Zhiyou Chen

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 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.

Engineering Design of the Superconducting Outsert for 40 T Hybrid Magnet

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 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.

Quench Analysis of the Hybrid-Magnet Superconducting Outsert

A hybrid magnet is under construction at the High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL). The hybrid magnet consists of a superconducting magnet and a resistive magnet. The superconducting magnet is wound with Nb3Sn Cable-in-Conduit Conductors. The resistive magnet is made of Bitter type conductors. The superconducting magnet and the resistive magnet will be charged by two separate power supplies. A trip of the resistive magnet due to a power supply or other fault will result in the increment of the magnetic field, current, and temperature in the superconducting magnet and consequentially influence the stable operation of the superconducting magnet. The thermal-hydraulic performance analysis of the superconducting magnet during a trip of the resistive magnet was performed and will be discussed in this paper.

Development of a Superconducting Magnet System for Microwave Application

An 11 T superconducting magnet has been manufactured for a 45 T hybrid magnet, the superconducting magnet has a large room temperature bore of 800 mm, so it can provide an 11 T background field for performance test of cable in conduit conductors (CICC). A test facility for superconducting CICCs has been designed as an insert combined with the superconducting magnet, wherein an 80 kA superconducting transformer has been designed to provide high operating current for the CICC samples. The CICC sample was designed to be a bifilar non-inductive solenoid coil. This paper will describe the principle design of the test facility and the overview of the 80 kA superconducting transformer.

Thermal-Hydraulic Performance Analysis of the Superconducting Magnet During the Trip of the Resistive Magnet in CHMFL Hybrid Magnet

A medium-sized superconducting magnet wound using NbTi wires was designed, fabricated, and tested. It has been developed for a superconducting magnetic energy storage system. The solenoid magnet has a clear bore of 250 mm, an outer diameter of 380 mm, and a height of 589 mm. The magnet consists of one main coil and two compensating coils and is dry wound using rectangular superconducting wires with dimensions of 1.28 mm × 0.83 mm. Grooves and reinforced bulks are designed on the supporting structure to improve the cooling ability and the mechanical strength. A cryogenic system has been designed to keep the liquid helium in the zero evaporation state. The magnet has been tested in a compact cryostat, and it generates a central magnetic field of 4 T at the designed operating current of 126 A. The results of the experiment show that the performance of the magnet reaches the requirements. The details of the design, fabrication, and test of the superconducting magnet are presented in this paper.