Simulation And Experimental Research Of Velocity Map Imaging System

Atmospheric aerosol is a system of suspended particles in the atmosphere,which cause great harm to human health,environment and climate.New particle formation is an important source of aerosols.It is of great significance to study the nucleation mechanism of new particle formation.Theoretical calculations and the observation of experimental instruments are usually combined to research the formation mechanism.The information of components and structures of the clusters can be analyzed by the combination of a mass spectrometer and a photoelectron spectrometer.Finally,a mass spectrum and a photoelectron spectrogram can be obtained in order to reveal the existence and properties of the compound.To identify different structural information in the clusters,it is necessary to ensure the resolution of the photoelectron spectrometer.Therefore,this thesis mainly aims at the problems found in the experiment of the mass spectrometer-photoelectron spectrometer.Through the simulation of the velocity map imaging system,it provides theoretical support for the actual design and parameter debugging of the instrument.A velocity imaging system based on four plates is proposed in order to improve the resolution of the instrument.1.In order to ensure that the intensity of the ion beam can meet the subsequent experimental conditions,the experiment is carried out by adjusting the voltage of each part of the mass spectrometer and the overall timing.The iodide ion beam with an intensity of 2000 mV is obtained.In addition,the power supply part of the micro-channel board of the optoelectronic spectrometer has been redesigned.The interference of the noise on the final superimposed image is reduced by adding a pulse switch.Finally,the experiment is carried out through the combination of mass spectrometry and photoelectron spectrometer.It is found in the experiment that the resolution of the instrument do not reach the expected target and the photoelectron signal display below the expected region.2.Aiming at the problems found in the experiment,the velocity map imaging system is simulated with electric potential,particle trajectory and focusing capability.By increasing the number of plates,a better simulation effect is obtained.Therefore,a four-plates-based velocity imaging system with three adjustable voltage parameters has been proposed.The focusing capability and resolution of the velocity imaging system are improved and the problem that an adjustable potential can only focus on a relatively narrow energy range is solved.It is beneficial to reduce the loss of photoelectrons and enhance the ability to resist laser drift.3.Based on the simulation results,a modification plan for the velocity map imaging system is developed.In addition,the modification plans for the ion beam intensity and timing control are proposed to improve the optoelectronic spectrometer.Through a series of improvements,the ion beam can accurately reach the predetermined position to meet the laser and the photoelectrons can focus well to the imaging detection system,which improves the overall resolution of the instrument.After the final experimental study,the resolution of the instrument reach 4.5%,which meet the design requirements of the miniaturized mass spectrometer-photoelectron spectrometer.