Slice parameter characterization of XFEL injector

Abstract

X-ray free electron lasers (XFELs) require electron beams with a peak current of several kA and a transverse emittance below 1 mm-mrad. The uncorrelated energy spread of the beam should be as small as 0.01% of the beam energy. The beam emittance and the slice energy spread are critical parameters to determine the FEL performance together with the peak current. A photoinjector generates an electron beam satisfying the requirements. However, the uncorrelated energy spread of the beam is too small, about one keV. A beam with such a low uncorrelated energy spread may suffer from the longitudinal microbunching instability when the beam is accelerated and compressed through a linear accelerator. A laser heater system in the injector minimizes the instability growth by controlling the uncorrelated energy spread of the beam. The Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) was constructed in 2015 and the beam commissioning was carried out in the spring 2016. The injector is running routinely for the PAL-XFEL user operation. The operational parameters of the injector have been optimized experimentally. This thesis shows the numerical study of the injector parameters and the commissioning result of the laser heater system. Furthermore, the review of the present operation condition for PAL-XFEL is introduced.