Insert Coil Research Articles

Dynamic Analysis of No-Insulation Insert Coil Under Changing Background Magnetic Field

Dynamic Analysis of No-Insulation Insert Coil Under Changing Background Magnetic Field

The first CICC-type Bi-2212 insert coil for high-field applications up to 20 T

Abstract As the need for high-magnetic field magnets, this article made the first cable-in-conduit conductor (CICC) -type Bi-2212 insert coil. The Bi-2212 conductor consists of 24 wires, an Ag tube, and a 316 LN jacket. With the optimized heat-treatment regime, the insert coil exhibited excellent current-carrying capacity under magnetic fields up to 20 T: the Ic of the coil was up to 5.4 kA under 20 T backfield. With the ‘Pre-OP before cabling’ process, the void fraction was precisely controlled. Besides, the insert coil exhibits excellent stability with the electromagnetic loads and quenching process: no obvious change in performance was detected even when the electromagnetic loads increased to 101 kN m−1; after the quench event where the voltage on the insert coil was up to ∼4000 times criterion, no degradation was detected. The excellent performance of the Bi-2212 insert coil gives a solid foundation for the development of full-size Bi-2212 CICC for high-field applications.

Screening-current-induced mechanical damage and critical current degradation in epoxy-impregnated REBCO insert coils

Screening-current-induced mechanical damage and critical current degradation in epoxy-impregnated REBCO insert coils

REBCO Insert Coils Toward High-Field, Large-Bore Magnet for Quantum Physics Research

REBCO Insert Coils Toward High-Field, Large-Bore Magnet for Quantum Physics Research

Intensification in Convective Heat Transfer by using Wire Coil Insert

Intensification in Convective Heat Transfer by using Wire Coil Insert

Experimental study on screening-current induced strain in REBCO insert coils: under critical current control and operation current cycles

The screening-current effect is an inhomogeneous distribution of current density inside the REBCO conductors. The additional strain induced by the screening current, known as screening-current induced strain (SCS), is considered to affect the structural integrity of REBCO windings, especially when operating high-field REBCO insert magnets. In this work, we wound and tested a series of 50-turn REBCO coils inside a 10 T LTS external to investigate the influencing mechanism of multiple electromagnetic factors on SCS. We varied the critical current in different coils by different heat treatment procedures. Each coil was tested individually, experiencing a external field cycle and multiple operation current cycles at constant external fields. The extreme scenario for each coil was being energized to 400 A while the external field was 10 T. We adapted the discrete-coupled model to estimate the hoop strain distribution, monitored the experimental results by multiple strain gauges at the outermost turn. Test coil with a lower critical current endured a lower maximum hoop strain. When we were energizing the test coils, hoop strain increased at the edge of REBCO tapes while remaining nearly constant in the middle region. Additionally, the maximum hoop strain at the outermost turn decreased after each excitation cycle. This work could be an experimental reference for optimizing the electromagnetic design and the excitation scheme during the development of high-field REBCO magnets.

Design and Preliminary Tests of a 20-T REBCO Insert Coil for a 35-T All Superconducting Magnet

Design and Preliminary Tests of a 20-T REBCO Insert Coil for a 35-T All Superconducting Magnet

Towards high-field applications: high-performance, low-cost iron-based superconductors.

High magnetic fields play a crucial role in advancing basic sciences, fusion energy, and magnetic resonance imaging systems. However, the widespread use of high-field magnets requires affordable high-temperature superconducting wires that can carry large supercurrents. Iron-based superconductors offer an economically attractive solution to push forward important yet costly scientific programs, such as nuclear fusion reactors and next-generation particle accelerators. In this review, we start with the fabrication of iron-based superconducting wires and tapes and continue to discuss several key factors governing the current transport properties. State-of-the-art wires and tapes are introduced with emphasis on grain boundary characteristics, flux pinning, and anisotropy. The architecture of flexible conductors enables low cost, high mechanical strength, and high thermal stability. Recent progress in practical applications, including superconducting joints and insert coils, is also reviewed. Finally, we propose several key questions faced by iron-based superconductors in future practical applications.

Experimental Analysis of the Improvement of Heat Transfer in Tube Heat Exchangers via Passive Flow Generators Using Wire Coil Inserts

Abstract Due to their high performance and low-cost demands, internally treated tube heat exchanger surfaces are one of the passive heat transfer enhancements that have caught the industry's attention. At bulk temperatures of 30 °C, an experiment for the insertion of 1 mm and 0.5 mm wire coils with a constant pitch length of 8 mm was carried out in this study. The results on the improvement of heat transfer, including the velocity profile, Nusselt number, friction factor, and thermal enhancement efficiency, were significant. Based on a lower surface temperature recorded beyond the uncertainty value, the results demonstrated an improvement in heat transfer for smaller diameters of wire coil inserts. Interestingly, this improvement is concentrated at low Reynolds numbers, indicating that there may be a point at which an increase in wire thickness does not necessarily result in an equivalent improvement in heat transfer. For both wire thicknesses, a Nusselt number increase of up to 5 times was observed. The friction factor penalty, however, varies depending on the wire thickness, with a higher magnitude (3.2-fold increase) obtained for 1mm as opposed to a 1.8-fold increase for the lower counterpart. This distinction results in the 0.5 mm coil insert gaining better overall performance with an average of 2.2 for the thermal performance ratio, further solidifying the advantage of this technique for enhancing heat transfer in conduits.

Screening-current-induced magnetic fields and strains in a compact REBCO coil in self field and background field

REBa2Cu3O7−x (REBCO) coated conductors, owing to its high tensile strength and current-carrying ability in a background field, are widely regarded a promising candidate in high-field applications. Despite the great potentials, recent studies have highlighted the challenges posed by screening currents, which are featured by a highly nonuniform current distribution in the superconducting layer. In this paper, we report a comprehensive study on the behaviors of screening currents in a compact REBCO coil, specifically the screening-current-induced magnetic fields and strains. Experiments were carried out in the self-generated magnetic field and a background field, respectively. In the self-field condition, the full hysteresis of the magnetic field was obtained by applying current sweeps with repeatedly reversed polarity, as the nominal center field reached 9.17 T with a maximum peak current of 350 A. In a background field of 23.15 T, the insert coil generated a center field of 4.17 T with an applied current of 170 A. Ultimately, a total center field of 32.58 T was achieved before quench. Both the sequential model and the coupled model considering the perpendicular field modification due to conductor deformation are applied. The comparative study shows that, for this coil, the electromagnetic–mechanical coupling plays a trivial role in self-field conditions up to 9 T. In contrast, with a high axial field dominated by the background field, the coupling effect has a stronger influence on the predicted current and strain distributions. Further discussions regarding the role of background field on the strains in the insert suggest potential design strategies to maximize the total center field.

Effect of charging sequence of background coil and insert coil on screening current in high-field non-insulated hybrid superconducting magnets

The hybrid superconducting magnet with low-temperature superconductor (LTS) for background coil and high-temperature superconductor (HTS) for insert coil is a dependable approach towards achieving high magnetic fields. However, challenges related to screening currents considerably limit the realization of higher field strengths. Due to the historical dependence of screening currents in superconductors on the magnetization path, the shunt currents in non-insulated (NI) superconducting coils can alter the effective magnetization path. Consequently, the charging sequence of LTS coils and NI HTS coils can influence the behavior of screening currents. We establish an electromagnetic and mechanical model for a 32 T NI hybrid superconducting magnet and conduct a comprehensive comparative analysis of screening current induced stress (SCIS), screening current induced field (SCIF), and loss under three different charging sequences. The results indicate that when the NI insert coils are charged first, the hoop stress is slightly lower compared to the other two charging sequences, but the instantaneous power and total losses are the highest. When both the insert and background coils are charged simultaneously, the hoop stress is the highest, yet the instantaneous power and total losses are the lowest, accompanied by a more uniform magnetic field ascent. These findings provide valuable insights for the design and selection of charging sequences of ultra-high-field NI hybrid superconducting magnets.

Development of the first Tesla class iron-based superconducting coil for high field application

This study has, for the first time, combined iron-based superconductor (IBS) with high field insert coil technology to generate a higher magnetic field. Nine large-sized iron-based superconducting double pancake coils (DPCs) were fabricated, and their performance was evaluated at 4.2 K. Subsequently, seven DPCs with superior performance were assembled to form an IBS insert coil and tested at the 20 T background field. The test results indicated that the insert coil successfully generated above 1 T magnetic field under the 0 T, 10 T, and even 20 T background field, respectively. Notably, the poorest IBS DPC still had a critical current of about 84 A at the background field of 20 T, which outperformed all previously reported performance tests of IBS coils. This paper provides a detail introduction to the design and fabrication process of the IBS insert coil, presents the test results, and discusses them.

Hydrothermal and energy-saving performances in a mini-channel heat sink under different wire coil inserts induced swirling flow

Energy conservation and emission reduction are crucial international policies. For micro/mini-channel heat exchangers, improving their thermal performances while consuming as little energy as possible is essential for implementing these policies. Swirling flow stands out as one of the most effective methods for heat transfer enhancement in channel. The wire coil insert, known as an effective swirling flow device, has been widely applied in traditional heat exchangers. However, the effects of different wire coil inserts on hydrothermal and energy-saving performances in the square micro/mini-channel remain unclear. Actually, some wonderful swirling flow generators achieve excellent thermal performance at the cost of sacrificing flow performance and energy conservation. This violates the primary intention of energy conservation and emission reduction. Therefore, this study designs several wire coil inserts with various shapes (square, circle, obverse or reverse trapezoidal, observe or reserve triangular, and hexagonal cross-section shapes) and different pitches (p=3–10.5 mm). Also, a numerical investigation on effects of these wire coil inserts on performances in mini-channels (a single mini-channel with 2×2 mm2 cross-section) at Reynolds number (Re) of 523–1120 is conducted. The results show that the square wire coil insert yields the best heat transfer and comprehensive thermal performance. This is attributed to the fact that wire coil inserts induce swirling flow, which promotes the separation and redevelopment of the flow and thermal boundary layers. Based on this, the effect of wire coil pitch is analyzed thoroughly. Increasing the pitch leads to an increasing first and then decreasing tendency in the comprehensive thermal performance. Overall, the mini-channel with a square wire coil insert at p=6 mm obtains the optimal comprehensive thermal performance factor (∼2.0) for Re = 1120. Moreover, it also presents an acceptable energy-saving performance. In addition, the comparison of this study and several other studies suggests that, square coil insert has great potential to improve comprehensive performance of mini-channel heat exchanger at higher Reynolds number.

Design and Assembly of a Large-Aperture Nb3Sn Cos-Theta Dipole Coil With Stress Management in Dipole Mirror Configuration

The stress-management cos-theta (SMCT) coil is a new concept which has been proposed and is being developed at Fermilab in the framework of US Magnet Development Program (US-MDP) for high-field and/or large-aperture accelerator magnets based on low-temperature and high-temperature superconductors. The SMCT structure is used to reduce large coil deformations under the Lorentz forces and, thus, the excessively large strains and stresses in the coil. A large-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn SMCT dipole coil has been developed and fabricated at Fermilab to demonstrate and test the SMCT concept including coil design, fabrication technology and performance. The first SMCT coil has been assembled with 60-mm aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil inside a dipole mirror configuration and will be tested separately and in series with the insert coil. This paper summarizes the large-aperture SMCT coil design and parameters and reports the coil fabrication steps and its assembly in dipole mirror configuration.

First Validation of Robust REBCO Insert Concept on a Large 20-Pancake Prototype Reaching Up to 25 T

We recently proposed a robust REBCO HTS (RareEarth BaCuO) insert coil concept in the framework of a project to upgrade the 25 T Cryogen-Free Superconducting Magnet at the High Field Laboratory For Superconducting Materials to reach 30 T. In this concept, the conductor consists of a two-tape bundle to mitigate the risks posed by local tape degradation. So-called edge impregnation is used to enhance the mechanical stiffness while reducing delamination risk, providing conduction-cooling capability at the same time. This insert is to be protected against the risk of thermal runaway simply by using dump resistor, thanks to an early detection concept. The different ideas forming the robust REBCO insert coil concept were tested successfully on various small scale prototypes. We report here their first implementation on a large-size insert coil, consisting of 20 stacked pancakes from the 30 T CSM upgrade insert. The mechanical behavior of the coil is modelled and validated with experiments. The thermal runaway detection setup is introduced. Its sensitivity and selectivity is discussed based on previous works on thermal runaway scenarios.

A 50 kA Superconducting Transformer for the Upcoming High-Field High-Current Testing Station at the BNL

Brookhaven national laboratory is upgrading its exist-ing user facility to support R&D for High Energy Physics (HEP) and Fusion Energy Sciences (FES). The goal of this upgrade is to host the testing of the superconducting cables, conductors, joints and insert coils under high magnetic field (10 T), with currents up to 50 kA (present limit 20 kA) and at temperatures varying from 4 K to 40 K. To provide a current up to 50 kA to the sample, a superconducting core-less transformer is under construction. The superconducting transformer would additionally reduce the heat loss at the current leads at high currents. The SC transformer consists of two coaxial coils. The primary coil is inside the secondary coil. The primary coil consists of 3048 turns of rectangular wires (1.91 mm × 1.27 mm), wound in 24 layers. The secondary coil consists of 13 turns of the secondary cable (18.35 mm × 5.96 mm), wound in one layer. The parameters of the transformer are chosen to satisfy the space re-strictions while using the available conductor. This paper presents the design of the 50-kA transformer.

Development of a Bi2212 Dipole Insert at Fermilab

A goal of the U.S. Magnet Development Program (US-MDP) is high-field magnets for accelerators with magnetic fields larger than 15 T, i.e., above the limits of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn accelerator magnets. Composite round wires and Rutherford cables made of high temperature superconductor Bi2212 may achieve this goal. Bi2212 is sensitive to transverse stresses and strains, and this requires stress management in the coil design. A stress management approach was developed at Fermilab for high-field large-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn accelerator magnets. Now it is being applied to high-field dipole insert coils based on Bi2212 Rutherford cable. This paper describes the insert coil design and main parameters, including the superconducting wire and cable. The coil will be installed inside a 60-mm bore Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole outsert coil and cold iron yoke. The Bi2212 coil will be tested individually and in series with the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn outsert coil. The expected Bi2212 insert test parameters are reported and discussed.

Degradation Characteristics of a 20 T REBCO Insert Magnet After a 4.2 K Standalone Test

A 20-T/17-mm High-Temperature-Superconducting (HTS) magnet was developed and tested, comprising a 15-T no-insulation (NI) REBCO insert (Coil 1) nested in a 5-T metal-insulation (MI) REBCO coil (Coil 2). Coil 1 consists of 20 NI double pancakes (DP), while Coil 2 consists of 28 MI DPs. The 20-T magnet was cooled in liquid helium and charged for five runs, the maximum power supply current reached 228.7 A. Multiple quenches occurred during the charging process, causing the power supply current to drop to zero within one second. The rapid current variation induced a large voltage inside the coil, which damaged Coil 1. After re-warming, Coil 1 was tested in liquid nitrogen, and its critical current was significantly degraded. To investigate the degradation, three representative DPs from Coil 1 were examined using continuous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> c measurement and observed with optical and scanning electron microscopes. Most degradation areas consisted of a bubble with a current breakdown point distributed throughout Coil 1. Probable causes were proposed in this article.

Analyses of Deformation Due to Screening-Current-Induced Force in Layer-Wound REBCO Insert Coil for 1.3-GHz LTS/HTS NMR

REBCO wires have high critical current density and thermal stability, and are being applied in various fields such as NMR, MRI, and accelerators. We are currently designing a 1.3-GHz LTS/HTS NMR magnet that operates in a persistent current (PC) mode. However, there are issues with using REBCO coils that need to be resolved. One problem unique to REBCO coils is non-uniform electromagnetic forces caused by screening currents. During the charging and discharging of the coil, screening currents are induced, resulting in a significantly non-uniform current distribution within the coil. As a result, non-uniform electromagnetic forces are generated within the coil due to these screening currents. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this study, we performed an electromagnetic stress analysis using a two-dimensional axisymmetric structural analysis that considered tension during winding, thermal stress during cooling, and electromagnetic force during charging. First, we compared the results of the numerical simulation of the layer-wound REBCO coil with the experimental results. Then, we conducted numerical simulations of an insert REBCO coil in a design example of a 1.3-GHz NMR to evaluate the stress and deformation of the REBCO coil.

Conceptual Design of 20 T Hybrid Accelerator Dipole Magnets

Hybrid magnets are currently under consideration as an economically viable option towards 20 T dipole magnets for next generation of particle accelerators. In these magnets, High Temperature Superconducting (HTS) materials are used in the high field part of the coil with so-called insert coils, and Low Temperature Superconductors (LTS) like Nb3Sn and Nb-Ti superconductors are used in the lower field region with so-called outsert coils. The attractiveness of the hybrid option lays on the fact that, on the one hand, the 20 T field level is beyond the Nb3Sn practical limits of 15-16 T for accelerator magnets and can be achieved only via HTS materials; on the other hand, the high cost of HTS superconductors compared to LTS superconductors makes it advantageous exploring a hybrid approach, where the HTS portion of the coil is minimized. We present in this paper an overview of different design options aimed at generating 20 T field in a 50 mm clear aperture. The coil layouts investigated include the Cos-theta design (CT), with its variations to reduce the conductor peak stress, namely the Canted Cos-theta design (CCT) and the Stress Management Cos-theta design (SMCT), and, in addition, the Block-type design (BL) including a form of stress management and the Common-Coil design (CC). Results from a magnetic and mechanical analysis are discussed, with particular focus on the comparison between the different options regarding quantity of superconducting material, field quality, conductor peak stress, and quench protection.