Mains-Synchronized Timing Trigger for Stability Enhancement in FEL Pulsed Microwave Systems
Pulsed microwave stability in linear accelerators (LINACs) is critical for maintaining high-quality electron beams in synchrotron radiation and free-electron laser (FEL) facilities. This study establishes and validates a zero-crossing synchronization strategy to suppress mains-induced disturbances in the Dalian Coherent Light Source (DCLS) accelerator. Through comprehensive numerical simulations at 10 Hz, 20 Hz, and 25 Hz repetition rates, we first demonstrate the temporal evolution of microwave amplitude perturbations under mains power disturbances. Experimental validation with the digital Low-Level Radio Frequency (LLRF) system reveals a substantial similarity between simulated and measured interference patterns, confirming the susceptibility of the klystron output to mains power modulation. The developed synchronization technique integrates real-time mains zero-crossing detection with precision timing sequence generation, effectively decoupling the microwave system from power frequency fluctuations. It achieves remarkable inter-pulse stability improvements, reducing microwave amplitude fluctuation from ~0.30% RMS to 0.07% RMS. This approach not only addresses the inherent bandwidth limitations of conventional proportional-integral-derivative (PID) controllers in low-repetition-rate accelerators but also provides a solution for troubleshooting power-related instabilities in advanced light source facilities.