Transport current density of high temperature superconductor (HTS) tape conductors is a key parameter for various applications such as power cables and magnets. BSCCO and YBCO tapes are widely used in superconducting applications because of their high performance. We made a 3 D scanning Hall probe system includes 3 Hall probes to measure 1 and 2 dimensions of the effective magnetic fields around BSCCO and YBCO tape conductors after applying 100 A to evaluate the transport current density profile. When a constant current is applied to different tape conductors, a remnant current can exist in HTS tapes after switching off the power supply. And therefore, the magnetic field also can exist around the HTS tapes. We measure also different dimensions of the residual magnetic fields near the HTS tapes by the Hall probes. The magnetic field profiles at the different cross-sections are different for the BSCCO tape the YBCO tapes. We evaluate the current density profiles at the different cross-sections and different dimensions of the HTS tapes. The magnetic field profiles and the current density profiles of BSCCO are different from those of YBCO, and the profiles of BSCCO are stable for time, but YBCO’s are changing with time. The characteristics of the differences are important to consider the applications of HTS tapes.

The authors thank Professor A. Iiyoshi, the Chancellor of Chubu University for his continuous encouragement to do the experiment.

Metallorganic decomposition (MOD) route with trifluoroacetate (TFA) has been successfully used to fabricate YBa₂Cu₃O_7−δ (YBCO) based coated conductors with an excellent performance in high and low magnetic field. The microstructure and superconducting properties of YBCO films were controlled by the substrate properties and the solution chemistry, or by regulating the processing parameters during the heat treatment of the samples.
In this work, three YBCO films with various porous structures, namely a fully dense sample, a cell-structured sample with dense regions surrounded by porous structure and a highly porous sample, were deposited on single crystalline substrates. The samples were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and magneto-optical imaging. All three films showed a high level of epitaxy and good superconducting properties (Tc onset about 89 K and Jc higher than 2 MA/cm² at 77 K in self field).
However, we found that the porous structures formed by different nucleation and growth mechanisms during the sintering process still have strong influence on the superconducting properties, especially when a magnetic field is applied to the samples. The pinning behavior in the films related to the nano-porous structures, characterized by magnetic moment measurements and visualized by the magneto-optical imaging will be discussed in detail.

We thank Prof. T.H. Johansen for providing MOI indicator films and supporting the MOI activity in the group at UiO.

YBCO coated conductors are of high interest for future energy application. One of the main scientific challenges for further optimization of such conductors is to understand the interplay between local microstructure and critical current density J_c. Therefore, we combined a detailed structural investigation with a local J_c analysis of YBCO layers grown simultaneously on the two major types of technical templates, i.e. ion-beam textured buffer layers and rolling assisted biaxially textured substrates (RABiTs).
The main difference between these templates is the grain size. In RABiTS, large substrate grains with a size of several tens of micrometers are separated by low angle grain boundaries (≤ 15°), where the texture inside each recrystallized grain is very sharp. This template feature is transferred by epitaxial growth to the deposited YBCO leading to typical granularity effects in the superconductor, such as current percolation and, hence, grain boundary J_c limitation. On the other hand, the grain size of the ion-beam textured templates is typically smaller than the grain size of the final YBCO layer. As neighboring YBCO nuclei grow on different buffer grains, the superconductor grains are only slightly misoriented with respect to each other and some IBAD grains may be overgrown.
We studied the local microstructure of about 1 µm thick YBCO layers grown by pulsed laser deposition on both templates using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The local critical current density was analyzed by high resolution Hall scans with a resolution down to 2 µm. By overlapping structural information with the local J_c information we will discuss the influence of the texture distribution on the critical current density on the grain level. The studies are accompanied by additional global measurements of intra- and intergrain J_c using SQUID measurements.

This work was supported by EUROTAPES, a collaborative project funded by the European Union's Seventh Framework Program (FP7 / 2007 - 2013) under Grant Agreement no. 280432.

Thickness is a significant topic for coated conductors as the performance-cost can be enhanced much due to: the less tools and higher product yield achievable if the less or thinner buffer layers are developed, and the higher Ic expectable if the thicker superconducting layers are improved highly, such as 5-10 µm. In the present talk, several oxide buffer layers on NiW are reviewed not only due to the lattice matching, but also residual stress releasing rate. It will be shown that artificial periodic interfaces or secondary-phase particles invovled, appear effective to modulate the residual stress in thick REBaCuO films, allowing the pure c-axis and biaxial texture growth, and then a higher Ic expected.

Project supported by the Science and Technology Commission of Shanghai Municipality (13111102300 and 11dz1100302), the National Natural Science Foundation of China (11174193 and 51202141), the Ministry of Science and Technology of China (973 Projects, 2011CBA00105), the Science and Technology Commission of Shanghai Municipality (14DZ2260700)

To date, there is a large set of experimental data on the investigation of coated conductors (CC) tapes by using Magneto-optical imaging (MOI) techniques. However, an analysis of the penetration of the magnetic flux in HTS tapes in the mode of formation of the critical state is described insufficiently.
In our work we have conducted detailed analysis of the results of the magneto-optical measurements of the field's topography in the CC tapes at various temperatures in order to study the distribution of the field and develop a simple method for determining the critical current density. Experimental data interpretation has difficulties due to significant difference between magnetic field distribution in a thin film and distribution predicted by a simple Bean model. In contrast to the bulk sample, there is non-zero currents in the Meissner region of the thin film, and only for the transverse component of magnetic field is shielded.
To interpret the MOI experimental results we obtained analytical expressions for the magnetic field distribution. The finite thickness of the film has been taken into account and the distribution of the two components of the magnetic field was calculated. Also analytical expressions was derived for fields, larger than the field of full penetration. For the initial section of the magnetization curve seminumerical solution has been obtained.
It is shown that the fitting of calculated field profiles to the results of the magneto-optical measurements gives a satisfactory agreement between the model and experiment. Also we proposed method for determination of the critical current density from measurements of the topography of the transverse field that is insensitive to the precise form of the current lines. Furthermore, it is shown that the experimentally observed asymmetry of the field profile is probably due to a slight misalignment between the MOI film and CC tape that possibly due to the presence of small transverse curvature of actual CC tapes.

Research was supported by Russian Science Foundation (project №14-22-00098).

Various deposition techniques used in the coated conductor industry result in the formation of different structural inhomogeneities within the superconducting film having impact on its electromagnetic properties. In this study, an attempt to complex characterization of (RE)BCO structure was performed in tapes from several major producers. Scanning and transmission electron microscopy techniques were used for characterization of inner architecture (cross-sections of (RE)BCO layer) and surfaces of superconducting layer obtained by selective etching. The examination was focused on structural inhomogeneities e.g. outgrowths, precipitates, stacking faults, nanorods and their mutual correlations. The structural study was correlated to critical current dependence on magnetic field and temperature, where the effect of particular structural inhomogeneities on functional properties was evaluated.

In order to realize reliable commercialization of coated conductors, it is necessary to develop optimized stacking architectures of the wires and improve transport properties. We can determine several significant amounts of the wires to make competition for manufacturing to be active. The performance of the commercially produced wires is analyzed by investigation of the microstructure and the pinning characteristics of the wires from American Superconductor Corporation (AMSC), Superpower, and SuNAM Co. Macroscopic structural properties and formation of the phases were investigated by X-ray diffraction patterns. Transmission electron microscopy with energy dispersive spectroscopy was used to describe the microstructure and composition of the wires. Variation of the critical current under magnetic field in direction and magnitude was obtained at 77 and 60 K. We deuce pinning parameters and estimate the irreversibility of fields using the Dew-Hughes formula. It is observed that the wires exhibit almost same pinning characteristics under the normal pinning mechanism despite of different compositions, microstructures, as a result different stacking structures. In this paper, we can expect and evaluate the structural and transport properties of the wires through several advanced tools.

The installation and the first measurements of critical current versus strain of MgB2 and high temperature superconducting wires at the Cryogenic Laboratory of the University of Ferrara and INFN Ferrara, Italy, are presented. The aim of the bench is the measurement of the critical current as a function of elongation or compression of a straight MgB2 or HTS wire at working temperature using a standard traction measuring machine. Currents up to 600 A will be supplied to a 100 mm long wire. The system is cryogen free: the sample is cooled down to 20 K by cold heads in vacuum. As the stress is constant along the wire cross-section, the measurement of the properties of a straight-wire represents a direct measurement of the strain versus critical current behavior of the superconducting wire.

In applications of high-temperature superconductors (HTS) such as fault current limiters (SFCLs), HTS tapes are often exposed to abrupt variations of temperature and transitions. The thermal effect in this conditions may affect to the tape characteristics e.g. with a degradation in its critical current.
On the other hand, in the design of SFCL, both inductive and resistive, great length of tape is often necessary to make arrangements with coils, meanders, etc., and therefore junctions between pieces of tapes are obliged. The properties of these junctions may be also influenced for those changes of the operating temperature.
So, the characteristics of the tape and junctions after undergoing to temperature cycles are an important key to be taken into account when SFCL are designed.
This work presents the results of several tests on different individual samples of second generation (2G) tapes subjected to successive transitions by heating and cooling cycles in order to determine how their characteristics might be modified. Also we check the response of different arrangements of tapes with clamped junctions without soldering between them.
All of tests were done in liquid nitrogen with an automated dipping setup to reproduce heating and cooling cycles previously designed.

The authors are grateful to the Spanish Ministry of Science and Innovation for partial financial support.

The presented HIP process densifies the superconducting fiber, enhances grain connectivity and make possible positive modification of reaction dynamics due to an increase of magnesium melt temperature and allows to obtain small grains. This factors lead to increase of critical current density. In this presentation we show results of the results of critical current density (Jc), the pinning force density (Fp) and critical temperature (Tc) have been shown for the multicore monel-sheathed type MgB2 wires manufactured by continuous in tube forming and filling e.g. (CTFF) method in Hypertech Inc. Ohio, USA. Some of the MgB2 wires were SiC doped. Such multicore wires samples of in situ type with Nb barrier and Cu stabilizer with the monel sheaths have been subsequently hot isostatic pressed (HIP) at Institute of High Pressure Physics (IHPP PAS) Unipress at 0.4 GPa – 1.4 GPa argon gas pressure medium at temperatures of 700 oC for annealing times of 15 min. The Jc measurements have been performed in magnetic fields up to 14 T in Bitter type magnet installed at ILHMFLT PAS. The perpendicular magnetic field configuration was applied to the samples of c.a. 20 mm lengths. The critical temperature was measured using four-probe resistive method using AC current (5 mA, 14 Hz) at International Laboratory of HMF & LT by using PPMS Model 7100 (Quantum Design – in the field ranging from 0 up to 14 T).
The microstructure investigations were performed with SEM and EDX. Our results indicate that high isostatic pressure increases significantly Jc and Fp in high magnetic fields and slightly decreases Tc. The best results of 100 A/mm2 at magnetic fields of 12 T and 4.2 K have been obtained in these investigations. The maximal Fp of 5 GN/m3 at 5 T/4,2 K was achieved.

This work was mainly supported by Grant-in-Aid for Scientific Research (C) 25420892 from Japan Society for the Promotion of Science (JSPS) and NIFS Fusion Engineering Research project (UFFF036 and UFAA014) and the NIFS Collaboration Research program (KECF013 and KECF014).

The effect of platinum group metals (PG = Ru, Os, Rh, Ir, Pd and Pt) on the microstructure and critical current density of Cu/Nb-sheathed MgB2 wires has been studied using Mg_1-xPG_xB₂ powders with low doping levels. It was found that Pt and Pd do not enter the MgB2 lattice and have no influence on Tc. In contrast, the other PG elements can be substituted up to a few atomic percent and induce a decrease of Tc. In all cases, secondary phases are formed when the solubility limit is exceeded, but they have different morphologies depending on the dopant. For some PG elements, flux pinning improvements have been observed at low fields. The results will be discussed in comparison with previous investigations using other transition metals for doping on the Mg site.

We used aromatic hydrocarbon, coronene (C24H12), as a carbon additive for both Power-in-tube (PIT) and Internal-Mg-diffusion (IMD)-processed MgB2 wires. At 4.2 K and 10 T, high Jc of 1.1 x 105 A/cm2 and high Je of 1.2 x 104 A/cm2 for IMD MgB2 wires and Jc of 1.8 x 104 A/cm2 for PIT MgB2 wires were obtained (Supercond. Sci. Technol. 27 (2014) 085012). C24H12 seems to be an effective carbon additive for MgB2 superconducting wires mainly due to its high carbon content of 96 wt% (suggesting less impurity) and its decomposing temperature about 600 ℃(near the reaction temperature between Mg and B, so fresh carbon is obtained). C24H12 has a melting point of 438 ℃, melting of C24H12 enables uniform C24H12 coating on other particles before its pyrolysis to carbon. C24H12 can be used as an additive for MgB2 with 3 kinds of boron treatment methods: (1) direct addition to boron powder, (2) C24H12 coating to boron powder, and (3) carbon coating to boron powder by C24H12 pyrolysis. (1) and (2) were applied in our above work, while (3) is actually a new carbon coating method (Nanotechnology. 26 (2015) 045602). We have obtained Jc of 8.5 x 104 A/cm2 and Je of 8.2 x 103 A/cm2 at 4.2 K and 10 T for IMD MgB2 wires fabricated with this uniformly carbon coated boron powders. MgB2 wires fabricated with this carbon coating method are now being optimized and higher critical currents are expected, because method (3) has no hydrogen compared to direct addition (1) and C24H12 coating (2). All the C24H12 converts to carbon suggests that the carbon amount can be controlled by controlling the amount of C24H12. Furthermore, C24H12 has advantages that it is no obvious toxic to human beings and abundantly exist in sedimentary rock. All these advantages suggest C24H12 is an ideal candidate of carbon additive to fabricate uniform MgB2 superconducting wires for large scale-applications with low cost.

This work is supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST).

MgB₂ wires have been prepared by diffusion process using pure Mg metal. Amorphous B powder mixed with 5 mol% SiC nano-sized powder addition was packed into the space between a Mg tube and a Mg rod which was coaxially in the center, and then the tube was inserted into a pure iron tube to form the Fe/Mg/B(powder)/Mg composite wires. The composite was initially groove-rolled and drawn into a round wires of 1.0 - 0.6 mm in diameter without intermediate annealing. The composite wires were heat treated at 630℃ for 5 h in Ar gas atmosphere.
The MgB₂ core in ring shape was synthesized through the bidirectional diffusion reaction between outside Mg tube, B powder with SiC addition and inside Mg rod. The MgB₂ core forms denser structure with no void in comparison with conventional in-situ PIT processed MgB₂ wires. The Ic values at 4.2 K for the MgB₂ wire of 0.8 mm in diameter reach to 92 A at 6 T and 15 A at 10 T, which correspond to the Jc of 1,600 A/mm^₂ and 250 A/mm², respectively. Since the Jc performance of the present MgB₂ wires is much higher than that of the conventional in-situ PIT processed ones, the Magnesium diffusion process may be promising for a fabrication method of MgB₂ wires.

A titanium clad magnesium diboride tape has been developed in the framework of a study on space radiation superconducting shields, co-funded by the European Union (EU FP7 SR2S Project). The superconducting tape, manufactured via ex-situ method, is 3 mm wide, 0.5 mm thick and has 19 MgB2 filaments. The superconducting to metal ratio is 0.2. A pure aluminum thin strip, having the function of quench protection, is soldered on titanium after having electroplated the surfaces with copper and tin. The conductor has been designed aiming to fulfill the main requirements (low weight, helium free cryogenics and stability) of the SR2S toroidal magnet, devised to operate in the outer space for two years protecting astronauts against solar particles and cosmic rays.

The resistivity and the magnetization measurements of a MgB₂ prepared by IMD (Internal Magnesium Diffusion) was studied. The MgB₂ was prepared inside of a Nb sheath using various boron precursors: standard boron with 99% of purity, elemental amorphous nano-Boron powder from Pavezyum and boron nanopowder from SMI. The samples were prepared by the modified IMD technique, when a tubular magnesium wire with axial hole in the middle was inserted into Nb sheath and filled with the boron powder. Then the wire was finished by swagging and rolling to final dimensions of 1.4 x 1.4 mm and annealed at 660ºC for 1 hour in argon atmosphere. After the diffusion of magnesium into boron powder, solid MgB₂ was created without the hole inside, but the separation gap between the core and Nb sheath was observed instead. The separation gap allowed good extraction of the core from the Nb sheath. Microstructural characterization of the MgB₂ cross sections was done by the both optical and electron microscopy. Resistive measurements of the extracted cores were performed by the four point method and the magnetization was measured in the external magnetic fields ranging up to 14 T. Critical current densities (J_c) were calculated for variable temperatures: 4.2 K, 10 K, 15 K, 20 K and 25 K using Beans critical state model. The best grain connectivity and critical current density was observed for the core with standard boron and commercial Pavezyum. Grain connectivity, critical temperatures and critical current densities of the samples used various boron precursors are compared and discussed.

Superconductive MgB₂ powder in tube conductor technology established in 2001 [1] has become a real competitor to NbTi and Nb₃Sn conductors for MRI applications working at elevated temperatures in the 15-20K range, presenting a great hope for the superconductive conductors operating as DC cables in data-centres and electromagnets in wind generators, where accessibility of the indirect cooling with hydrogen is plausible [2]. A need for large quantities of the superconducting conductors for a variety of applications puts real pressure on the manufacturing capabilities of traditional powder-in-tube technology of composite wires. We are presenting a novel manufacturing technology to produce infinitely long and low cost MgB₂ superconductive wires.
The method of a nanocomposite material in situ feeding system, patented by Epoch Wires Ltd, guarantee the possibility of virtually unlimited conductor length, as well as greater processing control ensuring quality superconductor for applications. A uniqueness of the process is that it enables production of the continuous conductor with graded properties and graded artificial pinning centres, tailored for the particular applications where magnetic field flux density changes in value.
New wire forming, feeding, sealing and reduction technology has been developed to introduce a high degree of densification achieving 83% of magnesium diboride’s theoretical density and equally, if not more importantly, high engineering critical current density Je of the conductor. Generic single core conductor enables manufacture of multifilamentary conductors with desired twist pitch for transient losses and AC applications. Presented development of MgB₂ wires made by new continuous process addresses some challenges, that are resolved by using Taguchi optimization methodology. The proposed low cost, long length, reliable MgB₂ conductor, is needed by the electrotechnology industry.
[1] B.A.Glowacki, M.Majoros, M.Vickers, J.E.Evetts, Y.Shi and I.McDougall, Superconductivity of powder-in-tube MgB₂ wires, Supercond. Sci. Tech., 14 (4) 193, 2001.
[2] B.A.Glowacki, W.J.Nuttall, E.Hanley, L.Kennedy, D.O'Flynn, Hydrogen Cryomagnetics for Decentralised Energy Management and Superconductivity, J. Supercond. Nov. Magn., 28 (2) 561-571, 2015.

The authors would like to acknowledge the financial support of the European Regional Development Fund, Low Carbon KEEP funding and also Smart Award, Technology Strategy Board, UK.

MgB₂ is one of the most important superconductor material used for practical application, due to the properties and to the low price of the precursor elements, as well as the possibility to operate with cryocoolers. Defects in superconducting materials can be an efficient mechanism to improve the transport properties due to the pinning of the magnetic flux lines penetrating in the material under an applied magnetic field. Doping is another way to change the intrinsic superconducting properties, as the critical temperature and upper critical magnetic field. In this work a multifilamentary MgB₂ wire with a simultaneous addition of VB₂ and SiC were developed and analyzed. High energy ball milling, in a controlled argon atmosphere, were used to mix the precursor powders, using the ex-situ method. The final wire is compounded for 6x7 filaments, sheathed for niobium and copper used for cryogenic stabilization. Several heat treatment profiles were performed. Detailed microstructural analyses were performed by scanning electron microscopy. VSM analysis was used to perform measurements of the magnetic moment versus temperature to determine the critical temperatures, and magnetic moment versus applied magnetic field, which were used to estimate the critical current densities of the samples. As a result, the methodologies used to develop the superconducting wire were satisfactory, presenting a material with good properties.

The authors wish to thank USP, CNPq, CAPES, and FAPESP for the financial support. DRJ is a CNPq researcher.

Magnetic system of trap-Galatea [1] for the confinement of high-temperature plasma must consist of several superconducting coils levitating in plasma volume. Assuming that superconducting coils conserve the trapped magnetic flux, the possibility of creation of the system, at least, of two superconducting rings levitating in the field of the third fixed ring has been shown theoretically [2]. For experiments on levitation realization, multiturn short-circuited coils-rings with diameter from 50mm up to 80mm have been made from HTSC tape of the SCS4050-i-AP 2G HTS type (manufactured at SUPER POWER). Coils consist of two windings (the half of turns in each), spaced in height. The value of the soldered joint resistance is ~30nOhm. Current has been excited by coils cooling by liquid nitrogen in the solenoid magnetic field. Coils time constants measured from the curve describing the decay of the magnetic field with the time lie in the interval 18-35min. The dependence of the residual magnetic field B_o (in HTSC coil centre) from the field value of the magnetizing solenoid B_s (in solenoid centre) has been measured for all coils. At first the field B_o linearly increases with the increase of B_s ((B_o≈ B_s/2), and then, with reaching the tape critical current, it reaches the saturation. In order to estimate the coils ability to conserve the trapped magnetic flux, HTSC coils, after exciting the superconducting current in them, have been placed in solenoid and subjected to short-term action of the solenoid field of reversed polarity. Carried out measurements and experiments on HTSC coils-rings levitation have been shown that, in contrast to the coils from HTSC ceramics [2], described by the model of Bean’s critical state, coils from HTSC tape show more complex behavior.
1. A.I. Morozov, V.V. Savel’ev. //Physics-Uspekhi. 1998, v. 41, №11, p.1049-1089.
2. A.M. Bishaev, A.A. Bush, M.V. Kozintseva, et. al. //Technical Physics. 2013, v. 58, №5, p. 684-691.

This study was supported by the Ministry of Education and Science of the Russian Federation and in part by the Russian Foundation for Basic Research (project nos. 13-08-00717).

It is known that 2G HTS tapes have asymmetry of critical current anisotropy depending on Lorentz force direction. Two hypotheses were suggested as a reason of this phenomenon: 1) this is the result of properties of crystal lattice in 2G HTS tape; 2) or this is spatial inhomogeneity of critical currents in HTS tapes. The verification of hypotheses can be done by cutting of wide 2G HTS tape to narrow ones and measuring of critical currents anisotropy in narrowed tapes. If the anisotropy is due to properties of crystal lattice the anisotropy will be the same in all narrow tapes cut from the wider tape and similar to the wide tape: the critical current will be more in certain direction of Lorentz forces. In case when the asymmetry of critical current of 2G HTS tape depends on inhomogeneity of current distribution across a tape (edge effects or some defects), then critical current will be more in different directions of Lorentz force in narrowed tapes. For the perpendicular external magnetic field, when Lorentz force is parallel to the surface of a tape, the critical currents will be more when Lorentz force is directed to the side of higher current density. In parallel external field the anisotropy of critical current will be different. It is known that homogeneity of superconductor in 2G HTS tape is better near a substrate and becomes worse at a distance from surface. Therefore, the critical current will be more for all narrow tapes in one direction of Lorentz force when Lorentz force directs from surface under superconducting layer to a substrate. In this paper we studied 12-mm 2G HTS tape produced by SuperOx with critical current above 500 A. We measured anisotropy of critical currents in the wide tape and then in narrow 4-mm HTS tapes that were cut from the wide one by a laser. All measurements were done in external magnetic field from 0 mT to 200 mT. During measurements the direction of transport current was changed to find out asymmetry of anisotropy of critical currents. The experimental results its discussion. We concluded that the reason of asymmetry of critical currents is the spatial inhomogeneity of critical current density in 2G tapes cross-sections.

Since novel iron-based pnictide of Sr_0.6K_0.4Fe₂As₂ superconductor was discovered, the applications to high magnetic field and large current transportation are highly expected due to its low cost and unique superconductivity such as low anisotropy, relatively high critical current density and critical temperature. Recently, we successfully developed the Fe-sheathed superconducting Sr_0.6K_0.4Fe₂As₂ tape with the critical temperature of 32 K and fairly high critical current density of 1.5×10⁸ A/m² at 10 T and 4.2 K. Since the critical current density is considered as one of the most important factors for the applications of superconducting materials, the detail investigation on the critical current characteristic and flux pinning mechanism in the supposed operation temperature range is necessary. In this study, the critical current densities in the temperature range of 20 K to 30 K and in the magnetic field of up to 7 T were measured by using an inductive method (Campbell’s method). It shows a sharp drop of critical current density when a small DC magnetic field below 0.5 T is applied, followed by gradually flat decrease when DC magnetic field increases continually from 0.5 T to 7 T. This results we obtained match well up with the previous data measured by the standard four-probe method at the temperature of 4.2 K. It turned out that critical current density of Fe-sheathed superconducting Sr_0.6K_0.4Fe₂As₂ tapes is fairly high during 20 K to 30 K. Furthermore, basing on the experimental results of the penetrating ac magnetic flux profile and the feature of ac magnetic field dependence of penetration depth, the flux pinning mechanism of the sample within 20 K and 30 K was discussed. Our results indicate that the flux pinning mechanism of the sample in the temperature range of 20 K to 30 K is similar with that in 4.2 K.

The trifluoroacetate metal-organic deposition (TFA-MOD) process is known as a cost effective process to fabricate coated conductors (CCs) with high critical current density (J_c). However, it has been further expected to improve J_c in the magnetic fields for expansion of the application. A variety of applications requires a high performance of the minimum values of the critical current density (J_c,min) and the critical current within the whole angles of the applied magnetic fields to the conductor surface. In this study, we have developed a newly modified TFA-MOD process for CCs with finely dispersed BZO nanoparticles in the YGdBCO matrix. The obtained tapes have revealed drastic improvement of J_c values in the magnetic fields. The results include a high J_c value of 4.64 MA/cm² at 77K, self-field, and J_c,min values of 0.34 MA/cm² and 1.63 MA/cm², at 77 K, 3 T and 65 K, 3 T, respectively. In addition, the angular dependence of the applied magnetic field has exhibited much less anisotropy than before. These results are as high as more than approximately 2 times of the J_c value obtained in the previous work. It should be noted that the J_c-B performance of the CCs fabricated in this study is in a higher level than that obtained by the PLD process. Details in the processing as well as J_c-B (I_c-B) performance will be presented.

This work was supported by the Ministry of Economy, Trade and Industry (METI) as the Japanese national project of "Development of Fundamental Technology for HTS Coils".

High temperature superconductor (HTS) films on long length metallic tapes, known as coated conductors, are quickly becoming a reality for use in superconducting motors and generators. One way to ensure good biaxial texturing of the HTS film is via the use of a buffer layer deposited by inclined substrate deposition (ISD). In order to improve the in-field performance of such coated conductors, nanoscale inclusions can be incorporated into the HTS layer to pin flux vortices. Until now it is not known how effectively such pinning centres can be incorporated into HTS films grown on ISD substrates due to the unique growth process of the HTS layer. In this work we have prepared GdBa₂Cu₃O_7-x films grown heteroepitaxially on ISD-MgO buffered tapes via e-beam evaporation. We show how such nanoscale inclusions are arranged within the film. We also present data for the in-field critical current anisotropy of such films, displaying the effectiveness of the incorporated inclusions as pinning centres.

The authors would like to thank colleagues from THEVA Dünnschichttechnik GmbH & the Institute for Metallic Materials at the IFW Dresden who provided insight and expertise that greatly assisted the research. This project was supported by THEVA Dünnschichttechnik GmbH.

Development of consistent electrodynamics of engineering superconducting materials with high anisotropic pinning (both LTS and HTS) remains one of the central problems of applied superconductivity. This work is a logical continuation of a series of studies on electrodynamics of cold-rolled Nb-Ti 10-μm foil with anisotropic pinning. This material is quite suitable object for studying of the abovementioned issues for the following reasons:

• well tested manufacturing technology assures homogeneity and reproducibility of the Nb-Ti foil,
• the structure and micro-structure characteristics can be easily investigated by modern TEM, SEM and synchrotron X-ray techniques;
• anisotropy of the pinning is not sophisticated with possible critical field anisotropy due to cubic lattice structure;
• flat sample geometry enables to investigate tensor nature of voltage-current characteristics (VCC);
• sample preparation is simple (we used laser cutting) and set of samples with various angles regarding rolling direction is used for a comprehensive description of the pinning potential;
• pinning microstructure can be easy changed by adjusting of the temperature and duration of annealing.

We investigated Tc and Hc2 of cold-rolled and annealed foils with thickness of 10 μm (the heat treatment of 385ºC, 25 h). We used laser cutting method to fabricate the set of samples with various angles (from 0 to 90 deg.) to the rolling direction. Then VCCs of the samples were investigated on a rotating probe that rotates on two axes in fields up to 13T at 4.2K. Changes in the pinning potential have been defined by registering both longitudinal and transverse VCCs.
Detailed TEM and SEM investigation of Nb-Ti microstructure were done using Titan S-TWIN 80-300 (FEI) microscope with resolution up to 0.08 nm. The phase and texture analysis were performed using Bruker D8 Discover diffractometer with Cu-Kα radiation. High resolution diffraction measurements were performed on the dedicated beamline on Kurchatov synchrotron radiation source (KSRS) in transmission geometry with the energy of 17998.4 eV and narrow beam size. The obtained two-dimensional diffraction patterns were used for texture analysis or integrated to the standard form to perform Rietveld method.
Relations of microstructure and superconducting properties of the material is discussed.

The filamentary (Sm_0.33Gd_0.33Dy_0.33)_1.18Ba_2.12Cu_3.09O_y (SGD111) and (Sm_0.25Gd_0.25Dy_0.50)_1.18Ba_2.12Cu_3.09O_y (SGD112) samples were prepared by a solution spinning method. Precursor filaments were partially melted at 1000-1070 °C in flowing 0.1%O₂+Ar, 3%O₂+Ar and 20%O₂+Ar atmosphere gases, and then oxygenated on pure O₂ gas. The J_c value higher than 10⁴ A/cm² at 77 K and 0 T were obtained for SGD111 filamentary sample heat treated at over a wide temperature range of 1000-1060 °C in 1%O₂+Ar and 3%O₂+Ar. However, SGD211 sample treated in 20%O₂+Ar atmosphere gas did not show a superconductivity at a temperature higher than 77K.
On the other hand, SGD112 sample partially melted at 1070 °C in flowing 20%O₂+Ar exhibited the J_c value of higher than 10⁴ A/cm². It was found that increasing Dy ratio was effective to enhance the J_c value of (Sm,Gd,Dy)-Ba-Cu-O heat-treated in high oxygen partial pressure. SGD112 filament thus prepared in 20%O₂+Ar, fine (Sm,Gd,Dy)₂BaCuO₅ particles about 1 μm in diameter were dispersed in (Sm,Gd,Dy)-Ba-Cu-O matrix.

Bi-2223 tapes are commonly used in a variety of applications, even though the real mechanism of transport of the currents through the tapes is not yet fully understood. Especially the transport properties along the transversal direction of a tape are hardly being investigated, but can be important for a possible failure. In this contribution, we investigate the resistance behavior and the I/U-characteristics of two powder-in-tube tapes stemming from two different manufacturers in both parallel and transversal direction employing fabricated microbridges. Measurements were performed with currents up to 5 A and in fields up to 10 T. The measurements reveal that the resistivity in the transverse direction is always higher than in the parallel direction. A correlation with the local microstructure of the tapes indicates that the local filament distribution in the tape is responsible for this behavior. From the data obtained, we calculated the pinning potentials via Arrhenius-plots for both materials and both directions. The pinning potentials in the parallel direction were found to be higher as the transverse direction in both materials investigated.

We report enhanced flux pinning properties of GdBa₂Cu₃O_7-δ (GdBCO) films by a post-annealing process. According to our preliminary study on GdBCO coated conductors by the RCE-DR (Reactive Co-Evaporation Deposition & Reaction) process, the post-annealing process can be effective for enhanced flux pinning properties of GdBCO films in which Gd₂O₃ particles are trapped in GdBCO matrix, since Gd₂O₃ and GdBCO can react to form rod-shaped clusters of the stacking faults aligned along the c-axis of GdBCO by a post-annealing process in oxygen pressures above ~ 300 mTorr. On the basis of these results, GdBCO films which were fabricated by pulsed laser deposition (PLD) using KrF (λ = 248 nm) eximer laser on CeO₂-buffered MgO (100) single crystal substrate were post-annealed at various temperatures of 750 ~800 °C in low oxygen pressures below 1 Torr. Details of the relationship among the post-annealing conditions, microstructure, and superconducting properties of GdBCO CCs are discussed in this presentation.

This work was supported by the Power Generation and Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (No. 20131010501800)

At CERN we are developing a six-around-one CORC strand based Cable in Conduit Conductor (CICC) for use in large scale magnets. The CICC comprises six CORC strands helically wound around a central tube and inserted in a square jacket sized 30 x 30 mm² and features a high mechanical performance with a large current carrying capacity of 45 kA at 10 T and 4.2 K. An important issue in the development of such CICCs is the design of a joint for mutual connections of the CICCs or to the bus-bar system. A major design challenge is finding a simple, yet low-resistive method of injecting current homogeneously into the CORC strands of the CIC conductor. For this purpose, a dedicated numerical computer model using a finite element method has been built to evaluate the electrical resistance and asses the local current distribution for different geometrical varieties of the CICC joints. The results are used to choose a joint geometry that fits best the requirements of future CORC strand based CICCs. In the production of joints for single CORC cables we currently are pursuing a method in which the different ReBCO layers at both ends of the CORC cable are trimmed such that a staircase like geometry appears. This allows current to flow directly into the inner ReBCO layers. A similar trimming method is developed for joints for the six-around-one CORC based CICC and is first tested in a demonstration joint using dummy CORC strands. This joint is also used for testing the various steps of the manufacturing process before fabricating a joint with real CORC strands. This paper presents an overview of the numerical computer model, various CICC joint designs and the different steps in the manufacturing process of the joint.

The use of Second Generation High Temperature Superconducting wires in power applications requires that the conductor be engineered to minimize ac losses. This can be accomplished by dividing the YBCO film into thin filament arrays and the periodic introduction of filament bridges along the conductor length to emulate geometries present in twisted conductors. In this work, we explore the use of laser lithography of commercial Ag coated 2G YBCO produced by AMSC. Laser lithography enables the formation of these filaments with sharp edges in a controlled manner without metal splatter. This technique is a data driven materials process that can be scaled up for industrial production. This paper will present details of the laser lithography process, results of I_c measurements on samples with various striation widths, and AC loss data to validate the efficacy of the process.


This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program and by ONR through an external grant.

The ITER magnet coils are wound from Cable-In-Conduit Conductors (CICC) made up of superconducting and copper strands assembled into a multistage, rope-type cable inserted into a conduit of butt-welded austenitic steel tubes. The conductors for the Toroidal Field (TF) and Central Solenoid (CS) coils require about 500 tons of strands while the Poloidal Field (PF) and Correction Coil (CC) conductors need around 250 tons of NbTi strands.
China contributes to ITER project includes PF conductors, TF conductors and CC/Feeder which requires about 170 tons NbTi strand and about 30 tons Nb₃Sn strand. As the unique supplier in China, Western Superconducting Technologies Co.,Ltd.(WST) will supply NbTi and Nb₃Sn strands for ITER, and over 6000 km of Nb₃Sn strands have been produced in the past three years. All the performances of the Nb3Sn strands is able to meet the ITER specifications and with highly stability. Up to now, more than 30 tons of Nb₃Sn strands has been registered and will be cabled, jacketed and integrated into TF conductor. Before and during mass production for Nb₃Sn strands production, Conductor Performance Qualification Samples(CPQSs) titled with TFCN2, TFCN3, TFCN4, and TFCN5 respectively, have been tested in SULTAN facility, located at CRPP, Switzerland and passed all the test.

High temperature superconducting REBCO in the form of coated conductor (CC) tapes is a promising material for generating high magnetic fields in standalone or insert magnets. In order to reduce the number of turns and the impedance of the magnet, CC tapes need to be assembled in compact cables. Because of their large width-to-thickness ratio, CC tapes suffer high magnetization AC loss in perpendicular magnetic field, which is an issue during ramping of the DC magnet or in AC applications.
Numerous works have already shown that introducing filaments in individual CC tapes significantly reduce their magnetization loss in perpendicular magnetic field. In this work we focus on developing a Roebel coated conductor cable and introducing filaments into this specific structure. The burning question is if such filaments reduce the AC loss in Roebel cable architecture as efficiently as they do in individual tapes. Roebel strands from SuperPower non-stabilized tape with 1, 5, 10 and 20 filaments were prepared, characterized in terms of critical current and AC losses, and finally assembled into 10-strand 12 mm-wide Roebel cables. The cables’ magnetization AC losses were subsequently measured both with the calibration-free method and with a calorimetric method monitoring the evaporation of liquid nitrogen. The results obtained with the two methods were compared and the efficiency of the striation method for reducing the losses analyzed.
This work is expected to provide useful information on the viability and effectiveness of the striation technique for reducing AC losses in Roebel cables.

Roebel type cables made of REBCO conductor are potential candidates for high field accelerator magnets. The necessity to promote large effective transverse section in Roebel cable in order to avoid local overstress leading to electrical performance degradation was recently addressed. In this paper a new geometry of meander tapes for Roebel cable that enhances both the transverse effective section and the current margin at crossing segments is introduced. As Roebel cables are bent over the coil ends, the modulation of the bending radius of strands along cable pitch leads to a shift of strands respect to each other’s. The magnitude of shift is analytically investigated in this paper as a function of cable and coil geometry. Finally, the determination of the minimum transposition pitch of Roebel cable as a function of the coil geometry is introduced.

Two types of high purity Aluminum stabilized Superconducting Cable were developed and produced for use in large aperture high field superconducting solenoids. One (Type A) has transverse rectangular dimensions of 5.27 mm x 20.1 mm while the other (Type B) is 5.52 mm x 30.1 mm. The superconductor for both cables is copper stabilized NbTi strand woven into a Rutherford Cable. The stabilizer for Type A cable is 5N aluminum while the stabilizer for Type B is an aluminum alloy of 5N aluminum with a 0.1wt% Ni addition. Continuous unit lengths up to 1700 m are required for production. In total over 18,000 meters are required for the project. 　A major goal of the R&D is to produce a cable having high shear strength between Cu and Al boundary while maintaining high RRR and strength in the AL parts. We report on the cable mechanical properties, RRR of Aluminum, sharing stress between Cu and Al and Ic of the cable as well as the progress towards the fabrication of long unit lengths for production.

CFETR which stands for “China Fusion Engineering Test Reactor” is a new tokamak device. Its magnet system includes the Toroidal Field (TF) winding, Center solenoid winding (CS) and Poloidal Field (PF) winding. The main goal of the project is to build a fusion engineering Tokamak reactor with its fusion power is 50–200 MW and should be self-sufficiency by blanket. The project of central solenoid model coil (CSMC) was firstly set up to develop the technique of coils manufacture. The Nb3Sn conductor is used in the coil, whose design refers to ITER CS. The short twist pitch was proposed to use in the conductor. Because of short twist pitch and low void fraction, the higher compaction ratio during cabling is required and the possibility of damage on strands increases. The cabling technology was developed in collaboration among Chinese cabling suppliers and ASIPP. Several key technologies will be described in this paper.

Advanced high-energy physics magnets, high-field research magnets and fusion reactors require the development of high-temperature superconducting cables for magnetic fields exceeding 20 T, or allow for operating temperatures above the boiling point of liquid helium. Using ReBCO coated conductors, Advanced Conductor Technologies is developing Conductor on Round Core (CORC) cables that will enable this next generation of magnets. We will discuss results of CORC magnet cable development including the results obtained in late 2014 of a critical current of close to 7 kA in a 6 mm diameter CORC cable at 4.2 K and a background field of 17 T. This is an engineering current density of 246 A/mm2 at 17 T, or about 213 A/mm2 at 20 T, making CORC cables a viable candidate for use in the next generation of accelerator magnets. The latest results of the performance of CORC magnet cables wound from tapes containing thin substrates of only 30 mm thickness and improved pinning performance at high field through 15 % Zr doping will be presented. The results show a clear path to CORC magnet cables with current densities exceeding 500 A/mm2 at 20 T in the near future, making CORC cables the only round, isotropic REBCO-based magnet cables that are flexible enough to be wound into high-field magnets.

This work is supported in part by the U.S. Department of Energy, under contract numbers DE-AI05-98OR22652, DE-SC0007660, and DE-SC0009545, the U.S. National Science Foundation under Cooperative Agreement number DMR-0654118 and the State of Florida.

High performance Nb3Sn strands with high critical current density and low hysteresis loss are required by the the International Thermonuclear Experimental Reactor (ITER). Multifilamentary Nb3Sn strand has been successfully prepared via bronze process at Western Superconducting Technologies (WST). The critical current reaches 242 A (12 T, 4.22 K) after 650°C for 100 hrs. The influences of processing, diffusion barrier material and reaction heat treatment were studied. The results indicate that the lower annealing temperature below 500°C is benefit the critical current. The annealing temperature above 500°C make the critical current low, since the intermediate phase formed during process and the filaments like “sausage”. The Ta and Nb barrier were used to compare the influence of different barrier materials on fabrication process and supercondcuting properties of Nb3Sn strands. Nb diffusion barrier increases the hysteresis loss largely and the hysteresis loss reaches 309mJ/cm3(±3 T，4.22 K), which is double of strand with Nb/Ta combined barrier. Various heat treatments like different dwell time at 650°C were carried out. The critical currents under various heat treatments also were studied.