Rare-earth Barium Copper Oxide Research Articles

Manufacturing the current flow diverter architecture in REBCO tapes using silver inkjet printing

Abstract A low normal zone propagation velocity (NZPV) combined with critical current inhomogeneities favor the nucleation of destructive hot spots in rare-earth barium copper oxide (REBCO) tapes. Increasing the NZPV using the current flow diverter (CFD) concept is a promising solution to mitigate the risk of developing hot spots. The fabrication method of CFD REBCO tapes implies several steps consisting in masking, silver etching, mask removal, and silver deposition, which takes time and remains a barrier to the implementation of a low-cost industrial production of long-length CFD REBCO tapes. This work presents a cost-effective and maskless CFD fabrication approach that relies on inkjet printing (IJP) of silver patterns directly on top of the REBCO layer to create a non-uniform interfacial resistance between the silver and the REBCO surface, along the width of the tape. The parameters of IJP and oxygen annealing were optimized to obtain highly conductive silver patterns deposited on the surface of the REBCO layer. CFD REBCO tapes were successfully fabricated using commercial REBCO tapes and the proposed method without degrading the superconducting properties. Experimental measurements revealed an increase of the NZPV by a factor of 6-7 compared to commercial REBCO tapes.

Development of a high current density, high temperature superconducting cable for pulsed magnets

Abstract A low AC loss Rare Earth Barium Copper Oxide (REBCO) cable, based on the VIPER cable technology has been developed by Commonwealth Fusion Systems for use in high field, REBCO based tokamaks. The new cable is composed of partitioned and transposed copper ‘petals’ shaped to fit together in a circular pattern with each petal containing a REBCO tape stack and insulated from each other to reduce AC losses. A stainless steel jacket adds mechanical robustness—also serving as a vessel for solder impregnation—while a tube runs through the middle for cooling purposes. Additionally, fiber optic sensors are placed under the tape stacks for quench detection. To qualify this design, a series of experiments were conducted as part of the SPARC tokamak Central Solenoid Model Coil program—to retire the risks associated with full scale, fast ramping, high flux HTS Central Solenoid (CS) and Poloidal Field (PF) coils for tokamak fusion power plants and net energy demonstrators. These risk study and risk reduction experiments include (1) AC loss measurement and model validation in the range of ~5 T/s, (2) an IxB electromagnetic loading of over 850 kN/m at the cable level and up to 300 kN/m at the stack level, (3) a transverse compression resilience of over 350 MPa, (4) manufacturability at tokamak relevant speeds and scales, (5) cable to cable joint performance, (6) fiber optic based quench detection speed, accuracy, and feasibility, and (7) overall winding pack integration and magnet assembly. The result is a cable technology, now referred to as PIT VIPER, with AC losses that measure fifteen times lower (at ~5 T/s) than its predecessor technology; a 2% or lower degradation of critical current (Ic) at high IxB electromagnetic loads; no detectable Ic degradation up to 570 MPa of transverse compression on the cable unit cell; end to end magnet manufacturing, consistently producing Ic values within 7% of the model prediction; cable to cable joint resistances at 20 K on the order of ~15 nΩ; and fast, functional quench detection capabilities that do not involve voltage taps. This cable technology will be tested comprehensively in a Central Solenoid Model Coil to prove its readiness for compact, high field tokamak operation.

Delamination analysis of the epoxy impregnated REBCO racetrack coil under thermal stress based on a 3D model

Superconducting coils made of Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) exhibit superior electromagnetic performance. Employing epoxy impregnation can improve the structural integrity of the superconducting coils. However, the delamination behavior is observed in the epoxy impregnated REBCO coil when the environment temperature cool from the room temperature to 77 K. In previous studies, there is a few researches on the delamination and mechanical behavior of the epoxy impregnated racetrack coil. Therefore, this study proposes a three-dimensional (3D) mechanical-thermal model which incorporates the cohesive zone material (CZM) to investigate the delamination mechanisms in epoxy impregnated REBCO racetrack coils during cooling. We found that the coil experienced a higher tensile radial stress at the semicircular part than the straight part during the cooling process. This leads to that the delamination area tends to appear initially in the semicircular part with large tensile radial stress. And the stress concentration generated at the edge of the delamination area in the semicircular part can cause the extension of the edge of the delamination area to the straight part. In addition, the influences of the thermal expansion coefficient (CTE) of the mandrel and overband on the coil delamination behavior are studied in this paper. It is found that the radial stress, the initial position of the delamination, and the degree of delamination are affected by the CTE of the mandrel and overband. And the delamination of the coil can be avoided by reducing the tensile radial stress of the coil through reducing the CTE of the mandrel or increasing the CTE of the overband. And the prevention of the delamination in the semicircular part can obviously avoid the occurrence of the delamination in the straight part of the racetrack coil.

Investigation of Gamma-Induced Changes to Screening Currents and AC Losses in Mono- Versus Multi-filamentary REBCO Coated Conductors Using DC and AC Magnetometry

REBCO (rare-earth barium copper oxide) coated conductor tapes are a highly attractive option for magnet materials in future tokamak fusion power plants. However, the threat of intense neutron and gamma radiation, together with AC losses during magnet coil ramping, has raised concerns around magnet coil lifetimes. Irradiation-induced changes to flux creep rate has been identified as a key performance-limiting factor in REBCO tapes at low temperatures and high fields post-irradiation with gamma rays; spontaneous flux creep contributes to hysteretic AC loss in REBCO cables under applied AC fields. Knowing that multi-filamentary tapes are under consideration for tokamaks as an AC loss mitigation, magnetic measurements and gamma irradiation experiments are presented here on striated and mono-filamentary YBCO tapes to investigate the differences in post-irradiation screening currents and AC losses. Reduction in AC losses improved magnetisation critical current density (Jc) retention after 1 MGy in the multi- relative to the mono-filamentary samples. After the 5 MGy dose, striations then made the multi-filamentary tape more susceptible to Jc degradation because of the thinner individual filament width. Scanning transmission electron microscopy analysis on an analogous GdYBCO mono-filamentary tape did not indicate the introduction of nm-scale amorphisation to the active GdYBCO layer after gamma irradiation. A potential theoretical explanation for the underlying mechanism altering the flux-pinning landscape across the REBCO layer surface in gamma-irradiated tapes is discussed. This work concluded that gamma effects on screening current capability should be considered in future tokamak REBCO tape qualification studies.

Intelligent surrogate model of a high-temperature superconducting cable for reliable energy delivery: short-circuit fault performance

High-temperature superconducting (HTS) cables are promising solutions for electric power transmission of renewable energy resources, where their fault performance study is vital to avoid power interruptions in the grid. In this study, a fast intelligent surrogate model was presented to estimate the fault performance of a 22.9 kV/50 MW HTS cable to make fast fault performance analysis of the HTS cables possible during the design stage. Different fault scenarios were considered under different fault durations, fault resistances, and types of faults. Then, the fault energy, fault current, fault type, fault duration, and fault resistance were fed into the surrogate model as inputs. The outputs were the temperature of the rare-earth barium copper oxide (ReBCO) tapes, the former temperature, the ReBCO layer current, and the total resistance of each phase. For surrogate modelling, cascade forward neural networks (CFNNs) were used. The results show that the CFNN-based model estimated the fault performance of the cable with an average accuracy of 99.1%. Finally, the impact of considering fault energy, fault current, and both, as the inputs of the models, on the final accuracy were explored. The results show that by considering the fault energy, the accuracy of the surrogate model can be increased.

A platform to study defect-induced behavior in high-temperature superconductor cables

High-temperature superconductor (HTS) cables and magnets are enabling a range of high-current and high-field applications, including compact fusion devices aiming to achieve net energy. Defects in HTS pose manufacturing, cost, and operational challenges. A rigorous understanding and predictive capability for defect-induced behavior at relevant scale has not been established. To address this shortcoming, we have developed a cable-level defect characterization experimental platform coupled to high-fidelity computational modeling. The cable ( Ic∼ 438 A at 77.4 K, self-field) comprises a non-twisted 70 cm-long copper former containing a soldered stack of five rare-earth barium copper oxide (REBCO) tapes (each with Ic = 115.7 A/4 mm-w at 77.4 K, self-field), which can contain a variety of induced defects. Spatially-resolved electric fields are measured with a high-density voltage tap array and absolute current distribution with six custom-wound embedded Rogowski coils. 3D circuit modeling uses nodal analysis and self-consistently accounts for the magnetic field dependence of critical current. The model successfully predicts the experimentally measured spatial and operating current dependencies of electric field and current distribution with no defects, one defect, and two defects, validating the defect characterization platform as a tool for improving the design, cost, fabrication, and operation of REBCO cables.

Investigation on characteristic of vanadium trioxide insulation mixed with metal powder for rare-earth barium copper oxide coils

This study examined the turn-to-turn contact resistance (R ct) between rare-earth barium copper oxide (REBCO) tapes and layers of vanadium trioxide (V2O3) and V2O3 mixed with metal powder mixture. V2O3 in single crystal structure was electrically characterised to exhibit resistivity with negative temperature dependence, allowing the turn-to-turn insulation to self-regulate the current bypass between REBCO tapes. To facilitate effective quench protection of V2O3-insulated REBCO magnets above the metal-insulator transition temperature (T rt), R ct must be further reduced to a level similar to those of non- and metal as insulated (NI and MI) REBCO magnets. Thus, we explored the mixing of conductive metal powders such as molybdenum (Mo) with V2O3 paste and investigated the transition properties of R ct. The resistance versus temperature characteristics, microscopic morphologies of the V2O3 layers, and thermal conductivity (k v) were appropriately assessed to determine the effects of mixing the metal powder with V2O3. The R ct of virgin V2O3 exhibited variations of 107–105 μΩ cm2 under 77–293 K. As the mixing concentration of the metal powder was increased, the reduction magnitude on R ct increased for > T rt (approximately 150 K). Furthermore, the transition slope became gentler for a wider temperature range of < T rt. For metal powder concentrations exceeding 50 wt%, R ct decreased by approximately 2 orders of magnitude (∼103 μΩ cm2) for > 150 K compared with that for virgin V2O3 paste. Moreover, compared to that of pure V2O3, k v demonstrated a remarkable increase of approximately 352% at 91 K for Mo powder mixed at a concentration of 60 wt%. The improved electrical and thermal properties of the V2O3 insulation layer owing to the mixing of metal powders can help REBCO magnets operate in an insulated state under normal conditions and effectively convert to a non-insulated state under quenching.

Mixed-mode fracture analysis of CORC cables with double-edge cracks under tension and torsion

The Conductor on round core (CORC) refers to a circular cable that is helically wound with rare-earth-barium-copper-oxide ((RE)BCO) high-temperature superconducting (HTS) tapes. This type of cable finds extensive applications in large superconducting magnets. However, the mechanical–electrical performance of CORC cables is hindered by microscopic edge cracks that occur during the mechanical slitting process of HTS tapes. In this paper, the mixed-mode stress intensity factor (SIF) of cracks in CORC cables under different loading conditions is investigated using the extended finite element method (XFEM). The design variables of CORC cables are optimized by considering the effect of various factors such as the crack parameter, the winding angle, the core radius, and the Poisson’s ratio of the winding core on the SIF. The results indicate that the impact of each factor on the mixed-mode SIF varies depending on the loading mode. Notably, the influence of the winding angle on the SIF is particularly significant and intricate. In the case of tensile loading, a smaller winding angle proves advantageous in impeding crack propagation. Conversely, the most dangerous winding angle for torsional loads is 45°. The divergence of these effects can be indirectly indicated by theoretical solutions regarding the tape strain along the helix direction. For the cases examined, the results have shown that the crack propagation path is independent of these factors, and the direction of propagation is perpendicular to the edge of the tape.

Characterization of a novel TORT cable wound of stabilized striated REBCO tapes for reduced magnetization AC losses

REBCO (rare-earth barium copper oxide) high-temperature superconducting tapes, have a high potential for winding of large magnet coils. Tapes on round tube (TORT) cables represent a promising option for achieving a conductor suitable for the winding of magnet coils. However, certain applications, such as accelerator magnets, require the use of superconducting cables with low magnetization alternative current (AC) losses. There are several methods to reduce AC losses in TORT cables. Our first approach was to get rid of eddy currents by replacing the copper former with dielectric materials based on polymers and composites, i.e. polyethylene terephthalate glycol-modified reinforced with carbon fibers. Additional reduction of hysteretic loss was achieved by striating of copper coated REBCO tapes. We employed chemo-mechanical striating, for these objectives. However, the superconductor is exposed during the striating process, which may lead to later moisture-related degradation. Hence multilayers based on Ti/AlN were deposited using magnetron sputtering in order to protect the superconductor immediately after the striating process from water and atmospheric moisture corrosion. Subsequently, striated tapes as well as the non-striated tapes were then wound onto formers with diameters of 10 mm, 7 mm and 5.5 mm, and then on the short TORT cables bending tests were performed. After each technological step, direct current measurements were performed on the samples and finally the AC losses were measured.

A facility for cryogenic ion irradiation and in situ characterization of rare-earth barium copper oxide superconducting tapes.

Superconducting magnets based on Rare Earth Barium Copper Oxides (REBCO) offer transformative capabilities in the fields of fusion energy, high energy physics, and space exploration. A challenge shared by these applications is the limited lifetime of REBCO due to radiation damage sustained during operation. Here we present a new ion-beam facility that enables simultaneous cryogenic irradiation and in situ characterization of commercial REBCO tapes. The ion source provides spatially uniform fluxes up to 1018protons/m2s with kinetic energies up to 3.4MeV, in addition to helium and higher-Z species. Using this facility, we can induce uniform damage profiles in the first 10-20 µm of REBCO tapes with less than 0.25 appm of hydrogen implanted in REBCO after a dose of 1020protons/m2. The tape can be held between 20 and 300K with an accuracy of ±0.1K and is connected to a four-point probe measuring the critical current, Ic, and critical temperature, Tc, before, during, and after irradiation with transport current ranging from 100 nA to 100A, and a typical voltage noise less than 0.1 μV. These capabilities are presently used to study the effect of irradiation temperature on REBCO performance change during and after proton bombardment, to assess the possibility of Ic and Tc recovery after irradiation through thermal annealing, and to explore the instantaneous and recoverable suppression of Ic and Tc observed during irradiation.

Numerical Study on Mechanical Behavior and Electromechanical Properties of Solder-Jointed REBCO-Coated Conductors.

As the second-generation high-temperature superconducting conductors, rare earth-barium-copper-oxide (REBCO) coated conductor (CC) tapes have good potential as high-field and high-energy superconductors. In superconducting applications, several joints are required for conjugating comparatively short REBCO CC tapes. Soldering lap joints are the simplest and most commonly applied REBCO CC joints. In addition to joint resistance, the mechanical behavior and electromechanical properties are also crucial for superconducting applications. In this paper, the electromechanical properties and mechanical behaviors of soldering lap joints at 77 K under a self-field were studied. The mechanical behavior was addressed by using a full three-dimensional multilayer elastic-plastic finite element model (FEM) with REBCO CC tape main layers and solder connecting layers. Then, the electromechanical properties were analyzed by using Gao's strain-Ic degradation general model on the basis of the FEM results. Both the mechanical behavior and electromechanical properties were verified by experimental results. The effects of soldering lap conditions including lap length, soldering thickness and lap style on the electromechanical properties and mechanical behaviors were discussed. The results indicate that shorter overlap lengths and a thinner solder can reduce the premature degradation of Ic due to stress concentrations nearby the joint edges; moreover, the irreversible critical strain is significantly higher in the back-to-back joint approach compared to the widely used face-to-face joint approach.

A newly developed 10 kA-level HTS conductor: innovative tenon-mortise-based modularized conductor (TMMC) based on China ancient architecture

We proposed a new type of high-temperature superconducting (HTS) conductor concept: modularized conductors (MCs) connected by Chinese traditional tenon-mortise (TM) connection structure, referred as TMMC (tenon-mortise modularized conductor). The conductor consisted of multiple concentric round sub-conductors with slots for stacking rare-earth-barium-copper-oxide (REBCO) tapes. Innovatively, the REBCO stacks in the adjacent sub-conductors were arranged with the fully-misaligned configuration to enhance the critical current’s isotropy with respect to magnetic field and reduce ac loss. For example, the angle between the adjacent stacks in the two adjacent sub-conductors was 45° if each sub-conductor contains 4 REBCO stacks. In order to construct the fully-misaligned configuration, the sub-conductors were designed with two open half-circular formers and connected by TM structure which makes the conductor modularized and simply to assembly and disassembly. Based on the design concept, a prototype conductor containing 160 REBCO tapes distributed in the four concentric sub-conductors was fabricated. The conductor’s measured critical current was 13.69 kA at 77 K and self-field, which was consistent to the simulation result. In order to further improve the TMMC’s engineering critical current density (J ce) and bending performance, we proposed two enhancement approaches: reducing the former’s thickness and re-arrange stacks in the outer sub-conductors. With the enhancements, both TMMC’s radius and J ce were comparable to the existing slotted-core conductor. The study shows the TMMC’s advantages of non-twisted structures, easy assembly, high-current carrying and low ac losses, which made it promising for constructing large-scale scientific devices.

Qualification and test of space compatible superconducting current leads (REBCO) designed for adiabatic demagnetization refrigerators

Many astrophysics observations require space telescopes, either to reduce atmospheric perturbation or simply to make these detections possible (in the X-Ray spectrum for example). One of these missions, Athena, is led by the European Space Agency (ESA), with additional international contributions, dedicated to X-Ray observation. Two instruments will be part of this mission and among them, X-IFU, will use Transition Edge Sensors (TES) to detect and precisely measure the energy of X-Ray photons. These sensors require a temperature of 50 mK to reach their ambitious sensitivity goals. In space, this temperature can be reached using Adiabatic Demagnetization Refrigeration (ADR) and such a cooling system is currently being developed for the X-IFU instrument. ADR utilizes magnetocaloric materials which, upon variation in magnetic fields, can produce a cooling effect. The magnetic field of the order of 1 T in a volume of 10s of cm3 is produced by a superconducting coil with high winding number and current limited to approximately 2 A. Even though this current is low compared to most earth-based systems, metallic current leads to link the high- and low-temperature stages would cause high thermal loads, unacceptable for the limited capacity of the cryogenic cooling chain of the spacecraft. Therefore, a harness consisting of superconducting current leads is planned to reduce the thermal loads at the low-temperature stage. As part of an ESA contract, our team designed, built and tested such a space-compatible harness. This harness includes the electrical interfaces at both ends as well as mechanical support. Its development is capable of operating between interfaces at 80 K and 4 K. The harness is based on industrially available Rare-Earth-Barium-Copper-Oxide (REBCO) High-Temperature Superconductor (HTS) tapes. The tapes were laser-cut by our group to fulfill our specifications, Parylene coated and reinforced with Kapton laminate tape for mechanical and insulating purposes. After characterization of the single tapes, the assembled harness has been subjected to an extensive qualification sequence including thermal cycling and mechanical testing based on launch loads requirements. This paper will summarize the technical design choices for this HTS harness. It will discuss the test results and propose some perspectives for the next iteration of the development.

Performance degradation due to thermal cycling in soldered Faraday and SuperPower HTS tape stacks

Soldering stacks of high temperature superconducting (HTS) tapes results in a current carrying matrix with high electrical, thermal, and mechanical stability. In some applications, these tape stacks may be exposed to elevated temperatures during thermal heat cycles. Previous research on thermal degradation of high temperature superconductors has been performed with isolated crystals or individual HTS tapes, showing that oxygen-out diffusion from the rare-earth barium copper oxide (REBCO) results in a reduction of the superconducting performance. In this work, the performance of Pb37Sn63 soldered HTS tape stacks with thermal cycling to 170∘ C is quantified through determination of the critical current Ic , the n-value, the linear resistance R in the pre-transition region of the tape stack current–voltage (I–V) traces, and the diffusion coefficient D associated with oxygen-out diffusion. The effect of tape manufacturer and nickel electroplating were considered; three soldered stacks each of unplated Faraday, nickel electroplated Faraday, unplated SuperPower, and nickel electroplated SuperPower tapes were fabricated. Across 20–30 one hour thermal cycles, there are no significant differences in degradation profiles observed between the unplated and nickel electroplated tape stacks for a given manufacturer. There is however a marked difference in degradation profiles observed between the SuperPower and Faraday tape stacks. For the unplated and plated SuperPower tape stacks, the degradation in Ic generally follows the model to describe oxygen-out diffusion from the superconducting REBCO layer. Significantly less degradation is observed in the unplated and plated Faraday tape stacks, and in some sections Ic even increases slightly across cycles. Further, cases of increasing Ic accompanied with decreasing n are observed, a decoupling between the two parameters. Across all samples, the linear resistance was highest in current-redistribution regions near the leads. Consistent with the model of oxygen-out diffusion and the formation of an increasingly wide oxygen deficient layer in the REBCO, the linear resistance increased with cycle number.

Experimental study on the an-isotropic critical current of REBCO tape.

Superconducting magnets are widely used in nuclear fusion reactors, high-energy particle accelerators, steady-state high magnetic fields, etc. Higher magnetic fields and higher operating temperatures are two application trends. High temperature superconducting (HTS) materials are the only choice for high temperature and high field magnets in the future. The first- and second-generation HTS materials have a typical tape structure; their critical performance is magnetic field angle and temperature dependent. A new test facility is developed for an experimental study on the an-isotropic critical current. The field angle can be changed from 0° to 360° with a resolution of 1°. The rotation deviation angle is measured to be 0.2° when the upper part rotates 90°. The temperature can be changed from 4.2 to 80K. The temperature errors are ±50, ±80, and ±135 mK for 4.2-20, 20-40, and 40-80K, respectively. The angle dependence of critical current (Ic) of the tested rare-earth barium copper oxide tape within 0°-30° is strong. From 30° to 90°, the sample Ic almost does not change with the magnetic field angle. The implementation of the project will not only promote the structural optimization of HTS tapes but also promote the miniaturization and economical application of HTS magnets.

The improved model based on the H-A formulation in large-scale HTS magnet

The rapid progression of the rare earth barium copper oxide (REBCO) coated conductor have paved the way for the development of high-field superconducting magnets. However, the elevated aspect ratio of REBCO tapes results in the generation of substantial screening currents, presenting a formidable challenge in the electromagnetic analysis of high-field superconducting magnets. Currently, the finite element method (FEM) stands as the dominant technique employed in large-scale superconducting magnet system for screening current computations in REBCO tapes, encompassing primarily the H formulation and the T-A formulation. However, these models exhibit certain limitations. In this paper, the two-dimensional axisymmetric H-A FEM model is introduced into the computation of REBCO tapes in high-field magnet, and the corresponding homogeneous model, partial homogeneous model and multi-scale model are established. It can be demonstrated that the model not only significantly accelerates computational speed but also enhances precision in comparison to the T-A model. Remarkably, the computational time of the H-A homogeneous model is approximately a quarter of that required by the T-A homogeneous model. It is anticipated that the model harbors substantial potential for future applications in the computational analysis of large-scale superconducting magnets.

Intelligent estimation of critical current degradation in HTS tapes under repetitive overcurrent cycling for cryo-electric transportation applications

Overcurrent cycling refers to the procedure of imposing repetitive overcurrent to superconducting tapes/devices for characterizing their critical current reduction. Characterizing the overcurrent cycling behaviour of Rare Earth Barium Copper Oxide (ReBCO) tapes is a crucial step in the design process of High Temperature Superconducting (HTS) devices. Multiple overcurrent incidents during the operation of an HTS device can significantly decrease the total critical current, leading to potential quenches and failures. Data-driven models have been proposed in the literature to estimate the Critical Current Degradation Rate (CCDR) of ReBCO tapes under multiple overcurrent scenarios. However, these methods have exhibited notable errors in the range of 8%–11%, in the estimation of the critical current reduction. This paper proposed methods based on Artificial Intelligence (AI) techniques aimed at the challenges of conventional methods of CCDR estimation. Different AI-based techniques were proposed, tested, and compared to show the effectiveness of the proposed intelligent approach, including Support Vector Regression (SVR), Decision Tree (DT), Radial Basis Function (RBF), and Fuzzy Inference System (FIS). Experimental data on critical current values of ReBCO tapes subjected to multiple and repetitive overcurrent cycles were employed for this investigation. The results demonstrated that the Mean Relative Error (MRE) of the SVR method is 23%, for the DT model is approximately 0.61%, the MRE of the FIS model is well above 0.06%, and the MRE value for the RBF method is about 1.1 × 10−6%. Moreover, the proposed AI models offer fast test times, ranging from 1 to 11 ms. These findings highlighted the potential of using AI techniques to enhance the estimation accuracy of the risks associated with overcurrent events.

Effect of doping on evolution of He&lt;sup&gt;+ &lt;/sup&gt;ion irradiation defects and superconductivity in EuBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7–δ&lt;/sub&gt; superconducting strips

Rare-earth barium copper oxide (REBCO) as a representative of the second-generation high-temperature superconducting materials possesses superior physical advantages such as high critical magnetic field, elevated critical temperature, and superior current density, which has been applied to many domains. Although the introduction of non-superconducting nanoscale particle dopants, as a critical method, can enhance the magnetic flux pinning capability of REBCO strips, the effect of the doping on the performance change and microstructure evolution of the strips under irradiation is ignored. In this work, undoped and 3.5% BaHfO&lt;sub&gt;3&lt;/sub&gt; (BHO) doped EuBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7–δ&lt;/sub&gt; strips are investigated in the room-temperature irradiation experiments (1.4 MeV He&lt;sup&gt;+&lt;/sup&gt; ions) with three distinct doses of 5×10&lt;sup&gt;14&lt;/sup&gt;, 5×10&lt;sup&gt;15&lt;/sup&gt;, and 5×10&lt;sup&gt;16&lt;/sup&gt; ions/cm&lt;sup&gt;2&lt;/sup&gt;, respectively. Electrical performance tests reveal that the undoped strips exhibit a slight increase in &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; after the low-dose irradiation. However, with dose increasing, &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; decreases by over 60%. In contrast, doped strips experience a significantly smaller decline in &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;, ranging only between 30% and 40% at high-dose irradiation. Raman spectroscopy and transmission electron microscopy characterizations confirm that the defects induced by He&lt;sup&gt;+&lt;/sup&gt; ion irradiation lead to amorphization and structural disorder within the superconducting layers, which is the primary reason for the decline in the superconducting properties of the strips. The results show that the introduction of localized strain through BHO nanophase in the superconducting layer changes the migration and aggregation behavior of irradiation-induced defects, repairing the damaged superconductor structure. Furthermore, the field dependence and temperature dependence of &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; of doped strips are irradiation-resistant due to BHO nanocrystals as strong pinning centers. Additionally, unlike the superconducting properties of the REBCO strips that can be repaired through oxygen annealing after neutron or heavy ion irradiation, the electrical properties of the two types of strips irradiated with high doses of He&lt;sup&gt;+&lt;/sup&gt; ions in this work are further deteriorated after being annealed. It is worth noting that compared with the undoped strip, the localized strain generated by BHO in the doped strip inhibits the size growth of helium defects in the three-dimensional direction at high temperatures, which changes the magnetic flux pinning characteristics and delays the disorder and amorphization of the superconducting layer structure caused by the severe growth of helium bubbles. This study provides a reference for the application of REBCO superconducting strips in the irradiation environment.

Elastoplastic mechanical behavior of high-field magnet of REBCO high temperature superconducting composite tape under extreme environment

Rare Earth-Barium-Copper-Oxide (REBCO) high temperature superconducting (HTS) coated conductors (CCs) are one of the best candidate materials for high-field magnets. However, due to its laminated structure, each component materials of the CCs are inevitably subjected to residual thermal stress and electromagnetic force during heat treatment, processing, cooling, coil winding, and operation of the magnet structure. It causes changes in its superconducting properties, and even leads to irreversible degradation of superconducting critical characteristics, brittle layer fracture and peeling delamination within the coil. To reveal the synthesis of the tape and the stress state of the high-field coil under multi-physical fields. The residual thermal stress/strain accumulation of each component material of the tape is investigated under two thermal processing and manufacturing methods by combining analytical theory with numerical calculation. In which, the two thermal processing methods are metal-organic chemical vapor deposition (MOCVD) process and one-step cooling simplified process respectively. The results show that the residual thermal stresses accumulated by five materials, Hastelloy, Buffer, REBCO, Ag and Cu, under the step-by-step synthesis process are about 14.7%, 97.3%, 96.3%, 80% and 49.2% of the simplified model, respectively. And the residual thermal strains are about 15.1%, 96.8%, 95.2%, 85.2% and 27.5% of the simplified model. In addition, after the five materials are manufactured according to the step-by-step thermal processing process, the accumulated residual thermal stresses are about 1.88%, 86.3%, 61%, 114.3%, and 34% of their respective yield strengths, respectively. The elastoplastic mechanical behavior of the magnet under the background of high magnetic field and strong current is also studied. The results indicate that the maximum values of effective and hoop stresses in each component material of the coil are distributed in the innermost side of the magnet, and decrease gradually along the radial direction of the magnet. In the innermost coil of the magnet, the effective stress of each component material increases with the increase of the transmission current. When the transmission current Iope = 183 A, the material Cu reaches the yield strength and enters the plastic deformation stage. Whereas the material Hastelloy reaches the yield strength and enters into the plastic deformation stage when the transmission current Iope = 222 A.

Electromechanical characteristic of stacked REBCO tapes under tension deformation

Stacking REBCO tapes is an effective way to increase the current-carrying capacity of the cable. Various loading conditions, including combined tension-bend, are applied to these tapes during fabrication and operation of the magnets. This paper investigates the degradation behaviors of critical current (Ic) in stacked rare earth–barium–copper–oxide (REBCO) coated conductor (CC) tapes under tension loading through experimental. Uniaxial tension experiments are conducted on single tapes and 4-tape cables with different stacking at 77 K. The critical current degrades rapidly when strain exceeds an irreversible threshold around 0.4-0.5%. A 3D finite element model analyzes the non-uniform stress distribution in the cable cross-section under tension, causing different degradation behaviors. An empirical model combining the Ekin law and Weibull distribution is proposed to relate Ic and axial strain. By fitting experimental data, the key parameters are determined. The Ic of a single tape reduces 20% at 0.4% strain. Face-to-face stacking decays at 0.45% irreversible strain, while back-to-back decays at 0.38%. The model provides an effective way to optimize the electromechanical performance of stacked REBCO cables.