Abstract：The high quality magnetic shielding system is one of the most important components of cesium fountain clock.Firstly, the three parameters for magnetic shielding performance evaluation were defined, i.e.uniform range, the starting position of uniform range and shielding factor.And then, the results for different configurations of three layer cylindrical magnetic shield sets using finite element calculation are presented.In particular, effects on shielding of radial and axial spacing between shield layers, the length of sleeves weld on the end cap and the connection geometry between end caps and shield cylinders are examined.From the calculation results, the performance of optimal configuration of three layer shield sets is compared with the four layer ones used in NIM5 cesium fountain clock.This is important in design and assemble the magnetic shielding for the next generation cesium fountain clock to improve the accuracy.
［1］ Clairon A, Ghezali S, Santarelli G, et al. Preliminary accuracy evaluation of a cesium fountain frequency standard ［C］//The 5th Symposium of Frequency Standards and Metrology, Singapore： World Scientific,1996,49-59.
［2］ 刘年丰, 李明寿, 李天初, 等.NIM5铯喷泉钟系统频移及其不确定度初步评定 ［C］//中国计量测试学会.全国时间频率学术会议.宜昌, 2007,135-139.
［3］ Sumner T J, Pendlebury J M, Smith K F. Convectional magnetic shielding ［J］.Journal of Physics D: Applied Physics, 1987, 20(9): 1095.
［4］ 牛刚, 贾志海, 王经.基于ANSYS的多极板电容传感器仿真研究 ［J］.仪器仪表学报, 2006, 27(3):280-284.
［5］ 张纳, 王博文, 李淑英, 等.基于磁场传感器的层状磁电复合材料动态特性的有限元模型研究 ［J］.仪器仪表学报, 2010, 31(7): 1528-1533.
［6］ Burt E A, Ekstrom C R.Optimal three-layer cylindrical magnetic shield sets for scientific applications ［J］.Review of Scientific Instruments, 2002, 73(7): 2669-2704.
［7］ 李天初, 李明寿, 林平卫, 等.NIM第二代铯喷泉钟NIM5的研制和初步评定不确定度进入3E-15 ［C］//中国计量测试学会.全国时间频率学术会议.宜昌, 2007,1-4.
［8］ Li T C, Lin P W, Li M S, et al.The Transportable Cesium Fountain Clock NIM5: its Construction and Performance ［C］//World Scientific.The 7th Symposium of Frequency Standards and Metrology, Pacific Grove, CA, USA,2008,314-320.
［9］ 高源, 高小珣, 张爱敏, 等.一种由NIM5铯喷泉基准驾驭实现的独立时标TA(NIM) ［J］.计量学报, 2011, 32(1): 66-69.
［10］ Gubser D U, Wolf S A, Cox J E. Shielding of longitudinal magnetic fields with thin, closely spaced, concentric cylinders of high permeability material ［J］.Review of Scientific Instruments, 1979, 50(6): 751-756.
2014, Vol. 35 
