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Polarized neutron scattering, as one of the experimental techniques of neutron scattering, is a powerful tool for exploring the microstructure of matter. In polarized neutron scattering experiments, magnetic field maintains and guides the neutron polarization, and determines the sample magnetic environment. For complex magnetic sample, it is often necessary to apply zero-field environment at the sample position, so that general polarization analysis becomes feasible. To achieve effective zero-field environment for polarized neutron experiment, carefully designed magnetic field is required. In this work, we demonstrate a zero-field sample chamber designed for polarized neutron experiment by utilizing both permalloy material and high-TC superconducting films. This design adopts a simple and low-maintenance ‘deep-well’ shape to achieve effective shielding. The study uses finite element simulation method to analyze the effect of dimensions on the magnetic field shielding performance of the device of the model, including height, arm length, opening radius, and superconductor distance. At optimal dimensions, the designed zero field chamber achieves an internal magnetic field integral of 0.67 G·cm along the neutron path under the geomagnetic field condition. The maximum neutron depolarization for 0.4 nm neutrons is 0.76%, which sufficient for general polarization analysis application. The finite element method simulation results are examined by neutron Bloch equation dynamics simulations and in-lab measurement . Based on the established effective zero-field shielding design, we further discuss the relationship between magnetic field shielding and the dimensions of the device. The application of the device to spectrometers and the future improvement in the device structure are also discussed. -
Keywords:
- magnetic field shielding /
- polarized neutron technique /
- Larmor precession /
- finite element analysis
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Google Scholar
[2] Moon R M, Riste T, Koehler W C 1969 Phys. Rev. 181 920
Google Scholar
[3] Kozhevnikov S V, Ott F, Radu F 2018 Phys. Part. Nuclei 49 308
Google Scholar
[4] Halpern O, Holstein T 1941 Phys. Rev. 59 960
Google Scholar
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Google Scholar
Tong X 2020 Physics 49 765
Google Scholar
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Google Scholar
[8] Janoschek M, Klimko S, Gähler R, Roessli B, Böni P 2007 Physica B: Condensed Matter 397 125
Google Scholar
[9] Tasset F, Lelièvre-Berna E, Roberts T W, Bourgeat-Lami E, Pujol S, Thomas M 1997 Physica B: Condensed Matter 241–243 177
Google Scholar
[10] Tasset F, Brown P J, Lelièvre-Berna E, Roberts T, Pujol S, Allibon J, Bourgeat-Lami E 1999 Physica B: Condensed Matter 267–268 69
Google Scholar
[11] Lelièvre-Berna E, Bourgeat-Lami E, Fouilloux P, Geffray B, Gibert Y, Kakurai K, Kernavanois N, Longuet B, Mantegezza F, Nakamura M, Pujol S, Regnault L P, Tasset F, Takeda M, Thomas M, Tonon X 2005 Physica B: Condensed Matter 356 131
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Google Scholar
[13] Takeda M, Nakamura M, Kakurai K, Lelièvre-berna E, Tasset F, Regnault L P 2005 Physica B:Condensed Matter 356 136
Google Scholar
[14] Hutanu V, Luberstetter W, Bourgeat-Lami E, Meven M, Sazonov A, Steffen A, Heger G, Roth G, Lelièvre-Berna E 2016 Rev. Sci. Instrum. 87 105108
Google Scholar
[15] Wang T 2015 Ph. D. Dissertation (Bloomington: Indiana University)
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Google Scholar
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Google Scholar
[18] Bloch F 1946 Phys. Rev. 70 460
Google Scholar
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Google Scholar
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图 1 混合屏蔽深井式方案整体设计示意图 (a) 零场腔设计与磁场元件分布图; (b) 基于原型设计进行计算的磁场模拟结果示意图
Fig. 1. Schematic diagram of hybrid shielding ‘deep well’ design: (a) Schematic diagram of design of zero field chamber (ZFC) and distribution of magnetic field elements; (b) schematic diagram of magnetic field simulation result based on prototype design.
图 3 零场腔磁场分布XZ平面截面图
Fig. 3. XZ-plane cross-sectional view of magnetic field distribution of ZFC
图 4 最优设计条件下零场腔内沿束流方向的磁场分布与极化演化 (a) 零场腔中子束流沿线磁场分布; (b) 零场腔内内中子束流沿行进方向的极化变化
Fig. 4. Magnetic field distribution and polarization evolution in direction of beam path in ZFC under optimal conditions: (a) Magnetic field distribution of ZFC along the neutron beam direction; (b) polarization evolution along neutron beam direction inside the ZFC.
图 5 不同高度条件对零场腔屏蔽性能的影响 (a)沿中子路径上的磁场分布对比; (b)零场腔内中子路径上的磁场积分随高度条件的变化
Fig. 5. Influence of height conditions on shielding performance of ZFC: (a) Comparison of magnetic field distributions along neutron beam path; (b) variation of magnetic field integral along neutron beam path inside ZFC with height.
图 11 不同坡莫合金材料厚度对零场腔屏蔽性能的影响 (a) 沿中子路径上的磁场分布对比; (b)零场腔内中子路径上的磁场积分随厚度条件的变化
Fig. 11. Influence of permalloy thickness conditions on shielding performance of ZFC: (a) Comparison of magnetic field distributions along neutron beam path; (b) variation of magnetic field integral along neutron beam path inside ZFC with permalloy thickness.
图 6 不同高度条件下的磁场分布XZ平面截面图 (a) h = 140 mm; (b) h = 200 mm; (c) h = 300 mm
Fig. 6. XZ-plane cross-sectional view of magnetic field distribution under different height conditions: (a) h = 140 mm; (b) h = 200 mm; (c) h = 300 mm.
图 7 不同半径条件对零场腔屏蔽性能的影响 (a)沿中子路径上的磁场分布对比; (b)零场腔内中子路径上的磁场积分随半径条件的变化
Fig. 7. Influence of radius conditions on shielding performance of ZFC: (a) Comparison of magnetic field distributions along neutron beam path; (b) variation of magnetic field integral along neutron beam path inside ZFC with radius.
图 8 不同臂长条件对零场腔屏蔽性能的影响 (a)沿中子路径上的磁场分布对比; (b)零场腔内中子路径上的磁场积分随臂长条件的变化
Fig. 8. Influence of arm length conditions on shielding performance of ZFC: (a) Comparison of magnetic field distributions along neutron beam path; (b) variation of magnetic field integral along neutron beam path inside ZFC with arm length.
图 9 超导体薄膜与零磁场腔端口的间距对零场腔屏蔽性能的影响 (a) 沿中子路径上的磁场分布对比; (b) 零场腔内中子路径上的磁场积分随超导体薄膜距离的变化
Fig. 9. Influence on shielding performance of ZFC caused by distance between superconducting thin film and end of arm: (a) Comparison of magnetic field distributions along neutron beam path; (b) variation of magnetic field integral along neutron beam path inside ZFC with distance between superconducting thin film and end of the arm.
图 10 不同间距条件下的磁场分布XZ平面截面图 (a) d = 1 mm; (b) d = 23 mm
Fig. 10. XZ-plane cross-sectional view of magnetic field distribution under different distance conditions: (a) d = 1 mm; (b) d = 23 mm.
图 12 FEM磁场模拟结果与实际测量结果的对比(屏蔽体两端口分别位于±151 mm处) (a)原型装置的磁场分布对比; (b)优化装置的磁场分布对比
Fig. 12. Comparison of magnetic field distribution results between FEM simulation and actual measurement (Ends of arm of ZFC are located at ±151 mm): (a) Magnetic field distribution comparison of prototype; (b) magnetic field distribution comparison of optimized device.
图 13 (a)优化前和(b)优化后零磁场腔的磁场分布XZ平面截面图
Fig. 13. XZ-plane cross-sectional view of magnetic field distribution of ZFC (a) before and (b) after optimization.
图 14 偏离中心线时沿中子行进方向上的磁场分布 (a) 偏离中心线5 mm时的磁场强度分布; (b)偏离中心线10 mm时的磁场强度分布
Fig. 14. Distribution of magnetic field along neutron path when off-centerline: (a) Magnetic field distribution at 5 mm deviation from centerline; (b) magnetic field distribution at 10 mm deviation from centerline
表 1 有限元模拟各材料物理性能定义
Table 1. Physical properties definition of different materials in FEM model.
材料 电导率 σ/(S·m–1) 相对磁导率 μr 空气 0 1 坡莫合金(80% Ni) $ 1.74\times {10}^{6} $ $ 80000 $ 铁 $ 1.12\times {10}^{7} $ $ 4000 $ 铜 $ 6.00\times {10}^{7} $ 1 YBCO薄膜(自定义材料) $ 1\times {10}^{10} $ $ 1\times {10}^{-10} $ 
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[1] Halpern O, Johnson M H 1939 Phys. Rev. 55 898
Google Scholar
[2] Moon R M, Riste T, Koehler W C 1969 Phys. Rev. 181 920
Google Scholar
[3] Kozhevnikov S V, Ott F, Radu F 2018 Phys. Part. Nuclei 49 308
Google Scholar
[4] Halpern O, Holstein T 1941 Phys. Rev. 59 960
Google Scholar
[5] 童欣 2020 物理 49 765
Google Scholar
Tong X 2020 Physics 49 765
Google Scholar
[6] Tasset F 1989 Physica B: Condensed Matter 156–157 627
[7] Brown P J, Forsyth J B, Tasset F Neutron polarimetry 1997 Proc. Royal Soc. London A: Math. Phys. Sci. 442 147
Google Scholar
[8] Janoschek M, Klimko S, Gähler R, Roessli B, Böni P 2007 Physica B: Condensed Matter 397 125
Google Scholar
[9] Tasset F, Lelièvre-Berna E, Roberts T W, Bourgeat-Lami E, Pujol S, Thomas M 1997 Physica B: Condensed Matter 241–243 177
Google Scholar
[10] Tasset F, Brown P J, Lelièvre-Berna E, Roberts T, Pujol S, Allibon J, Bourgeat-Lami E 1999 Physica B: Condensed Matter 267–268 69
Google Scholar
[11] Lelièvre-Berna E, Bourgeat-Lami E, Fouilloux P, Geffray B, Gibert Y, Kakurai K, Kernavanois N, Longuet B, Mantegezza F, Nakamura M, Pujol S, Regnault L P, Tasset F, Takeda M, Thomas M, Tonon X 2005 Physica B: Condensed Matter 356 131
Google Scholar
[12] Regnault L P, Geffray B, Fouilloux P, Longuet B, Mantegezza F, Tasset F, Lelièvre-Berna E, Bourgeat-Lami E, Thomas M, Gibert Y 2003 Physica B: Condensed Matter 335 255
Google Scholar
[13] Takeda M, Nakamura M, Kakurai K, Lelièvre-berna E, Tasset F, Regnault L P 2005 Physica B:Condensed Matter 356 136
Google Scholar
[14] Hutanu V, Luberstetter W, Bourgeat-Lami E, Meven M, Sazonov A, Steffen A, Heger G, Roth G, Lelièvre-Berna E 2016 Rev. Sci. Instrum. 87 105108
Google Scholar
[15] Wang T 2015 Ph. D. Dissertation (Bloomington: Indiana University)
[16] Wu M K, Ashburn J R, Torng C J, Hor P H, Meng R L, Gao L, Huang Z J, Wang Y Q, Chu C W 1987 Phys. Rev. Lett. 58 908
Google Scholar
[17] Parnell S R, Kaiser H, Washington A L, Li F, Wang T, Baxter D V, Pynn R 2013 Physics Procedia 42 125
Google Scholar
[18] Bloch F 1946 Phys. Rev. 70 460
Google Scholar
[19] Seeger P A, Daemen L L 2001 Nucl. Instrum. Methods Phys. Res. , Sect. A 457 338
Google Scholar
[20] Dong Y C, Wang T H, Kreuzpaintner W, Liu X T, Li Z H, Kang Y D, Zhang J P, Tian L, Huang C Y, Bai B, Tong X 2022 Nucl. Sci. Tech. 33 145
Google Scholar
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