Exploratory study of PWFA-driven FEL at CLARA

“克拉拉PWFA-FEL的探索性研究”项目将开发基于电子束驱动的等离子体尾场加速器(PWFA)的自由电子激光器(FEL)。自由电子激光是一种先进的相干光源，可以对超微小结构和超快过程进行成像。这些“发现引擎”，今天完全由直线加速器产生的电子束驱动，是STFC战略https://stfc.ukri.org/files/fel-report-2016/的主要组成部分。基于等离子体的加速器，无论是由激光尾场加速器(LWFA)中的激光脉冲驱动的，还是由等离子体尾场加速器(PWFA)中的电子脉冲驱动的，都是已知的产生短而强的高能电子束的替代加速方法。因此，它们越来越多地被认为是未来紧凑型系统中自由电子激光的驱动力。然而，众所周知，等离子体加速器的一个重大挑战是产生具有足够低发射度和能量扩散的电子束，以便在波动装置中实现激光。最近由Strathclyde/UCLA领导的“E210：特洛伊木马PWFA”合作的概念突破和在SLAC方面获得的第一个实验证据表明，PWFA可以产生发射度、能量扩散以及亮度比最先进的电子束高许多个数量级的电子束。这不仅可以使等离子体加速器的电子输出满足在自由电子激光中实现激光的严格要求，而且在发射度以及5D和6D亮度方面也比基于LCLS或欧洲XFEL的最先进的直线加速器机器高出许多个数量级。这种光束可能会产生革命性的影响，因为它们可能实现紧凑和成本效益高的自由电子激光，其性能超过现有的硬X射线自由电子激光，如LCLS或EU XFEL，包括相干阿秒级、高亮度、单尖峰硬X射线脉冲等新功能。我们的目标是在当前和即将到来的直线加速器驱动的自由电子激光之后，开发这项技术作为下一代光子源。

This project "Exploratory Study of PWFA-FEL at CLARA" will develop electron-beam driven plasma wakefield accelerator (PWFA) based free-electron-lasers (FEL). FEL's are advanced coherent light sources which allow imaging of ultrasmall structures and ultrafast processes. These 'engines of discovery', today driven exclusively by linac-generated electron beams, are a major part of the STFC strategy https://stfc.ukri.org/files/fel-report-2016/ . Plasma-based accelerators, either driven by laser pulses in laser wakefield accelerators (LWFA) or driven by electron pulses in plasma wakefield accelerators (PWFA), are alternative acceleration methods known to produce short and intense, high energy electron beams. They are therefore increasingly considered as drivers for FEL's in future compact systems. However, a well-known substantial challenge of plasma accelerators is the production of electron beams with sufficiently low emittance and energy spread in order to achieve lasing in an undulator setup. Recent conceptual breakthroughs by the Strathclyde/UCLA-led "E210: Trojan Horse PWFA" collaboration and first experimental evidence obtained at SLAC FACET suggests that PWFA can produce electron beams with emittance and energy spread as well as brightness many orders of magnitude better than state-of-the-art. This would not only allow plasma accelerator electron output to meet the strict requirements to achieve lasing in an FEL, but also to exceed the state-of-the art of the best linac-based machines such as LCLS or European XFEL by many orders of magnitude as regards emittance as well as 5D and 6D brightness. Such beams could have transformative impact, as they may allow the realization of compact and cost-effective FEL's with a performance exceeding those of existing hard x-ray FEL's such as LCLS or the EU XFEL, including novel capabilities such as coherent attosecond-scale, high brilliance, single-spike hard X-rays pulses. We aim to develop this technology as a next-generation photon source for the time after current and upcoming linac-driven FEL's.