Shunzhong Chen

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.

Quench Protection Design of a 1.5 T Superconducting MRI Magnet

A 1.5 T superconducting MRI magnet has been developed in our laboratory. A passive quench protection system is employed to avoid the damage through the quench event. The coils are subdivided into several groups and a heater network is implemented accordingly. With the control volume method, the numerical model of the quench time is introduced. Different design schemes of the heater strip are compared. The simulation results of currents and voltages are illustrated and the temperature rise of the coils and the heaters are discussed.

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.

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.

Synthesis of orderly nanostructure of crystalline GaN nanoparticles on anodic porous alumina membrane

Synthesis of an orderly nanostructure of crystalline GaN nanoparticles on anodic porous alumina membrane through a gas reaction of Ga2O vapor with a constant ammonia atmosphere at 900°C was achieved. The investigation using atomic force microscopy, x-ray diffraction, transmission electron microscopy and high resolution electron microscopy indicated that the orderly nanostructure consisted of polycrystalline GaN nanoparticles with a hexagonal wurtzite structure and about 10–20 nm in diameter. The growth mechanism of the orderly nanostructure of the GaN nanoparticles was discussed. The photoluminescence spectrum of the orderly nanostructure was also reported.

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.

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.