标题： 通过欧洲X射线自由电子激光器的自注入产生变换极限X射线脉冲 显示英文标题

标题： Production of transform-limited X-ray pulses through self-seeding at the European X-ray FEL

摘要： 任何先进的X射线自由电子激光器的重要目标是提供傅里叶限制的X射线脉冲。 这样，在实验大厅中不需要单色仪。 自种子技术是一种有前景的方法，可以显著缩小SASE带宽，产生接近变换限制的脉冲。 这些脉冲对于许多实验，包括三维衍射成像非常重要。 我们讨论了在欧洲XFEL的硬X射线线路上实现单晶体自种子方案。 对于该设施，变换限制的脉冲特别有价值，因为它们通过利用可调间隙基线波荡器的锥形结构，自然支持比饱和时提取更多FEL功率。 锥形结构包括从一段到另一段的波荡器间隙的分步变化。 基于处理欧洲XFEL最新参数的端到端模拟，我们显示FEL功率可达约400 GW，比SASE饱和水平（20 GW）高一个数量级。 此分析表明，我们的自种子方案不会受到非理想的电子相空间分布的显著影响，并且在电子束具有理想参数的情况下表现出相似的性能。 使用单晶体单色仪的自种子方案非常紧凑（约5米长），成本估算足够低，足以考虑在欧洲XFEL运行阶段开始时就将其添加到其能力中。 显示英文摘要

摘要： An important goal for any advanced X-ray FEL is an option for providing Fourier-limited X-ray pulses. In this way, no monochromator is needed in the experimental hall. Self-seeding is a promising approach to significantly narrow the SASE bandwidth to produce nearly transform-limited pulses. These are important for many experiments including 3D diffraction imaging. We discuss the implementation of a single-crystal self-seeding scheme in the hard X-ray lines of the European XFEL. For this facility, transform-limited pulses are particularly valuable since they naturally support the extraction of more FEL power than at saturation by exploiting tapering in the tunable-gap baseline undulators. Tapering consists of a stepwise change of the undulator gap from segment to segment. Based on start-to-end simulations dealing with the up-to-date parameters of the European XFEL, we show that the FEL power reaches about 400 GW, or one order of magnitude higher power than the SASE saturation level (20 GW). This analysis indicates that our self-seeding scheme is not significantly affected by non-ideal electron phase-space distribution, and yields about the same performance as in the case for an electron beam with ideal parameters. The self-seeding scheme with a single crystal monochromator is extremely compact (about 5 m long), and cost estimations are low enough to consider adding it to the European XFEL capabilities from the very beginning of the operation phase.