GdBCO Coated Conductor Research Articles

Enhancing in-field performance of GdBCO coated conductors by cooperative irradiation with Ti ions and protons

Irradiation can accurately manipulate defects and adjust pinning landscapes within REBa2Cu3O7-δ (REBCO, RE: rare earths) coated conductors (CCs). This study reports a productive method to dramatically boost the in-field critical current density (Jc) for GdBCO CCs using cooperative irradiation with Ti ions and protons. Remarkably, the in-field Jc of commercial CCs can be almost doubled at a wide range of temperatures and magnetic fields. Defects of various sizes induced by cooperative irradiation are more uniform distribution through the entire GdBCO film to improve the vortex pinning characteristics, thereby enhancing the in-field performance of the GdBCO CC. This method highlights how combining different particle irradiation types can tailor defect size and distribution, optimizing pinning landscapes for commercial REBCO CCs.

Unlocking the performance evolution of GdBCO coated conductors irradiated by deuterium plasma

REBa2Cu3O7-δ (REBCO, RE: rare earth) coated conductors (CCs) can generate a powerful magnetic field and are optimal for sustaining the reaction in fusion devices. However, the REBCO CCs will inevitably be exposed to neutron radiation during device operation. Transmutation produces gas atoms such as hydrogen will affect their properties. In this paper, GdBCO CCs were irradiated by 20 eV deuterium plasma. It was found that the irradiation introduced smaller (2–4 nm) pinning sites that formed a mixed pinning landscape with rare earth oxides (tens of nanometres) in the pristine samples, leading to an improved vortex pinning. At an irradiation fluence of 5.0 × 1018 D cm−2, the J c values of the samples irradiated by deuterium can maintain the best enhancement of in-field performance at 4.2 K. Excess irradiation results in a decrease in J c, a broadening of the superconducting transition width, and an enhanced disorder in GdBCO. This study provides some valuable insights for potential changes in the properties of REBCO CCs irradiated in fusion devices.

High-field critical current density enhancement in GdBCO coated conductors by cooperative defects

Irradiation can precisely control defects in, and improve the superconducting properties of, REBa2Cu3O7−δ (REBCO, RE: rare earth) coated conductors (CCs). Here we report an effective approach for enhancing the in-field performance of GdBCO CCs. The critical current density (J c) of GdBCO films was significantly improved through cooperative defects created by co-irradiation with O ions and protons, especially at low temperatures and high magnetic fields. Surprisingly, the in-field J c of commercial CCs can be nearly doubled. The cooperative irradiation-induced defects are uniformly distributed throughout the GdBCO layer, which promotes the overall performance of the CC. Moreover, the dimensions of these irradiation-induced defects closely match the coherence length of REBCO. This simple and efficient method is a practical post-production solution to improve the in-field performance of commercial REBCO CCs.

Effects of Precursor Film Thickness and Heat-Treatment Temperature On Joint Rate for a GdBa2Cu3Oy Superconducting Joint

GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (GdBCO) coated conductors (CCs) are promising wire materials because of their high critical temperature and critical current density in magnetic fields. The CCs must contain superconducting joints to create long wires. Previously, we fabricated a GdBCO CC with a superconducting joint by face-to-face crystallization of two CC samples with a GdBCO precursor film. To obtain a high current and low resistance, the crystallinity of GdBCO and a wide joint area are key considerations. This study investigates the effect of the heat-treatment temperature and precursor film thickness on these two factors. GdBCO samples were prepared without or with a precursor film of ∼50–200 nm thickness via pulsed laser deposition. The samples were set face-to-face and crystallized at 700-820 °C under a mechanical pressure of 40 MPa in an electric furnace. X-ray diffraction (XRD) analysis and optical microscopy revealed that both the peak intensity ratio of crystallized GdBCO and the joint rate at 800 °C were respectively 1.5 and 1.6 times higher than that at 720 °C. As the precursor film thickness increased from 50– 200 nm, the joint rate increased from 15.7– 25.4%, indicating that the heat treatment at ∼800 °C with a thick precursor film, is suitable. The results of this article lead to that the proposed method used in GdBCO CCs to reduce the electrical resistance.

In-situ measurements of the effect of radiation damage on the superconducting properties of coated conductors

An apparatus has been built to perform irradiation and electrical testing of REBCO coated conductors (CC) held below their critical temperature (T c). Patterned tracks of Fujikura GdBCO CC were irradiated with 2 MeV He+ ions in steps up to 4 mdpa whilst held at 40 K, and the critical current density (J c) determined from I–V characteristics. These ‘in-situ’ samples then underwent annealing experiments at room temperature. The superconducting performance, both before and after room temperature annealing, has been compared to equivalent samples irradiated at room temperature and then cooled for testing at 40 K to understand how the damage tolerance of these materials is affected by sample temperature. Details of the apparatus and experimental results from preliminary work are presented and discussed. These preliminary results show that both T c and J c values of patterned tracks degrade with irradiation dose, with most samples showing similar behaviour. The room temperature annealing of ‘in-situ’ irradiated samples resulted in a significant recovery of properties. We conclude that irradiation temperature does alter how the superconducting properties of GdBCO CC are affected by ion irradiation, and that this observation has implications for the design of high temperature superconducting magnets for future fusion reactors.

Characterization of the effect of ion irradiation on industrially produced GdBa2Cu3O7−δ superconducting tapes using a slow positron beam

To investigate the effect of irradiation-induced defects on the superconducting characteristics of industrially produced superconductor—GdBa2Cu3O7−δ (GdBCO)—coated conductors (CCs), we irradiated the GdBCO CCs with Au ions at 2 or 10 MeV and probed them using a slow positron beam. Vacancy clusters were detected in both unirradiated and irradiated GdBCO CCs. However, the effect of ion irradiation on the GdBCO CCs was characterized as a slight reduction in the positron annihilation rate with low-momentum electrons. We also found a correlation between the annihilation rate of low-momentum electrons and the superconducting transition temperature.

Reliability Evaluation Procedure of Electromechanical Properties in GdBCO CC Tapes Obtained by Uniaxial Tension and Fatigue Tests at 77 K

In the design of 2G superconducting magnets and coils, both the yield strength and the irreversible stress limit for critical current ( I c ) degradation of coated conductor (CC) tapes under various environmental conditions have been investigated. Equally important and yet often discounted are the reliability tests to evaluate the I c degradation induced by the fatigue loading expected during operation. Because I c degradation at the stress level below the reversible stress limit of the CC tapes is possible (e.g., under a static fatigue load), in this study, the procedures for evaluating the reliability of 2G CC tapes using characteristic limit values obtained through a series of electromechanical properties evaluations are introduced. I c behaviors were obtained at 77 K through specified loading against the elapsed time in a static fatigue test, while electromechanical fatigue limits of CC tapes were determined at a stress ratio (R) of 0.1 in a high-cycle fatigue test. The determination of electromechanical properties through uniaxial tensile and fatigue tests was established, and its long-term reliability was examined.

Strong flux pinning by columnar defects with directionally dependent morphologies in GdBCO-coated conductors irradiated with 80 MeV Xe ions

We show that Xe ion irradiation with 80 MeV to GdBa2Cu3Oy-coated conductors creates different morphologies of columnar defects (CDs) depending on the irradiation angles θi relative to the c-axis: continuous CDs with a larger diameter are formed for oblique irradiation at θi = 45°, whereas the same ion beam at a different angle (θi = 0°) induces the formation of discontinuous CDs. The direction-dependent morphologies of CDs significantly affect the angular behavior of the critical current density Jc. In particular, low-energy irradiation defects induce further improvement of Jc in a unique combination of irradiation angles of θi = 0° and ±45°: discontinuous CDs at θi = 0° and crossed CDs at θi = ±45° provide correlated pinning in a wide angular range, which is more strongly enhanced by each other via the pinning of kinks.

Finite element modeling of single-lap joint between GdBa2Cu3O7-x-coated conductors using cohesive elements

Both the initiation of cracking and delamination growth have been observed in the joints between the GdBCO-coated conductors, which causes the degradation of electrical property irreversibly. In this paper, firstly, the tension (lap-shear) test of the single-lap joint is simulated to verify the selected material properties and the numerical model. Then, the delamination behavior of the single-lap joint between the GdBCO-coated conductors is investigated based on the cohesive model. The multiple layers of zero thickness cohesive elements are implemented within the tapes and interfaces between the tape and solder. Different boundary conditions are also considered to determine the corresponding delamination position and value of debonding load. With the classical beam theory and linear elastic fracture mechanics, the approximate analytical solution is given to throw light on the behavior of the joint. The numerical results show that the interface parameters such as cohesive strength can affect the positions of crack formation and stable extension of crack. In addition, the debonding load is influenced by the overlap length of the joint and constraint condition.

Superconducting Joint of GdBa2Cu3Oy Coated Conductors by Crystallization of an Additionally Deposited Precursor Layer

A superconducting joint of REBa 2 Cu 3 O y (REBCO) coated conductors (CCs) has been demanded strongly to fabricate long length CCs for high field magnet applications such as nuclear magnetic resonance and magnetic resonance imaging. In the previous reports of superconducting joint, specimens of REBCO CCs were jointed via melting REBCO phases or via solid state diffusion of REBCO phases. In our study, we propose a new method of joint for REBCO CCs. A precursor layer is additionally deposited on GdBCO CC by a metal organic deposition process, and then two pieces of them are stuck together face-to-face and crystallized the precursor to form 123 phase under mechanical pressure in an oxygen atmosphere. The microstructures and temperature dependence of resistance of the jointed sample are characterized by a cross-sectional transmission electron microscopy (TEM) and a four-probe method, respectively. As a result, TEM observation reveals that two CCs are jointed together without formation of secondary phases at the joint interface. Also, temperature dependence of resistance shows Tc onset and Tc zero of 93 K and 82 K, respectively. Consequently, a superconducting joint has been completed successfully. The concept of this method is combining film growth and solid-state diffusion for the additionally deposited precursor layers.

The Magnetic Properties of Several HTS GdBCO-Coated Conductors

The magnetic properties of commercially available GdBCO-coated conductor (CC) tapes which were fabricated on Hastelloy and stainless steel (SS) substrates and which have different reinforcing/stabilizing layers (Ag-stabilized CC tape with SS substrate, brass-laminated CC tape with SS substrate, and Cu-plated CC tape with Hastelloy substrate) were investigated by a magnetometer magnetization method using Physical Property Measurement System. The background magnetic moment m values of the CC tapes with Hastelloy substrate are nearly zero, compared with those with SS substrate. The measurement of magnetic moment m(H) for the three CC tapes was carried out at temperatures between 10 and 90 K in fields up to 7.0 T. The magnetization loss of the CC tapes with SS substrate is much larger than that with Hastelloy substrate at the temperature range used in this study. The irreversibility magnetic moment Δm irr was obtained by measuring the m(H) curves. The critical current density J c values have been estimated from the Δm irr (H) data, using Bean's model. Brass-laminated CC tape with SS substrate was found to have larger J c and higher irreversibility field Hirr than Cu-plated CC tape with Hastelloy substrate.

The Superconducting Properties of a High-Temperature Superconducting GdBCO-Coated Conductor

The Superconducting Properties of a High-Temperature Superconducting GdBCO-Coated Conductor

Quench and recovery characteristics of second-generation high-temperature superconducting GdBCO coated conductor with various patterns of stabilizers

Abstract This paper investigates the quench and recovery characteristics of second-generation high-temperature superconducting GdBCO coated conductors (CC) with variously patterned stabilizers in over-current conditions. A chemical etching method was used to produce various patterns of stabilizer on GdBCO CC without degrading current-carrying capacity. From the results of the over-current testing of GdBCO CC tapes with variously patterned stabilizers, the tape that had stabilizer with longitudinally disconnected patterns exhibited higher voltage increase and slower recovery time than those that had continuity of stabilizers along the longitudinal direction, because the excessive heat and current could not be transferred through the stabilizers in the former. Overall, uniform heat and current distributions along the stabilizer of GdBCO CC are among the critical factors determining thermal and electrical stabilities of a GdBCO magnet in over-current conditions, especially when quench occurs.

The Effects of Gd-Free Impurity Phase on the Aging Behavior for the Microwave Surface Resistance of Ag-coated GdBa2Cu3O7−δ at Cryogenic Temperatures

High-TC GdBa2Cu3O7−δ (GdBCO) superconductor has been popular for making superconductive tapes that have much potential for various fields of large-scale applications. We investigated aging effects on the microwave surface resistance (RS) of Ag-coated GdBCO layer on Hastelloy substrate, so called GdBCO coated conductors (CCs), and Ag-coated GdBCO films on LaAlO3 (LAO) single-crystal substrates at cryogenic temperatures and compared them with each other. Unlike the RS of Ag-coated GdBCO films showing significant degradation in 4 weeks, no significant aging effects were found in our Ag-coated GdBCO CCs aged 85 weeks. The reactive co-evaporation deposition and reaction (RCE-DR) method was used for preparing the Ag-coated GdBCO CCs. Such durability of the Ag-coated GdBCO CCs in terms of the RS could be explained by existence of a protective impurity phase, i.e., Gd-free Ba–Cu–O phase as confirmed by transmission electron microscopy study combined with the energy-dispersive X-ray spectroscopy measurements. Although the scope of this study is limited to the Ag-coated GdBCO CCs prepared by using the RCE-DR method, our results suggest that a solution for preventing the aging effects on transport properties of other kinds of Ag-coated GdBCO CCs could be realized by means of an artificially-grown protective impurity layer.

Enhancement of In-Field Critical Current Density of BaZrO3-Added (Y, Gd) BCO-Coated Conductors by Using a Multi-Coating TFA-MOD Method

We have investigated the in-field critical current properties in BaZrO3-added (Y, Gd) Ba2Cu 3O7-δ (YGdBCO)-coated conductor fabricated by using a multi-coating trifluoroacetates metal-organic deposition (MOD) method. We compared these properties with EuBCO-coated conductor fabricated by the pulsed laser deposition (PLD) method. The sample using the 30-nm once-coat-layer-thickness d once shows superior in-field J c down to 4.2 K than that of the previous standard coating using 170–nm-thick layer for each coating. From the analysis of E – J characteristics, an analytical expression for J c as a function T and B has been derived. It was confirmed that the high J c region in sample with d once = 30 nm is widely spread in high-temperature and high-magnetic-field region. By comparison with the J c properties of the BaHfO3 -added PLD CCs, the minimum J c, which is estimated from magnetic field angle dependence, shows even higher value up to 5 T of magnetic field at 65 K and up to 3 T at 77 K. From these results, the new MOD-YGdBCO process using the thin once-coat-layer-thickness is very promising for the practically important mid field region such as 3 to 5 T.

A Noncontact &lt;italic&gt;T&lt;/italic&gt;c Evaluation Technique Using a Hall Probe Array

A noncontact superconducting transition temperature (T c ) measurement system using a Hall probe array was devised to measure T c of high-temperature superconductor (HTS) coated conductors (CCs) without physical contact to the surface, thereby avoiding contact with electrodes, which can cause damage to the conductor surface. The variations of the Hall voltage (V) distribution, which comes from the distribution of magnetic field on the surface of the CC, under a fixed applied field at different temperatures were used to estimate T c . The measured T c of the HTS GdBCO CC made by SuNAM was approximately 93.2 K by the noncontact T c method, as compared to approximately 93.5 K by the conventional four-probe-contact method in a commercial PPMS. Thus, the T c obtained by this system is comparable with that from the transport four-probe method. In addition, the noncontact T c measurement system devised and used in this study is simple because it does not need comparison and conversion with values measured by contact methods.

Angular Behavior of Jc in GdBCO-Coated Conductors With Crossed Columnar Defects Around ab Plane

We investigated in detail the flux pinning properties around B || ab for GdBCO-coated conductors with crossed columnar defects produced by heavy-ion irradiation, where the crossing angle Θi was systematically controlled in the range from ±5° to ±15° relative to the ab plane. A single peak of critical current density Jc centered at B || ab occurs for the crossing angle of Θ i = ±5°, where an upward shift in Jc can be observed compared to an unirradiated sample. As the crossing angle is larger, the Jc peak becomes smaller and broader while maintaining the peak at B || ab. Increasing Θi up to ±15°, three Jc peaks emerges at B || ab and at the two irradiation angles, independently from the others. The crossover behavior from the single peak to the triple one around the ab plane is attributed to the strong line tension energy of flux lines around B || ab , which derives from the elliptical nature of the core of flux lines in anisotropic superconductors.

Resistive REBCO Coated Conductor Butt-Joints Based on an Ultrasonic Welding Method

The development of low-resistance coated conductor (CC) joints is important in viewpoint of applications using power cables, coils, and magnets. In particular, a stable and reliable CC tape joint applicable to practical electrical devices should be developed. In this study, CC tape butt-joints with low joint resistance in terms of transport were fabricated by direct bonding at the interface of the Cu-Cu stabilizers in overlapped GdBCO CC tapes. Both ultrasonic welding and hybrid welding processes, which have been attempted recently to achieve low joint resistance in lap-joint CC tapes, were used. The joint quality of butt-joint CC tapes fabricated by various joining methods was evaluated and compared to that in lap-joints. The variation of joint resistance with joint length was also evaluated. The electromechanical properties of butt-joints were examined using the double-bending test. The minimum bending diameter for the retained critical current and joint resistance degradation was determined for CC butt-joints.

Depth profiling of the microwave surface resistance of high-JC GdBa2Cu3O7−δ coated conductors grown using the RCE-DR process

We study depth profiling of the microwave surface resistance (RS) of GdBa2Cu3O7−δ (GdBCO) coated conductors (CCs) grown using the reactive co-evaporation by deposition and reaction (RCE-DR) method, a method enabling extremely high deposition rate. GdBCO CCs with the critical current (IC) of more than 790 A cm−1 at 77 K in self-field are used for the study. The RS of the GdBCO CCs is measured at temperatures of 10–80 K using a 8.5 GHz TE011-mode rutile resonator, which is compared with that of YBa2Cu3O7−δ films and GdBCO films epitaxially grown on single crystal substrates. It turns out that there is significant inhomogeneity in the RS over the thickness of the GdBCO layer, with the RS value of the top part at 30 K being almost two times higher than the corresponding one of the bottom part. A transmission electron microscopy study reveals that Gd2O3 grains coexist with GdBCO grains with the average Gd2O3 grain sizes being ∼150 nm at the top and ∼100 nm at the bottom of the GdBCO layer. We relate the inhomogeneity in the RS of the GdBCO layer with the positional dependence of the Gd2O3 grain size, for which effects of the dielectric losses from the Gd2O3 grains on the measured RS of the GdBCO layer are considered. Our results imply that the critical current density, another important transport property of superconductors, could be inhomogeneous over the thickness of the GdBCO layer grown using the RCE-DR method.

Critical current degradation behaviour of GdBCO CC tapes in pure torsion and combined tension-torsion modes

Coated conductor (CC) tapes utilized in high-current-density superconducting cables are commonly subjected to different loading modes, primarily torsion and tension especially in the case of twisted stacked-tape cable. Torsion load can occur due to twisting along the length or when winding the CC tapes around a former, while tension load can occur due to pre-tension when coiled and as a hoop stress when the coil is energized. In this study, electromechanical properties of single CC tapes under torsion load were investigated using a new test apparatus. The results could provide basic information for cable designers to fully characterize stacked cables. Copper-electroplated and brass-laminated CC tapes fabricated with different deposition techniques were subjected to pure torsion and combined tension-torsion loading. The critical current, Ic degradation behaviours of CC tapes under torsional deformation were examined. Also, the effect of further external lamination on the Ic degradation behaviour of the CC tapes under such loading conditions was investigated. In the case of the combined tension-torsion test, short samples were subjected to twist pitches of 200 mm and 100 mm. Critical parameters including reversible axial stress and strain in such twist pitch conditions were also investigated.