High-temperature Superconducting Devices Research Articles

HTS Multimaterial Gradiometer Modules for YBa2Cu3O7 SQUID Systems

For the measurement of very small magnetic fields, systems based on superconducting quantum-interference devices (SQUIDs) have been manufactured and employed for many years. In liquid helium operated systems with niobium SQUIDs, wire wound gradiometers can be coupled to a shielded SQUID, but in ceramic high-temperature superconductors (HTS) this is not a common setup, since appropriate thin HTS wires with a bending radius of millimeters operating at liquid nitrogen temperature and the corresponding joining technology is not easily available. We investigated the potential of additive manufacturing to fabricate hybrid plastic and ceramic structures of the insulating perovskite SrTiO3 together with the high- Tc superconductor YBa2Cu3O7, reaching a $T_{c}$ of up to 84 K in the 3D-printed polycrystalline materials. With our measurement setup, the structures are characterized in terms of $T_{c}$ and $I_{c}$ . With the successful process, now larger sample sizes and arbitrary hybrid structures can be manufactured. A gradiometric pick-up loop was fabricated and characterized. These structures can be integrated in low-noise plastic holders and encapsulated by plastic-printed capsules to protect the HTS devices from humidity. By additive manufacturing very versatile ceramic HTS multimaterial hybrid modules can be employed for novel HTS SQUID systems.

Study of Heat Localization in HTS Wires at Overload Conditions

A common problem of superconducting devices is to survive during a fault with a current overload. At a fault, superconducting device will have strong overheating and burning out is possible. The problem becomes more serious in case if a high-temperature superconducting (HTS) wire has a weak point where the critical current is less than the average over a wire. Such a weak point could be the point of origination of strong overheating within a very localized area. This can lead to burning and destroying of an HTS device. To study this problem, we developed the experimental setup with the spatial resolution 2 mm and the time resolution 1 ms to observe a local temperature/voltage evolution in HTS tapes overloaded by currents. The preliminary experiments were performed to measure local heat/voltage development on 2G HTS tapes with an artificial weak point. Local heat/voltage evolutions have been measured and compared with calculations by our model developed earlier.

Система криообеспечения высокотемпературной сверхпроводимости устройств (СКР 001)

Система криообеспечения высокотемпературной сверхпроводимости устройств (СКР 001)

Optical Nanoscopy of High Tc Cuprate Nanoconstriction Devices Patterned by Helium Ion Beams.

Helium ion beams (HIB) focused to subnanometer scales have emerged as powerful tools for high-resolution imaging as well as nanoscale lithography, ion milling, or deposition. Quantifying irradiation effects is an essential step toward reliable device fabrication, but most of the depth profiling information is provided by computer simulations rather than the experiment. Here, we demonstrate the use of atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response obtained from light demodulation at multiple harmonics of the AFM tapping frequency, we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by ∼500 nm laterally. This unexpectedly widespread damage in morphology and electronic structure can be attributed to a helium depth distribution substantially modified by the internal device interfaces. Our study introduces AFM-SNOM as a quantitative tomographic technique for noninvasive 3D characterization of irradiation damage in a wide variety of nanoscale devices.

Performance analysis of cryocoolers based on reverse Brayton cycle and its modifications for cooling HTS devices

To maintain the superconducting state of high temperature superconductor (HTS) used for power application, higher refrigeration capacity cryocooler (>2 kW @ 70 K) is required. A reverse Brayton cycle based cryocooler with long-life and high reliability is one of the suitable candidates for cooling of HTS. The basic reverse Brayton cryocooler can be modified of basic configuration in order to achieve higher FOM. An analytical study focused on modified configurations of reverse Brayton cycle for HTS has been carried out. Neon is selected as working fluid since it has higher heat capacity than helium around 70 K. Six reverse Brayton based modified cycles are standard cycle, 2-stage compression, 2-stage series expansion, 2-stage parallel expansion (same pressure ratio), 2-stage parallel expansion (different pressure ratio), and modified cycle with intermediate cooling system for recuperator. The performances of the modified reverse Brayton cryocoolers are compared and reasons for performance variations are identified.

HTS Power Devices and Systems: Principles, Characteristics, Performance, and Efficiency

As the critical barriers to advanced high-temperature superconducting (HTS) device technologies are overcome, practical HTS devices and systems have been enabled and become available for commercial application. In identifying the applicability of various HTS devices, their operation principles, characteristics, performance, and efficiency are fundamental. Consequently, the corresponding verification of a wide range of HTS devices, especially the HTS power devices and their system technologies, has been comprehensively carried out, and the analytical results are presented in detail towards their practical applications.

Electromagnetic Analysis of YBCO Superconducting Cables With High Current Transporting for Electric Devices

Most high-temperature superconducting (HTS) electric devices have been built by employing a superconducting composite cable. These HTS devices generally have large current-carrying capacities. Therefore, the electromagnetic characteristic of a composite superconducting cable with high current density becomes a key point for the application of these HTS devices. A helical superconducting cable and a Roebel cable consisted of YBCO-coated conductors with a critical current of 500 A @ 77 K in the self-field are both proposed in this paper. The helical superconducting cable that has two conductor layers and the structure parameters of the helical cable are given. The Roebel cable has four layers with a critical current of 500 A. Two 3-D models are built for a helical cable and a Roebel cable with variable geometries. Their magnetic flux distributions along the axis are presented based on the finite-element analysis method, and their electromagnetic characteristics are discussed as well. The analysis model can be further applied for the large-scale HTS electric device design with high current-carrying ability.

High-Tc Step-Edge Josephson Junction Arrays: Comparison of Simulated and Experimental Voltage Responses

With the recent development of multijunction superconducting quantum interference device (SQUID) arrays and superconducting quantum interference filters (SQIFs) using high-temperature superconducting (HTS) materials, it has become increasingly desirable to accurately model HTS devices to enable the optimization of the design for enhanced performance before fabrication. Initially, to develop our simulation capability for HTS devices, we have been working with a commercial software package to fit the data obtained from the characterization of two HTS devices. The models were iteratively adjusted by increasing the number of parameters taken into account, including the aspect ratio of the SQUID loop and the bias injection point. These models were developed for devices fabricated using YBCO step-edge junctions formed on MgO substrates. It was found that the biasing mechanism affects the SQIF voltage response to applied magnetic fields. This has implications for the design of larger arrays.

Numerical models for ac loss calculation in large-scale applications of HTS coated conductors

Numerical models are powerful tools to predict the electromagnetic behavior of superconductors. In recent years, a variety of models have been successfully developed to simulate high-temperature-superconducting (HTS) coated conductor tapes. While the models work well for the simulation of individual tapes or relatively small assemblies, their direct applicability to devices involving hundreds or thousands of tapes, e.g., coils used in electrical machines, is questionable. Indeed, the simulation time and memory requirement can quickly become prohibitive. In this paper, we develop and compare two different models for simulating realistic HTS devices composed of a large number of tapes: (1) the homogenized model simulates the coil using an equivalent anisotropic homogeneous bulk with specifically developed current constraints to account for the fact that each turn carries the same current; (2) the multi-scale model parallelizes and reduces the computational problem by simulating only several individual tapes at significant positions of the coil’s cross-section using appropriate boundary conditions to account for the field generated by the neighboring turns. Both methods are used to simulate a coil made of 2000 tapes, and compared against the widely used H-formulation finite-element model that includes all the tapes. Both approaches allow faster simulations of large number of HTS tapes by 1–3 orders of magnitudes, while maintaining good accuracy of the results. Both models can therefore be used to design and optimize large-scale HTS devices. This study provides key advancement with respect to previous versions of both models. The homogenized model is extended from simple stacks to large arrays of tapes. For the multi-scale model, the importance of the choice of the current distribution used to generate the background field is underlined; the error in ac loss estimation resulting from the most obvious choice of starting from a uniform current distribution is revealed.

Analysis of Thermal Stability of Superconducting Windings Using Core Cable With YBCO Coated Conductors

High-temperature superconducting (HTS) device is a new application of superconducting technology in the electric power network. It shows several advantages, including small volume, light weight, high efficiency, strong capability of overload, and risk-free of fire. When HTS devices run in the power system, the superconductive tapes may quench due to power system fault and endure electromagnetism and mechanical stress caused by large or unbalanced current. Therefore, the research thermal impact on the superconducting tapes has become a key factor in HTS device protection. In this paper, first, a core cable is introduced that has a copper former, a conductor layer, and an insulation layer. Then, the simulation experiment on the thermal stability of the superconducting winding using the core cable is proposed to analyze the curves of temperature and voltage under quenching condition with different thermal disturbance. With the combination of the stability theory, we estimate the quench propagation velocity and analyze the factors affecting quench propagation velocity and minimum quench energy. It is obtained that the minimum quench energy of the core cable is related with the transmission current. When the quench propagation velocity of the core cable is faster, it is effective and convenient for the situation monitoring and fault diagnosis of HTS device.

Loss Analysis of High Power Stirling-Type Pulse Tube Cryocooler

For the purpose of cooling high-temperature superconductor (HTS) devices, such as superconductor motors, superconducting magnetic energy storage (SMES) and current fault limiters, cryocoolers should be compact in size, light-weight, and have high efficiency and reliability. In order to meet the demand of HTS devices world-wide, the cryocooler needs to have COP efficiency >0.1. We have developed a high power Stirling-type pulse tube cryocooler (SPTC) with an in-line expander. The experimental results were reported in June 2012[1]. The cooling capacity was 210 W at 77 K and the minimum temperature was 37 K when the compressor input power was 3.8 kW. Accordingly, the COP was about 0.055. To further improve the efficiency, the energy losses in the cryocooler were analyzed. The experimental results and the numerical calculation results are reported in this paper.

Effect of Discontinuities and Penetrations on the Shielding Efficacy of High Temperature Superconducting Magnetic Shields

High Temperature Superconducting (HTS) materials have been demonstrated to be suitable for applications in shielding of both DC and AC magnetic fields. Magnetic shielding is required for protecting sensitive instrumentation from external magnetic fields and for preventing the stray magnetic fields produced by high power density equipment from affecting neighbouring devices. HTS shields have high current densities at relatively high operating temperatures (40-77 K) and can be easily fabricated using commercial HTS conductor. High current densities in HTS materials allow design and fabrication of magnetic shields that are lighter and can be incorporated into the body and skin of high power density devices. HTS shields are particularly attractive for HTS devices because a single cryogenic system can be used for cooling the device and the associated shield. Typical power devices need penetrations for power and signal cabling and the penetrations create discontinuities in HTS shields. Hence it is important to assess the effect of the necessary discontinuities on the efficacy of the shields and the design modifications necessary to accommodate the penetrations.

Operational characteristics analysis of a 8 mH class HTS DC reactor for an LCC type HVDC system

Many kinds of high temperature superconducting (HTS) devices are being developed due to its several advantages. In particular, the advantages of HTS devices are maximized under the DC condition. A line commutated converter (LCC) type high voltage direct current (HVDC) transmission system requires large capacity of DC reactors to protect the converters from faults. However, conventional DC reactor made of copper causes a lot of electrical losses. Thus, it is being attempted to apply the HTS DC reactor to an HVDC transmission system. The authors have developed a 8 mH class HTS DC reactor and a model-sized LCC type HVDC system. The HTS DC reactor was operated to analyze its operational characteristics in connection with the HVDC system. The voltage at both ends of the HTS DC reactor was measured to investigate the stability of the reactor. The voltages and currents at the AC and DC side of the system were measured to confirm the influence of the HTS DC reactor on the system. Two 5 mH copper DC reactors were connected to the HVDC system and investigated to compare the operational characteristics. In this paper, the operational characteristics of the HVDC system with the HTS DC reactor according to firing angle are described. The voltage and current characteristics of the system according to the types of DC reactors and harmonic characteristics are analyzed. Through the results, the applicability of an HTS DC reactor in an HVDC system is confirmed.

Enabling High-Temperature Superconducting Technologies Toward Practical Applications

This work covers the high-temperature superconducting (HTS) technologies based on the highlights in recent achievements in the applied HTS field in China. Its comprehensive coverage includes practical HTS material manufacturing and characterization, large-scale applications, and electronic applications. The applied HTS technologies have been well enabled to build applicable devices, and their characteristics have been well verified in the HTS devices developed to be industrialized for practical applications. The highlighted HTS devices and their performance details reveal the trend and the necessary improvement required to reach the goal of industrial applications of HTS technologies.

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms, and predicting the performance of high-temperature-superconductor (HTS) tapes, wires, and devices. This is particularly true for ac loss calculation since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, which are based on different techniques and implementations, has been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy-current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications.

The Optimal Design of HTS Devices

In the design of high-temperature superconductor (HTS)-based electromagnetic devices, some of the major challenges include ac loss reduction, minimization of heat leakage, and reduction of the amount of HTS material used to decrease costs. This paper considers a computer model of HTS-based leads involving a multiphysics scenario that considers the electromagnetic and thermal behavior of the system. This paper attempts to address the requirements mentioned and provides an optimum solution by applying an approach based on multiobjective optimization. The differential evolution technique, a stochastic method, widely known for the ease of use and its ability to handle adequately non-differentiable, non-linear, and multimodal cost functions was used. The proposed framework provides a technique to optimize effectively HTS leads, which not only deals with the non-linear aspect of HTS materials, but also includes a multiphysics environment.

Model of Quench Development Inside HTS Coils Including Quench-to-Critical Current Ratio Evaluation

It is well known that the thermal quench current densities jq in high-temperature superconducting (HTS) coils can considerably differ from the “critical” short sample current densities jc(T, B) based on a definite voltage level, for instance 1 μV/cm. The ratio jq/jc (lift-factor) can be higher or lower than one depending on coil parameters. The reasons are smooth voltage-current curves and large temperature margins compared to low-temperature superconducting devices. Several approaches for the description of the quench development in HTS devices are known. However, they are either not suitable for windings with nonuniform magnetic field distribution or were developed for a particular HTS magnet in the limited range of its working parameters. In this paper, we analyzed the simple steady state model of an infinitely long solenoid with nonuniform radial distribution of magnetic field and temperature. It allows to evaluate the main thermal and electrical parameters of HTS coils in j <; jq region as a function of the tape critical properties, n-value of the j - E curve, cooling conditions, and radial thermal conductivity in a broad range of their values.

A double-acting thermoacoustic cryocooler for high temperature superconducting electric power grids

High temperature superconductors (HTSs) have brought the prospect of a revolutionary lossless electric power grid a major step closer to reality. Developing highly reliable, highly efficient, and economical cryocoolers for use with HTS devices is now an urgent necessity. In this paper, a double-acting thermoacoustic cryocooler is presented. It consists of three or six units, each composed of a thermoacoustic converter and a linear compressor. The acoustic field in the converters is determined by the number of units and by the orientation of the piston faces, which allows the convenient adjustment of the phase relationship. The specially designed expansion chamber can recover the acoustic power. With this new configuration, the coefficient of performance can exceed 0.13, a promising figure for HTS electric power grid applications.

Design of 154 kV Extra-High-Voltage Prototype SF6 Bushing for Superconducting Electric Power Applications

One of the critical components to be developed for high-voltage superconducting devices, such as superconducting transformers, cables, and fault current limiters, is a high-voltage bushing to supply a high current to devices without insulation difficulties in cryogenic environments. Unfortunately, suitable bushings for high-temperature-superconductivity (HTS) equipment have not been fully developed to address cryogenic insulation issues. As a fundamental step towards developing the optimum design of the 154 kV prototype SF6 bushing of HTS devices, the puncture and creepage breakdown voltages of glass-fiber-reinforced-plastic (GFRP) were analyzed with a variety of configurations of electrodes and gap distances in the insulation material. And design factors of high-voltage cryogenic bushings were obtained from the result of tests. Finally, the withstand voltage tests of manufacturing a 154 kV extra-high-voltage (EHV) prototype bushing has been performed. Consequently, we verified the insulation level of the newly designed 154 kV EHV cryogenic prototype bushings for superconducting electric power applications.

Conventional helicopters: an adaptiveness study for more electric and alternative propulsion technologies

The power plant and drive systems in a conventional helicopter cause high development and operating costs, compromise safety, and introduce performance limitations. Even though much effort is devoted to mechanical transmission systems, the use of electric components promises a higher reliability. Magnetic gearboxes address many of the problems in mechanical transmissions, but proved to be too heavy at this time. However, since this technology has not achieved its full potential, improvements are imminent and could allow its implementation in the near future. Several combinations with energy sources, amongst which liquid hydrogen (LH2), showed a turboshaft with kerosene to offer the lightest configuration. For the lower required power range, Avgas piston engines should at least be replaced with more efficient diesel engines. The possibility of using electric motors, such as the switched reluctance motor, to drive the tail rotor is possible at the expense of weight. The use of LH2, which has a threefold higher energy density than kerosene, in a helicopter seems feasible; though heavier due to an increased helicopter volume and tank weight, it offers a free cold source for high-performing high-temperature superconductive devices.