Double-pancake Coils Wound Research Articles

Development and performance evaluation of a conduction-cooled warm bore HTS steering magnet

A conduction-cooled warm bore high-temperature superconducting magnet has been designed, built and tested to serve high rigidity beam steering from K500 cyclotron at the Variable Energy Cyclotron center. The objective of the program is the design and fabrication of HTS magnet system for future accelerator magnet. The magnet is specified for beam steering of ± 3° in horizontal plane and ± 1.5° in vertical plane for maximum beam rigidity of 3.3 T-m. An optimized design has been carried out to achieve the specified field quality by suitably positioning the racetrack coils while satisfying several other design constraints. The window-type magnet is composed of double pancake coils wound with high-temperature superconducting tape mounted inside iron yoke and integrated with two-stage cryocoolers. The magnet was cooled down to operating temperature of approximately 20 K with cryocoolers and reached the designed field of 0.70 T (By-direction) and 0.35 T (Bx-direction). Test results demonstrate the technology feasibility of developing cryogen-free warm bore superconducting magnet for accelerator use. This paper describes the design, manufacture and test results of the HTS magnet.

High temperature superconducting magnetic system for neuron activity researches

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field. Keywords: superconductivity, high-temperature superconductor, REBCO tape, cryogen magnetic system, magnetic field, neuron activity.

Высокотемпературная сверхпроводниковая магнитная система для изучения нейронной активности

The paper describes a high-temperature superconducting magnetic system (HTS SMS) to equip an experimental stand intended for neuron activity researches under constant and low-frequency magnetic fields up to 1 T. The design of the magnetic system together with its electromagnetic and cryogenic parameters is briefly discussed. The test results of the preliminary experiments conducted in liquid nitrogen at 77 K for two interchangeable magnets are given. The first magnet was manufactured in the form of a double pancake coil wound with 4 mm high HTS tape. The second magnet was made of pure copper wire with no frame and was impregnated with a thermally conducting epoxy resin. The advantages of the HTS pancake coil were demonstrated in comparison with the cryo-resistive solenoid. Low energy consumption of the HTS magnetic system will allow conducting continuous non-invasive monitoring of biological objects in a magnetic field.

Shielding currents in multifilament coated conductors wound into pancake coils and layer-wound coils

The effect of multifilament coated conductors on reducing shielding currents was studied by numerical electromagnetic field analyses. We compared the behaviours of the shielding currents in stacked double pancake coils and layer-wound solenoid coils (SLCs) wound with the following conductors: a monofilament coated conductor, a copper-plated two-filament coated conductor, and an insulated two-filament coated conductor. Shielding-current-induced fields (SCIFs) in the layer-wound SLCs wound with copper-plated two-filament coated conductors decay more rapidly than in stacked double pancake coils wound with copper-plated two-filament coated conductors. In addition, we examined the behaviour of the shielding currents in the coils with and without normal metal terminals. The normal metal terminals made the decay time constants of the SCIFs in pancake coils longer, while the decay time constants of SCIFs did not change notably in the layer-wound SLCs with and without normal metal terminals.

Design and Performance Estimation of a 20 T 46 mm No-Insulation All-REBCO User Magnet

This paper reports on a proposed design and estimation of performance of a 20 T no-insulation (NI) high temperature superconductor (HTS) standalone user magnet for the National High Magnetic Field Laboratory. It consists of a stack of 18 double pancake coils wound with REBCO tapes from two different vendors, SuNAM and SuperPower, chosen for their complementary in-field critical current, mechanical properties and cost properties. The inner and outer winding diameters and overall height of the magnet are 46 mm, 102.6 mm, and 163.4 mm, respectively. The magnet is designed to generate a 20 T central field at its nominal operating current of 316 A in liquid helium at 4.2 K. The inductance and stored energy are 1.89 H and 94.4 kJ, respectively. In addition to the detailed design parameters, this paper presents a stress analysis, NI charging analysis and post-quench analysis, followed by discussion of design parameters and estimated performance of the proposed 20 T NI HTS magnet.

Design, construction, and operation of an 18 T 70 mm no-insulation (RE)Ba2Cu3O7−x magnet for an axion haloscope experiment

We report the design, construction, and operation results of an 18 T 70 mm cold-bore high temperature superconductor (HTS) no-insulation (NI) magnet, which is developed for an axion haloscope experiment. The magnet consists of 44 double-pancake coils wound with multi-width and multi-thickness REBa2Cu3O7-x (RE = rare earth) tapes. Owing to the NI feature, the magnet is highly compact; is 162 mm in outer diameter and 476 mm tall; and provides an environment of 0.22 T2 m3 within the cold-bore target space of 66 mm in diameter and 200 mm in length. After an initial performance test at SuNAM Co. Ltd., the magnet was installed at the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science in Daejeon, South Korea, in August 2017. The magnet has been successfully operating at the CAPP since then, except for maintenance in October 2018. The magnet may represent the first high field HTS user magnet that experienced long-term operation of over one year.

Design and Test of a Double Pancake Coil for SMES Application Wound by HTS Roebel Cable

A double pancake coil wound by HTS Roebel cable was designed, fabricated, and tested at 77 K. This coil winding had eight turns with the inner diameter of 340 mm and a total conductor length of 10 m. With ten ReBCO strands, the transposition length of the cable was 300 mm. To avoid delamination of ReBCO strands, this coil was impregnated with paraffin wax by a vacuum impregnation method. For protecting ReBCO strands, protective copper plates (PCP) were inserted and soldered between cable surface and external current terminal. The voltage probes were not directly soldered on strands, but on the PCP instead. The critical current and central flux density of the coil were measured at 77 K. With the criterion of 1 μV/cm, the critical current was 1025 A at 77 K. Finally, the additional resistance and the heat loss at 77 and 20 K caused by adding the PCP were estimated.

Design and Fabrication of a 1-MW High-Temperature Superconductor DC Induction Heater

The high-temperature superconductor (HTS) dc induction heater shows great potential in the efficiency increase and heating quality improvement, which has been validated by previous prototypes. Now, Shanghai Jiao Tong University has been developing and fabricating an industrial scale 1-MW HTS dc induction heater in China. The heater is utilized to preheat aluminum billets 446 mm in diameter × 800–1500 mm in length. Two cryocoolers are applied for coil cooling with pluggable sleeve and providing an additional safety margin whose normal operating temperature is 30 K. The magnet consists of a double pancake coils wound by REBa2Cu3O7-δ -coated conductors, which are produced by Shanghai Superconductor Technology Company. More than 12-km HTS tapes are used and the inductance of coil with iron is 98 H. The HTS magnet's critical current is 213 A. The 0.5-T dc magnetic field is set up in the two air gaps of HTS magnet with an iron core. The adjustable iron yoke distribution along the axial direction of billets can meet the 100 °C adjustable temperature gradient design requirement. The results will be helpful to design for the commercialization of the HTS dc induction heater.

Study on the Persistent Current Switch in HTS Coils Wound with 2G Wire for Compact NMR Magnets

High temperature superconducting (HTS) magnets wound with REBCO wires are used in many applications, and the superconducting magnet which is operated in persistent current mode has many advantages. Therefore, we have been developing compact NMR relaxometry devices using HTS coils operated at liquid nitrogen temperature. The required strength and homogeneity of magnetic field of proposed NMR relaxometry devices are 1.5 T and 150 ppm/cm3 respectively. The proposed HTS magnet for NMR relaxometry device consists with stacked HTS double pancake coils wound with REBCO wires and operated by persistent current mode (PCM) using superconducting joint between REBCO wires. In PCM operation, the ability of persistent current switch (PCS) is very important, so, in this study, the thermal properties of YBCO wire against the various thermal inputs by heater were investigated experimentally to design the PCS for PCM HTS magnets. The thermal behaviors of the YBCO wires were measured as functions of amount of heat input using two types of epoxy resin. The current bypassing properties on the YBCO loop coil with developed PCS were studied experimentally.

Development of REBCO-Based Magnets for Plasma Physics Research

The accessible performance range for most magnetic confinement plasma physics devices expands markedly with increasing magnetic flux density. The MIT Plasma Science and Fusion Center is investigating the use of high-temperature superconductors as a low cost means to significantly enhance the performance characteristics of small to moderate scale devices. Our initial investigation emphasized the no-insulation winding technique as a means to produce highly stable dc magnets for devices operating at moderate to high magnetic flux density. We present design, manufacture, and test results for a double pancake coil wound from a 500 m length of 12 mm wide REBCO tape. The coil provides on-axis magnetic flux density within an 8 cm clear bore in excess of 0.5 T when operated in liquid nitrogen and in excess of 6 T when operated in liquid helium. The ultimate aim of the program is to develop conduction-cooled HTS coil modules that can be used for both linear and toroidal plasma devices.

A Study on Mitigation of Screening Current Induced Field with a 3-T 100-mm Conduction-Cooled Metallic Cladding REBCO Magnet

A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1–2 $\mu {\text{m}}$ stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet

Design Study of a 10-T REBCO Insert Solenoid

As a first step to develop HTS insert technology, we plan to build a 10-T REBCO solenoid that will be tested at the French National High Magnetic Field Laboratory of Grenoble in France (LNCMI) at 4.2 K, in the aperture of a 20-T resistive magnet. Two winding approaches are being considered for the HTS insert, i.e., the no-insulation (NI) and metallic insulation (MI) winding technics. Both methods allow turn-to-turn bypassing current but differ in their turn-to-turn resistance value by three orders of magnitude. In this paper, we provide a comparative study between the two winding options using numerical simulations applied to a preliminary design of the insert, which features a cold bore diameter of 50 mm and is made of 15 double-pancake coils wound from a 6-mm REBCO tape.

26 T 35 mm all-GdBa2Cu3O7–x multi-width no-insulation superconducting magnet

A 26 T 35 mm winding diameter all-GdBa2Cu3O (GdBCO) magnet was designed by the MIT Francis Bitter Magnet Laboratory, and constructed and tested by the SuNAM Co., Ltd. With the multi-width (MW) no-insulation (NI) high temperature superconductor (HTS) winding technique incorporated, the magnet is highly compact; its overall diameter and height are 172 and 327 mm, respectively. It consists of a stack of 26 NI double pancake coils wound with MW GdBCO tapes in five different widths ranged 4.1–8.1 mm. In a bath of liquid nitrogen at 77 K, the magnet had a charging time constant of 16 min due to the intrinsic NI characteristics. In liquid helium at 4.2 K, the magnet generated a 26.4 T field at the center, a record high in magnetic fields from all-HTS magnets. The results demonstrate a strong potential of MW-NI GdBCO magnets for direct current high-field applications.

A Parametric Study on Overband Radial Build for a REBCO 800-MHz Insert of a 1.3-GHz LTS/HTS NMR Magnet.

A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting (HTS) nuclear magnetic resonance magnet (1.3 G) is currently being built at Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology. One of its key components is an 800-MHz HTS insert (H800) comprising three nested coils. Each coil is a stack of double-pancake coils wound with 6-mm-wide 75-μm-thick REBCO tape. For this H800 generating its self-field of 18.6 T and being exposed to a total field as high as 30.5 T, overbanding each pancake coil is necessary to keep the conductor strain at < 0.6%. Although electromagnetic and mechanical details of the H800 had been considered during its design stage, a parametric study on the overband radial build considering winding tension effect should further confirm the results of our previous analysis. Thus, in this paper, based on Maxwell's equations and the equilibrium equations for mechanical deformation, we examine stress levels that the H800 experiences as H800 undergoes winding-energizing sequences during operation at 1.3 GHz. We also discuss the effects of overband radial build and winding tension on conductor stress in each coil. Finally, based on this analysis, we may further optimize the stainless-steel overbanding and winding tension on each H800 coil.

Quench Detection Method for Cryocooler-Cooled YBCO Pancake Coil for SMES

In this study, we focus on a quench detection method for a cryocooler-cooled double pancake coil wound with an YBCO bundle conductor for superconducting magnetic energy storage. Because the local normal-zone propagation velocity is significantly slower in a high-temperature superconducting coil than that in a low-temperature superconducting coil, it is difficult to detect the local normal transition using a voltage between both coil ends. In the application of an YBCO coil for superconducting magnetic energy storage, quench detection is considered to be more difficult because of the noise of the converter or other equipment. Therefore, the normal transition and quench must be detected using some other method. A current detection method, which measures the current redistribution in the YBCO coil with hall probes, was proposed and verified to be able to determine the normal transition by the numerical simulations in the previous paper. In this study, on the basis of the current detection method, the experiments and numerical simulation were performed on a cryocooler-cooled small model double-pancake coil wound with an YBCO bundle conductor composed of four electrically insulated YBCO tapes. As the results, the current detection method was verified to be effective in detecting the local normal transition; Hall probes were used to measure the magnetic field and to estimate the current in individual YBCO tapes making up the bundle conductor.

Theoretical and Experimental Studies on $J_{c}$ and AC Losses of 2G HTS Coils

This paper begins with introducing the winding techniques of two superconducting double-pancake coils wound using 2G coated conductors. These winding techniques are able to guarantee a good performance for the superconducting coils. Then the coil critical currents were measured and compared with a simulation model. The results were consistent. Finally the coil AC losses were measured using an experimental circuit including a compensation coil. The simulation results are close to the experiment results.

Anisotropic thermal transport in double-pancake coil wound with DI-BSCCO® tape

We have measured the temperature dependence of the thermal resistances Rr(T) and Rz(T) of the parallelepiped samples cut from a double-pancake coil along the radial (r) and the thickness (z) directions, respectively. The double-pancake coil was wound with DI-BSCCO® tape fabricated by Sumitomo Electric Industries, Ltd. DI-BSCCO is a (Bi,Pb)2Sr2Ca2Cu3O10+x tape sheathed with silver. Both Rr(T) and Rz(T) increase monotonically with decreasing temperature. We analyze the thermal transport in the coil by use of the parallel and series heat current circuit of DI-BSCCO tapes and insulators.

Quench and recovery characteristics of a racetrack double pancake coil wound withYBCO-coated conductor

The reliability of high temperature superconducting (HTS) racetrack coils is one of themost important factors for the development of large-scale rotating machines. However, it isnecessary to investigate the stability and normal zone propagation characteristics ofracetrack coils for large-scale applications such as ship propulsion motors and powergenerators. In this study, the quench/recovery characteristics of a racetrack-type, doublepancake (DP) coil, which could be applied to HTS rotating machines, were investigatedusing the voltage and temperature profiles in a cryogenic conduction cooling system. Theminimum quench heating flux and quench propagation velocity of the racetrack DP coil arealso discussed.

Thermal characteristics of conduction cooled 600 kJ HTS SMES system

A 600kJ HTS SMES is developed and tested in Korea. The HTS SMES consists of 22 double pancake coils wound on each aluminum alloy bobbin. It is cooled by two GM cryocoolers down to around 6K and current is charged through HTS current leads up to 275A. Beside the heat penetration from room temperature structures, heat generation in the HTS coil is inevitable because of the joint resistances and the intrinsic property of the HTS tape such as index loss. Moreover, during the charging and discharging operation, AC loss of the HTS conductor and eddy current loss in the coil bobbin and metallic structures are generated. Therefore, the heat generation should be effectively removed by the cryocooler to ensure the stable operation of the coil. In the HTS SMES, aluminum alloy conduction plates outside the each coil are used as thermal paths to the cryocoolers. This paper describes the thermal characteristics of the HTS SMES for the charging and discharge operation.

Properties of an Experimental Coil Wound With YBCO Coated Conductor Carrying an AC Current With Frequencies up to 864 Hz

To study the properties of coils made out of the second generation superconducting wire, we designed, manufactured and tested an experimental double pancake coil wound with 4.2 meters of a 4 mm wide, copper stabilized YBCO coated conductor. The critical current of a short sample was 53 A at 77 K in self-field. The critical current of the single pancake coil based on the 1 V/cm criterion for the average electric field was approximately 30 A. The critical current of the complete double pancake was about 23 A. Using micro Hall probes, we measured the radial magnetic field component at the edges of the coil. The results clearly indicated the strong influence of the magnetization currents on the magnitude and distribution of the radial field component. AC losses in the coil were measured at frequencies of 54 Hz, 108 Hz, 216 Hz, 432 Hz and 864 Hz. At the critical current (16.2 A) and frequency 432 Hz the coil losses were 0.9 W. The magnetic measurements showed that the tape in the winding is exposed to a very inhomogeneous magnetic field. The experimental results of the field distribution in the winding were compared with the existing theoretical models.