Beam dynamics optimization of very-high-frequency gun photoinjector  

作　　者：Han Chen Lian-Min Zheng Bin Gao Zi-Zheng Li Ying-Chao Du Ren-Kai Li Wen-Hui Huang Chuan-Xiang Tang Duan Gu Zheng Qi Meng Zhang Hai-Xiao Deng Qiang Gu Dong Wang 

机构地区：[1]Department of Engineering Physics,Tsinghua University,Beijing 100084,China [2]Chinese Academy of Sciences,Shanghai Institute of Applied Physics,Shanghai 201800,China [3]Chinese Academy of Sciences,Shanghai Advanced Research Institute,Shanghai 201210,China

出　　处：《Nuclear Science and Techniques》2022年第9期80-92,共13页核技术（英文）

摘　　要：Very-high-frequency(VHF)gun photoinjectors,capable of producing high-brightness and high-repetitionrate electron bunches,are some of the best electron sources for driving MHz-class repetition-rate free-electron lasers.In this study,the beam dynamics optimization of a VHF gun photoinjector for Shanghai HIgh Repetition Rate X-ray Free Electron Laser and Extreme Light Facility(SHINE)is systematically demonstrated using a genetic algorithm.Through the inclusion of the solenoid geometry as an optimization variable into the genetic algorithm,the optimum projected normalized emittance for 100 pC bunches with bunch length of 1 mm rms is reduced to 0.1 mm mrad for 100%of the particles and 0.075 mm mrad for 95%of the particles,proving that sub-100 nm emittance can be achieved in the SHINE injector using a single-cell Tsinghua University(THU)VHF gun.This emittance fulfills the requirements not only of SHINE and Linac Coherent Light Source(LCLS)-II but also of LCLS-II-High Energy(LCLS-II-HE).We demonstrate that the optimal emittance in the VHF gun injector is reduced via the optimization of the solenoid geometry,thereby reducing solenoid spherical aberration.Through the inclusion of high-order(H.O.)energy spread among the optimization objectives,the H.O.energy spread can be reduced by a factor of nearly six using a high-harmonic cavity despite a 38%emittance growth.Finally,the beam dynamics in the SHINE main accelerator show that reducing the H.O.energy spread in the injector is of great significance to improving compression efficiency and reducing bunch current spike.

关 键 词：VHF gun photoinjector Multi-objective optimization EMITTANCE High-order energy spread 

分 类 号：TL503.3[核科学技术—核技术及应用] TN248[电子电信—物理电子学]