Coherent synchrotron radiation (CSR) is a collective effect that mainly occurs when the trajectory of an electron beam is bent in a dipole magnet. It affects the electron beam by distorting the phase space along its slice distribution, which leads to emittance growth. Therefore, CSR should be suppressed to transport electron beams without further degradation of the emittance. In linear optics, CSR-induced emittance can be suppressed by controlling the Twiss parameters along the electron-beam transfer line. However, owing to some physical constraints, transfer-line optics may be governed by higher-order terms in the transfer map, and the use of a sextupole magnet to suppress these terms would be very challenging for low-energy-spread and low-emittance beams. Therefore, without using a sextupole magnet, we estimate the region of the Twiss parameters where the first-order terms are dominant along the transfer line by introducing chromatic amplitude. In this region, we can apply the suppression condition that is valid in a linear matrix system. This minimization of the emittance growth becomes even more important when the electron-beam transfer line is used for external injection into a plasma wakefield because mismatched beam conditions could induce an additional increase in the emittance during the acceleration. In this paper, we discuss a method of emittance-growth minimization driven by the CSR effect along the transfer line, which is particularly used for electron-beam injection into plasma wakefields. In addition, using the particle-in-cell simulation, we investigate the evolution of electron beam parameters during the acceleration through plasma wakefields in the presence of the CSR effect on the electron beam. We confirm that the beam emittance growth is minimized when the CSR effect is properly controlled. Otherwise, it is found that 11%–32% emittance growths by the CSR effect along the transfer line lead to additional 20%–40% increase of the maximum slice emittance.

中文翻译：

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在电子束注入等离子体尾流场期间抑制相干同步辐射辐射引起的发射率增长

相干同步辐射（CSR）是一种集体效应，主要发生在偶极子磁体中电子束的轨迹弯曲时。它会通过沿其切片分布扭曲相空间来影响电子束，从而导致发射率增长。因此，应抑制CSR传输电子束而不会进一步降低发射率。在线性光学中，可以通过控制沿电子束传输线的Twiss参数来抑制CSR诱导的发射率。但是，由于某些物理限制，传输线光学器件可能会受到传输图中较高阶项的控制，并且使用六极磁体抑制这些项对于低能量扩散和低发射率将是非常具有挑战性的梁。因此，如果不使用六极磁铁，我们通过引入色度幅度来估计Twiss参数的区域，其中一阶项沿传输线占主导。在这个区域，我们可以应用在线性矩阵系统中有效的抑制条件。当电子束传输线用于外部注入等离子束流场时，这种最小化发射率增长变得尤为重要，因为不匹配的电子束条件可能会在加速过程中引起发射率的额外增加。在本文中，我们讨论了由CSR效应沿传输线驱动的最小化发射-增长的方法，该方法特别用于将电子束注入等离子束中。此外，使用粒子模拟 我们研究了在存在对电子束的CSR效应的情况下，通过等离子流场加速期间电子束参数的演变。我们确认，正确控制CSR效果后，光束发射率的增长将降至最低。否则，发现沿着传输线的CSR效应使发射率增加了11％–32％，从而导致最大切片发射率增加了20％–40％。