Article title: The MING proposal at SHINE: Megahertz cavity enhanced X-ray generation

文章标题：MING@SHINE：兆赫兹谐振腔增强X射线产生

DOI: doi.org/10.1007/s41365-022-01151-6

One sentence summary:

一句话概要：

The Megahertz cavIty enhanced X-ray generation (MING) has been designed and planned to be set up in China’s first hard X-ray free-electron laser (XFEL) facility i.e. SHINE.

本研究基于国内首台硬X射线自由电子激光用户装置SHINE，设计了谐振腔运行模式，提出兆赫兹谐振腔增强X射线产生（MING）的提案。

The Novelty (What)

创新性（主要内容）

This study thoroughly proposed the design of Megahertz cavIty eNhanced x-ray Generation (MING) which was meant to be set up in China’s first hard X-ray free-electron laser (XFEL) facility i.e. SHINE. The proposal covers crucial topics like principles and performance of MING, key components of MING, as well as X-ray transport and diagnostics. MING will be equipped with an undulator of period 26 mm and crystal cavity, covering the energy range of 6–15 keV. Moreover, MING will be able to generate X-ray with pulse bandwidth of a few tens of meV, while the pulse energies can achieve 300 µJ, corresponding to the spectral brightness increased by 2-3 orders of magnitude. Besides producing high-intensity fully coherent X-rays, MING allows for full control of the polarization of X-rays and can also deliver orbital angular momentum (OAM) light, indicating its superb scalability. To-date, the first cavity-based XFEL facility is yet to be completed. Therefore, the proposal of MING would definitely broaden scientists’ horizon on cavity-based XFEL’s potential and applications, leading to groundbreaking discoveries.

本研究针对我国第一台硬X射线自由电子激光(XFEL)装置SHINE，提出了兆赫兹谐振腔增强X射线产生(MING)的设计，并进行了深入的研究。 该提案涵盖了诸如MING的原理和性能、MING的关键部件以及X射线传输和诊断等关键主题。 MING将配备周期为26毫米的波荡器和晶体谐振腔，涵盖6-15 keV的光子能量范围。 此外，MING将能够产生光谱带宽仅几十meV的X射线，同时脉冲能量可以达到300 μJ，对应光谱亮度将提高2-3个数量级。 除了产生高强度的全相干X射线，MING还允许操控X射线偏振、产生轨道角动量(OAM)光等，具有极高的可扩展性。 到目前为止，国际上没有一个基于谐振腔的XFEL装置建成。 因此，MING的建立有望为科学家们探索谐振腔型XFEL的潜力和应用提供新的视野，产生开创性的发现。

The Background (Why)

研究背景（主要原因）

X-ray free-electron laser (XFEL) is a new generation X-ray source which facilitates the rapid progress of multiple research areas. SHINE (China’s first hard XFEL facility), an 8 GeV high-repetition-rate XFEL facility equipped with a continuous-wave (CW) superconducting radio frequency linear accelerator (RF linac), was proposed to be set up in Shanghai in 2017 and estimated to be complete in 2025. Despite being foreseen to deliver brilliant, nearly fully transversely coherent, and ultra-short X-ray pulses, scientists are also aware of its low longitudinal coherence and poor stability. Although the self-seeding technique (for hard X-ray regime) could overcome the problems, high intensity jitter might take place because self-seeding schemes are based on self-amplified spontaneous emission (SASE). Nonetheless, since SHINE will be providing 8 GeV electron bunches at ∼ 1 MHz, it bears the potential to operate a cavity-based XFEL (e.g. XFELOs and RAFELs) which produces fully coherent laser-like X-ray pulses. In order to materialize that within the context of SHINE, this study planned and proposed the design of Megahertz cavIty enhanced X-ray generation (MING) for generating X-rays in the energy range of 6–15 keV. With the optimum design and parameters, MING was predicted to be the key to push the performance of SHINE to a new level.

X射线自由电子激光(XFEL)是新一代X射线光源，它为多个领域的前沿研究的提供了全新的手段。 SHINE是国内首台硬X射线FEL装置，将装备8 GeV的配连续波(CW)超导射频直线加速器（RF LINAC），可以提供高重复频率高达MHz 的 X射线FEL脉冲。SHINE于2017年在上海开始建设，预计2025年建成。 SHINE基于自放大自发射(SASE)模式，能提供高亮度、几乎完全横向相干的短X射线脉冲，但也意识到它的纵向相干性和稳定性较差。 尽管硬X射线自种子技术可以克服纵向相干性差的问题，但由于自种子方案是基于SASE模式，因此其脉冲能量的抖动非常大。由于SHINE将在大约1 MHz的频率下提供8 GeV的电子束，它非常有希望运行谐振腔型XFEL（例如X射线FEL振荡器和再生放大型FEL)，以产生完全相干的类似激光的X射线脉冲。 为了在SHINE的背景下实现这一目标，本研究计划并提出了兆赫兹谐振腔增强X射线产生(MING)的设计，用于产生6～15keV能量范围内的全相干X射线。 通过优化设计和参数，MING有望将SHINE性能提升到全新的水平。

The SDG impact (Big Why)

SDG影响力（研究意义）

One of the ultimate goals of XFEL is to generate fully coherent pulses and the cavity-based FEL is a promising candidate to achieve this goal. Thus, cavity-based FELs could potentially bring tremendous advancement to various research fields including atomic and molecular science, photon science, and advanced materials. The realization of MING@SHINE will be a remarkable milestone in the evolution of XFELs and, hence, this study is well-aligned with UNSDG 9: Industry, Innovation & Infrastructure.

XFEL的终极目标之一就是产生完全相干的脉冲，而谐振腔型FEL是实现这一目标的非常有希望的候选方案之一。 凭借其优异的性能，谐振腔型自由电子激光有望为原子分子科学、光子科学和先进材料等领域带来巨大的发展。也可以预见，实现MING@SHINE这将是XFEL发展过程中的一个显著里程碑，因此，本研究符合UNSDG9：工业、创新和基础设施。