Bunch-by-bunch position measurement with sub-micron resolution at nanoseconds separation using wideband cavity beam position monitors

We developed a wideband RF cavity beam position monitor (CBPM) with a 217 MHz bandwidth centered at the 4.875 GHz dipole mode frequency as part of the preliminary research for a high-repetition-rate hard x-ray free electron laser project at the Chinese Academy of Engineering Physics. This paper presents new results demonstrating bunch-by-bunch position measurements on electron bunches spaced by 2.3 ns (4 bunches per train). Over a measurement range of ∼100 μm, this wideband CBPM achieved a spatial resolution of 0.8 μm at a bunch charge of 80 pC. Position and tilt variations between bunches on the order of 10 μm and 10 μrad, respectively, were clearly resolved. This high spatial and temporal resolution provides a valuable tool for experimental studies on long-range wakefield effects in multi-bunch operational light sources.