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ISSN: 2772-8307
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Abstract
Corresponding email:elekgomo@savba.sk
Progress in the manufacturing of the 2nd generation of electrical conductors based on high-temperature superconducting (HTS) compounds, commonly known as coated conductors (CC), has sparked interest in various fields of application, including large magnetic systems for nuclear fusion and particle accelerators. To achieve the required electrical transport capacity in the kA range, tens of tapes must be assembled into a cable. Then, knowing the vulnerability of individual tapes to mechanical deformation is essential. We studied the behaviour of filamentized CC tapes with REBCO layer deposited on patterned substrate. Before this study, it was not clear whether such superconductor filamentization would affect the minimum core diameter, Dc,min, at which it still retains the transport capability. In the first stage, a set of 12 mm wide research samples, prepared with various number of filaments, underwent off-axis bending tests. Microstructural investigation then enabled understanding of the observed fact that the filamentary architecture did not cause any visible loss of transporting capability. In the study continuation, we compared the off-axis bending performance of short samples taken from 4 mm wide tapes produced industrially in lengths exceeding 100 m. Encouragingly, these filamentized tapes exhibited an endurance comparable to that of an equivalent non-filamentized tapes. Finally, in the last part of the study, simple models of round cables containing longer pieces (30 cm) of filamentized tape wrapped around a round core were tested. Some deterioration of performance was observed, relative to previous tests when only ∼1 cm long portion of tape was affected. Nevertheless, the observed 100 % retention of critical current when bending the 4 mm wide filamentized tape on a 5.5 mm central core represents an important input to further discussion about adopting filamentized tapes, thanks to their better electromagnetic behaviour, in cables for future nuclear fusion reactors and particle accelerator magnets.
cited:3
Mechanical failure: A critical bottleneck for high-field high-temperature superconducting magnets
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Article Number:Article 100234
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Abstract
Corresponding email:gaopf@lzu.edu.cn
The pursuit of ultrahigh-field high-temperature superconducting (HTS) magnets faces a significant challenge: mechanical failure is a primary fundamental limiter of progress. In extreme cryogenic electromechanical environments, coupled multimode failures—namely interfacial delamination, intralayer fracture, substrate yielding, and buckling—form the critical bottleneck. These failure modes are intrinsically coupled: Lorentz forces generate destructive hoop stresses, thermal expansion coefficient mismatches induce radial interface-decoupling tensions, multiaxial stress states accelerate crack propagation, and cyclic loads cause irreversible performance degradation. Such mechanical failures typically precede quench events. The resolution of these issues demands convergent innovation integrating material-centric strategies, structural intelligence, and operational resilience. Overcoming this mechanical barrier is pivotal for incremental field gains and unleashing the transformative potential of HTS magnets in fusion energy, next-generation nuclear magnetic resonance, and compact medical devices. A cross-disciplinary paradigm fusing materials science, solid mechanics, and intelligent engineering is necessary to transcend this frontier.
cited:3
Magnetization and dynamic losses in full-scale twisted-stacked tape cables for HTS fusion applications
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Article Number:Article 100235
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Abstract
Corresponding email:Zhenan.Jiang@vuw.ac.nz
AC loss is a key factor in the design of twisted-stacked tape cables (TSTCs) for high temperature superconductor (HTS) fusion applications. Until recently, numerical analysis of AC loss in full-scale TSTCs has been limited by the computational demands of 3D models, which severely restrict tape number and mesh density. In this work, a 2D scanning method, assessed against 3D models and experimental measurements, is used to simulate the magnetization and dynamic losses in full-scale TSTCs. A simplified PIT-VIPER geometry with four stacks, each containing 20–100 tapes, is modelled under alternating external magnetic fields of up to 20 T, at a temperature of 20 K, with and without 50 kA DC transport current. The influence of field-dependent critical current on magnetization loss is examined by comparing tapes from different manufacturers. The critical currents of the cables are also simulated. Results show that, for low transport currents, reducing tape number can reduce AC losses, roughly in proportion with tape number. Furthermore, it is shown that the widely used 2/π scaling of loss in flat stacks introduces moderate error until relatively high fields for practical tape numbers.
cited:2
Mechanisms driving robust high-temperature superconductivity in complex metal hydrides under moderate pressure
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Article Number:Article 100236
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Abstract
Corresponding email:duandf@jlu.edu.cn; cuitian@nbu.edu.cn
Reducing the stabilization pressure of superconducting hydrides remains a major challenge for their practical application. While complex metal hydrides are recognized for their stability at low pressures, their promise as high-temperature superconductors has been largely overlooked. Here, we identify a family of superconducting complex transition metal hydrides (CTMHs), represented by Li3IrH9, and demonstrate a new mechanism for achieving robust superconductivity in this class of materials. In Li3IrH9, the broadening and overlap between the antibonding electronic bands of [IrH8]2- and adjacent H− orbitals not only drive the intrinsic metallicity of the hydrogen sublattice, generating hydrogen-dominated electronic states at the Fermi level, but also soften hydrogen-related optical phonon modes, inducing strong electron-phonon coupling that remains robust even under high pressure. Li3IrH9 is predicted to be thermodynamically stable at 100 GPa and maintains a high Tc above 100 K across a broad pressure range (8–150 GPa). Other isostructural compounds such as Li3RhH9 (Tc = 124 K at 20 GPa) and Li3CoH9 (Tc = 80 K at 10 GPa) also exhibit prominent superconductivity at moderate pressures. This work provides a new platform and original theoretical insights for the development of CTMH superconductors that exhibit robust superconductivity and promising practical applications.
cited:1
Square filamentary MgB2 wire fabricated by the internal Mg diffusion method
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Article Number:Article 100238
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Abstract
Corresponding email:Pavol.Kovac@savba.sk
It is well known that the highest current densities in MgB2 superconducting wires can be achieved using the internal magnesium diffusion (IMD) method. We present a square 19-filament MgB2 wire made by the IMD process with dominant rolling deformation, which yields a high MgB2 filling factor of 14.2% and, consequently, a high engineering current density. Non-insulated wind-and-react coils were made from 1.1 mm to 0.68 mm wire, and their critical currents were compared with corresponding short wire samples. The threshold engineering current density of the present 19-filament MgB2/Nb/CuNi wire, Jet = 104 A cm−2, was measured at an external field of 6.5 T and a temperature of 4.2 K, representing the best performance reported in the literature for undoped filamentary wires made by the IMD process. The presented results demonstrate progress in the quality of filamentary MgB2 wires produced by the IMD process, which could be of interest for future DC coil applications.
cited:1
Effect of rapid-heating process on the preparation of Nb3Sn superconductor and establishment of critical current density model
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Article Number:Article 100239
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Abstract
Corresponding email:zrzhang@gia.cas.cn
In this work, bulk-Nb3Sn superconductors were prepared by the powder metallurgy route under the heat treatment conditions of rapid-heating and short-holding and the effect of Cu content and rapid-heating process on the microstructure and superconducting properties of bulk-Nb3Sn superconductors were systematically investigated. The results showed that both of critical temperature (Tc) and critical current density (Jc) of bulk samples got decreased with increasing Cu content. The rapid-heating and short-holding process exhibited a 'healing' effect on the holes in Nb3Sn layers, significantly improving the compactness of the bulk samples. Moreover, the bulk sample, which was heat treated at 600 °C for 50 h, then induction heated to 1000 °C and isothermally held for 20 s, exhibited the highest Jc,non-Cu values of 2.38 × 109 A/m2 (at 4.2 K & 6 T). And this could be attributed to the small average grain size, high content of Nb3Sn superconducting phase, and the Cu(Sn) artificial pinning centers in the Nb3Sn layer. Besides, Nb3Sn wire by internal-tin method was processed using the same heat treatment schedule to validate the effectiveness of the rapid-heating process. The critical current (Ic) of the wire sample, measured via V–I characteristic curve at 4.2 K & 6 T, was determined to be 96 A, corresponding to a Jc,layer value of 4593 A/mm2. Moreover, a Jc,non-Cu model concerning with the microstructural parameters (x: superconducting phase content, y: average Sn content in Nb3Sn layer, and z: grain size of Nb3Sn) was proposed, providing a semi-quantitative reference to describe the Jc,non-Cu of bulk-Nb3Sn superconductors. Finally, it should be noted that the relevant conclusions in this work regarding the kinetics of rapid-heating and microstructural evolution of bulk samples may require adjustment or further validation when applied to the structure of wires.
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