Study On Temperature Field Of ~3He Polarized System By Spin Exchange Optical Pumping

Polarized ³He gas has been widely used in the fields of polarized neutron target,quantum gyroscope,nuclear magnetic resonance imaging（NMR）and high precision measurement due to its unique physical properties.The spin-exchange optical pumping（SEOP）method is the main method for generating polarized ³He gas.In the process of polarizing ³He using the SEOP method,the N₂ enables each excited alkali-metal atom to deexcite back to its ground state through a non-radiating process,in which process,an energy of ¹.5 e V is transferred to N₂ and dissipated as heat,causing the temperature of the cell increase.Temperature is a crucial parameter in the Spin-Exchange optical Pumping（SEOP）process of noble gas（³He）,which will directly affect the saturated ³He polarization.In this paper,the thermophysical process of SEOP system was studied by combining experimental measurement with computational fluid dynamics（CFD）simulation,and the temperature distribution of gas in the cell was obtained,which will provide reference for the research and development of ³He neutron polarization device in the future.Firstly,based on the off-line polarized ³He pumping station of China Spallation Neutron Source,the corresponding experimental platform was built to measure and analyze the temperature distribution on the cell wall under different pumping laser conditions,and the laser power distribution was described in detail to determine the boundary conditions required for simulation.Secondly,the flow and heat transfer characteristics of the cell under different pumping laser conditions were numerically simulated by CFD.The simulation results show that when the high-power pumping laser absorbed by the alkali metal vapor,the heat generated by the pumping laser will cause the temperature of the gas inside the cell to be higher than the temperature of the oven,and there is obvious natural convection inside the cell,resulting in the highest temperature at the top of the cell.At the same time,the heating process of the oven to the ³He cell will be transformed into a cooling process.The simulation results are compared with the experimental data,and the error is less than 9%,which verifies the accuracy of the simulation method and provides a reference for the development and improvement of SEOP system in the future.Finally,the oven of the CSNS in-situ polarized ³He system was designed and optimized.Under the premise of reducing the temperature difference of the ³He cell wall and the oven wall temperature as much as possible,the research and development of the new generation of CSNS in-situ polarized ³He device was completed in coordination with multiple disciplines,and the overall size of the system is reduced by49%compared with the previous version.In this paper,the temperature distribution of ³He cell and the flow law of ³He gas in the cell were obtained by studying the spin-exchange optical pumping polarized ³He system.The thermal physical process of SEOP system is further understood,which will help the related research of ³He polarization and promote the development of domestic polarized ³He technology.