The Design And Preparation Of The MgB₂Su-perconducting Magnet Cooled Directly By The Cryocooler

As a new type of superconducting material discovered in early2001, MgB2is by far the metal compounds superconductors with the highest critical temperature, whose supercon-ducting transition temperature is39K. As a kind of superconducting material, MgB2has a lot of advantages than others, such as the higher transition temperature, the larger coherence length, the higher upper critical field, no weak link between grain boundaries, the simper structure, and the lower cost, etc. These unique features open up great opportunities for the business application of MgB2. Therefore whether the MgB2wires can be made into MRI magnet coils used in medical imaging becomes a subject of interest among people.The content of this thesis mainly contains three parts. The first part is the production of the MgB2wire. The second part is the design of the uniform magnetic field plate. About the production of the MgB2wire, two elements need to be considered when the MgB2supercon-ducting coils used in MRI imaging. The first element is how to increase the critical current of the wires. The second element is how to increase the upper critical field of the wire. After comparing the data getting from the experiment, a phenomenon is discovered:the critical current of the wire is related to the temperature of the heat treatment. If the heat treatment temperature of the MgB2wire is appropriated changed, the critical current can be increased. Besides, the incorporation of C and Ti to the MgB2wire can increase the upper critical field. About the design of the uniform magnetic field plate, the main part is to study how to gener-ate a relatively uniform magnetic field by the uniform magnetic field plate. Using the perme-ability and magnetic theorem of the magnetic media in the electromagnetic, a fact is drawn out that the yoke made by pure iron can produce the field with the best effect. A rough size of the magnet is also worked out. Through the2D simulation of the iron yoke and the shape of the uniform field plate by the finite element analysis software ANSYS, and combined its own processing conditions of the uniform field plate, the exact size and shape of the iron yoke and uniform field plate can be got.In the stage of magnet coil production, a relatively complete process about how to pro-duce a MRI magnet coil by MgB2wire is summed up. In the process of coil production, it is very easy to damage the wire and these issues are also solved in this project. For example, the gap between the ending frame plates is uneven, but by the improvement of the winding ma-chine, a uniform tension can be applied when winding. Also it can avoid the damage of the wire caused by the sudden tension when the start and stop time of the winding machine. In addition, a set of workable solutions about the insulation of the coils are also summed up.About the magnet coil designed in this project, the center field strength is0.6T, and the cooling method of the magnet coil is Cryocooler directly cooling.