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. It found that YBa₂Cu₃O₇ (Y123) coated conductor tape with Hastelloy substrate has the excellent mechanical property of 1000 MPa hoop stress tolerance. We are carrying out the research and development of a 30 T all superconducting magnet immersed in liquid helium and a 23 T cryogen-free superconducting magnet, employing Y123 tape.     

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.     

Developments at the High Field Magnet Laboratory in Nijmegen

The High Field Magnet Laboratory at the Radboud University Nijmegen is rapidly expanding its capabilities. The developments encompass both organizational changes and new possibilities for research. The organization of the HFML was strengthened as a consequence of stronger participation of the Foundation for Fundamental Research on Matter (FOM), and an increase of the core-funding. This change makes that HFML is now considered on a national level as large research facility that operates at an international scale. At the same time work is underway to build new and powerful magnets, and provide electromagnetic radiation for magneto-spectroscopic studies. Electromagnetic radiation in the infrared and far-infrared spectrum will soon be available in the HFML with wavelengths between 3 μm and 1.5 mm, produced by the ‘FELIX’ facility, comprising the long-wavelength free electron laser ‘FLARE’ that in September 2011 produced its first light and the free electron lasers that have been moved from Rijnhuizen to Nijmegen. In magnet technology great strides are made to make magnets available for the user community with unprecedented performance: late in 2012 we hope to commission a new all-resistive magnet system that will generate a steady magnetic field as high as 38 T, by fully exploiting the maximum power of the installation, i.e. 20 MW, and using all available improvements in the design and construction of ‘Florida-Bitter’ resistive magnets. We are also well underway with the design of a 45 T hybrid magnet system, using Nb₃Sn superconductors and wind-and-react Cable-in-Conduit technology.     

Superconducting magnets for very high fields: status in Japan

Three projects on superconducting magnets for very high fields are now in progress in Japan. The Japan Atomic Energy Research Institute constructed TMC-1 having an inner diameter of 600 mm which could produce 11.1 T by using a multifilamentary Nb₃Sn conductor. The National Research Institute for Metals has developed a multifilamentary Nb₃Sn wire with Ti doping and fabricated a high-stability superconducting magnet which will produce a magnetic field of 15 T in an 180 mm bore. Combined with this magnet, a new superconducting magnet system, which may break the field record in the superconducting state, is under construction. The High Field Laboratory for Superconducting Materials at Tohoku University constructed a hybrid magnet, in which a Nb₃Sn superconducting magnet was combined with a polyhelix type water-cooled magnet and produced a total magnetic field of 29.3 T in a 32 mm bore, where 10 T was produced by the superconducting magnet with an inner bore of 430 mm. The present status of these projects is briefly described.     

The 42+ T Hybrid Magnet Project at CNRS-LNCMI-Grenoble

Hybrid magnets, the combination of a resistive inner coil with a superconducting outer one, allow to generate the highest continuous magnetic fields for a given electrical power installation. A new superconducting coil outsert has been designed to be integrated in the existing infrastructure at LNCMI-Grenoble (GHMFL). Based on the specific development of a Nb–Ti Rutherford Cable On Conduit Conductor (RCOCC) cooled at 1.8 K by a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m bore diameter. Combined with resistive insert coils, an overall continuous magnetic field of 42+ T will be produced in a 34 mm warm aperture. The main results of the conceptual study will be presented together with first developments and tests of the RCOCC.     

Magnet-Technology Development at the Dresden High Magnetic Field Laboratory

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached. We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload.     

The National High Magnetic Field Laboratory

The National High Magnetic Field Laboratory (NHMFL) is a collaboration between Florida State University, the University of Florida, and the Los Alamos National Laboratory. The DC Field Facilities are located at the main campus for the NHMFL in Tallahassee, Florida and are described in this paper. The DC Field Facility has a variety of resistive and superconducting magnets. The DC Field Facility infrastructure, the most powerful in the world, is able to provide 57 MW of continuous low noise DC power. Constant magnetic fields of up to 45 tesla in a 32 mm bore and 20 tesla in 195 mm bore are available at no charge to the user community. The users of the facility are selected by a peer reviewed process. Roughly 400 research groups visit the lab to conduct experiments each year. Experimental capabilities provided by the NHMFL are magneto-optics, millimeter wave spectroscopy, magnetization, dilatometry, specific heat, electrical transport, ultrasound, low to medium resolution NMR, EMR, and materials processing. Measurements of properties can be made on samples at temperatures from 20 mK to 1000 K, pressures from ambient to 10 GPa, orientation and currents from 1 pA to 10 kA.     

Research in High Magnetic Fields: The Installation at the University of Nijmegen

For research in the highest continuous and pulsed magnetic fields large, complex and powerful installations are needed. This paper describes the new 20 MW installation for continuous high magnetic fields that has been built at the University of Nijmegen. The ultra-low ripple power converter provides the capability to perform experiments up to 33 T with resistive magnets (up to 40 T with the hybrid magnet system under construction) and will be of great value for investigations in physics, chemistry and biology at the forefront of fundamental and applied research. Typically during experiments, the magnetic field is slowly varied or held constant for a period lasting from a few minutes to an hour. The cooling installation is designed to allow uninterrupted operation at maximum power for 3 hours, and when the magnetic field is being swept between zero and full field the cooling plant does not pose limits to the operation. When much higher fields are required, there is the option to go to pulsed magnetic fields with duration in the tens of milliseconds.     

Design and Performance of the First Dual-Coil Magnet at the Wuhan National High Magnetic Field Center

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected.     

Progress in the Development of the Wuhan High Magnetic Field Center

Since April 2008 the Wuhan High Magnetic Field Center (WHMFC) has been under development at the Huazhong University of Science and Technology (HUST) at Wuhan, China. It is funded by the Chinese National Development and Reformation Committee. Magnets with bore sizes from 12 to 34 mm and peak fields in the range of 50 to 80 T have been designed. The power supplies for these magnets are a capacitor bank with 12 modules of 1 MJ, 25 kV each and a 100 MVA/100 MJ flywheel pulse generator. The objective of the facility is to accommodate external users for extensive experiments in pulsed high magnetic fields. Up to seven measurement stations will be available at temperatures in the range from 50 mK to 400 K. The first prototype 1 MJ, 25 kV capacitor bank with thyristors, crowbar diodes and a mechanical switch has been developed and successfully tested. For the protection of the thyristor switch, a toroidal inductor is developed to limit the current at 40 kA. Five magnets have been wound with CuNb and copper wires and internal reinforcement by Zylon fiber; external reinforcement is a stainless steel shell encased by carbon fiber composite. Two Helium flow cryostats have been successfully tested and reached temperatures down to 4.2 K. Measurement stations for magneto-transport and magnetization are in operation. The design, construction and testing of the prototype system are presented.     

Present Status and Future Plan at High Magnetic Field Laboratory in Osaka University

We report on the development of experimental apparatus and the achievement of our research since 2006 when we reported “the present status and future plan of research in high magnetic fields” at the RHMF 2006 conference, after brief introduction of history and facility of the High Magnetic Field Laboratory at KYOKUGEN in Osaka University. As for our high-field and multi-frequency electron spin resonance (ESR) apparatus, we have expanded the magnetic field range up to 65 T and the frequency range up to 6 THz. In addition, ultra low temperature ESR apparatus down to 0.1 K for static fields and down to 0.6 K for pulsed fields have been fabricated. Furthermore, we have constructed a wide bore pulse magnet with the bore diameter of 48 mm? that enables us to perform resistivity measurements, which have been improved with the signal to noise ratio more than 100 times, under high pressure utilizing a diamond anvil pressure cell.     

Test and Operation of the WHMFC 12.6 MJ Capacitor Bank Power Supply System

The 12.6 MJ capacitor bank power supply system of the Wuhan National High Magnetic Field Center (WHMFC) at Huazhong University of Science and Technology (HUST) consists of 11 independent 1 MJ modules and 2 independent 0.8 MJ modules; it was tested and put into operation in October 2010. The capacitor bank power supply system connects to 8 measurement cells through three current collectors and four selectors. A number of nondestructive magnets for different bore sizes and peak fields have been energized by this system, including an 83 T dual stage magnet. The results of tests and operation are presented in this paper.     

Design of a 60 T Quasi-continuous Magnetic Field System with a Hybrid Capacitor/Rectifier Power Supply

At the Wuhan National High Magnetic Field Center, a 135 MW rectifier power supply is being installed nearby a 11 MJ capacitor bank power supply. By combining the two power supplies, a 60 T / 100 ms quasi-continuous magnetic field can be achieved in a monolithic copper coil magnet with a 22 mm diameter bore. Comsol Multiphysics 3.5a and Matlab 7.11.0 were adopted to verify the performance of the magnet and the hybrid power supply system. Details of the designed magnet, the power supply and the simulation results are presented.     

Development of a Superconducting Magnet System with Zero Liquid Helium Boil-off

A homogeneous magnetic field superconducting magnet with a cold bore of 250 mm and a central field of 4.3 T has been designed, manufactured, and tested with zero liquid helium boil-off. As a result of magnetic field homogeneity considerations, the magnet is composed of three coaxial coils: one main coil and two compensation coils. All coils are connected in series and can be charged with a single power supply. The magnetic field homogeneity is about ±3.0 % from ?200 mm to 200 mm in axial direction with 86 mm in diameter. The magnet can be operated in persistent mode with a superconducting switch. A two-stage GM cryocooler with a capacity of 1.5 W at 4.2 K was used to cool the superconducting magnet. The cryocooler prevents the liquid helium from boiling off and leads to zero helium loss during static operation. The magnet can be operated in liquid helium circumstance by cooling the gas helium with the cryocooler without additional supply of liquid helium. Under this condition, the magnet is successfully operated up to 4 T without quench. The magnet system can be generating 0.25 L/h liquid helium with the cryocooler by supplying the gas helium without loading the magnet. In this paper, the magnet design, manufacture, mechanical behavior analysis, and the performance test results of the magnet are presented.     

Design, development and experiment of a 1.5 T MgB2 superconducting test magnet

Superconducting magnets using MgB₂ tapes are potentially applicable in many areas, such as medical magnetic resonance imaging and fault current limiting. Under conduction cooling environments, the magnets can work at 15-20 K. In this work, a solenoid structured magnet with ∅ 100 mm bore is designed, built and tested. The maximum field at its center is up to 1.5 T. The field homogeneity, the thermal stability and the quench characteristics in the magnet are also investigated.     

Development of a cryogenic test bed for high amperage critical current measurement on high temperature superconductor wire

Many areas of research have benefited from the application of conduction-cooled superconducting magnet technology. The middle and small-scale magnets immersed in the liquid helium will be replaced by the easy-operating conduction-cooled superconducting magnet due to convenient operation, lower operating cost and easy for user. For the goal of superconducting magnet applications in the advanced testing for high temperature superconducting (HTS) wire and sample coils, a wide bore conduction-cooled superconducting magnet with available warm bore of ?186 mm and center field of 5-6 T for background magnetic field applications was designed, fabricated and tested. The system allows measurements to be performed in a repeatable and reliable fashion. In order to support the high stress in magnet, the detailed finite element (FE) analysis with electro-plastic model is proposed. The sample cryostat is designed with cryofree. It includes two GM cryocoolers. The detailed design, fabrication and thermal analysis are presented in the paper.     

Measuring the Magnetic Flux Density in the CMS Steel Yoke

The Compact Muon Solenoid (CMS) is a general purpose detector, designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6-m-diameter by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of construction steel. The return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. Accurate characterization of the magnetic field everywhere in the CMS detector is required. To measure the field in and around the steel, a system of 22 flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. Fast discharges of the solenoid (190 s time-constant) made during the CMS magnet surface commissioning test at the solenoid central fields of 2.64, 3.16, 3.68 and 4.01 T were used to induce voltages in the flux loops. The voltages are measured on-line and integrated off-line to obtain the magnetic flux in the steel yoke close to the muon chambers at full excitations of the solenoid. The 3-D Hall sensors installed on the steel–air interfaces give supplementary information on the components of magnetic field and permit to estimate the remanent field in steel to be added to the magnetic flux density obtained by the voltages integration. A TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. The results of the measurements and calculations are presented, compared, and discussed.     

New Fabrication Process of Cu–Nb Composite for Internal Reinforcement of Nb3Sn Wires

We developed Cu–20vol%Nb wires, for the reinforcement and stabilizing of Nb₃Sn wires, using a new Nb rod process. The electrical and mechanical properties of the CuNb wires prepared by different processes were measured to assess their suitability as reinforcing stabilizers for Nb₃Sn. All wires were heat-treated at 670 ^°C, which is the temperature required for formation of Nb₃Sn. After heat treatment, the mechanical properties of Nb-rod-processed CuNb were superior to those of in-situ-processed CuNb wires. The residual resistance ratio of the Nb-rod-processed CuNb was 64, and its magnetoresistivity was 0.16 μΩ?cm at 4.2 K and 15 T. These properties indicate that the new CuNb wire is suitable as a reinforcing stabilizer for using a high field, wide bore, superconducting magnet, such as the 20 T superconducting magnet with 400 mm room temperature bore being planned in Japan.     

Magnets for fields above 100 kg

Classifying coils above and below 100 kG does not separate types or methods, but rather indicates the degree of difficulty. It is no longer true that conventional dc fields above 100 kG require larger than existing or contemplated power supplies, and it has been established that superconducting materials will be suitable for fields approaching twice that field. Problem areas, economics, and experience above 100 kG are discussed in three major areas: 1) water-cooled dc magnets, principally those now in operation at the National Magnet Laboratory; 2) pulse magnets covering the continuum from sub-millisecond pulses to the low-duty cycle cryogenic magnet systems; 3) superconducting magnets with emphasis on hybrid systems, combining water-cooled copper magnets and superconducting coils.     

Testing of a 5.5 T High-Gradient Superconducting Magnetic Separator

A 5.5 T central field high-gradient superconducting magnetic separator (HGMS) has been designed, fabricated, and tested at the Institute of High Energy Physics, Chinese Academy of Sciences. It has been developed for processing kaolin, to increase the brightness or whiteness whether it is for paper or ceramic applications. The HGMS system mainly consists of an NbTi superconducting magnet, a double-canister system, and a PLC (Process Logic Controller) control system. The solenoid magnet, with operating current of 148 A, has a clear bore of 300 mm. By using a G-M cryocooler (35 W/50 K, 1.5 W/4.2 K), the results of the experiment show that the HGMS system can be run in zero boil-off regimes without any additional cooling. A pressure control system for the helium vessel can accurately respond to variations of pressure above the pressure outside the vessel. The system will process kaolin slurry at typically 0.6～2.5 cm/s, resulting in a production rate of approximately 80～120 tones per day (dry basis). The operation is fully automatic, with a simple system for adjusting the process parameters. The HGMS magnet suffered no quench and operated stably during many experiments since January 2012. The details of the design, fabrication, and performance results of the HGMS are presented in this paper.