Design,Implementation And Optimization Of ~3He Polarizability Measurement System

Since the theory of spin-exchange optical pumping(SEOP)polarized inert gas was introduced in 1960,many research institutions and scientists have conducted more in-depth research on this theory.For example,the National Institute of Standards and Technology(NIST)Center for Neutron Research(NCNR),Indiana University,USA,Jefferson National Laboratory,etc.At present,a typical area of polarization ~3He technology application is the neutron polarization domain.,which is also known as the most advanced neutron polarization technology.Three large neutron sources already built in China,China Mianyang Research Reactor(CMRR),China Advanced Research Reactor(CARR),China Spallation Neutron Source(CSNS),all plan to install polarized ~3He system for polarization neutron.Polarized ~3He can also be used for electron scattering experiments,new spin related physical detection,medical magnetic resonance imaging,quantum gyros and precision measurements.Based on China Mianyang research reactor,this paper builds a polarized ~3He system based on Rb-~3He spin exchange optical pumping(SEOP)technology.The system's light source is a 100W high-power diode array laser.The Chirped Volume Bragg grating is used to narrow the full width at half maxima of the spectrum to 0.2nm.The Merritt configuration coil is used to provide a constant magnetic field.The magnetic field gradient in the central region is less than 10-4 cm-1.The OVEN is made of high temperature resistant engineering plastic PEEK.The temperature control is realized by LABVIEW with an accuracy of 0.1 degrees Celsius.The polarizability measurement system is divided into the following three parts:1)Free induction decay(FID)nuclear magnetic resonance(NMR)system.This system is based on the principle of NMR and can detect the ~3He FID signal Used to observe the relative polarization of ~3He as a function of time.By analyzing the signal-to-noise ratio of the coil,the coil of the Brooks configuration is beneficial to improve the signal-to-noise ratio.When the radius of the coil is(a0+d)/(?),the signal-to-noise ratio is the largest,the signal-to-noise ratio and the turns of the coil are The wire diameter of the wire is irrelevant.The measurement of system noise shows that it mainly comes from ambient noise(0.27?V//(?))and data acquisition card noise(0.40?V/(?)),the total noise power spectral density of the system.About(?)G is the gain multiple of the amplifier.2)Adiabatic fast channel(AFP)nuclear magnetic resonance(NMR)system.This system is also based on the principle of NMR and is used to flip the nuclear spin of ~3He.The LAB VIEW and function generator are used to generate the oscillating electrical signal.The 40W power amplifier is used to amplify the signal,and the square Helmholtz coil is used to generate the RF field with a field strength of 1.48G.The loss of polarizability after the spin of the polarized ~3He core was tested to be<2%.3)Electron paramagnetic resonance(EPR)system.This system is based on the principle of EPR and is used to measure the absolute polarizability of ~3He.The system consists of a function generator,a radio frequency coil,a photodetector and a data acquisition card.In the process of optical pumping,a function of a linearly varying pulse is transmitted to the system through a function generator and a radio frequency coil.The intensity of the light detected by the photodetector will first become larger and then decrease,and the frequency corresponding to the peak is the ERP of Rb.frequency.In order to avoid the influence of pump light on the measurement,a D2 filter is added at the front end of the photodetector,and the EPR frequency of Rb is judged by the D2 line of Rb.The absolute polarization of Rb can be obtained indirectly by the EPR frequency shift of Rb before and after AFP.The EPR frequency shift of this system is 2?v=10.45kHz,and the absolute polarization of ~3He is 72.7%±0.4%.In this paper,the principle and implementation method of each part of ~3He polarizability measurement system and the construction of the whole optical pumping system are introduced in detail.According to our limited understanding,th This is the first time to realize the polarization ~3He system applied to polarized neutrons in China,and it has certain reference value for the study of domestic polarization ~3He polarization neutrons.