Abstract High-temperature superconducting coils are used in various large-scale applications, like rotating machines and high-field magnets. However, modeling these coils is a complicated and time-consuming process, especially due to the non-linearity of the current–voltage characteristics of the superconductors and the complex multiphysics involved. In this work, we used a fast homogenized method to model the coupled electromagnetic and electrothermal properties of racetrack and pancake coils for different applications. For this purpose, various formulations wielding homogenization methods are used and benchmarked with each other, as well as with models considering the detailed structure of the HTS tapes. We observe a very good agreement between different models (homogenized and detailed), and we discuss the pros and cons of the inclusion of insulating layers between the turns in homogenization. This work was performed under the collaboration of the COST action modeling teams and can be used as a review of the state-of-the-art superconductor modeling techniques, and a source for the development and benchmark of future numerical methods.

Abstract As the need for high-magnetic field magnets, this article made the first cable-in-conduit conductor (CICC) -type Bi-2212 insert coil. The Bi-2212 conductor consists of 24 wires, an Ag tube, and a 316 LN jacket. With the optimized heat-treatment regime, the insert coil exhibited excellent current-carrying capacity under magnetic fields up to 20 T: the Ic of the coil was up to 5.4 kA under 20 T backfield. With the ‘Pre-OP before cabling’ process, the void fraction was precisely controlled. Besides, the insert coil exhibits excellent stability with the electromagnetic loads and quenching process: no obvious change in performance was detected even when the electromagnetic loads increased to 101 kN m−1; after the quench event where the voltage on the insert coil was up to ∼4000 times criterion, no degradation was detected. The excellent performance of the Bi-2212 insert coil gives a solid foundation for the development of full-size Bi-2212 CICC for high-field applications.

Abstract Recently, in Teknowijoyo and Gulian (2024 Supercond. Sci. Technol. 37 035005) we introduced a new, rhenium–lutetium superconducting series (highest T c ≈ 7 K). In light of some other Re-based materials, our films are also a candidate to the time-reversal symmetry breaking family of superconductors. Both polycrystalline and amorphous materials in thin-film form have been reported, together with their basic properties, which include the estimates of the coherence length and London penetration length. In our original treatment, both of these quantities were deduced to be rather small ( ξ ( 0 ) , λ L ( 0 ) ∼ 5 nm) and the so-called Ginzburg–Landau parameter κ is about 0.9. The author of Comment brings in arguments in favor of the statement that the new material has κ ∼ 250 . We find that the discrepancy comes from the two-solution nature of the equation for λ L ( 0 ) . We agree with the Comment’s author that the London penetration depth in our films is more likely in the order of 1 µm, which makes Re–Lu a high-κ superconductor. Future research in both thin films and single crystals may shed more light in the accurate determination of the characteristic lengths of this material.

Abstract Ring–shaped homogeneous YBCO and DyBCO bulks were successfully fabricated using the Single–Direction Melt Growth (SDMG) method. The bulks were directly grown from ring–shaped compacted powder using ring–shaped molds with an outer diameter of 50 mm and inner diameters of 15, 20, and 25 mm. The ring–shaped bulks exhibited high trapped fields inside the rings up to 1.2 T at 77 K. Analyses of trapped field distributions revealed uniform current density distributions along the orbital direction. Stacked ring bulks demonstrated even higher trapped fields, reaching 2.0 T at 77 K. It was confirmed for the stacked bulks that time–independent uniform trapped fields can be achieved by magnetizing at lower fields than fully magnetizing conditions. Observed paramagnetic magnetization of the SDMG–processed YBCO bulk was negligibly small below the detection limit, which is considered to be more suitable for bulk NMR/MRI applications than DyBCO. Additionally, we proposed a method to quantitatively evaluate trapped fields of superconducting bulks with various diameters and thicknesses, where the estimated average current densities from the maximum trapped fields for all the obtained ring–shaped bulks were above 104 A cm–2 at 77 K. These results indicate that SDMG is an effective method for fabricating high–quality, large–scale ring–shaped bulks with superior field–trapping properties.

Abstract Among all the iron-based superconductors (IBSs), Fe-chalcogenides (Fe-Ch) possess the advan tages of simple structure, non-toxicity, low anisotropy and the potential for high-field applications.One of the most effective methods for preparing Fe-Ch films is pulsed laser deposition (PLD). However, high quality film growth is challenged by the significant volatility difference between the iron
and chalcogens (S, Se, Te), which affects stoichiometric transfer from target to substrate and subsequently impacts superconductivity. Currently, there is limited research on the correlation between the growth mechanism and preparation conditions of Fe-Ch films, particularly in explaining chalcogen volatility during deposition. Technically, PLD offers various adjustable parameters, among
which the substrate temperature (Ts) is the most critical one affecting film quality. It governs particle behavior on the substrate including adsorption, diffusion, bonding reactions, crystallization processes while also strongly affecting volatilization rates. In this study, we fabricated a series of FeSe films using PLD at different Ts ranging from 25 ℃ to 750 ℃.We reveal in detail the impact of
competitive processes between Se volatilization and reactive crystallization of Fe/Se on film quality. The optimal film was obtained at Ts=500 ℃ with a composition ratio of Fe1.01Se. We also investigate the correlations between Ts and film crystallinity, surface morphology, along with their influence on superconductivity. Additionally, the pinning mechanism in FeSe film grown at the
optimal Ts was briefly analyzed. Our results provide reliable experimental evidence regarding the growth mechanism of FeSe films while revealing comprehensive insights into how Ts affects both film quality and performance.

Abstract Accelerator laboratories worldwide are researching copper radio frequency (RF) cavities coated with superconducting thin films to exceed the limits of bulk niobium. The development and RF testing of thin films on small planar samples is vital before cavity depositions. A team at Daresbury Laboratory have developed a cost-effective facility using a novel 7.8 GHz Choke Cavity for the RF characterisation of planar samples. RF chokes ensure that no electrical contact is required between the sample and the cavity. The main advantages are: a simple sample design (90 − 130 mm diameter disk with no sample-cavity welding) and easy operation using a LHe-free cryostat. This enables high sample throughput, with up to 3 sample tests per week, making the facility suitable for quick, systematic scanning of deposition parameters. With the sample thermally and physically isolated from the test cavity, it is possible to measure the average surface resistance, R s, directly using an RF-DC compensation method. Facility commissioning has been performed with bulk and thin film niobium samples. These tests have demonstrated the ability to measure R s at temperatures in the range 4 − 20 K and sample peak magnetic fields up to 3 mT. The minimum resolvable R s is 0.5 μΩ with typical uncertainties of 9 − 15%. The design, operation and commissioning of this facility is reported in this paper.

Abstract Superconducting memory cells that use flux quanta as their storage medium can achieve ultra-fast access times with ultra-low power consumption. However, the data signal generated by a flux quantum memory (FQM) cell is usually too weak and too fast to be measured directly. Here, we present a method to characterize the real-time operation of an FQM cell. The storage loop of the FQM cell, configured with a Nb/NbN X /Nb Josephson junction, was proven the capability to store multiple flux quanta. The readout was demonstrated by a superconducting quantum interference device composed of underdamped Nb/Al-AlO X /Nb Josephson junctions. The writing and reading operations were achieved by a short pulse ranging from 0.1 ns to 2.5 ns, and a constant bit error rate of ∼2.46% was measured for the fabricated FQM cell. The method presented here can be used to study real-time operation of an FQM cell in a direct manner.

Abstract We numerically investigate the noise scaling in high- T c commensurate 1D and 2D SQUID arrays. We show that the voltage noise spectral density in 1D arrays violates the scaling rule of ∼ 1 / N p for the number N p of Josephson junctions in parallel. In contrast, in 2D arrays with N s 1D arrays in series, the voltage noise spectral density follows more closely the expected scaling behaviour of ∼ N s / N p . Additionally, we reveal how the flux and magnetic field rms noise spectral densities deviate from their expected ∼ ( N s N p ) − 1 / 2 scaling and discuss their implications for designing low noise magnetometers.

Due the integration of superconducting technologies into electrical networks around the world, its precise simulations in power grids are increasingly becoming a desirable outcome. Over the years, sophisticated methods have been used to model superconducting power cables and, in this way, predict its behavior under different conditions. Most of the available models, however, are not advisable to be used and embedded in power system simulators. In this manuscript, we focus on the development of a method specifically for modeling superconducting cables in traditional power grid simulators. We start developing the model through a case example, within the basic concepts are introduced and later expanded to general cases. The model also incorporates the transient behavior of the cooling media, which is mandatory for such cables. It has been observed that the proposed model requires less computational effort and is able to deliver accurate results when compared to more advanced methods.

We investigate the low-frequency electrodynamics in the vortex state of two type-II superconducting films, namely, a moderate-to-strongly pinned Niobium Nitride (NbN) and a very weakly pinned amorphous Molybdenum Germanium (a-MoGe) film. We employ a two-coil mutual inductance technique to extract the complex penetration depth, λ~ . The sample response is studied through the temperature variation of λ~ in the mixed state, where we employ a model developed by Coffey and Clem (the CC model) to extract different vortex lattice (VL) parameters, such as the restoring pinning force constant (Labusch parameter), VL drag coefficient and pinning potential barrier. We observe that a consistent description of the inductive and dissipative part of the response is only possible when we take the viscous drag on the vortices to be several orders of magnitude larger than the viscous drag estimated from the Bardeen–Stephen model.