Housheng Wang

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.

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.

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.

Analysis for Ring Arranged Axial Field Halbach Permanent Magnets

A formula is presented for the ring arranged axial field Halbach permanent magnet, which is designed for an electrodynamic suspension experimental system. The formula is based on a two dimensional (2-D) analytical analysis. The analytical solution is compared with the FEM and measured data of the practical magnet

Development of Large Scale Superconducting Magnet With Very Small Stray Magnetic Field for 2 MJ SMES

A superconducting magnet for the superconducting magnetic energy storage system (SMES) fabricated by NbTi monolithic conductor is cooled down and operated at the temperature of liquid helium. The large-scale superconducting magnet with four parallel solenoids was designed, fabricated and tested for the high storage energy density SMES. The superconducting magnet stores 2 MJ of energy with a current of 490 A and a peak magnetic field of 5.4 T. Two GM cryo-coolers cool the whole system to realize zero evaporation of liquid helium. The high temperature superconducting current leads of Bi2223 are used and cooled through one GM cryocooler. The ZnO resistor is used to protect the superconducting magnet. In the paper, the system of superconducting magnet is introduced in detail for the superconducting magnetic energy storage system.

Preliminary Mechanical Analysis of a 9.4-T Whole-Body MRI Magnet

A 9.4-T/800-mm superconducting magnet for whole-body magnetic resonance imaging system has been designed and will be constructed from NbTi conductors. Main coils wound on five aluminum alloy formers provide the center field strength of about 9.4 T. In addition, compensation coils wound on another aluminum alloy former are used to improve the field uniformity of the imaging region. The operating point of the inner main coil is very close to the critical properties of its wire, and its temperature margin is about 0.4 K. It is necessary to know the mechanical stress in the main coils during all operating conditions. The mechanical behavior of the main coils during winding, cooldown, and energizing is analyzed. The effects on mechanical disturbances are predicted, and one available method is proposed to reduce premature quench. In addition, the dimension variations and position changes due to pretension, thermal contraction, and magnetic compression are present.

Analysis of the Driving Force of a Levitated Spherical Superconducting Rotor

A spin drive device of superconducting rotor was designed based on the Meissner effect. The electromagnetic field generated by the stator coils engenders the rotating torque on the superconducting rotor through the windows on its inner wall. The driving force was calculated using finite-element analysis, and the results show that the driving torque is approximately proportional to the square of the driving current. The difference between calculation and experimental results of the driving torque is about 7%. These results will be good references for the further improvement of operating parameters and rotation stability of a superconducting rotor.

Conduction-Cooled Superconducting Magnet With Persistent Current Switch for Gyrotron Application

A superconducting magnet with a center field of 4.5 T cooled by GM cryocooler and operated in the persistent current mode has been designed, fabricated and tested for gyrotron. The superconducting magnet has a warm bore with diameter of 90 mm, the homogenous region with the diameter of 40 mm and length of 230 mm. The ratio of the axial field to the center field located at 180 mm is lower than 88%. In the other special points, the ratios of the radial field to the axial field should be less than from 3% to 11%. The thermally-controlled NbTi/CuNi switch with superconducting joint is connected to the conduction cooled magnet. In this paper, the detailed design, fabrication and test are reported.