In situ beam trajectory tilt measurement based on single cavity beam position monitor

In recent decades, high-gain free-electron lasers (FELs) based on linear accelerators has been successfully developed around the world. Advanced beam diagnostics and feedback technology is one of the key factors to further improve the performance of facilities. Both beam position deviation and trajectory tilt can weaken the interaction between the electron beam and photon beam in the undulator, and seriously affect the FEL radiation performance. Existing measurement methods are not sufficient to achieve accurate measurement of beam trajectory tilt between compact undulator segments. Based on the working principle of beam-cavity, this paper proposes a method based on the measurement results of a single cavity BPM signal, which can simultaneously achieve real-time and in situ measurement of beam position and trajectory tilt, thus opening up a new way to improve the efficiency of FEL radiation. The feasibility of the scheme has been verified with the CBPM system in the Shanghai Soft X-ray FEL facility (SXFEL). The preliminary beam experiment results show that the resolution of beam trajectory tilt is better than 13.3 mu rad with a bunch charge of 100 pC.