Non-destructive beam energy measurement using RF cavity beam arrival time monitor

Beam energy is a key parameter for free electron laser facilities (FELs). A commonly used nondestructive sys-tem uses a beam position monitor (BPM) to measure the bunch position in a magnetic bunch compressor. At the Shanghai Soft X-ray FEL facility (SXFEL), the chicane stripline beam position method is utilized for this pur-pose. However, this method relies on the initial bunch position before entering the chicane and has a limited linear region. A different non-destructive beam energy system, which measures the bunch flight time using two cavity-based bunch arrival time monitors, has been pro-posed and tested. This paper introduces the development of this system, including design details, build-up, and measurement results. Moreover, it also covers the compar-ison between the two different bunch energy measure-ment methods from several aspects: bunch position-based and bunch flight time-based.