HTS Tapes Research Articles

2-D Thin-Shell Model Based on the $H$-$\phi$ Formulation for Modeling HTS Tapes in COMSOL Multiphysics

2-D Thin-Shell Model Based on the $H$-$\phi$ Formulation for Modeling HTS Tapes in COMSOL Multiphysics

Influences of filament numbers on the sintering process of Bi-2223 HTS tapes

Influences of filament numbers on the sintering process of Bi-2223 HTS tapes

Optimization of heating profile for superconductor joint performance made by resistive joule heating process

The long-term heating (>60 min) of second generation high temperature superconductor (2G HTS) tape-joints at temperatures above 200 °C leads to the continuous deterioration of their superconducting properties. Previously, we proposed a resistive Joule heating process with a short heating time (∼10 min) that exhibited beneficial critical current (Ic), retention percentages (84–99 %), and joint resistances (74–697 nΩ cm2) in four independent experiments.In this study, we investigated two heating rates and three tape-joint areas. The results show that for the samples with different tape joint areas, the critical current retention percentages (97–100 %) and uniformity of specific joint resistances (82–272 nΩ cm2) were significantly improved at a high heating rate of ∼30 °C/min. The sintering of silver nanoparticles and oxidation characteristics of the copper stabilizers were observed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy to elucidate the effect of different heating profiles. This study opens new avenues for improving the quality of 2G HTS tape joint processes for ultrahigh magnetic field applications.

THE DESIGN OF THE POWER SUPPLY CURRENT LEADS TO A HIGH-TEMPERATURE SUPERCONDUCTING ELECTROMAGNET

The paper presents a theoretical and experimental analysis of thermal conditions imposed on the power supply conductor for an HTS YBCO-type high magnetic field electromagnet. For thermal stability during the operation of the electromagnet, it is essential to lower the heat flux from outside the system. The heat from the surrounding environment to the HTS winding is limited by using an adequately sized cryogenic system and the proper design of the current leads. The HTS winding and current leads are cooled with a two-stage GM cryocooler. If the power supply conductor's conductive heat flux exceeds the cryocooler’s heat load, the temperature of the HTS winding will increase, and system instability may occur. The power supply conductors are of two types: copper conductors and mixed HTS conductors. This work analyzes HTS conductors and junctions of HTS tape with copper terminals and their contribution to the cryocooler’s total heat load. Using HTS conductors reduces Joule heat when current passes through them (approx. 300 A) and the conductive heat flux to the HTS windings. Resistance for various soldering alloys was experimentally evaluated to evaluate the Joule heat of the junctions between HTS conductors and copper terminals.

Stiffness and loss characteristics of superconducting magnetic bearings using layered HTS tapes and a permanent magnet

This paper discusses some mechanical results from experiments on Superconducting Magnetic Bearings (SMBs) consisting of HTS tapes wound in a ring and a permanent magnet as could be applied to larger rotating machines and ultra-low temperature submerged motors. The wound-ring superconductors are made of 12 mm-width HTS tapes. The authors estimated the spring constant, k, after measuring the thrust force, as 3.85 × 103 N/m, for three-layered wound HTS tapes, and 2.44 × 103 N/m, for the single-wound HTS tape, respectively. The rotating losses for speeds of 500–4500 rpm in the constructed SMB system were also estimated and they were less than 10 W in the constructed measurement system.

Investigation of Pinning Properties in Second Generation HTS Tape Irradiated by Ions with Different Energy

Investigation of Pinning Properties in Second Generation HTS Tape Irradiated by Ions with Different Energy

Numerical modelling of HTS tapes under arbitrary external field and transport current via integral method: review and application to electrical machines *

Superconductors in practical use can be subjected to spatially non-uniform and time-varying external magnetic field as well as carrying a transport current, for example, in an electrical machine. This paper verifies that the integral method can be used in situations in which the external field is spatially non-uniform, by providing both theoretical reasoning and simulation results. Variations in the integral method are reviewed, such as how to impose transport current. Further, the integral method is applied to calculate ac loss in superconducting tapes in an air-cored electrical machine in a two-stage process: the external field is calculated in a COMSOL model without superconducting tapes, and exported into the integral method model that consists of the tapes only. The time taken by the integral method is a small fraction of the time taken by the full machine model in COMSOL, which uses the T-A formulation. There are good agreements between the full COMSOL model and two-stage method incorporating the integral method.

Prediction of 2G HTS Tape Quench Behavior by Random Forest Model Trained on 2-D FEM Simulations

Detailed Finite Element Method (FEM) based simulations for 2 G HTS tapes return high quality results, but the computation takes a long time due to the non-linearity of superconducting properties and they needed high mesh density. This work describes a method for prediction of quench behavior in a long 2 G HTS tape based on a series of 2D FEM model simulations for short length of tape in many different conditions. The random forest model is trained by the set of results from the short-pieces FEM calculations. Subsequently the model can be applied to any length of HTS tape with similar thermal characteristics. Comparison of quench simulation in 10 cm long HTS tape between a detailed FEM model and a fully trained random forest model show that the predicted temperatures are within 0.68 %, while the computation time is significantly faster: The random forest model ran in less than 1 s, while the run time of the FEM model was 5:30 min.

Novel Electrical Insulation Coatings for HTS Cables

To develop epoxy based electrical insulation for HTS power cable and other device applications, the suitability of two cryogenic rated commercial epoxies, (MASTERBOND EP29-LPSP and EP37-3FLFAO) were evaluated. Characterization of their electrical breakdown characteristics, mechanical strength, and the interfacial shear strength of the interface with HTS tapes were conducted at room temperature and 77 K. The epoxy materials are ductile at cryogenic temperatures to support their use as electrical insulation of HTS power devices.

Design Optimization of HTS Field Coils for High Power Density Motors Based on Continuum Sensitivity Analysis

This study proposes an optimization method for designing HTS field coils for high power density motors based on continuum sensitivity analysis. The continuum sensitivity of a superconducting system represents the gradient of the objective function with respect to the superconducting material shape, taking the critical current characteristics into account. The continuum sensitivity was coupled with the level set method through the design velocity field, and the design of the HTS field coil was performed by solving the level set equation. The applicability of the proposed method was verified by designing a 200 kW HTS motor to maximize the torque density. The design optimization provided an optimal solution through the evolution of the topology and shape of the HTS field coil. The optimized geometry was employed to design field coils consisting of racetrack coils wound with HTS tape. Finally, further designs with different cross-sectional areas of the field coils demonstrated that the proposed method can design HTS motors with minimal HTS tape for a given rated power and motor size.

HTS-Tape Magnetic Bearing for Ultra High-Speed Turbo Motor

This paper aims to design superconducting mag-netic bearing using HTS tape for a ultra high-speed turbo motor operating up to 120000rpm. Despite being a recent technology compared to conventional magnetic bearings, HTS passive bearings have many interesting features, such as re-duced dimensions, easy implementation and excellent dynamic response at high speed. The results of the finite element simulation are promising as the levitation forces and the stiffness of the superconductor bearing are compatible with the design requirements. The main contribution of this paper lies in the use of short-circuited HTS coils, unlike previous systems that used HTS bulk.

Numerical Evaluation on Current Behavior of No-Insulation Coils With Parallel HTS Tapes

No-insulation coil (NIC) has been proposed for improvement of thermal stability. NIC can reduce heat generation due to a current distribution that bypass the defect when a local hot-spot is formed. However, a charge delay because of no turn-to-turn insulation is one of the important characteristics of NICs. To decrease the charge delay of NIC, a winding technique with parallel HTS tapes without insulation between layers has been proposed. However, the increase of the number of parallel layers causes the significant current imbalance between parallel tapes. In this paper, the relationship between the number of parallel tapes and the effect on charge delay reduction is investigated. In addition, the effect on the thermal stability and magnitude of central magnetic field and thermal stability due to the current imbalance is also verified. Both analyses are carried out for both NIC with and without defects. The analysis results show that charge delay of NICs is reduced according to increase of number of parallel tapes. Current imbalance between layers increases in accordance with the increase of the number of parallel tapes. However, the analysis results also show that thermal stability and central magnetic field are not degraded by this imbalance current. In terms of NIC with the defect, thermal stability and fluctuation of central magnetic field are most improved by the effect of current sharing between parallel tapes when the number of parallel tapes is largest.

A Compact 2.0 T REBCO Magnet for Advanced Photoelectron Microscopy

Compact shielded high field magnets are required in a variety of fields including: electron microscopy, charged particle beam formation, and nuclear magnetic resonance spectroscopy amongst many. We are using a novel winding method for HTS tape with no solder joints at the centers of pairs of pancake coils. The full cryostat has been manufactured and leak checked, and the modified current leads have been fabricated, ready for final assembly and tests.

Influence of mechanical stress on electron transport properties of second-generation high-temperature superconducting tapes

Second-generation high-temperature superconductor (2G HTS) tapes have demonstrated the ability to generate high magnetic fields and critical currents at a wide operating temperature range. In this paper, we study the mechanical properties of 2G HTS tape measured simultaneously with its critical current. The lattice deformations in the tape’s substrate caused by applied mechanical stress were measured by neutron diffraction. In our experiments, the 2G HTS tape was exposed to uniaxial tensile force ranging from 250 to 1100 N at temperature 77 K. The current through the tape was scanned in the range from 22 to 42 A. The experimental results have been obtained in a cryogenic testing chamber for neutron scattering measurements of internal stresses under load with the incorporated HTS current leads. Critical stress is a vital parameter required for the modeling and designing of advanced superconducting magnets and also a variety of different superconducting applications based on 2G HTS tapes.

Straight and Curved Canted Cosine Theta Superconducting Dipoles for Ion Therapy: Comparison Between Various Design Options and Technologies for Ramping Operation

Canted Cosine Theta layout for accelerator magnets is a very attractive since such magnets can be manufactured and assembled without big tooling, and with a relatively modest number of parts and tools. In the frame of European Horizon2020 funds, two collaborations, HITRI <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">plus</i> and I.FAST, are developing a CCT design, of 80 mm free bore, 4 T central dipole field, and 0.4 T/s ramp-rate. This magnet is expected to be the bending element of a gantry, to control the beam delivery in therapy with ions (hadrontherapy). The paper illustrates first a comparison between CCT and more classical cosine theta layout, followed by the comparison between Nb-Ti, Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and HTS tapes coils. Relevant requirement for the magnets of this study is to be operated at low current, to limit the heat generation, in sight of a liquid-free cooling system. The results of the comparison is then applied to the design of two magnet demonstrators. Both adopt a low-losses Nb-Ti rope, consistently with the need for keeping the heat generation as low as possible. The first is a straight combined function dipole-quadrupole, while the second is a curved CCT dipole. The paper concludes with the first manufacturing tests for the CCT formers, for which aluminium -bronze, stainless steel and charged PEEK polymer are being explored as basic material.

Acoustic Sensor Development for Quench Detection in HTS Conductors

A MEMS (Micro Electro-Mechanical System) acoustic sensor-array quench detection method has been proposed for quick, unobtrusive, and precisely localized detection of quench events in superconducting magnets. A cryogenic probe was designed and built to study the quench event in a gaseous coolant induced in a segment of an HTS tape and verify the effectiveness of acoustic MEMS sensors in detecting such events. Prior work characterized the performance of a commercially available Vesper MEMS microphone, and associated amplifiers, in cryogenic conditions which were utilized in this work. Critically, the application specific integrated circuit (ASIC) used to amplify the MEMS piezo-sensor output signal fails to operate at temperatures below 110 K. Thus, the ASIC was removed from the microphone package and replaced with a custom low temperature preamplifier which we have shown performs with no loss of function at temperatures as low as 10 K. The quench experiment is conducted using the probe within a two-stage Gifford-McMahon (GM) cryocooler in a gaseous helium environment, at cryogenic temperatures between 20 K to 60 K. Three temperature sensors within the sample region monitor temperature of the HTS sample tape and environment. The HTS sample, a 2 mm wide REBCO tape, is mounted within a square G10 tube. A linear array of the repackaged sensors is mounted to the tube to detect the quench event. The quench detection behavior using the sensors is compared with the readings from voltage taps on the sample. The response characteristics of the Vesper acoustic piezo-sensor with the newly identified, cryogenic-safe preamplifier in detecting quench events of REBCO tapes in gaseous helium are presented.

Selected Materials and Technologies for Electrical Energy Sector

Ensuring the energy transition in order to decrease CO2 and volatile organic compounds emissions and improve the efficiency of energy processes requires the development of advanced materials and technologies for the electrical energy sector. The article reviews superconducting materials, functional nanomaterials used in the power industry mainly due to their magnetic, electrical, optical, and dielectric properties and the thin layers of amorphous carbon nitride, which properties make them an important material from the point of view of environmental protection, optoelectronic, photovoltaic and energy storage. The superconductivity-based technologies, material processing, and thermal and nonthermal plasma generation have been reviewed as technologies that can be a solution to chosen problems in the electrical energy sector and environment. The study explains directly both—the basics and application potential of low and high-temperature superconductors as well as peculiarities of the related manufacturing technologies for Roebel cables, 1G and 2G HTS tapes, and superconductor coil systems. Among the superconducting materials, particular attention was paid to the magnesium di-boride MgB2 and its potential applications in the power industry. The benefits of the use of carbon films with amorphous structures in electronics, sensing technologies, solar cells, FETs, and memory devices were discussed. The article provides the information about most interesting, from the R&amp;D point of view, groups of materials for PV applications. It summarises the advantages and disadvantages of their use regarding commercial requirements such as efficiency, lifetime, light absorption, impact on the environment, costs of production, and weather dependency. Silicon processing, inkjet printing, vacuum deposition, and evaporation technologies that allow obtaining improved and strengthened materials for solar cell manufacturing are also described. In the case of the widely developed plasma generation field, waste-to-hydrogen technology including both thermal and non-thermal plasma techniques has been discussed. The review aims to draw attention to the problems faced by the modern power industry and to encourage research in this area because many of these problems can only be solved within the framework of interdisciplinary and international cooperation.

Experimental measurements of contact resistivity between superconducting HTS tapes with or without metallic co-wound tape

REBCO No– or Metal-Insulation winding open the way to very high field magnets. However, in order to impose a reasonable loading time and to protect the magnet as well as possible, the value of the contact resistivity between turns must be controlled. In this paper, we first present our experimental station allowing measuring the contact resistivity between No-Insulation (NI) 6mm wide HTS superconducting tapes, as a function of the mechanical pressure and cooled down at liquid nitrogen temperature (77K). In a second part, we introduce the different types of winding pack measured in addition to NI: Metal-Insulation (MI), Soldered No-Insulation (SNI), Soldered Metal-Insulation (SMI) and double Metal-Insulation (2xMI). Changing the nature of the insulation between the turns changes the value of the contact resistivity and thus the behavior of a coil during a transient regime. These technologies are tested with superconducting tapes from different manufacturers: SuperPower (SP),Theva, ShanghaiSuperconductorTechnology (SST) and SuperOx. Then we will introduce and explain the different parameters of the superconducting and metallic tapes to have a contact resistivity between 1 and 107μΩ.cm2 in the case of our measurements.

Critical Current Degradation in HTS Tapes for Superconducting Fault Current Limiter under Repeated Overcurrent

Superconducting fault current limiters (SFCL) can be an alternative to conventional devices limiting short-circuit currents in power systems. SFCL use high-temperature superconducting tapes of the second generation (HTS 2G) in SFCL, which, after reaching the characteristic critical current of the tape, go into the resistive state (quenching), limiting the short-circuit current. The critical current determines the moment of activation of the SFCL. Therefore, its value should not change during the operation of the device due to repeated limitation of short-circuit currents. The constancy of the critical current is a prerequisite for proper cooperation with the power system protection devices. Multiple quenching can cause microdamage in the superconducting layers responsible for lowering of the value of the critical current of the HTS tapes. The article presents the research results on the degradation processes of 2G HTS tapes intended for the construction of SFCL due to the action of prospective short-circuit currents with values exceeding the critical current of the tested tapes. The decrease in the value of the critical current of the HTS tape as a result of multiple transitions to the resistive state was investigated. The amount of energy emitted during the test current pulse of 0.2 s duration was determined. The limitation values of the voltage drop on the tape, which does not cause accelerated degradation processes, were defined. The microstructural tests of cross-sections of new HTS tapes subjected to prospective short-circuit currents were performed.

Development of a Tape Winding Mechanism for HTS Power Cables

Manufacturing of HTS power cables requires winding the HTS tapes helically around a former. These HTS tapes are costly, and delicate and require sophisticated winding machinery which is expensive. In this paper, an in-house economic mechanism for converting a conventional lathe machine to a Tape Winding Mechanism (TWM) is discussed in detail. In addition to the developed prototype, the technical issues and challenges encountered during the development of TWM are listed. The developed TWM was instrumental in successfully winding 10 HTS tapes simultaneously around a tin-coated braided copper former of 19 mm diameter with a pitch length of 210 mm for a continuous length of 5 m HTS cable. The recommendation of modifying any existing cable winding machine to TWM is also discussed.