Optimization of Beam Arrival and Flight Time Measurement System Based on Cavity Monitors at the SXFEL

Abstract

To fully optimize the operation of a high-gain free-electron laser (FEL) facility and to offer opportunities for time-resolved experiments, a highly accurate synchronization between an electron bunch and a seeded laser is required. Thus, a high-precision and high-resolution beam arrival and flight time measurement system is built at the Shanghai soft X-ray FEL (SXFEL) facility. For the SXFEL, a beam arrival time resolution better than 100 fs is required. A phase cavity-based detection scheme for this measurement has already been adopted at the SXFEL. To further optimize system performance, the impacts of clock jitter, trigger jitter, and signal analysis length on the measurement uncertainties are analyzed, and related subsystems are upgraded and optimized accordingly. The beam arrival time is successfully measured, and the initial measurement uncertainty is better than 45 fs. Furthermore, a dual-cavity mixing scheme is realized to measure the beam flight time or pseudo-beam arrival time, and the measurement resolution of the beam flight time using this technique is 13 fs.