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Description
Beam stability in the FCC-ee collider is critically influenced by both transverse and longitudinal beam coupling impedance. The development of a flexible and comprehensive impedance model is essential for accurately evaluating and mitigating instabilities as machine parameters evolve.
The collimation system has been identified as a dominant contributor to the total machine impedance. This study provides a detailed investigation into its impact on the overall impedance budget of the FCC-ee and explores potential optimization strategies to mitigate its effects and improve beam stability.
Both resistive and geometric impedance contributions are systematically analyzed, with geometric effects found to play a particularly significant role in shaping the overall impedance landscape. A simplified model was used to isolate geometric and resistive wall dependencies. Despite its simplicity, this model accurately represents the actual jaw lengths and apertures and effectively highlights critical parameters that can be optimized to reduce impedance.
Continued improvements in the modelling of collimators’ geometric impedance are fundamental for assessing beam stability. Having a flexible and accurate model enables global impedance considerations, supports and easily incorporates further optimization solutions, and informs critical design decisions by accounting for interactions among various accelerator components.
