Superconductor Technology Research Articles

Simultaneous laser polishing and N-doping of niobium

Superconducting niobium is the base material for many modern particle accelerators. The high cleanliness requirements in all radio frequency superconductor technology have led to the development of complex cleaning processes in recent decades. High-pressure rinsing, heating processes under vacuum and gas atmospheres as well as chemical and electrochemical polishing are commonly applied procedures, that are required to obtain the properties needed for their application. In order to optimize the surface finish of Nb materials in a more environment-compatible way, i.e., with less energy consumption and avoiding hazardous liquids, we report on a combination of simultaneous N-doping and laser polishing here. A nanosecond laser was employed, and the prepared Nb surfaces were investigated with a combination of electron microscopy, x-ray fluorescence spectroscopy (EDX), optical profilometry, and x-ray absorption spectroscopy (EXAFS) to show the effect of different N2-pressures during the laser polishing procedure in an ultrahigh vacuum chamber. The results show that for N2-pressures above ca. 10−3 mbar, traces of nitrogen can be observed by both EDX and EXAFS. In parallel, a smoothing of the surfaces occur, with slightly different roughnesses and microstructures of the polycrystalline Nb surfaces depending on the N2-pressure.

Design and initial test results of a space-bound flux pump to energize the Hēki mission’s superconducting magnet

Despite repeated proposals to utilize superconducting magnets in space since at least the 1970s, examples of their use remain scant. One of the technical challenges is to maintain suitable cryogenic temperatures on a spacecraft. This challenge can be alleviated by the use of flux pumps to reduce the required cryogenic cooling power needed to energize the superconducting magnet. This paper describes the design and initial test results of the flux pump to fulfill the requirements of the Hēki mission that will operate a high-temperature superconducting magnet on an external platform of the International Space Station. A transformer-based, self-rectifier architecture was chosen for the flux pump. An effective circuit model used to design its electromagnetic properties and finite-element modelling used in its mechanical and thermal design. Liquid nitrogen tests were used to demonstrate that the electrical performance of the flux pump meets requirements. Higher-fidelity tests using flight-like copies of the hardware and software were undertaken and validated the thermal modelling. These tests also featured the continuous operation of the flux pump in a conduction-cooled setting for over 100 hours, reflecting an inherent reliability of this technology. Whilst further testing and flight qualification remains to be completed, we anticipate an on-orbit demonstration of this flux pump technology in February 2025. Such a demonstration will signal a maturing of this emerging superconducting technology for both in-space and terrestrial applications.

Characterizing anomalous peaks in the resistance–temperature profile of Bi2Sr2CaCu2O8+δ flakes featuring surface degeneration

Abstract This study focuses on an observed anomalous resistance peak in the temperature-dependent resistance (RT) curves of Bi2Sr2CaCu2O8+δ (BSCCO), attributed to surface degradation and pronounced electrical resistance anisotropy. Employing a standard four-point probe technique on the ab-plane, this research circumvents conventional c-axis testing limitations, enhancing the understanding of BSCCO’s electrical behavior by avoiding contact resistance and etching issues. A comprehensive three-dimensional model, developed using the finite element method, captures the strong resistive anisotropy and correlates the depth of surface degradation with the anomalous resistance peaks, explaining this phenomenon from a quantitative perspective, providing a more specific reference for future analysis of relevant signals. The fabrication process involved pre-patterning and mechanical exfoliation techniques to minimize atmospheric exposure and ensure device integrity. Despite these efforts, surface degradation impacting the superconductivity of surface layers was inevitable. The study’s experimental results, complemented by numerical modeling, reveal the intricate relationship between surface layer thickness and the anomalous resistance peak, providing an approach to gauge the extent of degradation in BSCCO devices. Moreover, it underscores the potential necessity of employing some critical techniques to avoid degradation, such as low-temperature exfoliation in other literatures where degradation signal is notably absent from RT curves. This work advances the understanding of BSCCO’s electrical properties and highlights the critical need for precise fabrication and environmental controls in developing high-temperature superconducting technologies.

Ultra-sensitive low-temperature luminescent thermometry based on Boltzmann behavior of the Stark sub-levels of Pr3+

The cryogenic sensor is critical for numerous applications such as cryobiology, aerospace space probes, and solid-state superconducting quantum technology. However, it is still a challenge to operate at temperatures below 100 K using luminescent intensity ratio (LIR) thermometers with typical thermal coupling levels based on the Boltzmann mechanism. In this work, a sensitive low-temperature luminescence thermometry approach has been developed utilizing Boltzmann behavior of the Stark sub-levels of Pr3+. Spectral Stark-splitting feature of the 1D2 multiplet of Pr3+ was observed in CaNb2O6: Pr3+ phosphor, and the luminescence intensity ratio (LIR) of high state (Stark sub-level (2)) and low state (Stark sub-level (0)) of 1D2 was employed for temperature sensing, resulting in a notable relative sensitivity (Sr) of 11.3 % K−1 at 60 K. In addition, the intervalence charge transfer (IVCT)-based strategy improves the temperature sensitivity above room temperature with maximum Sr up to 1.54 % K−1 at 420 K. This work consistently demonstrate high sensitivity at low temperature, indicating potential applications in cryogenic temperature sensor. These results provide a route to the development of luminescent thermometers with a high sensitivity at low temperatures and a wide range of operating temperatures.

CORC® wires allowing bending to 20 mm radius with 97.5% retention in critical current and having an engineering current density of 530 A mm−2 at 20 T

Abstract Low-inductance, high-field insert solenoid magnets and 20 T dipole magnets for particle accelerators require flexible cables, wound from high-temperature superconductors (HTS) such as RE-Ba2Cu3O7-δ (REBCO) coated conductors, that allow bending to a 20 mm radius without significant degradation in performance. They require an operating current of at least 5 kA and a high engineering current density (Je) exceeding 500 A/mm2 at 20 T. HTS cable technologies that target such demanding magnet applications so far haven’t been able to meet the combination of these requirements.
Here we present the development of the next generation of Conductor on Round Core (CORC®) wires that improves their bending flexibility by factor of more than 2 compared to previous generation CORC® wires. CORC® wires now allow for a bending radius of 20 mm with only 2 – 3 % performance degradation. They allow bending to a radius of 15 mm with a performance retention of 83.5 %. The performance of 30-tape CORC® wires wound from 2 mm wide REBCO tapes from SuperPower Inc, SuperOx and Shanghai Superconductor Technologies was measured at magnetic fields up to 12 T. The overall performance at high magnetic fields of the next generation of CORC® wires improved by a factor of 1.5 – 1.8, depending on the REBCO tape manufacturer. CORC® wires wound from production REBCO tapes achieved a new record Je of 751 A/mm2 at a current of 8.3 kA at 12 T, and a Je of 530 A/mm2 at a current of 5.8 kA when extrapolated to 20 T. 

Performance optimization of a neon turboexpander based on the Kriging model and genetic algorithm

The rapid development of high-temperature superconducting (HTS) technology has increased demand for stable and reliable cooling sources, with the neon refrigerator emerging as a favorable solution for HTS applications, among which neon turboexpander is the core component. This paper proposes an optimal design method tailored for the neon turboexpander, which combines a one-dimensional mean-line design, three-dimensional CFD analysis, adaptive Kriging surrogate model, and the genetic algorithm. The meridional contour of the turboexpander impeller is geometrically parameterized, and the three most critical structural parameters are selected through Sobol sensitivity analysis, and then the response surface analysis is carried out to analyze the coupling relationship between the structural parameters. After optimization, the total-to-static efficiency and output power of the neon turboexpander increased by 3.98% and 6.12%, respectively. Notably, the flow separation phenomenon within the optimized impeller is significantly improved, resulting in reduced flow loss. Furthermore, the optimized impeller demonstrates robust performance in a wide range of variable operating conditions. Therefore, the optimization design method has been proven effective, and the optimal turboexpander impeller structure can be obtained quickly and accurately.

Magnetic Flux Concentration Technology Based on Soft Magnets and Superconductors

High-sensitivity magnetic sensors are fundamental components in fields such as biomedicine and non-destructive testing. Flux concentration technology enhances the sensitivity of magnetic sensors by amplifying the magnetic field to be measured, making it the most effective method to improve the magnetic field resolution of magnetic sensors. Superconductors and high-permeability soft magnetic materials exhibit completely different magnetic effects. The former possesses complete diamagnetism, while the latter has extremely high magnetic permeability. Both types of materials can be used to fabricate flux concentrators. This paper compares superconducting and soft magnetic flux concentration technologies through theoretical simulations and experiments, investigating the impact of different structural parameters on the magnetic field amplification performance of superconducting and soft magnetic concentrators. This research is significant for the development of magnetic focusing technology and its applications in weak magnetic detection and other fields.

Applying High-Temperature SuperconducTechnologies into Power Systems

implementing of distribution and transmission power systems for urban areas and for future renewableenergy to meet future demand is a challenging task whenconventional cables and transformers are considered.Therefore, there are several methods, that have applied inconational power systems to reduce power losses, voltage regulator issues , capital cost of whole system and increasingpower delivering in urban areas and from offshore farms,such as carefully sited and operated distributed generation(DG) and distributed control techniques. However, thesetechniques may raise others challenges in networks such as stability, voltage regulators issues and increasing capital costof networks. Since High Temperature Superconductor(HTS) cables exhibit zero resistance when cooled to theboiling point of liquid nitrogen (77Keliven), they have thepotential to be used to address these issues in distribution and transmission networks. Consequently, this paperreviews super-conductor power systems: the workpreviously achieved in the DC and AC superconductorpower systems and describes the materials and methodswhich they used. In addition, it shows how the superconductor technologies can address these issues whenthey are used for distribution and transmission powe r systems.

Theoretical research on high-efficiency region in cryogenic micro flow heat transfer based on thermal and viscous Knudsen numbers

Cryogenic micro flow heat transfer (CMFHT) has been increasingly interest nowadays due to the urgent needs of superconductive technology, quantum engineering, space cryocooler and other frontier fields. Chasing its high-efficiency region is a key challenge as thermal penetration depth is limited in cryogenic microscale. Therefore, this paper focuses on high-efficiency region in CMFHT, and newly proposes two parameters: thermal and viscous Knudsen numbers (KnT and Knv) based on traditional Knudsen number Kn, which can improve the errors on micro measurement and the inconveniences on high-efficiency region analysis induced by Kn. High-efficiency region is modeled by the three Knudsen numbers and is separated into slip or continuum type bounded by Kn = 0.001. The effects of gas species, temperature and pressure on KnT and Knv are studied and it is found that the reductions of both thermal penetration depth and the range between thermal and viscous penetration depths with temperature dropping deteriorate heat transfer at low temperature. After applicability validations based on opened literatures, it is suggested that in cryogenics ensuring Kn>KnT (L<δT) is put in the first for good heat transfer, and the next is trying the best to ensure Kn<Knv (L>δv) or making Kn and Knv as close as possible.

Development of a superconducting undulator cryostat based on the thermosiphon effect

As a specific device for light production, undulators have been researched and developed since the third generation of synchrotron photon sources. Nowadays, superconducting undulators become a research hotspot. However, the cryostat, which is used to create a liquid helium temperature environment, often causes the failure of the superconducting undulator. In this paper, a cryostat for a superconducting undulator is designed and investigated. First, a new refrigeration distribution is proposed that can provide more excess cooling capacity at 4.2 K temperature. For the cooling of the superconducting magnet, a liquid helium circulation loop based on the thermosiphon effect is designed, which has no pump or any other moving parts. Next, based on high-temperature superconducting technology, six binary current leads are used to decrease the heat load. The beam chamber is cooled below 20 K to reduce possible effect on the magnet. In addition, for the tubes that connect the 4.2 K helium tank to the room temperature component, the thermoacoustic oscillation is studied. In the experiment, the superconducting magnet could be cooled and maintained at 4.2 K depending on the thermosiphon loop. No helium was discharged when the magnet went through a quench which generated large heat in a short time. There was no liquid helium consumption and the excess cooling capacity reached 2.2 W. The maximum magnet current is as high as 470 A. This study can provide a valuable reference for the development of superconducting undulator cryostats.

From high-temperature superconductivity to room-temperature superconductivity: From ambient to high pressure; from very high pressure to ambient again!?

This article will first briefly review the impressive advancements made in high-temperature superconductivity (HTS) before the arrival of room-temperature superconductivity (RTS). Accompanying the advancements made in superconductivity science and technology over the last century, a solid experimental framework concerning the search, development, and even authentication of new discoveries has been established. All these can serve as valuable references in the infancy of RTS research. In this spirit, we will comment on the current status of rare-earth hydride RTS and present our preliminary negative results on Lu-N-H and LK-99, the two most studied materials in the search for RTS in the last few months, although several more reports of negation than affirmation have appeared.

On-premises superconducting quantum computer for education and research

With a growing interest in quantum technology globally, there is an increasing need for accessing relevant physical systems for education and research. In this paper we introduce a commercially available on-site quantum computer utilizing superconducting technology, offering insights into its fundamental hardware and software components. We show how this system can be used in education to teach quantum concepts and deepen understanding of quantum theory and quantum computing. It offers learning opportunities for future talent and contributes to technological progress. Additionally, we demonstrate its use in research by replicating some notable recent achievements.

AC loss study on a 3-phase HTS 1 MVA transformer coupled with a three-limb iron core

High-temperature superconducting (HTS) technology provides an alternative approach to achieve compact transformers. Addressing AC loss in the HTS winding is crucial for HTS transformer applications. Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores. This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it. AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional (3D) T-A homogenization method. When the iron core is incorporated, the saturation magnetic fields of iron materials, flux diverters (FDs) with different geometries, and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding. The inclusion of the iron core leads to a 1.2% increase in AC loss for the transformer winding while simulating at the rated current. We attribute this slight difference to the non-inductive winding structure of the transformer winding, where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.

Towards practical superconducting accelerators for machine learning using U-SFQ

Most popular superconducting circuits operate on information carried by ps-wide, \(\boldsymbol{\mu}\) V-tall, single flux quantum (SFQ) pulses. These circuits can operate at frequencies of hundreds of GHz with orders of magnitude lower switching energy than complementary-metal-oxide-semiconductors (CMOS). However, under the stringent area constraints of modern superconductor technologies, fully-fledged, CMOS-inspired superconducting architectures cannot be fabricated at large scales. Unary SFQ (U-SFQ) is an alternative computing paradigm that can address these area constraints. In U-SFQ, information is mapped to a combination of streams of SFQ pulses and in the temporal domain. In this work, we extend U-SFQ to introduce novel building blocks such as a multiplier and an accumulator. These blocks reduce area and power consumption by 2 \(\times\) and 4 \(\times\) compared with previously-proposed U-SFQ building blocks, and yield at least 97% area savings compared with binary approaches. Using these multiplier and adder, we propose a U-SFQ Convolutional Neural Network (CNN) hardware accelerator capable of comparable peak performance with state-of-the-art superconducting binary approach (B-SFQ) in 32 \(\times\) less area. CNNs can operate with 5-8 bits of resolution with no significant degradation in classification accuracy. For 5 bits of resolution, our proposed accelerator yields 5 \(\times\) -63 \(\times\) better performance than CMOS and 15 \(\times\) -173 \(\times\) better area efficiency than B-SFQ.

Harnessing stochasticity for superconductive multi-layer spike-rate-coded neuromorphic networks

Conventional semiconductor-based integrated circuits are gradually approaching fundamental scaling limits. Many prospective solutions have recently emerged to supplement or replace both the technology on which basic devices are built and the architecture of data processing. Neuromorphic circuits are a promising approach to computing where techniques used by the brain to achieve high efficiency are exploited. Many existing neuromorphic circuits rely on unconventional and useful properties of novel technologies to better mimic the operation of the brain. One such technology is single flux quantum (SFQ) logic—a cryogenic superconductive technology in which the data are represented by quanta of magnetic flux (fluxons) produced and processed by Josephson junctions embedded within inductive loops. The movement of a fluxon within a circuit produces a quantized voltage pulse (SFQ pulse), resembling a neuronal spiking event. These circuits routinely operate at clock frequencies of tens to hundreds of gigahertz, making SFQ a natural technology for processing high frequency pulse trains. This work harnesses thermal stochasticity in superconducting synapses to emulate stochasticity in biological synapses in which the synapse probabilistically propagates or blocks incoming spikes. The authors also present neuronal, fan-in, and fan-out circuitry inspired by the literature that seamlessly cascade with the synapses for deep neural network construction. Synapse weights and neuron biases are set with bias current, and the authors propose multiple mechanisms for training the network and storing weights. The network primitives are successfully demonstrated in simulation in the context of a rate-coded multi-layer XOR neural network which achieves a wide classification margin. The proposed methodology is based solely on existing SFQ technology and does not employ unconventional superconductive devices or semiconductor transistors, making this proposed system an effective approach for scalable cryogenic neuromorphic computing.

Impact of Superconductor Technologies on Network Design and Energy Cost- a Case Study in Libya

Several studies and investigations haveattempted to introduce a new design for the conventionaldistribution networks. This proposed design aims to offer a reduction in substation installation cost and in power losses by eliminating some voltage levels in networks. Sine, this is difficult to achieve with conventional distribution networks, when the conventional cables and transformers are used, where the impedance of conventional equipment is high. Due to High-Temperature Superconductor (HTS) materials provide extremely low impedance to AC when cooled to the boiling point of liquid nitrogen (77K), the interest in using HTS materials to produce power cables and transformers is increased. The present paper investigates the practical impacts of installing HTS cables and transformers and seeks to introduce a future network design which leads to the best implementation for superconducting networks, thus, a drop in the substation installation cost and energy losses cost by eliminating some voltage levels in the traditional networks.

Investigations on NbTi superconducting racetrack coils under pulsed-current excitations

One of the key issues in the technology of superconductors is the protection against quenches. When designing a superconductor as a magnet, a coil or even current leads, the design should be made such that the superconductor withstands all operational conditions, especially those occurring rapidly, as fast discharges or pulsed loads. A model for a superconducting racetrack coil based on NbTi winding is investigated under pulsed transport current conditions (zero external field) utilizing finite element analysis within the Simulia Opera platform. A pulse duration of a few milliseconds and a peak current exceeding 1 kA is yielded by discharging a capacitor into an RLC circuit that includes the superconductor coil as an element. A quench multi-physics analysis has been performed comprising both thermal and electromagnetic solutions. The transition to normal state and quench occurrence has agreed with the expected critical curve together with the load-line estimated for the existing coil geometry.

Unraveling the electronic structure of LuH, LuN, and LuNH: building blocks of new materials.

Advances in superconductor technology have been pursued for decades, moving towards room temperature models, such as a postulated nitrogen-doped lutetium hydride network. While experimental observations have been contradictory, insight into the building blocks of potential new superconductor materials can be gained theoretically, unravelling the fascinating electronic structure of these compounds at a molecular level. Here, the fundamental building blocks of lutetium materials (LuH, LuN, and LuNH) have been examined. The structures, spectroscopic constants for the ground and excited states, and the potential energy curves have been obtained for these species using complete active self-consistent field (CASSCF) and multireference configuration interaction with Davidson's correction (MRCI+Q) methods. For LuNH, the energetic properties of its isomers are determined. The bond dissociation energies of the three building blocks are calculated with the state-of-the-art f-block ab initio correlation consistent composite approach (f-ccCA) and the high accuracy extrapolated ab initio thermochemistry (HEAT) scheme. As well, an analysis of different formation pathways of LuNH has been provided.

IRIS - The Italian research infrastructure on Applied Superconductivity for Particle Accelerators and Societal Applications

The Italian Minister for University and Research has recently funded a large program for an Innovative Research Infrastructure on applied Superconductivity (IRIS) in Italy. Based on the LASA laboratory in Milan, it is a partnership, in the form of a strongly coordinated work, of existing laboratories of various institutes: INFN (leader, participating with 4 labs: Frascati, Genoa, Milan, Salerno); CNR (SPIN institute in Genoa, Naples and Salerno); five Universities: Genoa, Milan, Naples, Salento and Salerno. IRIS will be an upgrade of existing infrastructures, with new state-of-the-art instruments, reinforcing the capability of Italy in the domain of superconductivity aimed to accelerators. IRIS foresees a strong coordination of the activity of the participating laboratories until 2035, at least, thus enhancing the participation of Italian laboratories to future projects requiring advanced superconducting technology, like FCC or the Muon-Collider, and also for developing societal applications of technologies, pursued for high-energy accelerators, especially for the energy domain and the medical sector. In this paper, we present the two novel demonstrators, part of the initial IRIS program: 1) a green superconducting line, 130 m long and designed for 40 kA current capability at 25 kV; 2) a 1 m long HTS dipole magnet with some characteristics similar to LHC dipoles: 10 T, 50 mm × 80 mm bore, but operating at 20 K rather than 1.9 K.

Prospects of an alternative superconductor technology for fusion reactors

New concepts for Tokamak fusion reactors are enabled by ReBCO high temperature superconductors, either to achieve toroidal magnetic fields in the range of 20 T, and/or by operating temperatures above 4.2 K, e.g., 20 K. The application of ReBCO tapes is challenging because common techniques for the manufacturing and quench protection of magnets, developed for classical multifilamentary superconductors, such as NbTi and Nb3Sn, cannot be applied directly. Less risky would be the use of a ternary molybdenum chalcogenide (TMC) superconductor, which was under development before the discovery of high temperature superconductors. Although a low temperature superconductor, the upper critical field is extremely high resulting in a comparable field dependence of the critical current to ReBCO. Because of the improved superconductor fraction of a multifilamentary TMC conductor, the expected engineering current density can be one order of magnitude higher. In addition, a TMC conductor has the potential for cost efficiency and a performance index around 1 $/kAm at 20 T seems be possible.