Critical current degradation in an epoxy-impregnated rare-earth Ba_(2)Cu_(3)O_(7-x)coated conductor caused by damage during a quench

High-temperature superconducting(HTS)rare-earth Ba_(2)Cu_(3)O_(7-x)(REBCO)coated conductors(CCs)have significant potential in high-current and high-field applications.However,owing to the weak interface strength of the laminated composite REBCO CCs,the damage induced by the thermal mismatch stress under a combination of epoxy impregnation,cooling,and quenching can cause premature degradation of the critical current.In this study,a three-dimensional(3D)electromagnetic-thermal-mechanical model based on the H-formulation and cohesive zone model(CZM)is developed to study the critical current degradation characteristics in an epoxy-impregnated REBCO CC caused by the damage during a quench.The temperature variation,critical current degradation of the REBCO CC,and its degradation onset temperature calculated by the numerical model are in agreement with the experimental data taken from the literature.The delamination of the REBCO CC predicted by the numerical model is consistent with the experimental result.The numerical results also indicate that the shear stress is the main contributor to the damage propagation inside the REBCO CC.The premature degradation of the critical current during a quench is closely related to the interface shear strength inside the REBCO CC.Finally,the effects of the coefficient of thermal expansion(CTE)of the epoxy resin,thickness of the substrate,and substrate material on the critical current degradation characteristics of the epoxy-impregnated REBCO CC during a quench are also discussed.These results help us understand the relationship between the current-carrying degradation and damage in the HTS applications.

Research on CeO2 cap layer for YBCO-coated conductor

Two groups of coated conductor samples with different thicknesses of CeO2 cap layers deposited by pulsed laser deposition （PLD） under the same conditions have been studied. Of them, one group is of CeO2 films, which are deposited on stainless steel （SS） tapes coated by IBAD-YSZ （IBAD-YSZ/SS）, and the other group is of CeO2/YSZ/Y2O3 multilayers, which are deposited on NiW substrates by PLD for the fabrication of YBCO-coated conductor through the RABiTS approach. YBCO film is then deposited on the tops of both types of buffer layers by PLD. The effects of the thickness of the CeO2 film on the texture of the CeO2 film and the critical current density （Jc） of the YBCO film are analysed. For the case of CeO2 film on IBAD-YSZ/SS, there appears a self-epitaxy effect with increasing thickness of the CeO2 film. For CeO2/YSZ/Y2O3/NiW, in which the buffer layers are deposited by PLD, there occurs no self-epitaxy effect, and the optimal thickness of CeO2 is about 50 nm. The surface morphologies of the two groups of samples are examined by SEM.

Transient liquid assisted nucleation mechanism of YBa_2Cu_3O_(7-δ) in coated conductor films derived by BaF_2 process

It is significant for low-cost preparation of YBa2Cu3O7-δ（YBCO） coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF2-derived YBCO crystallization. In the present work,a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal–organic deposition（MOD） or the physical vapor deposition BaF2 process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.

Fabrication of IBAD-MgO and PLD-CeO2 Layers for YBCO Coated Conductors

MgO thin films with different textures are fabricated by the ion beam assisted （IBAD） method on the Y2O3/Al2O3 buffered C276 tape. Then a CaO2 layer is directly grown on the IBAD-MgO film by the pulsed laser deposition （PLD） method. Effects of lBAD-MgO texture, substrata temperature and thickness on the grain alignment of the CeO2 layer are investigated. Film characterization is performed by x-ray diffraction and atomic force microscopy. It is found that the orientation and texture degree of the CaO2 layer are very sensitive to the IBAD-MgO texture. By optimizing the IBAD-MgO texture, CeO2 has pure （002） orientation and excellent biaxial texture deposited in a broad substrata temperature range. In addition, the PLD-CeO2 layer has a thickness effect. Under the optimized experimental condition, the PLD-CeO2 layer has a high in-plane texture of △φ = 2.9° and a smooth surface with an rms surface roughness of less than 2nm. The critical current density Jc of a 0.4μm-thick YBCO film deposited on the CeO2 layer is 6.25 × 106 A/cm2 at 77K and a self-field.

Preparation and Characterization of CeO_2/YSZ/CeO_2 Buffer Layers for YBCO Coated Conductors

CeO2 seed layer was deposited on rolling-assisted biaxially textured metal substrates by direct-current （DC） magnetron reactive sputtering. The effect of deposition temperature on epitaxial orientation of CeO2 thin films was examined. High quality CeO2 layers were achieved at deposition temperature from 750℃ to 850℃.Subsequently yttria-stabilized zirconia （YSZ） and CeO2 films were deposited to complete the buffer layer structure via the same process. The best samples exhibited a highly biaxial texture, as indicated by FWHM （full width half maximum） values in the range of 4°-5°, and 2°-4° for in-plane and out-of-plane orientations,respectively. Secondary ion mass spectrometer analysis confirmed the effective prevention of buffer layer against Ni and W metal interdiffusion. Atomic force microscope observations revealed a smooth, dense and crack-free surface morphology, which provided themselves as the good buffer structure to the YBa2Cu3O7-δ（YBCO） coated conductors.

Growth and Characterization of Doped CeO_2 Buffers on Ni-W Substrates for Coated Conductors Using Metal Organic Deposition Method

CeO2 and Ce0.8M0.2O2-d films （M = Mn, Y, Gd, Sm, Nd and La） with （00l） preferred orientation have been prepared on biaxially textured Ni-W substrates by metal organic decomposition （MOD） method. The factors influencing the formation of cracks on the surface of these CeO2 and doped CeO2 films on Ni-W substrates were explored by X-ray diffraction （XRD）, scanning electron microscopy （SEM） analysis, atomic force microscopy （AFM） and differential scanning calorimetry （DSC）. The results indicate that many factors, such as the change of the ionic radii of doping cations, the transformation of crystal structure and the formation of oxygen vacancies in lattices at high annealing temperature, may be related to the formation of cracks on the surface of these films. However, the crack formation shows no dependence on the crystal lattice mismatch degree of the films with Ni-W substrates. Moreover, the suppression of surface cracks is related to the change of intrinsic elasticity of CeO2 film with doping of cations with a larger radius. SEM and AFM investigations of Ce0.8M0.2O2-d （M = Y, Gd, Sm, Nd and La） films reveal the dense, smooth and crack-free microstructure, and their lattice parameters match well with that of YBCO, illuminating that they are potentially suitable to be as buffer layer, especially as cap layer in multi-layer architecture of buffer layer for coated conductors.

Phase Transformation and Optimized Growth of TFA-MOD REBa_2Cu_3O_(7-x) Films for Coated Conductors

Several types of REBa2Cu3O7-x （REBCO, RE=Y, Ho etc.） films are prepared on single crystal substrate LaAIO3 by TFA-MOD method. The phase transformation and optimized growth conditions in the crystallization are studied. Compared with SmBCO and GdBCO, high quality YBCO and HoBCO films are relatively easy to produce. It is revealed that the YBCO grains can form at low temperatures such as 730 ℃ during the initial heating ramp. With a high heating rate of 20 K/min and a low oxygen pressure of 100 ppm, the optimum growth temperature is around 780℃, at which the films show a Jc value of 2.88 MMcm2. Further decrease of the heating rate may produce the highquality YBCO Film with a higher Jc of 3.65 MA/cm2. The temperature dependence of resistances in various magnetic fields up to 9 T shows that the present TFAMOD YBCO and HoBCO films have similar superonducting transition temperature and magnetotransport properties.

Preparation of a Cube-Textured Ni-7at.%W Based Template Used for Coated Conductors

Although Ni-W substrate with high W content (>5at.%) substrates have been developed successfully, the quality of cube texture and grain boundary, as well as extensive applications in coated conductors should be further improved. In the present work, once intermediate annealing treatment (IAT) at 500°C for 2 h has been employed to optimize the deformation and recrystallization textures in Ni-7at.%W (Ni7W) substrates. As a result, competitive high cube texture content (<10°) and low angle grain boundary fraction (<10°) were realized (98.5% and 91.2%, respectively). A Gd2Zr2O7 (GZO) buffer layer with strong cube texture and high-quality surface deposited successfully on the Ni7W substrate using the chemical solution deposition method, demonstrating the advanced GZO/Ni7W template is promising for coated conductors.

Fabrication of YBCO Coated Conductors on Biaxial Textured Metal Substrate by All-Sputtering

CeO2/YSZ/CeO2 buffer layers were prepared on biaxial textured Ni-5at.%W substrate by direct-current magnetron reactive sputtering with the optimum process. YBCO thin films were deposited on CeO2/YSZ/CeO2 buffered Ni-5at.%W substrate at temperature ranging from 500℃ to 700℃ by diode de sputtering. By optimizing substrate temperature, pure c-axis oriented YBCO films were obtained. The mierostruetures of CeO2/YSZ/CeO2 buffer layers were characterized by X-ray diffraction. A smooth, dense and crack-free surface morphology was observed with scanning electron microscopy. The critical current density Jc about 0.75 MA/cm2 at 77 K was obtained.

Interface properties and failures of REBCO coated conductor tapes:Research progress and challenges

RE‐Ba‐Cu‐O(REBCO,where RE=Y,Gd,Sm,and other rare earth elements)coated conductor(CC)tapes are promising for applications in high‐energy physics and high‐field science owing to their significant advantages such as high critical magnetic field,high current density,and the ability to achieve superconductivity at liquid nitrogen temperatures.Nevertheless,the mechanical and superconducting performances of these CC tapes are significantly affected by interface failures,such as interfacial delamination and coating fractures,which arise from the complex interplay of mechanical stress induced by magnet processing,thermal mismatch stress during cooling,electromagnetic stress under high magnetic fields,and thermal stress during quenching.This study comprehensively reviews the interface properties and failure behavior of REBCO CC tapes.First,the research progress in characterizing the intricate interface properties of REBCO CC is systematically reviewed.Furthermore,the interface failure behavior in extreme multifield environments was analyzed and summarized.Subsequently,this study outlines optimization strategies to mitigate interface failure risks in REBCO superconducting magnet structures.Finally,we address the current challenges and future perspectives on interface issues in REBCO CC tapes.By addressing these challenges,this study offers valuable insights for advancing the development and practical implementation of superconducting technologies in diverse applications.

Effect of Polymer Inclusion in Preparation of Thick LZO Buffer Layers for YBCO Coated Conductors

In this work, water-based precursor solutions suitable for dip-coating of thick La2Zr2O7 （LZO） buffer layers for coated conductors on Ni-5%W substrates with an inclusion of polymeric polyvinyl pyrrolidone were developed. The effect of varying percentage of the polymer addition on the preparation of the deposited films with maximum crack-free thickness was investigated. This novel water-based chemical solution deposition method involving polymers in two different chelate-chemistry compositions revealed the possibility to grow single, crack-free layers with thicknesses ranging from 140 to 280 nm, with good crystallinity and epitaxial growth. The effect of increasing polymer concentrations on the morphology and the structure of the films was studied. The appropriate buffer layer action of the films in preventing Ni diffusion was studied by X-ray photoelectron spectroscopy.

Tailoring surface roughness of LaMnO_(3) buffer layers for YBCO-coated conductors

LaMnO_(3)(LMO) cap layers with different surface roughness were prepared on epi-MgO/ion-beam-assisted deposition (IBAD) MgO/solution deposition planarized (SDP) Y2O3/Hastelloy tape. The effects of the surface roughness of LMO on the crystallization, texture and superconducting properties of Yba2Cu3O7?δ (YBCO) films were systematically investigated. The crystallization and epitaxial texture of resulting YBCO film are significantly improved with the surface roughness of LMO decreasing from 7.0 to 1.3nm. High-performance YBCO-coated conductors could be achieved if surface roughness of LMO cap layer is well controlled.

Onset temperature of intrinsic pinning in a REBCO coated conductor from critical current anisotropy

The field‐angle dependence of the critical current in a REBa_(2)Cu_(3)O_(7) coated conductor has been measured over a fine range of temperatures from 15 K to 80 K.The particular sample is demonstrated to have a very low fraction of extrinsic planar defects by its near‐isotropic critical current at 77 K.At a representative magnetic field of 3 T we are able to track the emergence of the ab‐plane peak usually associated with intrinsic pinning and quantify its evolution with temperature by fitting to a maximum‐entropy function.We are also able to observe the evolution of dip and peak features in the angle dependence of the power‐law index n with decreasing temperature and show that a dip appearing at 65 K is supplanted by a sharper positive peak from 50 K.The combination of critical current and power‐law index temperature dependences shows the onset of intrinsic pinning at 50 K.

The Mechanism of Cube Texture Formation in Ni-7 at%W Substrate

In order to obtain the sharp cube texture,a new process,the intermediate annealing rolling technique,has been introduced to prepare the Ni7W substrate.In this paper,a cubic texture content up to 98.5%within 10°of the standard cubic orientation is obtained in the final substrate and the influence of this improved rolling technique on the cube texture formation has been discussed.The results show that the increased cube texture in the Ni7W substrate is caused by the optimized deformation texture and the increased nucleated fraction of the cube grains.

Directional Motion of Droplets in a Conical Tube or on a Conical Fibre

Manipulating the directional movement of liquid droplets is of significance for design and fabrication of some microfluidic devices, An energy-based method is adopted to analyse the directional movement of a droplet deposited in a conical tube or on a conical fibre. We perform an experiment to investigate the directional motion of a droplet in an open conical tube. Our theoretical analysis and experimental observations both demonstrate that surface tension can drive the droplet to move in the conical tube. The critical condition of the liquid moving in the conical tube is presented. We also analyse a droplet on a conical hydrophilic fibre, which can move from the thinner to the thicker end.

Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection

A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.

Dielectric Response and Broadband Microwave Absorption Properties of Three-Layer Graded ZnO Nanowhisker/Polyester Composites

We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.

Temperature Effects on Prism-Based Surface Plasmon Resonance Sensor

We theoretically analyse the temperature effects on a surface plasmon resonance （SPR） sensor in Kretschmann configuration. The temperature effects include the thermo-optic effect and the dispersion of thermal-optic coefficient in the dielectric along with the thermal expansion effect, phonon-electron scattering and electron-electron scattering in the metal layer. We simulate the temperature dependence of the resonance position and the sensitivity of the SPR sensor under wavelength-interrogation and angular-interrogation mode of operation and the differences are pointed out in the two modes.

Synchronously Pumped Femtosecond Optical Parametric Oscillator Based on MgO-Doped Periodically Poled LiNbO3

We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti：sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300hm and from 2080 to 2930nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130mW at the wavelength of 1225nm is obtained, pumped by 900roW of 800hm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.

Effect of humidity on microstructure and properties of YBCO film prepared by TFA-MOD method

Epitaxial YBCO superconducting films were deposited on the single crystal LaAlO3 （001） substrate by metal organic deposition method. All YBCO films were fired at 820 ℃ in humidity range of 2.6%-19.7% atmosphere. Microstructure of YBCO thin films was analyzed by means of X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Superconducting properties of YBCO films were measured by four-probe method. XRD results showed that the second phase （such as BaF2）and a-axis-oriented grains existed in the films prepared at 2.6% humidity condition; a-axis-oriented grains increased in the film prepared at higher than 4.2% humidity condition; almost pure c-axias-oriented grains existed in the films fired at 4.2% humidity condition. Morphologies of the YBCO films showed that all films had a smooth and crack-free surface. YBCO film prepared at 4.2% humidity condition showed Jc value of 3.3 MA/cm^2 at 77 K in self-field.