Frontier Technology Research Of High Brightness Photocathode RF Electron Gun

The electron gun is the source of the particles being accelerated in the electron accelerator and determines the beam performance of the entire accelerator.The low emittance and high brightness electron beam required by facilities such as free electron laser makes the electron gun widely explored and concerned.The emergence and development of photocathode RF electron guns has driven the development of freeelectron lasers,ultrafast electron diffraction and other facilities,and will continue to drive the development of these facilities toward ultra-compactness and efficiency.As scientific research continues,the future ultra-compact and high brightness light source technology also puts forward the demand for lower emittance and lower energy spread for the next generation of photocathode RF electron gun.The Shanghai Soft Xray Free-Electron Laser(SXFEL)has been successfully developed over the years and will continue to provide high-quality free-electron laser pulses for user facilities.During the commissioning and operation of the facility,it was found that the beam emittance could not be further reduced,and the long electron bunch generated by a laser profile shaped by the stacking technique can lead to many microstructures that will complicate the FEL amplification.In addition,the Shanghai high repetition rate XFEL and Extreme light facility(SHINE)is being designed and built due to the demand for a high repetition frequency free electron laser unit.In view of this,there is a requirement to develop both high peak brightness photocathode injectors based on cryogenic electron guns and shorter driving laser pulses and high average brightness photocathode injectors based on continuous wave photocathode electron guns.In this thesis,the design and research work of the cryogenic C-band electron gun are discussed in detail.Firstly,the resonant cavity theory of the acceleration structure and the beam dynamics of the injector are systematically described,and the factors affecting the beam quality at the exit of the injector are introduced,and the requirement to use a higher gradient acceleration structure is proposed.Then the simulation and design of the C-band cryogenic electron gun was completed by analyzing the nature of the highgradient technology and cryogenic structure using three-dimensional electromagnetic field simulation software.The processing of the prototype and the cryostat was completed by using the precision machining technology,and the design of the cryogenic C-band electron gun was verified using the cryogenic experimental results of the prototype,after which the processing of the C-band electron gun and the respective low power tests at room temperature and cryogenic temperature were completed.Since the cryogenic C-band electron gun is designed to operate on an accelerator at high-power states,this paper also describes the layout and construction of a high-power test platform for this electron gun.In addition to the cryogenic electron gun,another research focus direction of electron gun,Continuous Wave electron gun,is also introduced in this thesis.This electron gun can operate continuously at room temperature.The design of the continuous wave electron gun requires a comprehensive consideration of the compromise of each RF parameter,thus a multi-objective optimization algorithm is introduced to optimize the cavity.In addition,multipacting that can occur in this electron gun is also suppressed,and the continuous and stable operation of this electron gun in the designed state is verified by simulations of multi-physics fields.