m the non –vacuum copper plating technique is targeting the urgent need for simplified conductors and reduced cost/ performance ratio. We report about the electric and chemical parameters of a robust reel-to-reel facility to improve the deposition rate and increase the Cu shunt production speed up to 60 – 80 m/hour.

We report on the fabrication by all-chemical deposition method of highly textured YBa₂Cu₃O_7-x (YBCO) films using a 10 mol % Gd-doped CeO₂ (CGO) capping layer deposited by the new polymer assisted deposition (PAD) technique on top of yttria stabilized zirconia (YSZ) buffered stainless steel substrates by alternating beam assisted deposition (ABAD) (^ABADYSZ/SS). PAD utilizes an aqueous polymer to bind metals in a complex that serves both to encapsulate the metals, in order to prevent chemical reaction and to maintain an even distribution of the metal in the solution. The main advantage of PAD technique is the very long stability of the precursor solution (years- essential for the scalability process) and it is environmentally friendly. An optimization study of the epitaxial growth of the PAD-CGO buffer layer on ^ABADYSZ/SS for the fabrication of coated conductors is presented. Structural and morphological properties were investigated by X-ray diffraction (XRD) and atomic force microscopy. It has been demonstrated the efficiency of the PAD-CGO buffer layers for the growth of epitaxial YBCO from low-fluorine solution. The ^CSDYBCO/ ^PADCGO/^ABADYSZ/SS architecture was characterized by XRD and SEM analyses. Tc values of 91.1 K and Jc at 77K of 1 MA/cm² were obtained.

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

Since the second generation (2G) superconducting wires started to be produced in a large scale almost a decade ago, the quality of the materials manufactured has been continually improved. Every year the manufactures present new materials with better electrical properties, increasing the critical current density, critical magnetic field and the total length produced with continuous homogeneity. The mechanical properties of the coated conductor should be taken in account, since electro-dynamical forces appear in working conditions as stress in the cooling and heating processes. In applications as fault current limiters, SMES, Transformers, electromagnets, motors, cables, etc, the consideration of is mandatory to the project of those devices. In this context, the present work studies the electrical and mechanical properties of 12 mm 2G wires samples under torsion. Critical current is measured as a function on the torsion angle. Details of the experiment and their results will be presented.

The authors would like to thank to the Brazilian agency CNPq for the partial support of this work - grant “ciências sem fronteiras”.

Electromechanical tests were carried out at 77K on REBCO-based second generation (2G) HTS wires made by IBAD-MOCVD to study the dependence of critical current (Ic) on different mechanical loadings including uniaxial tension, combined torsion with axial tension, and transverse compression. Under uniaxial tension, the relationship between the Ic and the tensile strain was found to be independent of the thickness of the substrate and stabilizer. On the other hand, the relationship between the Ic and the tensile stress depends on the substrate/stabilizer thickness ratio. From the uniaxial tension testing, a well-defined critical stress as well as an irreversible stress can be determined as the electromechanical properties to describe the tensile strength of a wire. For a wire under combined torsion and axial tension a critical tensile stress can also be determined, which was found to be affected by the twist pitch. The effect of wire width was investigated under this loading condition. For a wire under transverse compression along the c-axis of the REBCO film, the experimental result suggested that the critical stress corresponding to the 95% original Ic retention can be as high as 1,000MPa.

Coated conductors have many existing and potential applications which require high currents. For instance high field magnets for NMR, particle accelerators and fusion reactors are currently under consideration. The self-field critical current density at liquid helium temperature is about one order of magnitude higher than at liquid nitrogen temperature. This ratio is even larger at higher magnetic fields which makes low operation temperatures especially interesting for high-field magnet technology.
The critical currents in coated conductors become so high at low temperatures, that heating of the contacts and current leads often inhibits direct transport current measurements. One method to address this issue is to etch bridges into the tapes. This was done with 4 mm wide tapes where we reduced the superconducting cross section by a factor of ten. However, an inhomogeneous critical current density across the width would lead to wrong predictions of the critical current in the entire tape.
To overcome this difficulty, the deposited energy had to be minimized. We built up a current pulse station which can produce current pulses above 3000 A and enables I-V-measurements within milliseconds. The results of the different measurement methods are compared.

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. We gratefully acknowledge financial support by ÖAW-KKKÖ. We wish to thank SuNAM, SuperPower, AMSC and SuperOx for providing us samples of their coated conductor tapes.

Mechanical loads which HTS coated conductors are able to withstand determine their viability in many applications including magnets, motors, SMES and cables.
Presently, we report an investigation results on influence of substrate composition and substrate treatments on mechanical and electrical properties of HTS coated conductors.
Coated conductors employed in mechanical study were processed via (i) an alternating beam assisted deposition (ABAD) in order to grow a bi-axially textured template of yttria-stabilized-zirconia buffer layer on surface of metallic substrate, (ii) a multi-beam pulsed-laser-deposition (MB-PLD) used for processing of buffer cap-layer of CeO₂ and HTS film, and (iii) a metallization by physical vapour deposition of silver layer and, finally, by copper galvanic plating of thick (15-50µm) copper layer.
Thresholds in critical current–stress/strain dependences as well as reversibility ranges are determined at 77K, SF.
Mechanical features including strain–stress curves and creep effects are studied in differently treated substrates at both 77 K and 300 K temperatures.
Influence of tape bending on critical current is investigated depending on thickness of copper plating and bending direction (concave/convex).
Comparison of critical currents in non-stressed and stressed HTS coated conductors based on Cr-Ni stainless steel and Hastelloy is provided and discussed.
Irregularities of local values of critical current across the tape length (up to 200 m) are discussed in terms of stability of substrate parameters.

Understanding the processes occurring during the transition to the normal state of the coated conductors (CC) when induced by the application of large currents is of first importance for the implementation of devices including CCs in the power grids, as well as from the fundamental point of view. In this contribution, the influence of surface defects, in particular of a-axis grains, on the transition to the normal state induced by high current densities in YBa2Cu3O7-δ (YBCO) thin films and in a commercial 2G-coated conductor is investigated extending previous studies [1]. For that purpose, the surface of the samples is observed by scanning electron microscopy and isothermal current-voltage curves are measured at different temperatures with pulsed currents up to the quenching value I*. The microscopic observations show striking differences in the surface aspect of the various samples, that are related to their electrical properties.The ratio of I* to the critical current is large if a-axis grains are not visible at the surface of the YBCO films, while it is much lower if the surface includes a-axis grains, as this is the case for the coated conductor. The connection between the transition onset and the vortex dynamics, as well as the role of the a-axis grains in this process are discussed. The relation between the I* values obtained from thermal calculations and those resulting from vortex dynamics considerations is also discussed, as well as the possible consequences suggested by this work for the different applications of the coated conductors .

[1] P. Bernstein, G. Ferro, C. Harnois, C. Mc Loughlin, J. Noudem, M. R. Osorio, Y. Thimont, J. A. Veira, D. Vidal and F. Vidal, Journal of Applied Physics 115, 053910 (2014)

Filamentization of coated conductors effectively reduces alternating current losses, but generally results in a decrease in the critical current per tape width. A two level undercut-profile substrate (2LUPS) concept has recently been introduced to enable full operational width of the superconducting layer. This concept is based on two levels of plateaus connected by a curved wall with an undercut-profile. Such a profile has previously been demonstrated to produce a shading effect during subsequent physical deposition of buffer and superconducting layers, which resulted in self-forming filaments in the coated conductor. To verify if the 2LUPS concept can also be applied to coated conductors manufactured using chemical solution deposition techniques, we produce and investigate a 2LUPS made from a standard cube-textured Ni-W tape. It is shown that plateaus with curved walls and undercut-profiles are formed in this tape, and that both plateaus and the walls are completely covered by Gd2Zr2O7 after dip coating and sintering of buffer layers. The microstructure and texture of the new substrate characterized by both the EBSD technique and XRD are also presented in this work.

Despite great improvements in critical current performance, the high cost of commercial (RE)Ba₂Cu₃O_7-x coated conductors remains prohibitive, and AC losses further deter their selection for electric power applications. Hysteresis losses can be effectively addressed by striation or etching, but these subtractive processes further increase the production cost and complexity.
Inkjet printing combines the scalability and low cost typical of chemical solution deposition (CSD) routes with digital control and high resolution patterning. It has previously been demonstrated by the present authors that superconducting YBa₂Cu₃O_7-x (YBCO) filaments can be successfully printed on technically relevant substrates without subtractive processing steps.
In the present work, the AC loss and critical current performance of two different inkjet-printed multifilamentary coated conductor architectures has been measured and compared with theoretical models. The samples were prepared by printing a low-fluorine YBCO precursor solution on SS/ABAD-YSZ/CeO₂ substrates. In one case, YBCO filaments were deposited directly on the buffered substrate by piezoelectric inkjet printing; and in the other case, resistive CeO₂ tracks were first deposited to template a subsequently over-printed YBCO film, creating a multifilamentary superconducting structure by an inverse technique. The two approaches will be compared, and their suitability for scaled-up industrial production discussed.

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

The technical advantage of high Tc superconductors (HTS) operating at 4.2 K is the high current density at high field beyond 20 T where conventional superconductors are not applicable. The industrial development efforts, previously focused on high current applications such as power cables operating at elevated temperatures, are now targeting the enhancement of low temperature in-field performance with magnet applications in view. Although the existing HTS conductors have many desires to be fulfilled on the technical aspects such as the production length, homogeneity, and mechanical strength to be improved, they have already been sufficient to motivate the projects aimed at constructions of state of the art high field insert magnets. Such demands and prospects of HTS conductor applications require direct characterizations of in-field transport properties as it has been pointed out that no comprehensive relationships exist between the readily accessible 77 K self-field data and the high field performance at 4.2 K. Motivated by the need for direct measurement of full width HTS conductor, we have constructed and tested the high current capacity measurement probes for high field beyond 20 T using the facility available at LNCMI-Grenoble, and report here the measurement results of recent commercial conductors relevant to high field applications.

Magnetic fields can be shielded effectively with superconducting tapes. They can be used either to attenuate magnetic field (closed shields) or to improve its homogeneity (open shields). Both low and high temperature superconductors can be used for this purpose.
In this work magnetic field changes due to the presence of a superconducting shield are investigated. Both experimental and model results are shown. Several types of shields with different materials and geometries were used. Specimens were subjected to DC and low frequency AC magnetic field (up to 150 Hz). Attenuation and homogenization of field inside a shielded cavity were observed. The dependence of shielding effect on magnetic field strength and frequency was analyzed. Computer model of a shield has been developed.
The additional increase of shielding effect was observed above certain threshold frequency depending on geometry and material properties of a screen. Magnitude and limits of this increase were investigated. It was observed to be linear in some frequency interval and to weaken at higher frequencies.
Analyzed shields may find multiple applications in devices where DC and low frequency magnetic fields are present. Their construction is simple and they are relatively cheap. Medicine and science can greatly benefit from this method of magnetic field homogenization and attenuation.

Superconducting tape can be cut and arranged into slabs to form composite bulks with proven potential to act as trapped field magnets [1,2]. One of their main advantages is the ability to generate very predictable and controlled trapped fields due to the well-defined and uniform properties of commercial superconducting tape. The work reported here builds on field cooling magnetization of arrays of tape previously reported, but using offcuts resulting from the manufacture of Roebel cables. The offcuts are approximately 6.5 x 40 mm trapezoidal sections punched out from 12 mm wide HTS tape and represent more than 50% of wasted material from the original commercial tape. Trapped field results from field cooling various overlapping arrangements of the superconducting tapes at 77 K will be reported, showing that some arrangements can produce flatter and more uniform fields than previously achieved using stacks of tape. The results are a step towards developing stacks of tape as an economical permanent magnet that may have potential for applications such as desk-top NMR devices, which require high uniformity of magnetic field.

[1] Patel A, Filar K, Nizhankovskii V I, Hopkins S C, and Glowacki B A, 2013 Trapped fields greater than 7 T in a 12 mm square stack of commercial high-temperature superconducting tape, Appl. Phys. Lett., 102 102601-5
[2] Selva K and Majkic G, 2013 Trapped magnetic field profiles of arrays of (Gd, Y)Ba₂Cu₃O_x superconductor tape in different stacking configurations, Supercond. Sci. Tech., 26 115006

This work was supported in part by the Engineering and Physical Sciences Research Council, U.K.

This report presents the results of transport critical current and magnetization measurements of 2G HTS wires with different architecture of the HTS layer. A series of MOCVD-YBCO samples on IBAD-textured templates have been prepared. The samples differed in the architecture of the HTS layer: (1) monolithic YBCO layer, (2) multiple 200-300 nm thick YBCO layers interleaved with epitaxial 20 nm thick Y2O3 layers, and (3) three YBCO layers interleaved with two epitaxial 20 nm thick Y2O3 layers. The overall thickness of all YBCO layers in each architecture type was approximately 2 microns. Transport critical current measurements at 77 K showed that the multi-layered samples had higher Jc in magnetic field and different in-field angular anisotropy of Jc than the monolithic samples. Based on magnetization measurements in the 5-77 K temperature range, we calculated Jc values at T < 77 K, as well as Jc temperature and magnetic field dependences. The correlations between the Jc values and behavior and the YBCO layer epitaxial quality, morphology and microstructure studied with XRD, SEM and TEM are discussed.