Speaker
Description
RF phase stability is important for linear accelerators, especially for high-repetition-rate free electron lasers (FELs), where phase feedback is required. Compared with direct RF field measurements, methods based on beam energy spread measurements can reflect the impact of RF perturbations on beam quality and are more suitable for feedback. Conventional screen-based destructive measurements are not applicable to high-repetition-rate operation and real-time feedback requirements. Therefore, nondestructive energy spread monitoring has been developed for RF phase feedback. A quadrupole moment measurement method based on the TM$_{220}$ mode of a rectangular RF cavity has been proposed. Using its narrowband response, high signal-to-noise ratio (SNR) measurement of the beam quadrupole moment is achieved. The monitor has been validated in beam experiments. At 350 pC, the energy spread measurement uncertainty is below $10^{-5}$, and RF phase resolution is better than 1°. Meanwhile, an eight-stripline monitor system with optimized electrode structure has also been developed for bunch-by-bunch energy spread measurements in a dispersive section. The system integrates MHz repetition-rate electronics. An online resolution evaluation method based on error propagation is proposed, enabling resolution characterization using a single monitor. Beam experiments confirm stable energy spread measurement and RF phase monitoring capability. This work provides an experimental basis for high precision RF phase feedback based on beam diagnostics.
Funding Agency
This work is supported by the National Key R&D Program of China under Contract No. 2022YFA1602201, the Quality Engineering Project for Anhui Province Higher Education Institutions No.2024yjsxxsfkc001.
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