Development of Spin-echo NMR Technique for High-gradient Magnetic Field Measurement

迄今为止，人们一直担心不可能将NMR技术应用于高梯度磁场的精确测量，例如加速器中使用的四极磁体。为了克服磁场梯度带来的困难，我们发展了自旋回波核磁共振技术，通过对自旋回波信号中自旋进动频率的检测，对自旋回波信号检测的模拟研究和自旋回波谱的理论信噪比，预示了在高梯度磁场中观测自旋回波信号的可能性。在理论研究的基础上，我们用一个简单的固定频率自旋回波探测器，在场强为2.35kG，梯度为0.55T/m的条件下，观测到了清晰的自旋回波信号。自旋回波信号中出现的恢复的核磁旋进频率取决于NMR样品的大小，但在自旋回波信号中出现的旋进频率与样品的大小无关。 ...更多信息 180°脉冲的射频频率与由样品中的平均场强确定的NMR频率一致的频率。在教育部科研资助项目的支持下，我们研制了一种用于场强搜索和消除样本量效应的变频自旋回波探测器。目前，我们正处于系统优化的最后阶段。在与探测器的发展，我们研究了现场测量的自旋回波信号的频谱分析方法。应用改进的FFT分析自旋回波信号，我们获得了0.45G的分辨率为2.35kG的现场测量，我们证实了实验的样品尺寸效应。在探测器调试完成后，我们将在KEKB/LER偏转磁体上进行15 G/cm梯度磁场下的长期性能测试。在最后一步中，我们将尝试测量KEKB加速器的四极磁铁的磁场梯度为10 T/m。少

Until now it has been concerned impossible to apply the NMR technique to the precise measurement of high-gradient magnetic fields such as in quadrupole magnets use in accelerators. To overcome difficulties due to the field gradient, we have developed the spin-echo NMR technique for magnetic field measurement where the spin precession frequency in the spin-echo signal is detected.Simulation studies of spin-echo signal detection and the theoretical signal-to-noise ratio of the spin-echo spectrum predict the possibility of spin-echo signal observation in a high-gradient magnetic field. In an experiment based on theoretical studies, we observed spin-echo signals clearly at a field strength of 2.35kG with a gradient of up to 0.55T/m using a simple fixed frequency spin-echo detector. This result can be scaled to a gradient of 5T/m at 10kG.The precession frequency of the recovered nuclear magnetization appearing in the spin-echo signal depends on the NMR sample size, except in the case of res … More onance where the rf frequency of the 180°-pulse coincides with the NMR frequency determined by the average field strength in the sample. We developed a variable frequency spin-echo detector to search the field strength and to eliminate the sample size effect with the support of a Grant-in-Aid for Scientific Research from the Ministry of Education. At this moment we are in the final stage of system tuning. In parallel with detector development, we studied methods for spectral analysis of the spin-echo signal for the field measurement. Applying an improved FFT analysis to the spin-echo signal, we obtained a resolution of 0.45G for the field measurement at 2.35kG, and we confirmed the sample size effect experimentally. This result indicates that we can realize a resolution smaller than 0.1G without serious difficulties.After completion of detector tuning, we will perform a long term performance test in the gradient field of 〜15G/cm at a KEKB/LER bending magnet. In the final step, we will attempt field measurement of a quadrupole magnet of the KEKB accelerator with 〜10T/m field gradient. Less