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ISSN: 2772-8307
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cited:89
Low-temperature superconductors: Nb3Sn, Nb3Al, and NbTi
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Article Number:Article 100047
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Abstract
Corresponding email:banno.nobuya@nims.go.jp
Low-temperature superconducting (LTS) wires are of significant importance in high-field magnet applications. Current developments of the LTS wires are attributed to many studies. Particularly, Nb3Sn is an attractive superconductor with substantial potential for performance improvement in view of an ideal microstructure that maximizes flux pinning properties. To date, various reviews have been reported on the physical properties of low-temperature superconductors. Therefore, this review focuses on understanding the fundamental phase formations and microstructural controls of low-temperature superconductors from the perspectives of growth kinetics, nucleation theory, and chemical potentials to facilitate the syntheses of these superconductors and advancement of wire production. Taking Nb3Sn as an example, the effect of Cu addition to Nb3Sn on Nb/Sn reactive diffusion is briefly described. Then, representative Nb3Sn formations are schematically summarized to broaden our understanding of the development behaviors of Nb3Sn. These behaviors are qualitatively reviewed in terms of Sn chemical potential. After mentioning the potential for performance improvement of Nb3Sn, the influences of element additions, specifically those of Zr and Hf additions, resulting in breakthrough microstructural refinements, on Nb/Sn diffusion are investigated. Subsequently, strengthening of the matrix via element additions is reviewed. Thereafter, taking Nb3Al as an example, the features of Nb3Al formation and basic development processes, including low-temperature processes, metastable phase transformations, and microstructural control, are described. Strain sensitivity, one of the most important properties of Nb3Al, is also briefly reviewed. Then, taking Nb alloy as an example, α-Ti precipitation in a binary Nb–Ti system is concisely summarized. Subsequently, recently reported new artificial pin incorporation based on a powder method is introduced, followed by a unique study of the application of high-temperature-tolerable Nb superconducting alloys in superconducting joints. This review makes a novel contribution to the literature as it provides a comprehensive understanding of phase formation in low-temperature superconductors.
cited:8
Effect of Gd addition on the superconducting properties of Ti-based V, Nb, Ta alloys
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Article Number:Article 100048
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Corresponding email:sheikramjan1995@gmail.com
The critical current density () of the body centered cubic (bcc) V0.6Ti0.4 alloy enhances significantly after the addition of rare earth Gd as the latter is immiscible in the matrix [S. Paul, et.al, IEEE Trans. Appl. Supercond. 31, 5 (2021)]. Very low solubility of Gd in other bcc elements like Ta and Nb is also well known [Jr. KA Gschneidner in Prog Sci Technol Rare Earths, vol. 1, pp. 222–258, 1964 M Neuberger, et.al in Handbook of Electronic Materials, Vol 4, 1972]. We use these facts to find the effect of adding 1 at.% Gd into the Nb0.6Ti0.4 and Ta0.4Ti0.6 alloys on the superconducting properties e.g., the transition temperature (), , flux pinning force density () and the microstructure. In spite of Gd being ferromagnetic, the in these alloys change only marginally (increase by 0.3 K in Ta0.4Ti0.6 and decrease by 0.15 K in Nb0.6Ti0.4 after Gd addition. The ( T, T = 4 K) increases by 5 and 1.5 times respectively in the Gd containing Nb0.6Ti0.4 and Ta0.4Ti0.6 alloys, which is quite small as compared to the increase observed in the V0.6Ti0.4 (20 times) system. With Gd addition, the grain size reduces approximately by 65% and 10% respectively in Nb0.6Ti0.4 and Ta0.4Ti0.6. Our analysis indicates that grain boundaries are the major flux line pinning centres in these alloys and the role of Gd in increasing the depends on the effectiveness of Gd in reducing the grain size. The grain boundary density depends strongly on the distribution of Gd precipitates, which is quite different from each other for two alloy systems under study. Moreover, our results suggest that the addition of Gd to commercial Nb-Ti (Nb0.37Ti0.63) alloy is a new promising route for achieving higher values.
cited:48
J-A formulation: A finite element methodology for simulating superconducting devices
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Article Number:Article 100049
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Corresponding email:gdsantos@id.uff.br
High-temperature superconductors are a powerful technological option to be applied in the current scenario of energy transition. Their applications include fault current limiters, power electrical cables, and electrical machines, for example. Due to the non-linearities of superconductors, it is computationally costly to run real models of superconducting equipment. Therefore, it is of paramount importance to have a reliable and fast formulation to model superconducting devices. This paper proposes a new hybrid J-A formulation to simulate superconducting devices. The new formulation is validated with 5 case studies, some of which are benchmarks. The J-A formulation agrees in all cases and has a smaller computation time when compared with the T-A formulation. Moreover, due to the simple implementation, the proposed formulation allows the possibility of running the J and A formulations in the same order and presents itself as a potential feature to speed up and help the design of the superconducting devices.
cited:42
Numerical modelling of high-temperature superconducting dynamos: A review
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Article Number:Article 100033
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Corresponding email:mark.ainslie@kcl.ac.uk
The high-temperature superconducting (HTS) dynamo enables injection of large DC currents into a superconducting coil, without the need for thermally-inefficient current leads. Because of this important advantage, there is significant interest in using such technology to energise superconducting coils in superconducting rotating machines and NMR/MRI magnets. Despite the extensive experimental work carried out over the past decade, there was – until very recently – considerable confusion and debate regarding the physical origin of the HTS dynamo’s DC output voltage. Numerical modelling has played a key role in elucidating the underlying physics of such devices and several different numerical models have now been developed as useful and cost-effective tools to not only explain and further examine experimental results, but also optimise and improve dynamo designs. This review summarises all of the developments in this important area over recent years, including modelling the open-circuit voltage behaviour in 2D and 3D, the definition of a new benchmark problem for the HTS modelling community, investigating key dynamo parameters, modelling dynamic coil charging behaviour and calculating losses. A view towards the future is provided, including the outstanding challenges and the developments required to address these.
cited:24
Critical current parameterization of high temperature Superconducting Tapes: A novel approach based on fuzzy logic
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Article Number:Article 100036
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Corresponding email:mohammad.yazdani-asrami@glasgow.ac.uk
In this study a novel method was presented to parameterize the critical current of Yttrium Barium Copper Oxide (YBCO) tapes based on their width, thickness, magnetothermal operational conditions, and the applied strain. For this purpose, a fuzzy-logic-based model was developed that take tapes structures and their operational conditions as inputs to calculate their critical current, as output. The results of critical current parameterization by fuzzy-logic-based model showed that the relative error of the proposed model is less than 3% comparing to experimentally acquired data. Then, the results of presented model was compared to results of semi-analytical fitting-based models and fully-analytical fitting based models. The comparisons showed the better performance in terms of accuracy and error of fuzzy logic model over fitting-based methods. At last, the results were also compared with the Artificial Neural Network (ANN)-based parameterization model and Adaptive Nero-Fuzzy Interference System (ANFIS)-based parameterization model. The proposed method had 6% to 8% higher accuracy and about 47% to 54% lower root mean squared error.
cited:21
Analytical analysis of hollow CORC cable under thermo-mechanical loads
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Article Number:Article 100037
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Corresponding email:tangyj@mail.hust.edu.cn
According to engineering experience, the axial shrinkage caused by the refrigerant seriously endangers the performance of long-distance conductor on round core (CORC) cables. Since outage maintenance of high-temperature superconducting (HTS) cables is inevitable, providing appropriate compensation for cyclic temperature is one of the key technologies in the actual application of power cables. Therefore, this paper presents an analytical solution for hollow CORC cables under thermo-mechanical loads. First, regarded as an axisymmetric composite structure, the radial temperature distribution of CORC cable under Dirichlet boundary or mixed boundary conditions was calculated. Then, assuming cable ends were axially fixed, a recursive method without variables is used to evaluate its displacement, strains, and stresses. Then, an algebraic method with axial strain as a variable is developed to analyze the mechanical behavior of the CORC cable more directly. Finally, concluded from the above derivation, a matrix equation is constructed based on continuity equations and boundary conditions, which applies to isotropic and orthotropic materials with orientations. Calculation results show that the analytical solution agrees with finite element method (FEM) results. Compared to the trial results of a 360 m CORC cable, the calculation error of axial shrinkage is within 1.63 cm, and the relative error is within 6.1%. In addition, the recursive method is the fastest to calculate axial strain, while the matrix method has a significant efficiency advantage in calculating the stresses and strains of each layer.
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