Shousen Song

High Magnetic Field Superconducting Magnet System Up to 25 T for ExCES

The ultra-high-field superconducting magnets have been widely applied in scientific instruments for condensed matter physics. A superconducting magnet with the center field of 25 T in a warm bore-size of 32 mm in diameter has been designed for the Extreme Condition Experimental Science Facility (ExCES). The superconducting magnet consists of NbTi, Nb3Sn superconducting coils and YBCO high-temperature superconducting (HTS) insert operated at the 4.2 K. In order to prove the technical feasibility to achieve the target of 25 T, high-temperature superconductor YBCO and Bi2223 inserts have been designed, fabricated and tested in the operating temperature of 4.2 K. Inner diameter, outer diameter, and height for the YBCO insert are 40 mm, 68.9 mm, and 253 mm, respectively. The larger Bi2223 insert has the inner diameter, outer diameter, and height of 120 mm, 212 mm, and 268.8 mm, respectively. Tests at liquid helium temperature show that the YBCO and Bi2223 inserts can generate the center field of 5 T and 5.05 T, respectively. The assembly of the Bi2223 and YBCO insert coils can generate a center magnetic field of 7.6 T when tested at the liquid helium temperature. In this paper, the design, fabrication, and test of the HTS insert and the 25 T magnet are reported.

A Superconducting Magnet System for Whole-Body Metabolism Imaging

A 9.4 Tesla superconducting magnet is designed and fabricated with a warm bore of 800 mm for neuroscience research. The superconducting magnet will be made of a NbTi Wire-in-Channel (WIC) conductor with a higher ratio of copper to non-copper, which thus sustains the high stresses. It is cooled to operate temperature at 4.2 K liquid helium. The cryostat system is cooled through GM cryocoolers, some used to cool the radiation shield, and the others realize the re-condensed liquid helium. The MRI magnet system has a high level of stored energy, about 134 MJ, and a relatively-lower nominal current, about 212.5 A. The magnet will be operated in a persistent current mode with a superconducting switch. The WIC wires are employed to meet the cryostability criteria to avoid any risks from quench. The protection circuit with the subdivision of the coil reduces the terminate voltage and hot-spot temperature. In the paper, the specifications of magnet system will be presented.

Tests on a 6 T Conduction-Cooled Superconducting Magnet

A 6 T conduction-cooled superconducting magnet was designed, fabricated and tested. The magnet is composed of two coaxial NbTi solenoid coils with identical axial length. Clear bore of the magnet is phi 226 mm. The magnet is installed in a vacuum cryostat with a phi 100 mm room temperature bore. The cryostat is designed in a support frame to be rotatable in a horizontal or vertical direction. A two-stage 4 K Gifford-McMahon (GM) cryocooler is used to cool down the superconducting magnet from room temperature to 4 K. The cooling power of the 4 K cold head is 1 W. A pair of Bi-2223 high temperature superconducting current leads was employed to reduce heat leakage into 4 K cold mass. Total cold mass of the superconducting magnet is about 115 kg. It takes 82 hours to cool down the magnet from 300 K to 4 K directly through the cryocooler. The superconducting magnet reached the designed central magnetic field of 6 T in the warm bore when a 115 A energizing current is applied. The superconducting magnet was stably operating more than 275 hours continuously in full field. Further, a Nb3Sn coil insert to be installed, the magnet can provide the maximum center field of 10 T with effective warm bore of phi 100 mm. In this paper, the detailed design, fabrication and test are presented

High Magnetic Field Superconducting Magnet for 400 MHz Nuclear Magnetic Resonance Spectrometer

A superconducting magnet with the center field of 9.4 T is designed and fabricated for 400 MHz Nuclear Magnetic Resonance. Superconducting coil with NbTi/Cu superconducting wire is employed and cooled by re-condensed liquid helium and the magnet system with the clear-bore of 54 mm. The pulsed tube refrigerator with separated valve is employed to cool the magnet system. The superconducting magnet has an active shield with high pure copper shield to protect during quench of the shielding coil. The paper reports the electromagnetic design, and fabrication is detailed.

Fabrication of NbTi Superconducting Joints for 400-MHz NMR Application

NbTi superconducting joints (SJs) for a 400-MHz nuclear magnetic resonance (NMR) magnet system were fabricated using the superconducting solder matrix replacement in an open-air condition. A detection device for testing the resistance of SJ has been established. The results show that the overall resistance of SJs is 9.58 × 10-12 Ω under the background field of 1 T by summation of individual joint resistance. The resistance of SJs and the capability for current load should meet the demands of the NMR system. The SJs are placed inside the cylindrical vessel above the magnet. The magnetic flux inside the top of the vessel is no more than 0.3 T to assure performance of joints. As results, there is only 0.0001 ppm for homogeneity deviation caused by SJs on this NMR system, and therefore, the negative effect is negligible.

Structural Design of a 9.4 T Whole-Body MRI Superconducting Magnet

A project to develop a 9.4 T magnetic resonance imaging system is proposed for bioscience research applications. A whole body superconducting magnet system will be manufactured and test in the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). This magnet system features a room temperature bore of 800 mm in diameter, helium bath cooing, 9.4 T center magnetic field and passive iron shielding. The magnet is designed with radial layer-winding method. Five coaxial coils will be wound independently and assembled together as the main magnet. Coil length of the magnet is 3000 mm. In the magnet design, current density grading is performed to optimize the magnetic field distribution and stress level in the coil windings. The maximum magnetic field is 9.505 T, corresponding to an operating current of 224.515 A. The total magnetic energy storage is 138 MJ. Detailed magnetic and mechanic structure design as well as structure stress analysis are presented in this paper.

An 8 T Superconducting Split Magnet System With Large Crossing Warm Bore

A conduction-cooled superconducting split magnet system with large crossing warm bore is designed and will be developed for material processing applications. The magnet is composed of eight coaxial coils and assembled in the form of split coil groups. Both the Bi2223/Ag HTS superconducting tape and NbTi LTS superconducting wires are used to generate a central magnetic field of 8 T, maximum of 11 T in the horizontal warm bore. The split gap between the coils is as large as 136 mm to accommodate the crossing warm bore of 100 mm in diameter. The superconducting split magnet will be conduction-cooled by two GM cryocoolers. The HTS coils and NbTi coils are to be operated in driven mode with two independent power supplies. The operation currents are 200 A (HTS) and 136 A (NbTi) respectively. Magnetic design, stress and strain analysis as well as magnet operation and protection are presented in this paper.

A Passive Quench Protection Design for the 9.4 T MRI Superconducting Magnet

A passive quench protection design of the 9.4 T whole-body magnetic resonance imaging superconducting magnet is proposed. The design of the coil subdivision with shunt resistors is introduced. The selection of the configuration of the heater network is detailed. The optimization of the geometric parameter of the heater strips and the thickness of the insulation binding outside the heater strips are discussed. A winding sequence that could accelerate the quench propagation in the compensating coil is proposed. The calculation results show that the optimized quench protection design can guarantee the safety of the magnet in the case of any coil as the quench initiation coil.

Laboratory test of an industrial superconducting magnetic separator for kaolin clay purification

An industrial magnetic separator with 0.5 m warm bore, 1 m effective length, 3.5 T central field superconducting magnet system, a high gradient reciprocating canister and corresponding slurry and control systems for kaolin clay purification has been constructed. Laboratory tests at different magnetic fields (1-3.5 T) and slurry velocities (0.5-3 cm/s) have been conducted. The results show the stable operation and the productivity of 3 t/h dry clay powder with 3.5-5 points brightness enhancement. >

Open MRI Magnet With Iron Rings Correcting the Lorentz Force and Field Quality

A magnetic resonance imaging (MRI) superconducting magnet with openness can reduce claustrophobia of a patient. To fabricate an open MRI magnet, a new magnet configuration with iron rings and pole plates balancing the force between the coil and the yoke, and correcting the field homogeneity has been proposed. An MRI magnet with the center field of 0.7 T generated by split-pair coils and yokes is fabricated. The coils are contained in the cryostat with separated vessels connected with two pipes. The coils are separated with a room temperature gap of 480 mm and the diameter spherical volume (DSV) of 300 mm in which the homogeneity is 3 ppm in peak-to-peak. The cryogenic system is cooled by one GM cryo-cooler to realize the zero boiling off liquid helium. In the paper, the detailed design, fabrication, and test will be reported.