Design and optimization of low-emittance C-band photocathode RF electron gun

Abstract

BackgroundFree electron laser (FEL) has extremely high requirements on emittance of the electron beam. In recent years, electron guns that can produce short electron bunches and have high brightness properties have become an important challenge and research hotspot for the development of high-performance FEL.PurposeThis study aims to increase the acceleration gradient in the RF electron gun by design and optimization of the C-band photocathode of the RF electron gun.MethodsBased on Shanghai XFEL facility, a new scheme was proposed to optimize the microwave field of electron gun, design the solenoid and set the initial beam distribution in terms of space charge effect. The effect of RF gradient in the RF gun on the beam dynamic was simulated. The principle of emittance compensation was analyzed in detail. The ASTRA code was used to optimize the current ratio of the solenoid's main and auxiliary coils from the engineering point of view, and the influence of the initial bunch distribution on the emittance was investigated. [ResultsandConclusions] The results show that by optimizing the number of electron gun cavities, the current ratio between the main and auxiliary solenoid coils of the solenoid and the initial bunch distribution, the emittance of the output bunch of the electron gun is significantly improved, satisfying the low emittance requirements of the FEL light source for the electron gun.

Keywords

• photocathode
• rf gun
• emittance
• space charge force