Wenge Chen

A Conceptual Design of Model Coil for the 40-T Hybrid Magnet Superconducting Outsert

The High Magnetic Field Laboratory of the Chinese Academy of Sciences will develop a 40-T hybrid magnet. The superconducting outsert, which consists of a NbTi coil and a Nb3 Sn coil, will provide more than 11 T of central field in a 580-mm bore. The superconducting coils will be wound of cable-in-conduit conductor (CICC) and cooled by flowing 4.5-K supercritical helium. A model coil of the Nb3Sn coil has been designed and will be manufactured to develop the technology of cabling, jacketing, winding, heat treatment, etc., and the model coil can also simulate the performance of the Nb3Sn superconducting coil under its operating conditions. This paper gives an overview of the conceptual design for the model coil and predicts its current-sharing temperature (Tcs).

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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

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.

Engineering Design of the Superconducting Outsert for 40 T Hybrid Magnet

The superconducting magnet for a 40-T hybrid magnet is being developed at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The hybrid magnet consists of a resistive insert and a superconducting outsert providing 29 and 11 T, respectively. The superconducting magnet was designed to be wound with four grades of cable-in-conduit conductors (CICCs). The superconducting coils contain over 5000 kg of Nb3Sn/Cu CICC in seven piece lengths. Three dummy conductors and seven prototype conductors have been successfully fabricated without incident. The conductor design, strand cabling, and conductor fabrication details will be introduced in this paper.

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

Quench propagation analysis of the superconducting outsert for the 45-T hybrid magnet being built at the High Magnetic Field Laboratory, Chinese Academy of Sciences was performed. The superconducting outsert was wound with a Nb3Sn cable-in-conduit conductor cabled in a 316LN jacket cooled with supercritical helium at 4.5 K. The superconducting outsert can produce 11.0-T central magnetic field at an operating current of 13410 A. An active protection circuit with a dump resistor of 0.272 Ω was adopted to transfer the stored magnetic energy during a dump operation. In this paper, the magnetic field and strain of the superconducting outsert were analyzed. During a quench, the hot spot temperature of the cable and the helium pressure inside a jacket for different quench delay times were introduced.

Cable-in-Conduit Conductor Fabrication for the Hybrid Magnet of CHMFL

A model coil developed at the High Magnetic Field Laboratory, Chinese Academy of Sciences, will be wound with a Nb3Sn cable-in-conduit conductor (CICC). In this paper, we first introduce the model coil structure and its design requirements and then explicate the important components of the model coil structure, such as the preload structure, joint, cooling circuit, etc. Stress analyses of the preload structure, lead-in and lead-out CICC, joint, transitive CICC, and some supporting structures are performed, and the results are compared with the International Thermonuclear Experimental Reactor metallic and composite structural component design criteria.

Quench Analysis of the Hybrid-Magnet Superconducting Outsert

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.