Beam Quality Optimization And Application Research For IMP 50MeV Electron LINAC

The 50 Me V electron LINAC for high-energy electron radiography built by the Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS)has entered a stable operation stage since 2019.The key component of the equipment that can provide high quality electron beam is the alpha magnet.However,in the first stage of the design,because the fringe field effect of the alpha magnet and the influence of the space charge effect were not fully considered,the space for improving the beam quality was limited,and it was difficult to meet the needs of the imaging terminal to further improve the resolution.And due to the imperfection of beam diagnosis components,the operating efficiency is greatly reduced.In this paper,the idea of combining the intelligent optimization algorithm and the dynamic calculation software GPT is used to conduct a global optimization simulation based on the space charge effect about the IMP 50 Me V electron LINAC,which improves the beam quality at the exit of the accelerating tube.In addition,the beam quality was diagnosed experimentally by the beam position monitor(BPM)and coherent transition radiation(CTR),so the beam parameters are diagnosed and optimized in the actual operation,which improved the quality and stability of the beam and provided support for the terminal experiment.Finally,the application of IMP 50 Me V electron LINAC is expanded,the optimization scheme of high-power infrared free-electron laser(IR-FEL)is designed,and the optimized parameters of the accelerator and the specific structural parameters of FEL are given,and then expand the research field of the device.The main content of the dissertation is divided into the following four parts.The first part introduces the operation status of 50 Me V electronic LINAC,and analyzes the optimization direction of the beam according to application direction.The second part simulates and optimizes the beam quality of the 50 Me V electron LINAC,designs a global optimization scheme based on the existing beamline,uses the new alpha magnet incident correction angle to adjust the beam path,and obtains optimal beam distribution under the space charge effect.And the optimal beam phase space matching at the entrance of the alpha magnet through emittance scanning analysis is the focused beam in the x direction and the defocused beam in the y direction.The third part conducts online measurement and optimization of the 50 Me V electron beam,mainly including beam parameter measurement based on BPM,bunch length measurement based on coherent transition radiation and beam position alignment technology based on BPM.From an experimental point of view,online diagnosis and optimization of beam quality has been achieved.The fourth part is based on the application research of IMP 50 Me V electron LINAC.The high quality electron beams from the accelerating tube can be used in high energy electron imaging experiments,material biological irradiation experiments,generation of infrared free electron lasers,and other applications based on high-energy short-pulse electron beams.The achromatic transmission beamline from the exit of the accelerator to the entrance of the free electron laser was designed,and based on the target wavelength of the free electron laser in the middle and far infrared bands,finally a effective optimal design schemes of high power oscillator type free electron laser was be proposed.The research idea adopted in this thesis is to combine the intelligent optimization algorithm with the beam dynamics software,and the process of optimizing the beam quality is more efficient through the use of the optimization algorithm.The global optimization of the accelerator is carried out based on the genetic algorithm.The main goal of optimization is the mutually restrictive beam quality parameters.The Pareto fronts are obtained through multiple iterations,and the optimal solution is selected from them.On the other hand,optimization algorithms can be used to solve related parameter selection problems by refining the mathematical models in physical problems.The design of the emittance measurement beamline,the collimation of the beam position and the design of the high-power free-electron laser are all based on the particle swarm optimization algorithm.After sorting out the key variables and objective functions that meet the requirements,the PSO algorithm can be used to quickly obtain reliable convergence results,thereby simplifying the design process.In summary,this paper has carried out simulation optimization,experimental diagnosis and application expansion on the IMP 50 Me V electron LINAC,which has theoretically improved the performance of the accelerator and provided beam diagnosis methods for beam operating staff,and it has made sufficient preparations for the next beamline transformation and further optimization of the experimental beam quality,making the IMP 50 Me V electron LINAC to a relatively excellent and mature user device.The upgraded design of IR-FEL can expand the application direction of the device,and it is expected to conduct experimental research in multi-field basic science.