Design and fabrication of button-style beam position monitors for the HEPS synchrotron light facility

At the High Energy Photon Source (HEPS), a high orbital stability of typically 10% of the beam size and angular divergence must be achieved. The beam size at the insertion devices is 10 mu m horizontally and 1 mu m vertically, which implies that the beam orbit must be stabilized to the sub-micrometer level. This results in stringent tolerance and quality control requirements for the series production of beam position monitor (BPM) pickups. In this study, analytical formulas were used and CST simulations were performed to analyze the effects of the mechanical tolerances of BPM pickups on beam position measurement. The results of electromagnetic field simulations revealed how various mechanical errors, such as button size and location accuracy, as well as the related button capacitance, exert different influences on the beam position measurement. The performance of an actual BPM pickup was measured, along with an assessment of the error on the beam position measurement. Additionally, a wakefield analysis, including an investigation of trapped resonant modes and related thermal deformation, was conducted.