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<p>Preserving beam quality during the transport of high-brightness electron bunches is crucial for advanced accelerator applications, such as particle colliders, free-electron lasers, and recirculating linacs. However, coherent synchrotron radiation (CSR) significantly degrades beam quality when electron bunches pass through multi-bend isochronous beamlines, particularly for short bunches with non-ideal longitudinal profiles. Although several methods have been proposed to mitigate CSR effects, most rely on small-angle approximations or are limited to idealized bunch profiles. In this study, we present two improved methods for designing isochronous triple-bend achromat (TBA) beamlines that effectively mitigate CSR-induced emittance growth and longitudinal profile distortion without relying on small-angle approximations. The first method, an enhanced integral optimization approach, simplifies numerical optimization and can accurately handle larger deflection angles, making it suitable for practical applications that require flexible lattice configurations. The second method, an optimized <i>I</i>-matrix approach, completely cancels steady-state and transient CSR kicks through specific matrix constraints and higher-order dispersion optimization, enabling effective CSR suppression even with very large deflection angles. Systematic simulations demonstrate that both methods achieve excellent preservation of transverse emittance and longitudinal profiles.</p>

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Mitigating emittance and longitudinal profile degradation of non-ideal bunches caused by CSR in multi-bend deflecting beamlines

  • 期刊论文

  • 发表日期：

    2026年1月10日

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  • Xiu-Ji Chen,
  • Si Chen,
  • Hai-Xiao Deng,
  • Dong Wang

摘要

Preserving beam quality during the transport of high-brightness electron bunches is crucial for advanced accelerator applications, such as particle colliders, free-electron lasers, and recirculating linacs. However, coherent synchrotron radiation (CSR) significantly degrades beam quality when electron bunches pass through multi-bend isochronous beamlines, particularly for short bunches with non-ideal longitudinal profiles. Although several methods have been proposed to mitigate CSR effects, most rely on small-angle approximations or are limited to idealized bunch profiles. In this study, we present two improved methods for designing isochronous triple-bend achromat (TBA) beamlines that effectively mitigate CSR-induced emittance growth and longitudinal profile distortion without relying on small-angle approximations. The first method, an enhanced integral optimization approach, simplifies numerical optimization and can accurately handle larger deflection angles, making it suitable for practical applications that require flexible lattice configurations. The second method, an optimized I-matrix approach, completely cancels steady-state and transient CSR kicks through specific matrix constraints and higher-order dispersion optimization, enabling effective CSR suppression even with very large deflection angles. Systematic simulations demonstrate that both methods achieve excellent preservation of transverse emittance and longitudinal profiles.