Design and test of a C band local oscillator and clock device in LLRF

BackgroundThe linear accelerator of Shanghai soft X-ray free-electron laser facility (SXFEL) operates at 5 712 MHz frequency. In the low level radio frequency (LLRF) system, C band microwave signals were down converted from the 5 686.556 MHz local oscillator (LO) signal to 26.444 MHz intermediate (IM) signal, and then quadruple frequency sampled by the 105.778 MHz clock signal. The stability of LO signal and clock signal can make great influence on the performance of the LLRF system.PurposeThis study aims to design and manufacture a local oscillator and clock device for satisfying the theoretical design requirements of the LLRF in SXFEL.MethodThe LO signal and clock signal were designed to be auto-correlated with the master oscillator signal. All the functional discrete device modules were installed in a shielded aluminum alloy shell, and were matched and interconnected by RF connectors after debugging and testing separately. The phase jitter integral of clock signal and LO signal, as well as the possible temperature sensitive nonlinear modules, i.e., temperature control of frequency divider and frequency multiplier, in clock Lo equipment were experimentally tested.ResultsThe experimental results show that the additional phase jitter integral of LO signal is 21.43 fs, better than the requirement of 40 fs.ConclusionsThe performance of this manufactured LO and clock device can meet the theoretical requirement of the SXFEL.