Development of Precise Shimming Technique With Materials Having Low Saturation Magnetization
Development of Precise Shimming Technique With Materials Having Low Saturation Magnetization
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低饱和磁化强度材料精密匀场技术的发展
DOI：
10.1109/tasc.2022.3190803
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发表时间：
2022
影响因子：
1.8
通讯作者：
Ogitsu T.
中科院分区：
文献类型：
--
作者：
Sasaki K.;Sugita M.;Abe M.;Iinuma H.;Ogane C.;Mibe T.;Shimomura K.;Ogitsu T.
测试了使用低饱和磁化强度材料的磁场匀场，以实现小于1 ppm的空间磁场均匀性。测量了三种候选材料，即镍、磁性流体和磁性油灰的每单位质量的磁矩，并证实这些材料具有适合于低于1 ppm的精确匀场的低磁矩。在1.2 T下使用用于MuSEUM实验的MRI磁体，用铁板、Ni薄板和磁性油灰进行磁匀场测试。采用两步匀场方案进行铁板匀场，六次匀场试验后，均匀性可达到0.29 ppm峰-峰（ppm）。然后用镍薄板和磁性腻子进行精密匀场，均匀度镍可达0.16ppm峰-峰，磁性腻子可达0.17ppm峰-峰。即使在两个月后也没有观察到腻子在磁场中的变形。两个月的磁场监测表明，磁场强度和均匀性很大程度上取决于温度，在匀场测试的圆周条件下，必须将磁室温度控制在0.35摄氏度以内，才能保持磁场变化和均匀性在0.1 ppm以内。此外，还指出MuSEUM磁体系统中LHe的再填充应每29天进行一次，并提出了在现有磁体系统中使用带孔塑料垫片的磁性腻子的实用实施方法。
Magnetic field shimming using low saturation magnetization material was tested to realize spatial magnetic field homogeneity of less than 1 ppm. The magnetic moment per unit mass were measured for three candidates, that is, Nickel, magnetic fluid and magnetic putty, and it was verified that those have low magnetic moments suitable for precise shimming below 1 ppm. The magnetic shimming test was performed using MRI magnet for MuSEUM experiment at 1.2 T with iron plates, Ni thin plates and magnetic putty. The magnetic shimming with iron plates was conducted employing the two step shimming scheme, and the homogeneity could be reached to 0.29 ppm peak-to-peak (ppm) after six shimming trials. Then, the precise shimming was carried out with Ni thin plates and magnetic putty, and the homogeneity could be reached to 0.16 ppm peak-to-peak with Nickel and 0.17 ppmwith magnetic putty. No deformation of putty in the magnetic field was observed even after two months. The magnetic field monitoring for two months showed that magnetic field strength and homogeneity largely depended on the temperature, and the temperature of the magnet room has to be controlled within0.35 degC under the circumference condition of the shimming test in order to keep the magnetic field change and the homogeneity within0.1 ppm. In addition, it is showed that the refilling of LHe in the MuSEUM magnet system should be performed once per 29 days The practical implementation method for magnetic putty was suggested for the existing magnet system by using plastic spacers with holes.