Dependence Of Critical Current Research Articles

Solving mystery with the Meissner state in La3Ni2O7-δ

Recently, zero resistance state in highly compressed La3Ni2O7-δ has been observed. However, all attempts of many research groups to detect the Meissner state in the La3Ni2O7-δ have been failed. To explain this puzzle, an exotic superconducting state (for instance, filamentary superconductivity) in the La3Ni2O7-δ has been supposed. Here, I extracted temperature dependent self-field critical current, Ic(sf,T), dataset from current-voltage curves and performed the Ic(sf,T) analysis. As a result, I found that highly compressed La3Ni2O7-δ to exhibits d-wave superconductivity with the gap-to-transition temperature ratio 2Δ(0)/(kBTc) = =4.0 ± 0.3, a very large ground state London penetration depth, λ(0, P = 16.6 GPa) = 6.0 μm, and a very high Ginzburg-Landau parameter k(0, P = 16.6 GPa) = 1500. This implies that the ground state lower critical field Bc1(0, P = 16.6 GPa) = 34 μT is of the same order as the Earth’s magnetic field. Based on this, to detect the Meissner state in the La3Ni2O7-δ becomes a very challenging task. I can hypothesize that the magnetic flux trap effect recently proposed to eliminate the diamond anvil cell (DAC) background in experiments on magnetic properties of the superconducting hydrides can also apply in studies of magnetic properties in the La3Ni2O7-δ superconductor.

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.

Evidence of striped electronic phases in a structurally modulated superlattice.

The electronic properties of crystals can be manipulated by superimposing spatially periodic electric, magnetic or structural modulations. Long-wavelength modulations incommensurate with the atomic lattice are particularly interesting1, exemplified by recent advances in two-dimensional (2D) moiré materials2,3. Bulk van der Waals (vdW) superlattices4-8 hosting 2D interfaces between minimally disordered layers represent scalable bulk analogues of artificial vdW heterostructures and present a complementary venue to explore incommensurately modulated 2D states. Here we report the bulk vdW superlattice SrTa2S5 realizing an incommensurate one-dimensional (1D) structural modulation of 2D transition metal dichalcogenide (TMD) H-TaS2 layers. High-quality electronic transport in the H-TaS2 layers, evidenced by quantum oscillations, is made anisotropic by the modulation and exhibits commensurability oscillations paralleling lithographically modulated 2D systems9-11. We also find unconventional, clean-limit superconductivity in SrTa2S5 with a pronounced suppression of interlayer relative to intralayer coherence. The in-plane magnetic field dependence of interlayer critical current, together with electron diffraction from the structural modulation, suggests superconductivity12-14 in SrTa2S5 is spatially modulated and mismatched between adjacent TMD layers. With phenomenology suggestive of pair-density wave superconductivity15-17, SrTa2S5 may present a pathway for microscopic evaluation of this unconventional order18-21. More broadly, SrTa2S5 establishes bulk vdW superlattices as versatile platforms to address long-standing predictions surrounding modulated electronic phases in the form of nanoscale vdW devices12,13 to macroscopic crystals22,23.

Magnetic field dependence of critical currents of cross-type Josephson junctions with inhomogeneous critical current density under oblique magnetic fields

Abstract Studies of the magnetic interference of sandwich-type Josephson junctions in which perpendicular or oblique magnetic fields are applied to the junction plane have received less attention than those where the applied magnetic fields are parallel. Recently, it has been theoretically demonstrated that a variety of magnetic interferences of the critical currents appear when oblique magnetic fields are applied to a cross-type junction with homogeneous critical current density. We theoretically investigated the effect of the inhomogeneous critical current density in the junction plane, and found that more complicated magnetic interferences appeared. We considered the distribution of the current density flowing through the junction plane to explore the cause of these complex magnetic interferences.

Comparison of the Field Trapping Ability of MgB2 and Hybrid Disc-Shaped Layouts.

Superconductors have revolutionized magnet technology, surpassing the limitations of traditional coils and permanent magnets. This work experimentally investigates the field-trapping ability of a MgB2 disc at various temperatures and proposes new hybrid (MgB2-soft iron) configurations using a numerical approach based on the vector potential (A→) formulation. The experimental characterization consists in measurements of trapped magnetic flux density carried out using cryogenic Hall probes located at different radial positions over the MgB2 sample, after a field cooling (FC) process and the subsequent removal of the applied field. Measurements were performed also as a function of the distance from the disc surface. The numerical modelling of the superconductor required the evaluation of the critical current density dependence on the magnetic flux density (Jc(B)) obtained through an iterative procedure whose output were successfully validated by the comparison between experimental and computed data. The numerical model, upgraded to also describe the in-field behavior of ARMCO soft iron, was then employed to predict the field-trapping ability of hybrid layouts of different shapes. The most promising results were achieved by assuming a hollow superconducting disc filled with a ferromagnetic (FM) cylinder. With such a geometry, optimizing the radius of the FM cylinder while the external dimensions of the superconducting disc are kept unchanged, an improvement of more than 30% is predicted with respect to the full superconducting disc, assuming a working temperature of 20 K.

Tuning the superconducting performance of YBa2Cu3O7-δ films through field-induced oxygen doping.

The exploration of metal-insulator transitions to produce field-induced reversible resistive switching effects has been a longstanding pursuit in materials science. Although the resistive switching effect in strongly correlated oxides is often associated with the creation or annihilation of oxygen vacancies, the underlying mechanisms behind this phenomenon are complex and, in many cases, still not clear. This study focuses on the analysis of the superconducting performance of cuprate YBa2Cu3O7-δ (YBCO) devices switched to different resistive states through gate voltage pulses. The goal is to evaluate the effect of field-induced oxygen diffusion on the magnetic field and angular dependence of the critical current density and identify the role of induced defects in the switching performance. Transition electron microscopy measurements indicate that field-induced transition to high resistance states occurs through the generation of YBa2Cu4O7 (Y124) intergrowths with a large amount of oxygen vacancies, in agreement with the obtained critical current density dependences. These results have significant implications for better understanding the mechanisms of field-induced oxygen doping in cuprate superconductors and their role on the superconducting performance.

Analysis of Critical Current Dependence on Specimen Length and Crack Size Distribution in Cracked Superconductor.

In order to describe the dependence of critical current on specimen length and crack size distribution in the superconducting tape with cracks of different sizes, a Monte Carlo simulation and a model analysis were carried out, employing the model specimens of various lengths constituted of multiple short sections with a crack per each. The model analysis was carried out to evaluate the effects of the two factors on the critical current of a specimen. Factor 1 is the size of the largest crack in a specimen, and Factor 2 is the difference in crack size among all sections at the critical voltage of critical current. Factors 1 and 2 were monitored by the smallest ligament parameter among all sections constituting the specimen and by the number of sections equivalent to the section containing the largest crack at the critical voltage of the critical current of the specimen, respectively. The research using the monitoring method revealed quantitatively that the critical current-reducing effect with increasing specimen length is caused by the increase in the size of the largest crack (Factor 1), and also, the critical current-raising effect is caused by the increase in the difference of crack size (Factor 2). As the effect of Factor 1 is larger than that of Factor 2, the critical current decreases with increasing specimen length. With the present approach, the critical current reducing and raising effects under various crack size distributions were evaluated quantitatively as a function of specimen length, and the specimen length-dependence of critical current obtained by the Monte Carlo simulation was described well.

Angular dependence of resistance and critical current of a Bi-2223 superconducting joint

Low resistance and high critical current are prerequisites for superconducting joints used in persistent-mode magnets. Herein, we use a joint resistance evaluation system, previously developed by us, to systematically evaluate the angular dependence of resistance and critical current of a Bi-2223 superconducting joint in a closed-loop sample. The current decay is measured by rotating the sample incrementally. The time dependence of the loop current is evaluated at 4 K, 0.15–0.28 T, and magnetic field angles ranging from 90° to 0, wherein 90° corresponds to the direction parallel to the tape surface. The results suggest that the resistance and critical current of the joint depend on the angle of the magnetic field. The evaluated critical current increases as the angle increases. The angular dependence of resistance can be divided into three regions: low-resistance, transition, and high-resistance regions. The low-resistance region exists at high angles close to 90°. In this region, the decay of the loop current is small, and the persistent current continues to flow. Furthermore, the joint resistance is less than 1.4 × 10−13 Ω. In the transition region, the joint resistance significantly increases by three orders of magnitude with sample rotation. This significant increase is attributed to an increase in the perpendicular component of the magnetic field, which decreases the critical current of the joint. At lower angles, the joint resistance remains high, ranging from 10−11 to 10−10 Ω. A significant decay in the loop current is observed in the high-resistance region. Based on these findings, we conclude that the design of a persistent-mode magnet must consider not only the magnitude but also the direction of the magnetic field applied to superconducting joints.

Electromagnetic-mechanical coupling analysis of high-temperature superconducting racetrack coil

The second-generation high-temperature superconducting (HTS) coated conductor has been recognized as one of the most promising materialsfor high field magnets due to its superior electromagnetic and mechanical performances. HTS racetrack coils wound with the coated conductors are an extensively used configuration in engineering applications, such as HTS machines and high-speed maglevs. In this paper, in order to analyze the electromagnetic and mechanical behaviors of HTS racetrack coils, a 3D coupled electromagnetic-mechanical model is used to consider the effect of coil deformation and the strain dependence of critical current. The effectiveness of the coupled model is validated by comparing the numerical results with experimental data in the literature. A numerical simulation of a 3D HTS racetrack coil subjected to an external electromagnetic field is carried out using coupled and uncoupled models. The results indicate that the structure deformation can reduce the penetration depth of the screening current, and the hoop stress and strain are mainly concentrated on the circular part of the racetrack coil. Afterwards, the influences of various parameters on the electromagnetic and mechanical responses of the HTS racetrack coil are also investigated.

Tunable Dimensionality of Pinning Centers From Silver-Ion Irradiation of REBCO Coated Conductors

Heavy-ion irradiation of solids produces damage tracks with radii typically of the order of 1 nm, depending on the ion species and energy. In cuprate superconductors this is close to the coherence length, which makes these defects highly effective flux pinning centers. Varying the ion-beam energy allows tuning of the dimensionality of the defects created, with higher-energy ions tending to produce columnar tracks and lower-energy ions tending to produce point-like defects. Starting with consistent production-standard REBCO tape from American Superconductor we have explored the energy-dependence of silver-ion irradiation and characterized the irradiated samples with angle-dependent transport critical current measurements. Using silver ions with energies in the range 50 MeV to 150 MeV and fluence of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> we have been able to tune the irradiation-induced damage from point-like defects to columnar tracks, manifesting in changes to the pinning landscape ranging from isotropic critical current enhancement to the production of strong peaks in the angle dependence of critical current.

Thermomagnetic instabilities in 3D network of superconducting lead nanofilaments in porous glass

Thermomagnetic instabilities in the lead-porous glass (Pb-PG) nanocomposite in superconducting state were studied, and a model was proposed that relates magnetization jumps and heat release spikes with average critical current density. The samples were created by filling porous glass (characteristic pore size d = 7 nm) with lead from a melt under pressure, which created a 3D multiply connected system of lead filaments. The critical temperature of superconducting transition in Pb-PG T c = 7.2 K is the same as for bulk lead and the critical magnetic field H c (0) ≈ 40 kOe is much higher than H c bulk (0) ≈ 800 Oe for bulk lead. Hysteresis and magnetic flux jumps were observed in the magnetization curves m(H) of the Pb-PG nanocomposite, which are connected with the formation of magnetic flux gradients in a system of interconnected contours. Magnetic flux jumps are thermomagnetic processes accompanied by heat release which was directly observed by measuring adiabatic temperature change in the sample during magnetic field sweep. The flux jumps in the magnetization and heat release events were almost periodic in the magnetic field. The period dependences on the magnetic field are similar to the calculated average critical current density dependence j c (H).

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

• A detailed analysis is given of the evolution with temperature of the angle dependence of critical current in a REBCO coated conductor. • Particular attention is given to the development of the ubiquitous ab -plane peak for field parallel to the plane of the tape. We highlight that this peak appears as the result of two distinct mechanisms, stacking faults at higher temperatures and intrinsic pinning at lower temperatures. • This peak is unusually weak at 77K, due to process conditions favouring a low density of stacking fault defects. • The peak grows rapidly with decreasing temperature relative to the c-axis critical current starting from 60K, signalling the onset of intrinsic pinning by the layered structure of REBCO. • This growth is quantified through fitting with maximum entropy functions. • The angle dependence of n -values is also shown. With decreasing temperature, the ab -plane feature appears first as a dip at 65K, then a sharper peak starting from 45K. Both of these features broaden with decreasing temperature. 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.

Magnetic and Electromechanical Characterization of a High-JC RRP Wire for the HL-LHC MQXF Cable

In this work, we summarize the results of a series of inductive and transport measurements aimed at the evaluation of the electromechanical performance of a 0.85 mm diameter RRP wire procured for the HL-LHC project. The critical current dependence on the magnetic field and uniaxial applied strain (between −0.2 and 0.5%) has been investigated in a temperature range between 4.5 K and 10 K. Furthermore, the wire magnetization up to 12 T has been measured at different temperatures (4.3 K–14 K) to determine the wire's effective filament diameter and to complement the critical current density in the temperature and field range where transport current measurements were not available. The experimental results have been analysed in the framework of the Extrapolative Scaling Expression, by using a multi-step approach for the data fitting. These results provide an accurate parameterization of the critical surface in terms of field, temperature and strain, and can be used as a general reference for magnet design.

Study of Quench Behavior of No-Insulation REBCO Pancake Considering Complex Critical Current Density Distribution

This study analyzes the quench behavior of No-insulation (NI) REBCO pancake. An quench analysis simulation model considering the complex critical current density distribution was developed and validated experimentally. The developed model includes an equivalent circuit model, a thermal model, a magnetic model, and a magnet critical current estimation model. The simulation model is based on a co-simulation using MATLAB and COMSOL, considering the balance of accuracy and computation time. The lumped parameter of the NI magnet was used to solve the governing equations of the equivalent circuit module and thermal module in MATLAB. To accurately calculate the non-uniform electromagnetic field distribution over the coil, a magnetic finite element method was used in COMSOL. A neural network was used to predict the temperature-field-angle dependent magnet critical current. Considering the numerical convergence at different over-current phases, adaptive simulation was used to reduce the total simulation time. The quench behavior was analyzed using the proposed model, and the results were verified experimentally. The simulation results showed that when the azimuthal current is greater than the magnet critical current, it will gradually saturate and approach the magnet critical current, and then decrease at a similar speed. The rate of decrease is equal to the rate of decrease of the magnet critical current. Through the analyses, the corresponding sudden-discharging behavior was simulated and analyzed. The proposed model can be used to perform the post-quench and sudden discharging analyses of pancake coil and has promising applications in multi-pancake post-quench studies.

Effects of TiO2 nanoparticle addition on the flux pinning properties of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ ceramics

The effects of adding TiO2 nanoparticles on the flux pinning properties of the Bi–Pb–Sr–Ca–Cu–O (BPSCCO) system were investigated. Polycrystalline samples of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x, where x = 0.000, 0.002, 0.004, 0.006, 0.008, and 0.010, were fabricated by the conventional solid-state reaction method. The X-ray diffraction (XRD) results showed that all samples consisted of Bi-2223 and Bi-2212 phases. The Bi-2223 volume fraction decreased with the addition of TiO2. Scanning electron microscopy (SEM) examination presented a degradation in texture structure with increasing misoriented grain and porosity with high doping contents. The critical temperature was decreased by TiO2 appearance in relation to Bi-2223 deceleration. Critical current density dependence on the magnetic field Jc(B) was enhanced with x = 0.002, 0.004 and reached maximal values on the x = 0.002 sample. In the collective pinning theory framework, the small bundle field (Bsb) and the large bundle field (Blb) were estimated, revealing the extension of the small and large bundle regimes with proper amounts of dopant. The temperature-dependent normalized critical current density (j) indicated that δl pinning is the dominant flux pinning mechanism in all samples. The Dew-Hughes model analyzed the pinning center properties and confirmed that TiO2 nanoparticles create normal core point pinning centers in the matrix.

Design and modelling tools for DC HTS cables for the future railway network in France

The use of high-temperature superconducting (HTS) cables in power systems increases the transmission capacity, whereas reducing the volume of the installation. In addition, in high current applications, HTS cables considerably reduce power losses, right-of-ways and total system mass. This paper presents different multi-physics studies to be performed to accurately design the direct current (DC) HTS cables for the future railway network planned by the French company SNCF. The process used to design DC cables for high operating current (between 5 kA and 20 kA at 1750 V) made of commercial (RE)BaCuO tapes is presented. In this design process, the critical current density dependence J c(B, θ, T) of the superconducting tapes, the thermal properties of the materials used as well as different cable cooling configurations are considered. Finally, we discuss the selection of the appropriate cooling configuration to ensure adequate cooling of the cable.

Multiple andreev reflections in topological insulator nanoribbons

Superconducting proximity junctions made of topological insulator (TI) nanoribbons (NRs) provide a useful platform for studying topological superconductivity. We report on the fabrication and measurement of Josephson junctions (JJs) using Sb-doped Bi2Se3 NRs in contact with Al electrodes. Aharonov–Bohm and Altshuler–Aronov–Spivak oscillations of the axial magneto-conductance of TI NR were observed, indicating the existence of metallic surface states along the circumference of the TI NR. We observed the supercurrent in the TI NR JJ and subharmonic gap structures of the differential conductance due to multiple Andreev reflections. The interface transparency of the TI NR JJs estimated based on the excess current reaches τ = 0.83, which is among the highest values reported for TI JJs. The temperature dependence of critical current is consistent with the short and ballistic junction model confirming the formation of highly transparent superconducting contacts on the TI NR. Our observations would be useful for exploring topological Josephson effects in TI NRs.

Method for critical current angular dependencies analysis of superconducting tapes

Various applications of superconducting materials require accounting of the critical current anisotropy relative to magnetic field direction - I c7(θ). However, today there is no sufficiently comprehensive model that takes into account the anisotropy, therefore the angular dependences are usually not analysed, but only described using various mathematical formulas. As a result, the fitting parameters have no physical meaning and it is difficult to correlate the picture with the features of the microstructure. In this paper, we propose a method for analysing the critical current angular dependences based on the anisotropic pinning model. The applicability of this model for conventional superconducting Nb-Ti tapes with one peak in the I c7(θ) dependence is shown. The possibility of extending this model to analyse the angular dependences of HTS materials is discussed.

Numerical Study on Ring-shape Superconducting Trapped Field Magnet Based on Circuit Model

The so-called ring-shape superconducting trapped field magnet has been proved as a potential candidate to replace commercial permanent magnets in practical industrial applications on account of its jointless structure. In this paper, a circuit method based on Bean model, E-J power law and Faraday law has been built to investigate the magnetization mechanism of ring-shape magnet. The field dependent critical current of superconducting materials has been taken into consideration for further optimization. The numerical model was verified by both finite element method (FEM) and experiments. Compared with other methods, the circuit-based simulation method has the advantages of high efficiency, fast speed and wide applicability. On basis of this method, the paper also studied characteristics of ring-shape magnets under different working conditions to provide a guideline for the magnet design.

A robust nitridation technique for fabrication of disordered superconducting TiN thin films featuring phase slip events

Disorder induced phase slip (PS) events appearing in the current voltage characteristics (IVCs) are reported for two-dimensional TiN thin films produced by a robust substrate mediated nitridation technique. Here, high temperature annealing of Ti/Si3N4 based metal/substrate assembly is the key to produce majority phase TiN accompanied by TiSi2 & elemental Si as minority phases. The method itself introduces different level of disorder intrinsically by tuning the amount of the non-superconducting minority phases that are controlled by annealing temperature (Ta) and the film thickness. The superconducting critical temperature (Tc) strongly depends on Ta and the maximum Tc obtained from the demonstrated technique is about 4.8 K for the thickness range ~ 12 nm and above. Besides, the dynamics of IVCs get modulated by the appearance of intermediated resistive steps for decreased Ta and the steps get more prominent for reduced thickness. Further, the deviation in the temperature dependent critical current (Ic) from the Ginzburg–Landau theoretical limit varies strongly with the thickness. Finally, the Tc, intermediate resistive steps in the IVCs and the depairing current are observed to alter in a similar fashion with Ta and the thickness indicating the robustness of the synthesis process to fabricate disordered nitride-based superconductor.