REBCO Tapes Research Articles

Characterization of residual-resistance-ratio of Cu stabilizer in commercial REBCO tapes

Residual-resistance-ratio (RRR) of Cu stabilizer in REBCO coated conductor is an important design parameter for REBCO magnets. Cu stabilizer with high RRR is especially beneficial for quench protections of REBCO magnets. In this work, we study RRR of electroplated Cu stabilizer in commercial REBCO tapes. We present RRR of over 180 samples measured for the quality assurance programs of REBCO magnet projects at the National High Magnetic Field Laboratory, USA (NHMFL). To investigate the factors that influence RRR, several samples were analyzed extensively by using scanning electron microscopy, secondary ion mass spectroscopy, and inductively coupled plasma mass spectroscopy. We found that RRR is strongly correlated with the grain size of Cu, which suggests that resistivity at low temperatures is dominated by grain boundary resistivity. In addition, low RRR corresponds to high concentration of chlorine impurity. This is explained by that higher chlorine impurity hindered the grain growth in the self-annealing process at room temperature which resulted in smaller grain size and low RRR. Annealing at 300C significantly enlarged the grain size and enhanced RRR. Due to the concern of critical current degradation, however, annealing is not recommended as a practical method to improve RRR of Cu in REBCO tapes.

Modelling the mechanics of 32 T REBCO superconductor magnet using numerical simulation

High-temperature REBCO superconducting tapes are very promising for high-field magnets. With high magnetic field applications there are high electromechanical forces, and thus a concern for mechanical damage. Due to the presence of large screening currents and the composite structure of the tape, the mechanical design of these magnets is not straightforward. In addition, many contemporary designs use insulated winding. In this work, we develop a novel two-dimensional axi-symmetric finite element tool programmed in MATLAB that assumes the displacement field to be within a linear elastic range. The stack of pancakes and the large number of REBCO tape turns are approximated as an anisotropic bulk hollow cylinder. Our results agree with uni-axial stress experiments in the literature, validating the bulk approximation. Here, we study the following configuration. The current is first ramped up to below the critical current and we calculate the screening currents and the forces that they cause using the minimum electromagnetic entropy production method (MEMEP) model. This electromagnetic model can now take insulated magnets into account. As a case study, a 32 T REBCO superconductor magnet is simulated numerically. We perform a complete mechanical analysis of the magnet by including the axial and shear mechanical quantities for each pancake, unlike in previous work where only radial and circumferential quantities were focused on. The effect on mechanical quantities without the screening current is also calculated and compared. It is shown that including the screening current-induced field strongly affects the mechanical quantities, especially the shear stress. The latter may be a critical quantity for certain magnet configurations. Additionally, in order to overcome high stresses, a stiff overbanding of different materials is considered and numerically modelled, which significantly reduces the mechanical stresses. The finite element-based model developed is efficient in calculating the mechanical behaviour of any general superconductor magnet and its devices.

Current sharing in double-sided REBCO tapes

Current sharing between RE–Ba–Cu–O (REBCO, RE = rare earth) tapes within a high-temperature superconducting coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by the contact resistivity between adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit of excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.

Numerical Investigation on Current Behaviors of NI/PI REBCO Coils Wound with Many Bundled Tapes for Sudden Discharge

Abstract For future applications such as compact fusion reactors, it is necessary to investigate some characteristics of meter-class D-shaped no-insulation (NI) REBCO coils. In recent years, several kinds of NI winding techniques, such as multi-tape-bundled REBCO tapes and a partial-insulation winding technique, have been proposed and experimented to improve the current characteristics of REBCO coils, such as an excitation delay and a large induced current. In this paper, the sudden discharging has been simulated to investigate not only the current behaviors but also the Joule heats for meter-class D-shaped REBCO coils with a few different NI winding techniques: (1) complete no-insulation between tape-to-tape/turn-to-turn for multi-tape-bundled windings and (2) partial-insulation for turn-to-turn of multi-tape-bundled windings without tape-to-tape insulation. The simulation results show that the amount of Joule heats emitted in a short time is large for many-tape-bundled NI REBCO coils. Also, the simulation result show that the greater number of tapes bundled on an NI REBCO coil, the more unbalanced current distributions are observed among the bundled tapes. Furthermore, the partial-insulation REBCO coils show a particular current distribution. These results reveal that cooling systems should be considered depending on the winding techniques.

A Novel Aluminum-Stabilized Stacked REBCO Tape Cable

A Novel Aluminum-Stabilized Stacked REBCO Tape Cable

Experimental study on screening-current induced strain in REBCO insert coils: under critical current control and operation current cycles

The screening-current effect is an inhomogeneous distribution of current density inside the REBCO conductors. The additional strain induced by the screening current, known as screening-current induced strain (SCS), is considered to affect the structural integrity of REBCO windings, especially when operating high-field REBCO insert magnets. In this work, we wound and tested a series of 50-turn REBCO coils inside a 10 T LTS external to investigate the influencing mechanism of multiple electromagnetic factors on SCS. We varied the critical current in different coils by different heat treatment procedures. Each coil was tested individually, experiencing a external field cycle and multiple operation current cycles at constant external fields. The extreme scenario for each coil was being energized to 400 A while the external field was 10 T. We adapted the discrete-coupled model to estimate the hoop strain distribution, monitored the experimental results by multiple strain gauges at the outermost turn. Test coil with a lower critical current endured a lower maximum hoop strain. When we were energizing the test coils, hoop strain increased at the edge of REBCO tapes while remaining nearly constant in the middle region. Additionally, the maximum hoop strain at the outermost turn decreased after each excitation cycle. This work could be an experimental reference for optimizing the electromagnetic design and the excitation scheme during the development of high-field REBCO magnets.

Effect of Conductive Metal Powder Incorporation on Vanadium Trioxide Insulation Between REBCO Tapes

Effect of Conductive Metal Powder Incorporation on Vanadium Trioxide Insulation Between REBCO Tapes

Critical current stability of 2G REBCO tape for space-flight HTS leads

High reliability is an essential requirement for all spaceflight hardware. Like the Hitomi x-ray observatory, its follow-on mission XRISM uses 2G REBCO tapes as current leads for the superconducting magnets that are a key component of the Adiabatic Demagnetization Refrigerator (ADR) that cools the detector array. While the Hitomi Soft X-ray Spectrometer (SXS) worked flawlessly in orbit, during its development there were indications that the critical current of its specialized REBCO tapes could degrade over time when exposed to normal-humidity air. To demonstrate that the updates to the XRISM HTS lead assemblies had mitigated this risk, a series of tests were carried out to measure the stability of Ic of dozens of samples over a period greater than the flight assemblies were exposed to air during integration and test. The test rig allowed not only the measurement of the sample Ic , but also the localization of the voltage rise as the current approached Ic . We will discuss the trends in the critical current of the samples, as well as localization of lower Ic regions.

Self-Shielding HTS DC Cable Made by REBCO Tapes With Different Widths

Self-Shielding HTS DC Cable Made by REBCO Tapes With Different Widths

Numerical Study on Fault Current Characteristics of Self-Shielded HTS DC Cables Made of REBCO Tapes in Parallel With Stainless Steel Tapes

Numerical Study on Fault Current Characteristics of Self-Shielded HTS DC Cables Made of REBCO Tapes in Parallel With Stainless Steel Tapes

Fault Current Characteristics of Self-Shielding HTS DC Cable Made of REBCO Tapes

Fault Current Characteristics of Self-Shielding HTS DC Cable Made of REBCO Tapes

Characterization of Critical Fields and Flux Pinning Energy of REBCO Tapes

Characterization of Critical Fields and Flux Pinning Energy of REBCO Tapes

Magnetic Field Angle Dependence of Critical Current in REBCO Tapes Produced by Different Techniques

Magnetic Field Angle Dependence of Critical Current in REBCO Tapes Produced by Different Techniques

Comparison of AC Loss Reduction Methods Based on Striation of Ag-Stabilized REBCO Tapes

Comparison of AC Loss Reduction Methods Based on Striation of Ag-Stabilized REBCO Tapes

Current Distribution and Critical Current Characteristics of a Novel HTS Cable Woven by Transpositional REBCO Tapes

Current Distribution and Critical Current Characteristics of a Novel HTS Cable Woven by Transpositional REBCO Tapes

Significantly Improving the Flux Pinning of YBa2Cu3O7‐δ Superconducting Coated Conductors via BaHfO3 Nanocrystal Addition Using Multistep Film Growth Method

AbstractA novel multistep film growth method is developed to prepare high‐performance BaHfO3(BHO)‐nanocrystal‐added YBa2Cu3O7−δ(YBCO) tapes. Upscaled YBCO tapes with high concentrations of 6.2 nm BHO nanocrystals exhibit better self‐field and in‐field performances when grown by the multistep method compared to those grown by the traditional method. The in‐field critical current (Ic) of the 1.6‐µm‐thick BHO‐added YBCO film at 30 K@3 T is enhanced by 50% in the optimal traditional cases, whereas it is further increased to 180% using a multistep growth strategy. The high‐performance YBCO layer is thickened to 2.3 µm using the multistep method, and the improvement of in‐field Ic at 30 K@3 T is enhanced by 215% to 360 A per 4 mm‐width compared to the pristine. The BHO size evolution during the high‐temperature process reveals that the added nanocrystals coarsened by 4 to 10.5 nm in both the traditional and multistep cases, thereby indicating that the further improvement in performance is attributed to the better film quality grown by the multistep method. This technique can be applied directly to the preparation of scaled REBCO tapes with a length of hundreds of meters.

Gamma radiation effects on high-temperature superconducting ReBCO tape

High-temperature superconducting (HTS) magnets are crucial components in future fusion reactors, subjected to prolonged irradiation and complex mechanical conditions. While the irradiation sensitivity of HTS materials has been extensively studied, limited research has explored the effects of force conditions during irradiation. This study investigated the influence of irradiation on ReBCO tapes. An irradiation experiment was conducted utilizing a Co60 source irradiation device. Superconductor properties were evaluated through the induction method, while microstructure analysis was performed using x-ray diffraction measurements. The results indicate that the critical current initially increases and subsequently decreases, while the critical temperature remains relatively stable. Furthermore, the bending degree during irradiation affects the critical current density, with a decrease in radius corresponding to a first increase and then subsequent decrease in critical current density. The force applied during irradiation exhibits a impact on the superconducting properties, underscoring the importance of considering force conditions in future investigations.

Numerical analysis of delamination behavior in an impregnated HTS Roebel cable during cooling

The delamination failures of REBCO tapes inside impregnated HTS Roebel cables during cooling have been observed in existing experiments. In this work, the finite element analysis (FEA) based on the cohesive zone model (CZM) is applied to simulate the delamination failure within impregnated Roebel cable during cooling from 300 K to 4.2 K. The modified three-dimensional (3D) Roebel geometric model is adopted. Simplified calculation strategies are developed to reduce the modeling complexity and computational cost. As a result, delamination characteristics observed in previous experiments can be captured based on the numerical simulation. Parametric analyses indicate that the mismatch in thermal expansion between impregnating materials and REBCO tapes has a more severe impact on the delamination than the edge pre-crack during cooling. Meanwhile, the various levels of delamination damage among REBCO tapes are observed, and the effects of delamination strength on the numerical results are discussed.

Performance study of REBCO multi-filament tapes/CORC cables prepared by reel-to-reel mechanical incision

REBCO high-temperature superconductor (HTS) has widely used in high magnetic field applications, because of the excellent critical current properties and high critical temperature. However, REBCO tape has an extremely large width-to-thickness ratio (typically in the range of 1000–10000) to cause too high power dissipation in the applications. In order to reduce the shielding current effect and AC loss generated during the application of REBCO HTS tapes, a roll-to-roll mechanical incision device was developed for the preparation of REBCO multi-filaments tapes. The microscopic morphology, critical current IC, and hysteresis loss of the tapes before and after incision were comparatively characterized using optical microscope, standard four-probe method, and physical property measurement system (PPMS) and other equipment and methods. The results show that the developed device prepares multi-filaments tapes with incision grooves depths of ∼ 30 μm and grooves widths of ∼ 20 μm on the superconducting layer, and the hysteresis loss of the 3-filaments is reduced by up to 48.6 % compared to that of the non-striated tapes under different temperature conditions. In addition, the IC of the short samples of the 3-filaments tapes was reduced by ∼ 18 % compared with that of the non-striated tapes under 77 K and self-field test conditions, whereas the samples of the 3-filaments tapes and the non-striated tapes were hand-wound respectively onto a metal core with a diameter of 5.25 mm to make a single-layer CORC cable, and there was no significant reduction in the IC of either of them.

Alternative analytical models for HTS tapes considering their AC hysteretic and resistive losses

This work proposes two alternative analytical models to evaluate the ac losses of high-temperature superconducting (HTS) tapes during their hysteretic and resistive modes. These models intend to extend the application range of state-of-the-art analytical models for current values higher than the critical one, i.e. for the resistive state, and to correctly predict the ac losses during the transition between the hysteretic and resistive modes. Two analytical models are proposed, one considering an extension of the Norris model for the HTS tape’s resistive mode and the other based on a sigmoid function to characterize the hysteretic losses and their smooth transition to the resistive mode. Analytical models capable of estimating ac losses of superconducting (SC) tapes are an important tool for the design of complex SC systems, such as SC fault current limiters, SC electrical machines and SC cables. The proposed models are validated experimentally, for a 1st generation BSCCO tape and a 2nd generation REBCO tape. Finite element simulation is also carried out to verify the accuracy of the proposed models. Results show that the proposed extended-Norris model presents some deviation at the transition between the hysteretic and resistive modes, while the sigmoid model presents very accurate results for the whole spectrum of applied current. Also, the parameters of the sigmoid models are independent of the tape geometry.