Comprehensive Analysis of Transverse Gradient Undulator for Compact X-Ray FELs based on Laser Plasma Accelerators

大规模射频加速器驱动的x射线自由电子激光器（FELs）彻底改变了我们捕捉运动中的原子和分子图像的能力。等离子体加速是一项尖端技术，它能以比传统加速器快一千多倍的速度加速电子。特别是，激光等离子体加速器正引领着自给式紧凑型加速器和光源的发展。该奖项将研究一种基于激光等离子体加速器生产极紫外和x射线自由电子激光器的新方法。这一进展将用于开发激光等离子体加速器在紧凑和相干辐射源中的实际应用。该奖项还将支持斯坦福大学研究生的培训，使他们参与先进光束和自由电子激光理论和模拟工具的开发。激光等离子体加速器（LPAs）已经显示出利用高强度激光在厘米级等离子体中相互作用，将电子束从静止加速到几GeV的能力。虽然光束具有相对较低的发射度和较高的峰值电流，脉冲持续时间只有几个飞秒，但光束的能量传播比传统射频加速器的传播大两个数量级。如此大的能量扩散会使正常波动中的FEL相互作用变得非常无效。如果电子能量与其在横向梯度波动器中的位置相关，则可以利用横向梯度波动器来补偿电子束能量扩散的影响。以往的理论和数值研究表明，这样的概念可以大大提高LPA FEL的性能。该合同将通过研究具有所需光学特性的LPA到TGU内部的光束传输和动力学，以及通过开发考虑TGU中各种效应的FEL仿真工具，将这一概念付诸实践。为了验证结果，在适用的情况下，将通过外部合作与TGU实验进行比较。

Our capabilities to capture images of atoms and molecules in motion have been revolutionized by X-ray free-electron lasers (FELs) driven by large-scale radio-frequency accelerators. Plasma acceleration is a cutting-edge technique that accelerates electrons more than a thousand times faster than these conventional accelerators. In particular, laser-plasma accelerators are leading the way toward self-contained compact accelerators and light sources. This award will investigate a novel way to produce extreme ultraviolet and X-ray free-electron lasers based on laser-plasma accelerators. The advancement will be used to develop practical applications of laser-plasma accelerators in compact and coherent radiation sources. The award will also support the training of graduate students at Stanford University, engaging them in the development of advanced beam and free-electron lasers theory and simulation tools. Laser-plasma accelerators (LPAs) have shown the abilities to accelerate electron beams from rest up to a few GeV using high-intensity lasers interacting in centimeter-scale plasmas. Although the beams have relatively low emittance and high peak current with only a few femtosecond pulse duration, the beam energy spread is two orders of magnitude larger than the spread from conventional radio-frequency accelerators. Such a large energy spread can make the FEL interaction in a normal undulator very ineffective. A transverse gradient undulator (TGU) can be used to compensate the effects of beam energy spread if the electron energy is correlated with its transverse position in the TGU. Previous theoretical and numerical studies have shown that such a concept may drastically improve the LPA FEL performance. This award will take the concept to practice by studying beam transport and dynamics from a LPA to and inside a TGU with the desired optics properties, and by developing FEL simulation tools that take into account various effects in a TGU. For verification of results, comparisons will be made, where applicable, to TGU experiments through external collaborations.