High-brightness electron bunches, such as those generated and accelerated in free-electron lasers (FELs), can develop small-scale structure in the longitudinal phase space. This causes variations in the slice energy spread and current profile of the bunch which then undergo amplification, in an effect known as the microbunching instability. By imposing energy spread modulations on the bunch in the low-energy section of an accelerator, using an undulator and a modulated laser pulse in the center of a dispersive chicane, it is possible to manipulate the bunch longitudinal phase space. This allows for the control and study of the instability in unprecedented detail. We report measurements and analysis of such modulated electron bunches in the 2D spectrotemporal domain at the Fermi FEL, for three different bunch compression schemes. We also perform corresponding simulations of these experiments and show that the codes are indeed able to reproduce the measurements across a wide spectral range. This detailed experimental verification of the ability of codes to capture the essential beam dynamics of the microbunching instability will benefit the design and performance of future FELs.

中文翻译：

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通过时间调制的激光脉冲进行微泡不稳定性表征

高亮度电子束（例如在自由电子激光器（FEL）中生成和加速的电子束）可以在纵向相空间中形成小规模结构。这会导致切片的能量分布和束的电流分布发生变化，然后进行放大，这就是所谓的微束不稳定性。通过在加速器的低能部分中在束上施加能量扩散调制，并在分散的斜角的中心使用波荡器和调制的激光脉冲，可以操纵束的纵向相空间。这允许以前所未有的细节来控制和研究不稳定性。我们针对三种不同的束压缩方案报告了在费米FEL的2D光谱时域中此类调制电子束的测量和分析。我们还对这些实验进行了相应的模拟，并表明这些代码确实能够在很宽的光谱范围内重现测量结果。对代码捕获微束不稳定性的基本光束动力学能力的能力进行的详细实验验证将有益于未来FEL的设计和性能。