Water-cooled Resistive Magnet Research Articles

Conceptual design of hybrid IBS-REBCO magnet and a study on joint technology for high-field application

The REBa2Cu3Ox (REBCO) tape, known for its exceptional mechanical properties, stands as an optimal conductor for high-field applications. Nevertheless, stress degradation attributed to the membrane and monofilament structure of REBCO tape often occurs in high-field REBCO coils. On the other hand, iron-based superconductor (IBS) tapes offer notable advantages, including multifilament structure and upper critical field above 150 T, rendering it an appealing choice for high magnetic field applications. In this context, we first propose a methodology for designing a new type of compact hybrid magnet that integrates REBCO coils with multifilament IBS coils and a water-cooled resistive magnet to generate a high magnetic field. This paper presents the preliminary design of a hybrid magnet and employs a numerical simulation model to assess the magnet's electromagnetic and mechanical configuration, the simulation results show that the stress and strain experienced by all coils is within safe limits. Furthermore, details of the fabrication and testing of the IBS-REBCO joint are also provided. We hoped that the resistance of the IBS-REBCO joint would be less than 50 nΩ, however the resistance of the joint we developed did not meet our expectations. We discuss the reasons and propose the next plan to improve the performance of the IBS-REBCO joint.

Performance of first insert coil with REBCO CICC sub-size cable exceeding 6 kA at 21 T magnetic field

The Institute of Plasma Physics at the Chinese Academy of Sciences is developing the REBCO cable in conduit conductor (CICC) technology for applications in next-generation nuclear fusion devices. The aim is to develop a CICC comprised of six REBCO sub-cables to satisfy the requirements of operation with a current of around 40 kA and a peak field of up to 20 T. To qualify the performance of the sub-size REBCO cable to be used in the CICC, two 25-turn insert solenoids have been designed, manufactured and tested at a current exceeding 6 kA subjected in a background field supplied by a water-cooled resistive magnet. The insert solenoid, wound from a 11.5 m long REBCO CORC® cable, was designed to investigate its current carrying capacity under high field and electromagnetic (EM) load at 4.2 K. Tests were performed under a background magnetic field up to 18.5 T, resulting in a peak magnetic field on the innermost layer turns of around 21.1 T at an operating current of 6.3 kA. The effects of operation with cyclic EM loads were tested by repeated current ramps to around 95% of the critical current. Moreover, the V–I characteristics were measured at 77 K and the self-field, to check the effects from warm-up and cool-down (WUCD) cycles between room temperature and 77 K with liquid nitrogen. The results show no obvious degradation after dozens of high-current test cycles in background fields ranging from 10 T to 18.5 T. The insert solenoid demonstrates the stable operation of the REBCO sub-size cable for CICC with EM loads of about 90 kN m−1 and WUCD cycles between room temperature and 77 K. These promising results indicate the potential of this technology for further applicationsin particular, for full-size CICC for high-performance fusion magnets.

Analysis and redesign of the thermal shield for the 40-T hybrid magnet at the CHMFL

A 40 T hybrid magnet has been constructed and commissioned at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL). It consists of a 10 T superconducting outsert magnet and a 30 T resistive insert magnet. As an important component of the hybrid magnet, the 80 K thermal shield is located inside of the cryostat protecting the superconducting magnet from thermal radiation. During the commissioning phase, a trip of the water-cooled resistive magnet triggered the quench protection system of the superconducting magnet, huge induced currents resulting in expansion and rupture of the oxygen-free copper thermal shield. In this paper, the cause of thermal shield rupture was investigated via finite element simulations. And the structure design and mechanical assessment of a new alternative thermal shield adopted for the 40 T hybrid magnet is presented.

Preliminary Design of Power Supply for Water-Cooled Resistive Magnet Based on Three-Level Buck Converters

Water-cooled resistive high-field magnets require a high power supply with an extremely high current stability, and a low current ripple and noise. The conventional resistive magnet power supply uses thyristor rectifiers, followed by a passive filter and an active filter to reduce the voltage ripple. This Paper describes a new circuit topology design of the resistive magnet power supply, which consists of uncontrolled rectifier bridges and three-level buck converters in series instead of the conventional thyristor rectifiers. The three-level buck converters work at a higher switching frequency, which can greatly reduce the cost, volume and weight of the filter. According to simulation and analysis results, it is seen that the three-level buck converter structure provides a lower voltage and current ripple than the conventional thyristor rectifiers, reduces the voltage stress of the power electronic devices. Beside, this new design can achieve a higher power factor than the power supply based on thyristor rectifiers.

The Design and Magnetic Measurement of a SuperBend Dipole Magnet at SSRF

In order to increase the critical photon energy, and to save space for accommodating more insertion devices, four normal bend magnets will be replaced by high field ones during the phase-II beamline project of the Shanghai Synchrotron Radiation Facility (SSRF). The design of these superbends has been finished; the first one has been manufactured and measured recently at SSRF. This water-cooled resistive magnet has a total length of 1000 mm and a steering field of 2.32 T. An air slot in the magnet pole was used to control the uniformity of the field integral distribution. The design as well as the magnetic measurement results are presented. Also presented is a newly developed field shimming method, which has been verified as effective and convenient in the field integral shimming of a magnet with straight air slots in the poles.

Improvement of a Large Bore Cryogen-Free Superconducting Magnet for a Hybrid Magnet

A 360-mm room-temperature bore cryogen-free superconducting magnet (CSM), consisting of Nb 3Sn coils and NbTi coils, for a hybrid magnet (HM) has generated the maximum magnetic field of 9.5 T. However, the magnetic field of the CSM has been limited to 8.5 T in the hybrid magnet mode because of a cooling problem. As a result, the hybrid magnet composed of a 19-T water-cooled resistive magnet (WM) had the utmost field generation of 27.5 T. Therefore, we improved the CSM to generate higher magnetic fields. For the improvement of the cooling problem, Nb 3Sn coils were replaced, and thermal conduction was improved between coils and a 4K-GM cryocooler. Furthermore, support structures with a tensile strength over 80 kN and a spring support were adopted against the magnetic force to support the self-weight of coils and to absorb stress caused by thermal contraction difference between each coil. After the improvement, the CSM generated 9.5 T within 1 h and the maximum magnetic field of 9.7 T in a 360-mm room-temperature bore. The HM succeeded in generating 28 T in a 32-mm room-temperature bore with the CSM operated at 9.0 T.

Wide Variety of Experiments Using a Cryogen-Free 27.5 T Hybrid Magnet and a Cryogen-Free 18.1 T Superconducting Magnet

A cryogen-free hybrid magnet without liquid helium for operation, generating 27.5 T in a 32 mm room temperature bore of an 8 MW water-cooled resistive insert magnet in an 8.5 T background field of a cryogen-free superconducting outsert magnet, is being operated for basic research at low temperatures down to 17 mK in combination with a dilution refrigerator. In addition, we are developing functional materials using a differential thermal analysis DTA at high temperatures up to 1473 K in high fields up to 27 T. This cryogen-free hybrid magnet will be upgraded to generate 29 T by improving the outer superconducting magnet. A cryogen-free 18.1 T superconducting magnet with a 52 mm room temperature experimental bore, consisting of a Bi2Sr2Ca2Cu3O10 (Bi2223) insert coil, has been developed using a GM-JT cryocooler. Recently, bronze-tape-laminated Bi2223 has revealed excellent irreversible stress tolerance of 250 MPa at 77 K. In addition, the critical current properties for recent Bi2223 tapes are largely improved from 200 to 400 A/cm-width at 77 K in a self-field. Therefore, the stainless steel reinforcement tape incorporated for the previous Bi2223 insert coil is no longer needed for a new Bi2223 one. A new Bi2223 insert coil with almost the same size as the existing insert coil can generate two times higher fields at the elevated operation current from 162 to 191 A. An upgraded cryogen-free superconducting magnet can offer a long-term experiment at the constant magnetic field of 20 T for an in-field heat-treatment investigation.

Investigation of 15 to 24 MW Resistive Insert Magnets Built Into a 20 T $\varnothing$440 mm Room-Temperature Bore Superconducting Outsert Magnet

The Tsukuba Magnet Laboratory and the High Field Laboratory for Superconducting Materials collaborated on developing the next-generation 50 T-class hybrid magnet. One of the properties to be incorporated into this next-generation hybrid magnet is energy-saving operation in generating a high-strength magnetic field. This report presents the estimated performance of this hybrid magnet, on the basis of a 20 T O440 mm room temperature bore for the superconducting outsert magnet, DC power of 15-24 MW for a three-layered Bitter resistive insert magnet, and a O32 mm room-temperature bore for the resistive insert magnet. Cu-Zr (Cu-Ag) alloy is assumed material to be used for the outermost layer (inner two layers) of the Bitter magnet. The estimation indicates that the hybrid magnet generates magnetic fields beyond 47.9 T (49.1 T) for a resistive insert magnet operation power of 15 MW (24 MW) in a 20 T background magnetic field, where the upper-limit design stress on the innermost Bitter coils is tentatively assumed to be 800 MPa. An ultimate tensile strength exceeding 1140 MPa with a conductivity of 72% International Annealed Copper Standard (IACS) for a Cu-Ag alloy plate would be necessary to meet the design stress of 800 MPa. Using this material, we could make the 15 MW water-cooled resistive insert magnet (WM) for this energy-saving, compact hybrid magnet that generates magnetic fields of 47 T and beyond. For a moderated upper-limit design stress of 760 MPa, the corresponding magnetic fields of the hybrid magnet are 47.5 and 48.5 T.

Thermal properties of a large-bore cryocooled 10 T superconducting magnet for a hybrid magnet

A cryocooled 10T superconducting magnet with a 360mm room temperature bore has been developed for a hybrid magnet. The superconducting magnet cooled by four Gifford–McMahon cryocoolers has been designed to generate a magnetic field of 10 T. Since superconducting wires composed of coils were subjected to large hoop stress over 150MPa and Nb3Sn superconducting wires particularly showed a low mechanical strength due to those brittle property, Nb3Sn wires strengthened by NbTi-filaments were developed for the cryocooled superconducting magnet. We have already reported that the hybrid magnet could generate the resultant magnetic field of 27.5T by adding 8.5T from the superconducting magnet and 19T from a water-cooled Bitter resistive magnet, after the water-cooled resistive magnet was inserted into the 360mm room temperature bore of the cryocooled superconducting magnet. When the hybrid magnet generated the field of 27.5T, it achieved the high magnetic-force field (B×∂Bz/∂z) of 4500T2/m, which was useful for magneto-science in high fields such as materials levitation research. In this paper, we particularly focus on the cause that the cryocooled superconducting magnet was limited to generate the designed magnetic field of 10T in the hybrid magnet operation. As a result, it was found that there existed mainly two causes as the limitation of the magnetic field generation. One was a decrease of thermal conductive passes due to exfoliation from the coil bobbin of the cooling flange. The other was large AC loss due to both a thick Nb3Sn layer and its large diameter formed on Nb-barrier component in Nb3Sn wires.

Effect of the M/Co substitution on magnetocrystalline anisotropy and magnetization in SmCo5−xMx compounds (M=Ga;Al)

The isothermal magnetization curves were carried out on magnetically aligned powder of the SmCo4Ga and SmCo4Al samples; they have been measured at 4.2 K in applied field up to 33 T produced by a water-cooled resistive magnet. The intrinsic magnetic properties such as saturation magnetization, anisotropy constant, and anisotropy field have been derived. Whereas some properties, such as the saturation magnetization or the Curie temperature are found to be strongly reduced upon Ga or Al for Co substitution, on the contrary the magnetocrystalline anisotropy is much larger for the substituted compounds. Hysteresis cycles are presented also and coercivity ranging from 4.5 to 6 T are reported. The mechanism at the origin of the coercivity is also modified from a nucleation type for SmCo5 to a pinning type for the Ga or Al containing compounds.

Tohoku High Magnetic Field Research Activities Using Cryogen-Free Superconducting Magnets

In order to realize a hybrid magnet with no need of liquid helium for operation, we have designed a 28 T cryogen-free hybrid magnet with a 32 mm room temperature experimental bore, and actually tested to generate the peak field of 27.5 T. An easy-to-operate cryogen-free hybrid magnet is now operating for basic research in high fields up to 27 T at low temperatures down to 40 mK, using a dilution refrigerator. In addition, we are intending to develop a 100 mm wide bore water-cooled resistive insert magnet combined with a cryogen-free superconducting outsert magnet for X-ray diffraction measurements in steady magnetic fields up to 20 T.

Thermal analysis of the cryocooled superconducting magnet for the liquid helium-free hybrid magnet

The liquid helium-free hybrid magnet, which consists of an outer large bore cryocooled superconducting magnet and an inner water-cooled resistive magnet, was developed for magneto-science in high fields. The characteristic features of the cryogen-free outsert superconducting magnet are described in detail in this paper. The superconducting magnet cooled by Gifford–McMahon cryocoolers, which has a 360mm room temperature bore in diameter, was designed to generate high magnetic fields up to 10T. The hybrid magnet has generated the magnetic field of 27.5T by combining 8.5T generation of the cryogen-free superconducting magnet with 19T generation of the water-cooled resistive magnet. The superconducting magnet was composed of inner Nb3Sn coils and outer NbTi coils. In particular, inner Nb3Sn coils were wound using high-strength CuNi–NbTi/Nb3Sn wires in consideration of large hoop stress. Although the cryocooled outsert superconducting magnet achieved 9.5T, we found that the outsert magnet has a thermal problem to generate the designed maximum field of 10T in the hybrid magnet operation. This problem is associated with unexpected AC losses in Nb3Sn wires.

20 T Compact Superconducting Outsert Employing Y123 Coated Conductors for a 45 T Hybrid Magnet

We have been developing high-strength Nb3Sn strand cables to construct a high-field superconducting outsert for a 45 T hybrid magnet with a 25 T water-cooled resistive magnet. Evidence for cold work strengthening of repeated bending treatment (prebending effect) on Nb3Sn strands internally reinforced with CuNb stabilizer, which exhibits significant enhancement of the critical current density, has been found in the superconducting magnet fabrication process using a react-and-wind method. The strand cables were designed by controlling the constituent number of CuNb/Nb3Sn strands with the prebending effect and stainless steel strands, which are expected to have a stress limit 580 MPa at 0.4% strain. In order to design a compact superconducting outsert, high-strength strand cables are adopted in a magnetic field region below 14 T to maintain relatively large engineering current densities (Je). In a higher-field region above 14 T, YBa2Cu3O7 (Y123) coated conductors are employed for an insert coil. Using combination of Y123, Nb3Sn and NbTi superconductors, a 20 T superconducting outsert with a room temperature bore of 400 mm consisting of three layers made of Y123, two layers of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are 440 mm inner diameter, 1080 mm outer diameter and 1138 mm coil height. A very compact 20 T superconducting outsert with a stored magnetic energy 72 MJ at an operation current 903 A can be developed for a 45 T hybrid magnet.

100 mm Wide Bore Cryocooled Hybrid Magnet for a High Field X-ray Diffractometer

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> To carry out long-term experiments requiring a large bore and a constant high magnetic field, a 100 mm bore water-cooled resistive magnet has been designed, which is combined with a cryocooled superconducting outsert as a cryocooled hybrid magnet. The designed double Bitter magnet will produce 10.1 T under a use of 4.5 MW power for a long time operation, and a cryocooled hybrid magnet will be able to keep 18 T in a backup field of 8 T for ten hours economically. Main application of the wide bore cryocooled hybrid magnet is X-ray diffraction measurement under high magnetic fields. The development of a Debye-Scherrer camera system for a 10 T-100 mm bore cryocooled superconducting magnet has started as the first step. </para>

小型冷凍機冷却ハイブリッドマグネット用大口径超伝導マグネットの開発

A cryocooled superconducting magnet with a 360-mm room-temperature bore has been developed for hybrid magnets. Magnetic fields of 9.5 T in individual mode operation and 27.5 T in hybrid mode operation were successfully achieved when used in combination with a high-power water-cooled resistive magnet, although quenching occurred at 8.6 T during the first operation due to an unexpected rise in temperature. We discuss the thermal behavior of the innermost coil, where quenching was generated, through the analysis of temperature distribution measurement and two-dimensional thermal conductivity.

Advances in the First Cryogen-Free Hybrid Magnet

In order to solve problems of a large amount of liquid helium supply for a wide bore superconducting magnet of a hybrid magnet, we intended to construct the first cryogen-free 23 T hybrid magnet, consisting of an outer wide bore cryogen-free superconducting magnet and an inner water-cooled resistive magnet. Up to now, the wide bore cryogen-free superconducting magnet was tested to generate a total central field 6.0 T in a 360 mm room temperature bore. The world's first cryogen-free hybrid magnet achieved 21.5 T in a 52 mm room temperature bore, combining with 15.5 T water-cooled Bitter magnet. As the result, the cryogen-free hybrid magnet no longer needs a troublesome handling time for liquid helium transfer, and the machine time is extremely enlarged. The improvement of the maximum magnetic field generation toward our design value of 23 T is being carried out continuously. Furthermore, we have started a new construction project of a cryogen-free 30 T hybrid magnet. Since the magnetic force field BdB/dz of 2274 T/sup 2//m is obtained at 21.5 T, the cryogen-free hybrid magnet can provide a large magnetic force field enough to levitate diamagnetic materials. For new processing of materials development, a YAG laser furnace was installed into the cryogen-free 23 T hybrid magnet. A container-less melting for paraffin was examined by controlling a thermocapillary convection. We succeeded in fabricating a magnetic field oriented ball in magnetic levitation.

First performance test of the cryogenfree hybrid magnet

We are now constructing a cryogenfree 23 T hybrid magnet at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. At present, an outer section coil employing NbTi multifilamentary wires for a cryogenfree superconducting magnet of the hybrid magnet was combined with an inner 15.5 T water-cooled resistive magnet, and was tested as the world's first cryogenfree hybrid magnet. The NbTi coil with 491 mm inner diameter and 584 mm outer diameter generated 4.59 T at 198 A, and the central magnetic field of 20.0 T was generated in a 52 mm room temperature experimental bore. The magnetic force field of 2030 T/sup 2//m was obtained, and a piece of paraffin was levitated at 1200 T/sup 2//m. Using a CO/sub 2/ laser combined with the cryogenfree hybrid magnet, a containerless melting experiment in magnetic levitation was demonstrated easily for paraffin.

Cryogen-free hybrid magnet for magnetic levitation

The development of a cryogen-free hybrid magnet with no use of liquid helium was intended. A cryogen-free hybrid magnet is composed of an outer conduction-cooled superconducting magnet using GM-cryocoolers and an inner water-cooled resistive magnet. As a first step, we constructed a cryogen-free NbTi superconducting magnet with a 360 mm room temperature bore, which generated 4.5 T at a magnet center. The thermal stability concept of the critical current margin is adopted for magnet design. A 20 T static magnetic field and a magnetic force field corresponding to 2030 T 2/m by combining with the 15.5 T water-cooled magnet were obtained. A container-less melting experiment was carried out using a newly developed 20 T cryogen-free hybrid magnet. A great interest is focused on Marangoni convection in container-less melting. Thermocapillary convection known well as Marangoni is being investigated in the non-gravity state due to high magnetic fields, using the world’s first cryogen-free hybrid magnet.

Construction of the cryogen-free 23 T hybrid magnet

In order to settle problems requiring a large amount of liquid helium and limiting the operation time for a wide bore superconducting magnet of a hybrid magnet, a cryogen-free 23 T hybrid magnet is being constructed at the High Field Laboratory for Superconducting Materials for the first time. An outer compact superconducting magnet is wound with highly strengthened CuNb/Nb/sub 3/Sn multifilamentary wires and is refrigerated conductively by GM-cryocoolers. The maximum stress value of 210 MPa was designed for the CuNb/Nb/sub 3/Sn coil. The cryogen-free superconducting magnet will be operated using dual power supplies independently, and has potential to generate central fields of 4.59 T at 198 A for the outer section NbTi coil and 3.41 T at 145 A for the inner section CuNb/Nb/sub 3/Sn coil. When the cryogen-free 7.5 T superconducting magnet with a 360 mm room temperature bore is combined with an inner 15.5 T water-cooled resistive magnet, a cryogen-free hybrid magnet will achieve 23.0 T in a 52 mm room temperature experimental bore.

Hybrid magnets and cryogen-free superconducting magnets developed at the High-Field Laboratory for superconducting materials

Fundamental and application-oriented research for superconducting materials has been conducted as the main objective during the past 20 years at the High-Field Laboratory for Superconducting Materials, HFLSM, Institute for Materials Research, Tohoku University. A 30 T hybrid magnet proved to be a powerful experimental tool for high-temperature superconductors. Since HFLSM has succeeded in demonstrating the world’s first practical cryogen-free superconducting magnet, CSM, using high-temperature superconducting current leads in 1992, various kinds of CSM have been developed for advanced uses. As a next step, we are developing a cryogen-free hybrid magnet, CHM, consisting of a cryogen-free wide bore superconducting magnet and a water-cooled resistive magnet. High-strength (Nb,Ti) 3Sn superconducting wires will be employed for CHM, in order to make a wide bore superconducting magnet as compactly as possible.