P. He

Characterization of

A 40-T hybrid magnet under construction at the High Magnetic Field Laboratory of the Chinese Academy of Sciences will use cable-in-conduit conductors for its superconducting outsert. The design necessitates the use of high current density (Jc) Nb3Sn strands (Jc ≥ 2100 A/mm2 at 12 T/4.2 K). The high Jc restacked-rod-processed Nb3Sn strand from Oxford Instruments Superconductor Technology was selected as one of the candidate strands. A series of tests was carried out to qualify the strand performance. Tests mainly included magnetization and critical current measurements as a function of axial strain, magnetic fields, and temperature. The test results are presented and discussed.

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A thermal-hydraulic performance analysis of a model coil for a 40-T hybrid magnet superconducting outsert being built at the High Magnetic Field Laboratory, Chinese Academy of Sciences, was performed. The model coil was wound with a cable-in-conduit conductor cabled in a 316LN jacket cooled with supercritical helium. The model coil, in combination with 7.5-T NbTi solenoid coils, will be capable of generating a 12-T central field. Only one cooling channel was used to cool the model coil due to its short length. Both the temperature margin associated with a given scenario and the quench propagation following an artificial disturbance are discussed. The thermal-hydraulic analysis of the temperature margin showed that there is a sufficient minimum temperature margin for 100-A/s current ramp rate under a 7.5-T background magnetic field. The quench analysis showed that the hot-spot temperature of the cable is about 60 K, which is less than the maximum allowable value of 150 K for 0.7-s delay time. In addition, the convergence study was carried out for different time steps and space sizes.

Strands for a 40-T Hybrid Magnetic Model Coil

A dummy coil is being wound at the High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL). Building the dummy coil will develop the manufacturing technology for the CICC, especially the cabling, forming and winding techniques of the rectangular conductor. This paper will present the manufacturing process of the dummy coil. It will include the cabling of the wire, the mechanical performance test of the 316LN conduit at low temperature, the forming technology of the rectangular conductor, the CICC insulation, the tension winding, and the vacuum pressure impregnation of the dummy coil.

Thermal–Hydraulic Analysis of a Model Coil for 40-T Hybrid Magnet Superconducting Outsert

A 40 T hybrid magnet system will be built at the Chinese High Magnet Field Laboratory (CHMFL), Chinese Academy of Sciences. It will include a 29 T resistive insert with a clear bore of 32 mm and a 11 T superconducting outsert with a room temperature bore of 580 mm. The superconducting outsert, which will be wound with cable-in-conduit conductors (CICC), is graded in function of the magnetic field. The high field section of the superconducting outsert will use superconductors and the low field section will be made of NbTi superconductors. At present, the preliminary design of the superconducting outsert has almost been completed. This paper describes features, such as conductor design, coil winding, heat treatment, support structure design, mechanical stress analysis.

Dummy Coil Development for the Cable-In-Conduit Conductors Superconducting Outsert Coils of a 40 Tesla Hybrid Magnet

The main goal of the model coil is to demonstrate the feasibility of `Insulation-Wind-React manufacturing process and to confirm the feasibility of the superconducting outsert design. The model coil was wound with Cable-in-Conduit Conductor (CICC) using restacked-rod process (RRP) Nb3Sn strand, and cooled with forced-flow supercritical helium with inlet temperature of 4.5 K. The test of the model coil in the 7.5 T background field has been completed, and the test program included cool-down, full DC characterization before and after cyclic loading, AC losses, and so on. The test results have confirmed the characterization of the Nb3Sn conductor and the mechanical performance of the model coil, and validated the 40 T hybrid magnet superconducting outsert design.

Engineering Design of the Superconducting Outsert for 40 T Hybrid Magnet

A 40 T hybrid magnet system will be designed and constructed at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The superconducting outsert consists of two concentric superconducting coils. After the conceptual design of the superconducting magnet, the R&D of the model coil is now being carried out as an explorative research item. In this paper, the preliminary structural design of the model coil is introduced. For comparison, two different methods are used to analyse the mechanical behavior of the coil during normal operation; the first is a traditional method called global-local finite element technique, the second is a detailed 2-D FEA method.

Test Results of the Model Coil for the 40 T Hybrid Magnet Superconducting Outsert

Two kinds of Nb3Sn CICC joints have been designed for the superconducting coils of the 40 T hybrid magnet. The “terminal joint” is for the joints between the terminals of the superconducting coils. The “interlayer joint” is for the joints between the layers of the coils. Both the terminal joint and the interlayer joint are fabricated before heat treatment. The interlayer joint is not processed any more after heat treatment. The copper soles of the terminal joints are attached to each other with PbSn solder to join the superconducting coils to each other and to the current leads that connect to the power supply. Two full-size joints are being manufactured and will be tested in the High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL). This paper will describe an overview of the joints design and fabrication, and the predicted joint resistances will be also presented.

Mechanical Behavior Analysis of Model Coil for the 40-T Hybrid Magnet Superconducting Outsert

A model coil for the 40-T hybrid magnet is under construction at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The model coil is layer wound with a rectangular Nb3Sn cable-in-conduit conductor and adopts wind-and-react manufacturing technology. The model coil will simulate same electromagnetic loads of B × I as the superconducting outsert of the 40-T hybrid magnet in the performance tests. The thermohydraulic behavior of the model coil during various operating scenarios was simulated by the numerical model Gandalf. The charging process and the cyclic operation of the model coil are analyzed in this study. The temperature rise and margin of the conductor due to the ac losses are computed and presented.

Design and Manufacture of the Low-Resistance

A superconducting magnet with an available warm bore of 100 mm and a central field of 5 T has been designed, manufactured and tested for the research of microwave application. The magnet is composed of three coaxial coils based on magnetic field homogeneity considerations, namely 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 less than ±2.5% in a 20 mm diameter and 250 mm length of a cylindrical volume. In addition, a two-stage GM cryocooler with a capacity of 1 W at 4 K was used to cool the superconducting magnet. The cryocooler used can prevent the liquid helium from boil-off and lead to a zero loss during static operation. In this paper, the magnet design, manufacture, mechanical behavior analysis, and the performance test results of the magnet are presented.

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The heat treatment of Nb(3)Sn coil with the glass fabric insulation is one of the key and critical processes for the outsert solenoids of the 40 T hybrid magnet, which could be wound with cable-in-conduit conductors using the insulation-wind-and-react technique. The manufacturing of the large vertical type vacuum/Ar atmosphere-protection heat treatment system has been completed and recently installed in the High Magnetic Filed Laboratory, Chinese Academy of Sciences. The heat treatment system composed mainly the furnace, the purging gas supply system, the control system, the gas impurities monitoring system, and so on. At present, the regulation and testing of the heat treatment system has been successfully finished, and all of technical parameters meet or exceed specifications.