This paper presents a method that uses a gap scan of the phase shifter to optimize the intensity of a free-electron laser (FEL) by matching its phase with that of the electron beam. Phase shifters are essential instruments especially for a long undulator line, which is segmented by drift sections. The phase-matched (in-phase), and the 180 off-set (out-of-phase) conditions are investigated using linear theory, FEL simulations, and experiments to understand how the phase shifter affects FEL optimization. We show that the FEL intensity is dominantly reduced by phase mismatch in the saturation region, where the micro-bunched electron beam is sufficiently developed, and that the difference of FEL intensity between the in-phase and out-of-phase is an effect of evolution of the bunching factor. At PAL-XFEL, the gap scan of the phase shifter at 9.7 keV increased FEL intensity by 60 to the calculation set of the phase shifter. This intensity increase was obtained dominantly in the saturation region.

中文翻译：

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利用移相器优化X射线自由电子激光器的强度

本文提出了一种使用相移器的间隙扫描来通过使自由电子激光器（FEL）的相位与电子束的相位匹配来优化其强度的方法。移相器是必不可少的工具，特别是对于长波浪线（由漂移部分分段）而言。使用线性理论，FEL仿真和实验来研究相匹配（同相）和180个偏移（异相）条件，以了解移相器如何影响FEL优化。我们显示，在饱和区域（微束电子束充分发达）中，相位失配会显着降低FEL强度，并且同相和异相之间FEL强度的差异是聚集因子的演变。在PAL-XFEL上，移相器的间隙扫描为9。7 keV使移相器的计算集的FEL强度提高了60。该强度增加主要在饱和区域获得。