Inhibition of microbunching instability in the Shanghai soft X-ray Free-Electron Laser User Facility.

A microbunching instability (MBI) driven by beam collective effects can deteriorate electron beam quality in advanced x-ray free electron lasers. In this paper, we demonstrate a scheme to suppress microbunching instability by adjusting the compression ratio of two-stage bunch compressor in linear accelerator of the Shanghai soft X-ray Free-Electron Laser User Facility (SXFEL-UF). The calculation of the microbunching instability gain and the mechanism of MBI suppression scheme can be revealed by the theoretical model in this paper. Numerical simulations are presented to verify the analytical results. Furthermore, benefit by the high temporal resolution of transverse deflecting structure (TDS), beam experiments for direct analysis of MBI were carried out at SXFEL-UF. Theoretical calculations as well as simulation and consistent experimental results illustrate that the suppression of microbunching instability can be achieved by increasing the first stage compression ratio of the linac in the SXFEL-UF. The feasible theme provides a promising beam optimization method for future X-FEL facilities. [ABSTRACT FROM AUTHOR]