Research Of MgB₂Superconducting MRI Magnet

MgB2, as a newly discovered superconducting material, its initial temperature of superconducting transition can be39K. So far this is the highest critical temperature found in the metal compounds. The superconducting material has many advantages, such as simple crystal structure, long coherent length, which making the application of this materials promising in many aspects.General application of MgB2lies in the production of small high-field magnets, which has achieved very good results internationally and domestically. In2006, Italy and the United States made a breakthrough in MgB2superconducting MRI magnet technology, which proves the possibility of the application of MgB2in magnetic resonance. In this study, we designed and produced an MgB2superconducting MRI magnet prototype applied to the body.The theory and experiment of this HTS magnet for0.6T MgB2production techniques were studied in detail. An overview of the general theory of superconducting magnet design was introduced; the critical current and mechanical properties of MgB2strip used in this study were researched. The measured critical current of short sample was156A@20K. The stress influence on critical current of strip was investigated. As a result, the impact of stress on critical current of strip was obtained; The process of magnetic field analysis by finite element analysis software is introduced in detail. The distribution of0.6T magnetic field is obtained.Secondly, the design of the Dewar was studied in detail. Dewar shell was designed. The strengthened structure of the Dewar shell was also designed. The suspension support structure that can withstand large electromagnetic force was designed. The yield stress of a single rod is5558N. The length of the rod can be adjusted by this device. The vacuum of Dewar system was discussed; the related knowledge of vacuum equipment, selection of vacuum valve, vacuum insulation and vacuum measurement was introduced. Moreover, the low-temperature equipment-cryocooler, vacuum insulation and temperature measurement method which used in this study were also introduced. Thirdly, the designed various components were assembled. Vacuum and low temperature tests were performed, the production of O-ring was introduced, and the vacuum chamber was cleaned. We used vacuum unit formed by mechanical pump and diffusion pump to obtain vacuum, the maximum vacuum is2.6×10-4Pa. The superconducting coil is precooled by liquid nitrogen and then refrigerated by G-M cryocooler. Good test results are obtained. Finally, the first prototype MgB2superconducting MRI magnet in China was completed.