Sub-micron resolution rf cavity beam position monitor system at the SACLA XFEL facility

Abstract: We have developed and constructed a C-band (4.760GHz) rf cavity beam position monitor (RF-BPM) system for the XFEL facility at SPring-8, SACLA. The demanded position resolution of the RF-BPM is less than , because an electron beam and x-rays must be overlapped within precision in the undulator section for sufficient FEL interaction between the electrons and x-rays. In total, 57 RF-BPMs, including IQ demodulators and high-speed waveform digitizers for signal processing, were produced and installed into SACLA. We evaluated the position resolutions of 20 RF-BPMs in the undulator section by using a 7GeV electron beam having a 0.1nC bunch charge. The position resolution was measured to be less than , which was sufficient for the XFEL lasing in the wavelength region of 0.1nm, or shorter. [Copyright &y& Elsevier]