Enhancing The Signal-to-Noise Ratio In Optically Pumped Cesium Beam Tubes Using A Hexapole Magnetic System

High accuracy and good long-term stability of frequency are the characteristics of cesium atomic clock that is widely used in the fields of science and technology.The optical pumping scheme makes the utilization of cesium atoms is greatly improved,which leads to the enhancement of the Signal-to-Noise Ratio（SNR）of cesium beam tubes,the frequency stability of cesium clock is also significantly enhanced.Increasing the length of the interaction region,the temperature and the opening area of cesium oven can narrow the line width and improve the SNR,respectively.However,these methods will reduce the SNR or make the improvement of the SNR limited.As is known,the frequency stability can be improved through increasing the utilization of cesium atoms.This paper proposes a magnetic focusing method,by adding a hexapole magnetic system to utilize the atoms with large emission angles.The calculation model includes single channel and multiple channels.The calculation results of the single channel calculation model show that the maximum emission angle and the total number of cesium atoms with the hexapole magnetic system are 2.8 times and 9.5 times that of the unused one,respectively.The calculation results of the multiple channels model show that the maximum emission angle and the total number of cesium atoms is 4.5times and 9.6 times that of the unused one,which expectedly increases the SNR by 3times when only considering the shot noise of the cesium beam tube,the second-level frequency stability will has the potential to enter the order of10^-13To be closely integrated with experimental verification,the length and magnetic bore radius of the hexapole magnetic system were optimized,and the process of installing the system to the cesium beam tube with guide rail was designed.The magnetic induction intensity of the magnetic pole tip has different values in the hexapole magnetic system,and these values are substituted into the calculation model of multiple channels.The calculation results show that the total number of cesium atoms with the hexapole magnetic system is 8.2 times that of the unused one,which have laid a firm foundation for experimental verification.