The Research On The YBCO Block Magnets Of Magnetic Resonance Microscope

MRM is a small magnetic resonance imaging system, mainly the study of physiology, pathology and other disciplines in vivo imaging. MRM systems in high-field magnets are all low-temperature superconducting magnets, the magnet is not only costly, but MRM system is too expensive, resulting in a lot of research work MRM technique can not be used. The emergence of high-temperature superconductors to find a solution to this problem, this paper dedicated to the research based on yttrium barium copper oxide (YBCO) HTS blocks MRM magnets.MRM is a small magnetic resonance imaging system, and it is mainly used to the study in vivo imaging of physiology, pathology and other disciplines. The high-field magnets in the MRM systems are all low-temperature superconducting magnets. The magnet is costly, and MRM system is too expensive, so many research works cannot use the MRM technique. The emergence of high-temperature superconductors gives a solution to solve this problem, and this paper dedicates to research the MRM magnets based on YBCO.Firstly, in order to study the YBCO bulk properties of the magnetic flux capture, i use pulse magnetization way to build a bulk magnet pulse excitation system. In the zero-field cooling mode, i study the magnetic flux characteristics of some samples by using the system applied to the conventional copper windings to generate pulsed magnetic field magnet. The results show that YBCO bulks can reach the target magnet field 0.2T at 77K, and we can get that the magnetic field can be displayed substantially stable based on the measured attenuation of the field strength.Secondly, the magnetic field strength is poor and its liquid nitrogen is rapidly evaporating in conventional copper windings magnets, in order to solve these problems, I design and implement a U-type liquid nitrogen temperature YBCO bulk magnets. I compare two kinds of excitation methods:superconductor zero fields cooled and field cooled, which shows that the remanence of the field cooling mode is significantly higher than the zero-field cooling way. and the highest magnet field strength of liquid nitrogen temperature is up to 0.38T. I study the attenuation with time of the different samples of the field strength, after one hour after the rate of change of the field strength is approximately 280ppm/s, and it indicates that the magnetic field is stable in the zero-field cooling mode.Finally, in order to obtain the higher magnetic field strength than U-shaped magnet in liquid nitrogen temperature, I design and implement the YBCO bulks with direct cooling refrigerator. Dewar structure is designed to connect together by two cylindrical and two cold shields is designed to be installed up and to link two superconducting block. There is a square room space to the intermediate space. Simultaneously, I combine the superconducting block cold shield, Dewar outer and tube refrigerator together. I conduct a superconductor magnet temperature experiment. The measured minimum temperature decrease magnet is 74.5IK.These studies have shown that the way of using YBOC high-temperature superconductor magnet to design the MRM feasibility is feasible and it achieves a U-style magnet YBOC with liquid nitrogen temperature. However, the magnetic field strength is low, so i design the MRM magnets cooled by refrigerator directly, and implement the YBCO bulk magnet that are slower than the temperature of liquid nitrogen initially.