Development of high-resolution Cavity BPM systems for SHINE

摘要: The Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE), currently under construction, is poised to become one of the most advanced free-electron laser (FEL) facilities globally. Designed to generate coherent X-rays with wavelengths ranging from 0.05 to 3 nm, and a maximum repetition rate of 1MHz. SHINE requires precise beam trajectory monitoring and stable alignment of electron and photon beams within the undulator, to meet these demands, cavity beam position monitors (CBPMs) with beam pipe diameters of 35 mm for the linear accelerator (LINAC) and bunch distribution sections, and 8 mm for undulators were developed. These systems requires transverse position resolution better than 1μm and 200 nm, respectively, for a single bunch of 100 pC. This paper details the design, fabrication, and performance evaluation of the CBPM system. The beam test bench has been established at the Shanghai Soft X-ray FEL facility (SXFEL), and preliminary beam experiments have shown that, with a bunch charge about 100 pC, the position resolution of the CBPM-35mm and CBPM-8mm are better than 312 nm and 41 nm, respectively, within the dynamic range of ±1 mm and ±300 μm. These results not only align with theoretical predictions but also surpass SHINE’s operational requirements, marking the highest resolution achieved by a cavity BPM system in an FEL facility under typical operational conditions.