Optimization Analysis and Experimental Verification of FID NMR Coil in Polarized 3He Systems

The application of hyperpolarized 3He gas is extensive in fields such as neutron polarimetry, fundamental physics, and diagnostic medicine. The polarimetry measurement is crucial for 3He polarization systems. Typically, a free induction decay nuclear magnetic resonance (FID NMR) coil is used to detect the FID signal of 3He atoms. The measurement signal-to-noise ratio (SNR) of the coil is correlated with factors such as diameter, number of turns, and relative position to the cell. There is limited literature and insufficient experimental verification on the optimization analysis of FID NMR coils. In this study, an SNR model for the coil was established through theoretical analysis of the FID signal and coil noise. The FID NMR coil was experimentally validated in a 3He polarization system based on the metastability-exchange optical pumping (MEOP) technique, which is known for its high polarization efficiency. The experimental results indicated that for a cylindrical cell with both radius and height of rcell, the optimal SNR of the coil was achieved at a radius of rcell/2, which was consistent with the theoretical analysis. The relative error of the fitted SNR model was less than 10%, demonstrating its effectiveness. These research findings hold significant practical implications for optimizing the design of 3He polarization systems.