Design And Experimental Study Of High-Performance Room Temperature Photocathode RF Gun

In recent years,the developement of electron accelerator-based devices such as Free Electron Laser(FEL),Ultra Fast Electron Diffraction(UED),and Ultra Fast Elec-tron Imaging(UEM)experience hypergrowth after the application of photocathode RF electron gun.Since the growth of user demand and the advancement of accelerator tech-nology,electron accelerator-based devices have developed rapidly.These applications place extremely high requirements on the emittnce and bunch length of the electron beam.Therefore,an electron gun that can produce short electron bunches and has low emittance is the core part of the development of electron accelerators,and it is also an important challenge and research hotspot.In order to improve the electron beam quality of the electron accelerator device,this article starts from the principle of emit-tance,and introduces the research of two electron gun schemes based on FEL,UED and UEM devices.The emittance in the photocathode microwave electron gun mainly includes thermal emittance,RF emittance and space charge emittance.Under a certain bunch length,a promising direction to reduce the thermal emittance and space charge emittance is to increase the acceleration gradient in the RF electron gun;a promising di-rection to reduce the RF emittance is to introduce in the RF electron gun High-frequency harmonics form a two-frequency microwave electron gun.The normal temperature RF electron guns currently used in FEL are mainly VHF band,L band and S band.Compared with the electron gun below 2856 MHz that is currently operating,the C-band frequency is 5712 MHz,so the tolerable gradient is also higher.Although domestic and foreign scientific research institutions such as INFN,THU,PSI,USTC have conducted preliminary simulations of C-band electron guns,and the results all show that C-band has great advantages in improving beam quality.However,for electron guns used in FEL,the core device parameters of C-band electron guns have not been systematically analyzed.Therefore,this paper developed a new type of 3.6 cell C-band electron gun based on the existing Shanghai Soft XFEL RF electron gun and optimized structure and technology.For the RF structure of the electron gun,the electron gun disc and aperture are optimized,the cathode plate vacuum port is added,and the RF asymmetry in the electron gun is suppressed.For the beam dynamics of the electron gun,the number of cavities and the length of the first cavity were compared,and the suppresed compensation solenoid was designed.The high-power test of the electron gun and the measurement results of the solenoid are in agreement with the simulation results.The current research on two-frequency electron guns focuses on the S-band and S-band third harmonic X-band.Due to the high cost of the X-band power source,and the problem of dual-frequency electron gun microwave power crosstalk has not been fully resolved,this paper discusses the application of the S-band and S-band second harmonic C-band two-frequency electron gun combination to UED and UEM,like low RF emittance and low flight time jitter.It has designed a two-frequency electron gun microwave structure that can solve the RF power crosstalk and RF asymmetry of the two-frequency electron gun.