High Temperature Superconductor Current Research Articles

Feasibility of high temperature superconducting cables for energy harvesting in large space-based solar power satellite applications: Electromagnetic, thermal and cost considerations

The aim of this paper is to present feasibility of application of High Temperature Superconducting (HTS) cables for Space-Based Solar Power (SBSP) application. SBSP is a promising technology that can deliver an infinite amount of clean and eco-friendly energy to the Earth. To deliver the harvested solar energy to the power systems on Earth, efficient energy transmission is critically important. To address the challenges of conventional transmission means, an ideal solution would be using HTS cables. In this research, the design procedure of a Direct Current (DC) HTS cable considering electromagnetic, thermal, and cost constraints is presented. The study considered a 2 MW bipolar DC HTS cable in five operational temperatures: 20 K, 30 K, 50 K, 65 K, and 77 K. The results were showed that the cost and weight of the designed HTS cables were increased by operational temperature increase. However, the cooling cost of HTS cable in higher temperatures, was less than lower temperatures. Also, the total efficiency of the HTS cable and cooling system were increased, when operational temperatures were changed from 20 K to 77 K, from 99.70% to 99.97%, respectively.

Complete and robust magnetic field confinement by superconductors in fusion magnets

The fusion created by magnetically confined plasma is a promising clean and essentially unlimited future energy source. However, there are important problems hindering controlled fusion like the imperfect magnetic confinement and the associated plasma instabilities. We theoretically demonstrate how to create a fully confined magnetic field with the precise three-dimensional shape required by fusion theory, using a bulk superconducting toroid with a toroidal cavity. The vacuum field in the cavity consists of nested flux surfaces. The coils creating the field, embedded in the superconducting bulk, can be chosen with very simple shapes, in contrast with the cumbersome arrangements in current experiments, and can be spared from large magnetic forces between them. Because of the superconductor properties, the system will tend to maintain the optimum field distribution in response to instabilities in the plasma. We numerically demonstrate how a fully-confined magnetic field with the three-dimensional spatial distribution required in two of the most advanced stellarators, Large Helical Device and Wendelstein 7-X, can be exactly generated, using simple round coils as magnetic sources. Current high-temperature superconductors can be employed to construct the bulk superconducting toroid. This can lead to optimized robust magnetic confinement and largely simplified configurations in future fusion experiments.

MOSFET-based HTS flux pump

We have developed a high-temperature superconducting (HTS) flux pump using high-power metal-oxide-semiconductor field-effect transistors (MOSFETs) for switching. For its primary coil, two commercial transformers are utilized, each consisting of two copper coils wound on a single iron core, which enables changing the load current over primary current ratio (101 or 194) between the primary and secondary coils. Full-wave rectification is achieved with two half-wave secondary circuits, each of them having six HTS one-turn coils to lower the resistance. Each secondary coil is composed out of nickel-reinforced BSCCO tapes, where 12 MOSFETs have been soldered in parallel straight to the tapes and controlled with analog electronics. Secondary coils are clamped to custom-made copper-stabilized HTS current leads. A support structure for keeping the HTS coils in place was 3D-printed using cryogenic-compatible composite material PETG-CF20. Resistances of the two secondary circuits were measured to be 4 and 7 at 77 K with a total critical current of 980 A. We successfully ramped up a 50 µH Conductor on Round Core solenoid at 77 K using our HTS flux pump with 50 Hz AC voltage source. We achieved a maximal load current of 900 A and exceeded the 715 A critical current of the solenoid. During the thermal runaway of the magnet, the increased load voltage limits the maximum load current supplied by the flux pump.

Degradation Characteristics of REBCO Tapes According to Electrical Breakdown

Second-generation (2G) high-temperature supercon-ducting (HTS) coated conductors are widely used to develop high-voltage superconducting apparatuses, such as HTS fault current limiters and HTS cables. In this study, experiments on electrical breakdown were performed in saturated liquid nitrogen (LN2) at a temperature of 77K to verify the relation between the applied voltage and electrically degraded characteristics of REBa2Cu3Ox (REBCO, RE: rear earth) tapes, such as the critical current (Ic) and index n. We used three types of REBCO tapes to determine the effect of the stabilizer material on the electrical degradation characteristics of silver, copper, and brass. A sphere electrode sys-tem was used to conduct electrical breakdown experiments under AC and lightning impulse voltages. Accordingly, we determined that the electrical degradation characteristics of REBCO tapes de-pend on the stabilizer material according to the applied voltage.

Magnetization Loss Measurement of Twisted Stacked Tape Cable and Comparison With CORC

High Temperature Superconducting (HTS) cables for large current capacity are being studied in several forms for power device applications. Currently, the cables are being developed for DC applications rather than AC applications. However, if a technology for reducing AC loss is developed, it will be possible to apply HTS cables to various AC devices. Twisted Stacked-Tape Cable (TSTC) is one of the large current HTS cables. It is made by stacking and twisting multiple HTS tapes for large current capacity. The HTS tapes in TSTC should be twisted for the uniformity of current distribution in each tape. Since the HTS tape has a wide thin film shape, it is very difficult to twist itself. In this paper, we measured the magnetization losses of TSTC samples without the striations under AC magnetic fields that had peak values below 0.1 T. Several molds for the TSTC samples were made by using a 3D printer. TSTC samples had several numbers of stacked tapes and two kinds of the tape width. The magnetization losses of the samples in the molds were measured under uniform AC magnetic fields. The experimental results were compared to those of the straight HTS stacked cables and conductor on round core (CORC) cables.

Raising critical currents in YBaCuO-type high-temperature superconductors by Mo substitution

In this work, we investigated the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains. The single crystals were annealed in oxygen at low (130–140 atm) and high (255 atm) pressure, which significantly influenced the observed properties. Magnetic hysteresis loops were measured at various temperatures in fields up to 14 T, for both H||c and H⊥c. On the basis of these measurements, the densities of critical currents were calculated using the Bean critical state model. Then, using the Kramer approach and the Dew-Hughes model, scaling of the pinning force was performed and the type of pinning centers and pinning mechanisms dominant in different field and temperature ranges were determined. Due to Mo substitution, the critical current density in single crystals annealed in oxygen under high pressure increased several times at lower temperatures, e.g., 3–4 times for T = 4–35 K and μ0H = 1–8 T, and by an order of magnitude at higher temperatures, e.g., for T = 65–75 K and μ0H = 2–3 T. For these single crystals, Δκ volume-like pinning centers (Mo2O11 octahedra dimers) and normal point-like pinning centers (interstitial oxygen) were identified as dominant at lower and higher fields, respectively.

Copper electroplating technique for development of HTS current leads bottom joints using MgB2 wires

Low resistance, helium leak tight, cryo-stable superconducting (SC) joints with sufficient strength to absorb thermo-mechanical stress are commonly used in large sized magnets, their feeders and current leads (CL). Among high temperature superconductor (HTS), cuprate oxide based tapes are the popular options for CL applications. Recently composite magnesium diboride (MgB2) wires with superconducting transition temperature of 39 K are getting wide attention for low field applications. Use of Monel as a sheath material in MgB2 wires poses a major challenge while fabricating SC joints due to its low wettability and flowability using PbSn alloy based solder material. To tackle this issue, we exploited Cu electroplating technique to ease fabrication of MgB2 – NbTi: Cu as well as HTS: Cu - MgB2 joints. The details of in-house electroplating technique developed to fabricate bottom joints of BSCCO-2223 based HTS CL using MgB2 wires are reported. To study the morphology of such Cu coated MgB2 wires microstructural investigation is performed using Scanning Electron Microscope with energy dispersive X-ray spectroscopy (SEM/EDX) analysis. Similar Cu plated MgB2 wires are used to fabricate bottom joints of a prototype HTS CL. The performance of joints is preliminary attempted in the HTS CL test experiment up to 1.5 kA at 20 K.

An HTS Magnet With Individually Controllable Coil Currents Energized by a Single Power Source

This paper reports a feasibility study of a high temperature superconductor (HTS) magnet with individually controllable coil currents energized by a single power source. An HTS magnet, a stack of four double pancake (DP) coils, was designed, constructed, and tested. We fabricated four DP coils using no-insulation winding technique and then connected them in parallel to build the HTS magnet. Each DP coil has two current leads, inlet and outlet, and they are electrically soldered to two HTS current leads connected to a single power source in series. The joints between HTS current leads and each coil’s current lead, to be named “control resistors,” are used to measure and control coil currents in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">passive</i> way. A charge-discharge test was performed with the HTS magnet in a liquid nitrogen bath at 77 K. We investigated the electromagnetic behaviors of the HTS magnet by measuring currents, voltages, and magnetic fields. The measurements were described with a numerical simulation using an equivalent circuit model. Two advantages of the HTS magnet were demonstrated: 1) the controllability of coil currents by using “control resistor”; and 2) the improvement of the central magnetic field performance by sharing coil currents.

Design and modelling tools for DC HTS cables for the future railway network in France

The use of high-temperature superconducting (HTS) cables in power systems increases the transmission capacity, whereas reducing the volume of the installation. In addition, in high current applications, HTS cables considerably reduce power losses, right-of-ways and total system mass. This paper presents different multi-physics studies to be performed to accurately design the direct current (DC) HTS cables for the future railway network planned by the French company SNCF. The process used to design DC cables for high operating current (between 5 kA and 20 kA at 1750 V) made of commercial (RE)BaCuO tapes is presented. In this design process, the critical current density dependence J c(B, θ, T) of the superconducting tapes, the thermal properties of the materials used as well as different cable cooling configurations are considered. Finally, we discuss the selection of the appropriate cooling configuration to ensure adequate cooling of the cable.

A Linear-Motor Type HTS Flux Pump With Pumped Current Exceeding 640 A

In this paper, we present the fabrication and performance of a linear-motor type flux pump with a pumped current larger than 640 A. This high-temperature superconducting (HTS) flux pump can be used for magnetic resonance imaging (MRI) magnets and HTS electric machines. We use the flux pump to charge 10 superconducting closed-loops, and show the tested results of pumping current under different applied frequencies and magnetic field amplitudes. This flux pump device can output direct current larger than 640 A at 77 K. The output of this flux pump equals to a DC power source with low output voltage and high output current. Comparing with the traditional power supply of the same rated current, the size of this HTS flux pump is much smaller, while it also eliminates the harmful metal current leads that cause heat leakage. We show that, by increasing the length of the travelling wave region of this flux pump, there is no limit to the output of the current output, which can reasonably reach the kilo-ampere level. The purpose of this paper is to test the reliability of the methodology for the large current HTS flux pump.

Overview and first operation of the high temperature superconductor current leads during integrated commissioning of JT-60SA

The Karlsruhe Institute of Technology (KIT) has constructed and tested the High Temperature Superconductor Current Leads (HTS-CL) for the tokamak JT-60SA within the frame of the Broader Approach agreement between Europe and Japan. In total six HTS-CLs for 25.7 kA for the Toroidal Field (TF) coils and 20 HTS-CLs for 20 kA for the Equilibrium Field (EF) and Central Solenoid (CS) coils were manufactured and all of them were tested at operating temperatures in the test facility CuLTKa at KIT. After delivery, the CLs were integrated into the coil-terminal boxes (CTB) and connected to the TF, EF and CS coils via superconducting feeders. In the present paper the design, manufacture and acceptance tests of the HTS-CL at KIT, their integration into the CTBs, and first results of their operation during integrated commissioning are presented.

Experimental investigation of the thermal performance of the thermosyphon cooling system with rotating

Rotating machine applications with superconductors attract much interest in the industry. For maintaining the operating temperature of high-temperature superconductor (HTS) field poles, a sophisticated cooling system is required. A thermosyphon (TS) is one of the ways for this purpose. The cryo-mechanical system composition is relatively simple, lightweight, and based on natural convection therefore not using any mechanical pump. It can supply the refrigerant from the static condenser part to the rotating evaporator part by using a successful rotary joint. The operating temperature of the TS cooling system depends on the refrigerant. Considering the current HTS materials, the suitable refrigerant is neon, hydrogen. Nitrogen which provides a higher operating temperature than neon and hydrogen is employed for future development. In this work, we focused on and investigated the heat transfer capacity of TS using nitrogen as the refrigerant. The heat transfer performance with rotating was also studied. As a result of the experiment, the TS cooling system could maintain the evaporator temperature by rotating. Moreover, it could transfer the 90 W heat load with rotating.

Conceptual design of HTS magnets for fusion nuclear science facility

Second-generation high temperature superconductors (HTS) are available for producing >20 T at the magnet bore compared to 13–16 T for lower temperature superconducting (LTS) toroidal field magnets proposed in recent fusion energy systems studies (FESS) of Fusion Nuclear Science Facility (FNSF). HTS may enable higher fusion power density and smaller device size. High current density cables of multi-layered REBCO tapes have achieved >10 kA at 4–20 K operation in short sample tests for fusion. High current density cables are required for engineering design of FNSF to allow space for interior plasma components. High current density HTS magnets are particularly attractive in reducing the size of a fusion device, beneficial for compact tokamaks, due to their space constraints. Successful HTS magnet development may enable the design of smaller and cheaper fusion pilot plants with a mission of demonstrating net electricity. It may also offer significant cost and performance advantages in non-fusion applicants such as nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). We developed HTS magnet design concepts for a compact FNSF radial build in order to define the coil size, winding pack mechanical loading and engineering requirements. Partnering with vendors in the US, PPPL is also testing high current cable prototypes aiming at enabling low cost cable technology toward 100 A/mm2 engineering current density over the winding pack desired in high field model coil development for compact fusion pilot plants.

Rotating magnetization method for inspection of local defect in HTS conductor

High temperature superconducting (HTS) magnet used for a accelerator for high energy physics or a large-scale magnetic confinement system for nuclear fusion requires large current capacity HTS conductor in order to dump the stored magnetic energy quickly to protect the coil when quench has been occurred. To realize the HTS conductor, superimposed or stacked HTS tapes conductors are invented. However, local degradation of the critical current has been observed in the production of HTS conductors. Therefore, to confirm the soundness of the HTS conductor, it is necessary to establish the non-destructive detection method for the observation of degraded HTS tapes. In this study, we have investigated to inspect the degradation position in stacked HTS tapes by adopting rotating magnetization measurement method. This measurement method is measuring magnetization signal by rotating and transporting stacked HTS tapes in a static magnetic field. As a result, intentionally introduced buckling defect positions were detected by this measurement method.

Fiber optic quench detection for large-scale HTS magnets demonstrated on VIPER cable during high-fidelity testing at the SULTAN facility

Fiber-optic thermometry has the potential to provide rapid and reliable quench detection for emerging large-scale, high-field superconducting magnets fabricated with high-temperature-superconductor (HTS) cables. Developing non-voltage-based quench detection schemes, such as fiber Bragg grating (FBG) technology, are particularly important for applications such as magnetic fusion devices where a high degree of induced electromagnetic noise impose significant challenges on traditional voltage-based quench detection methods. To this end, two fiber optic quench detection techniques—FBG and ultra-long FBG (ULFBG)—were incorporated into two vacuum pressure impregnated, insulated, partially transposed, extruded, and roll-formed (VIPER) high-current HTS cables and tested in the SULTAN facility, which provides high-fidelity operating conditions to large-scale superconducting magnets. During surface heater induced quench-like events under a variety of operating conditions, FBG and ULFBG demonstrated strong signal-to-noise ratios (SNRs) ranging from 4 to 32 and measured single-digit temperature excursions; both the SNR and temperature sensitivity increase with temperature. Fiber thermal response times ranged between effectively instantaneous to a few seconds depending on the operating temperature. Strain sensitivity dominates the thermal sensitivity in the conditions achievable at SULTAN; however, measurements at higher quench evolution temperatures, coupled to future work to increase the thermal-to-strain signal, show promise for quench detection capability in full-scale magnets where temperature and strain may occur simultaneously. Overall, FBG and ULFBG were proven capable to quickly and reliably detect small temperature disturbances which induced quench initiation events for high current VIPER HTS conductors in realistic operating conditions, motivating further work to develop FBG and ULFGB quench detection systems for full-scale HTS magnets.

Cold Performance Tests of the ITER 68 kA HTS Current Lead Prototypes

• The cold performance test under 4 K is crucial and essential for the most challenged TF prototype HTS current leads. Detailed test process and method are presented. • Many overcurrent and over cooling case were performed to study the TF current leads, and the 1-hand test results and some analysis were presented • The test process and result is important for all the series TF current leads and for the operation in the future. The Toroidal Field (TF) current leads which supply 68 kA DC current for the TF coils are the largest capacity High Temperature Superconducting (HTS) current leads among the three types of HTS current leads for ITER. Two TF HTS current leads prototypes have been successfully built and cold tested at the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP). The cold performance test is a crucial step to verify the design parameters and manufacturing process before starting the series production. The cold performance test includes rated current steady state operation and Loss Of Flow Accident (LOFA) test, different Heat eXchanger (HX) boundary operation, over-current, joint resistance, and heat conduction tests. This paper will present the major results of those tests.

Tensile strength for high-temperature superconducting joints fabricated with incongruent melting

We recently suggested a joint method by using incongruent melting for high-temperature superconducting (HTS) wires, such as joint between RE123-coated conductors and between Bi2223 multi-filamentary tapes. It is important to obtain a suitable mechanical performance in joint to develop a persistent current HTS magnet, and this joint method with the melting is considered to have a higher tensile strength than the solid diffusion. In this study, the tensile strength of such a joint at critical current under tension was investigated toward application in a HTS magnet, such as Bi2223-NMR. We prepared two types of lap joint samples between RE123-coated conductors and between Bi2223 multi-filamentary tapes, with wrapping Ni sheets on junction (joined part in joint sample). The critical current of the samples was a similar value about 15 A at 77 K. The Ic of the samples showed a dependence on a small tension of junction below 40 MPa. With the reinforcement effect of the Ni sheet, the tensile stress tolerance of both joints that Ic of joint is reversible was higher than 90 MPa.

An approach to development of the HTS magnet for SMES at JINR

Particle accelerator complex NICA (Nuclotron-based Ion Collider fAcility) comprises superconducting Booster and Nuclotron synchrotrons which magnets operating at pulse mode in opposite phase with period of about 4 seconds. Summary stored energy of Booster and Nuclotron magnets will vary from 1 to 2.6 MJ during the period. NICA power supply system can be significantly improved by Superconducting Magnetic Energy Storage (SMES) application that will help to move the energy back and force between Booster and Nuclotron. The useful energy at this SMES must be about 1.6 MJ so the maximum total SMES energy should be 3-5 MJ. SMES with this energy should have several Tesla magnetic fields to keep a reasonable size. SMES operating current can be not less than Booster and Nuclotron magnets current so it might be 10-12 kA. It is better to make such a SMES magnet from an HTS (high temperature superconductor) cable for the stability at 6-7 T and 4 s pulse mode. The SMES magnet is planned to be wound as a short solenoid (Brooks coil) of cables optimized for several coaxial sections. HTS cables with helical structure similar to well-known CORC (conductors on round core) cables are under the development at JINR. The HTS cabling technology is based on the same principle as Nuclotron type cable manufacturing technology. HTS tapes, cables and magnets experimental study and testing methods are being developed on the base of an existing test facility at LHEP. First HTS cable short sample with 6 HTS tapes was prepared and tested at 77 K in self-field. Its critical current is about 800 A that will allow achieve required operating currents of SMES magnet with a reasonable amount of HTS tapes in cables. Developments of high field high current fast cycling HTS magnets for accelerators are also being planned at JINR.

Practical Estimation of HTS Dynamo Losses

In High Temperature Superconducting (HTS) DC magnet applications, the current leads contribute a significant fraction of the cooling load. Higher current operation requires larger current leads and a larger thermal bridge into the cryogenic superconducting components. Removal of current leads into the cryogenic environment would lead to a significant reduction in cooling load and hence reduce ongoing operation costs. Superconducting dynamos are a non-contact method of energising HTS coils, capable of producing significant currents in the connected superconducting circuits that exceed usual current lead arrangements. The use of superconducting dynamos has the potential to reduce the size and mass of a complete magnet system by replacing the power source, current leads, and cryocooler. Previous work on superconducting dynamos has focused on driving larger currents, and understanding the underlying physical principles of operation, but has not investigated the AC losses associated with operation. In this work the losses of a kA class multi-stator squirrel-cage superconducting dynamo are investigated experimentally, and compared to the losses expected in the conventional copper current lead based energisation method. The thermal load associated with conduction cooled copper leads prevents practical application of kilo-amp class dc HTS magnets, however we demonstrated the feasibility of using this superconducting dynamo as an energisation method to enable feasible portable high current HTS magnet systems.

Research and Experiment on Quench Detection Technology of HTS Current Leads Based on Distributed Optical Fibers

High-temperature superconductor (HTS) current leads are important components of the EAST and CFETR tokamaks, which are responsible for operating the high parametric current. HTS current leads are made of Bi-2223/Ag-Au alloy tapes, which have the characteristics of slow quench propagation speed and weak quench signal. Traditional thermometers are easily damaged by the high voltage from the current leads, and the terminal voltage signal cannot reflect the hot spot changes of current leads in real time. In this paper, a novel quench detection method based on optical frequency domain reflection technology is proposed. Temperature variations of HTS can be obtained in real time by demodulating the Rayleigh scattered spectrum from the distributed optical fiber attached to the surface of HTS stacks. This paper describes a quenching experiment for one pair of 1-kA small current leads. The external thermal disturbance is increased to explore the quench propagation of HTS current leads under the condition of a self-field, 77 to 80 K air and conduction combined cooling method. From the experimental results, the temperature distribution map of the whole HTS lead is obtained. Compared with the quench voltage, the spectral shift of the fiber appeared to be about 2 s ahead, and the hot spot position can be located with 1-cm accuracy.