Chunzhong Wang

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.

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.

Optimal Design for High-Field MRI Superconducting Magnet

An optimal design method for high-field MRI magnet is put forward. The design procedure can be divided into two steps. First step is to design a set of coils to achieve the necessary center field, which is called the background field, and it is based on the optimal algorithm of minimum volume consumption by SQP. During the optimization, the safety factor of superconducting wires has been considered. The second step is to design a set of correction coils to achieve the necessary homogeneity, and the magnetic field produced by previous coils is set as background field, then optimize the homogeneity based on the nonlinear Least Square Method.

Design of Axial Shim Coils for Magnetic Resonance Imaging

An efficient design method of axial shim coils for Magnetic Resonance Imaging is presented. The axial shim coils are designed to improve magnetic field homogeneity which compensates for the unavoidable construction tolerances, cold shrink of magnet frame and some other negative effects. For simplifying design complexity of axial shim coils and reducing the difficulty of engineering, two sets of three pairs of single-layer coils in series are designed to eliminate all of the lower six orders of spherical harmonics (Z1, Z2, Z3, Z4, Z5, and Z6) for one time. Computing search method is employed to optimize positions of the shim coils. Details of the design method for a sample of a Baby MRI scanner and the calculation results are presented.

Design of Adjustable Homogeneous Region Cryofree Conduction-Cooled Superconducting Magnet for Gyrotron

A conduction cooled superconducting magnet with the center field from 1.3 to 4 T and the warm bore of 100 mm in diameter has designed, fabricated and tested. The magnet was designed on the basis of the hybrid genetic optimal method. The superconducting magnet has the adjustable homogenous regions with the lengths from 200 mm to 320 mm. The magnet generated the multi-homogeneous regions with the constant lengths of 200, 250 and 320 mm. The homogeneity of magnetic field is about plusmn0.5% with the constant homogenous region lengths and plusmn1.0% for adjusting homogenous lengths. The magnetic field is decayed to 1/15-1/20 from the front point of homogeneous region to 200 mm. The magnet is cooled by one 1.5 Watt 4 K GM refrigerator. In the paper, the results on the design, fabrication and test of the superconducting magnet are presented.

Development of Conduction-Cooled Superconducting Magnet for Baby Imaging

A magnet with very high homogeneity for the baby imaging is designed and will be fabricated. The optimal design method of short actively shielded superconducting magnet is presented based on nonlinear least square method. The superconducting magnet is cooled through a pulse tube refrigerator (PTR) with isolated vibration. The available diameter for the superconducting magnet is ¿ 500 mm. Diameter Sphere Volume (DSV), homogeneity and center magnetic flux density are ¿ 300 mm, 2 ppm and 1.5 Tesla, respectively. In the paper, the Electromagnetic (EM) design, stress analysis, quench protection and cryogenic system for the magnet are presented.

Development of Testing Device for Critical Current Measurements for HTS/LTS

For the goal of superconducting magnet applications in the advanced testing device for high temperature superconducting (HTS) wire and sample coils, a wide bore conduction-cooled superconducting magnet with available warm bore of phi 186 mm and center field of 5 T for the background magnetic field applications was designed and fabricated and tested. A sample cryostat with two GM cryocoolers is inserted in the background magnet. The system allows measurements to be performed in a repeatable and reliable fashion. The detailed design, fabrication and thermal analysis are presented in the paper.

Shape optimization of HTS magnets using hybrid genetic algorithms

Publisher Summary This chapter presents two kinds of optimal methods and test of their abilities for searching optimal solutions with consideration of the constraints, such as central magnetic filed, field homogeneity, and B-I characteristic. The Genetic Algorithm (GA) is to mimic some of the processes observed in natural evolution. It can escape from local minima and deal with constrained nonlinear optimization problems. A 12 T high temperature superconducting (HTS) magnet by Bi-2223/Ag tape is designed according to the methods. A new configuration of the HTS magnet which can reduce the winding volume and improve the efficiency of superconductor utilization effectively is suggested. A new configuration of HTS magnet (case E) that can reduce the winding volume effectively is found. By using optimal methods, the efficiency of superconductor utilization can be improved; the amount of superconductor needed in the magnet and the electrical power wasted in refrigeration can be saved.