Research On Key Technologies In Slow Positron Microbeam Pulsing System

Positron is the first antimatter particle discovered by humans.Because of the time information,energy information and momentum information that can be generated by annihilation with electrons,positron annihilation technology has unique advantages in characterizing the microstructure of materials at the atomic level.In order to meet the needs of the development of materials science in the new period,slow positron beam technology which can obtain more detailed and comprehensive microscopic information has emerged.Meanwhile,because of the microbeam pulsing system is the core component of the slow positron annihilation lifetime measurement technology,so the research on key technologies in microbeam pulsing system has been a hot and difficult point in the field of slow positron.This article choses the slow positron beam device based on solid-state Ne moderator at the Institute of High Energy Physics,Chinese Academy of Sciences as the platform,to build a slow positron annihilation life measurement system,especially for the key technologies in the microbeam pulsing system.Firstly,two kinds of microbeam pulsing system design schemes are proposed and the simulation of beam dynamics is completed by Parmela;An accelerated electric field with Faraday cup is designed based by Geant4 for the purpose of continuous adjustable energy of slow positron beam;Finally,the CST software is used to optimize the main-buncher in 3D and complete the structural drawing under normal working parameters.The following results are obtained:(1)The initial energy,energy spread and beam spot of the slow positron beam measured by blocking potential method,CCD camera with fluorescence target are 30 e V?5 e V and 6mm,respectively.(2)The ideal modulation signal and approximate modulation signal waveforms of the microbeam pulsing are deduced,and the composition of the microbeam pulsing system is introduced in detail.By analyzing and measuring the influencing factors of the slow positron annihilation life measurement system,the design indicators of the devices in the paper are determined.(3)Based on beam dynamics,the structure of “prebuncher-chopper-mainbuncher”determined as the microbeam pulsing system because the simulation results are more advantageous under the same beam characteristic parameters and modulation parameters.(4)When the slow positron beam incident energy range is 0.5?30 ke V,the bunching efficiency is up to 87% and the positron utilization rate is up to 20% of the slow positron pulses at 150 ps(FWHM)(These two values will be higher if the time width is 200 ps?250ps or 300 ps).After researching the above contents,a microbeam pulsing system has been established which can provide slow positron beam pulses with narrow time width,high bunching efficiency and positron utilization rate.The design of this system not only accurately obtains positron annihilation measurement,but also improve the measurement efficiency of slow positron annihilation lifetime.In addition,the 3D composition of the system will also provide a design model and reference for the processing and construction of the slow positron annihilation life measurement platform,which has high practical application value.