Phase-Space Investigation of Laser-Driven Weakly Relativistic Electron Beams

这项研究项目将测量激光和等离子体相互作用产生的相对论电子束的一些最重要的属性。新型激光驱动电子加速器有可能成为未来加速器技术的重要组成部分。特别是，激光-尾波场加速器利用激光-等离子体相互作用产生高质量的相对论电子束，脉冲宽度极短，仅为几飞秒(万亿分之一秒)，已显示出巨大的进步。然而，由于描述这些以接近光速的速度移动的极短电子脉冲的特殊挑战，它们的确切性质仍然广为人知。这项研究将通过使用额外的激光脉冲来完成，这些脉冲与电子束相互作用，从而可以推导出关于电子的时间分布及其初始轨迹的基本信息。这项实验工作将得到理论工作的支持。具有弱相对论束能的低发射度、少飞秒电子脉冲作为未来电子加速器或超快电子衍射的注入器是非常有意义的。可以使用激光尾波场加速来产生这样的脉冲。然而，这种脉冲的全时间分辨电子相空间分布在很大程度上仍然是未知的。在这个项目中，我们将从实验和理论上研究弱相对论束流能量为几兆电子伏特的激光尾波场加速电子束的注入过程和特性。相对较低的光束能量允许使用与较高能量的光束不兼容的时间诊断。更具体地说，将使用通过有可能达到1飞秒时间分辨率的驻波增强的有质动力散射。这将与束能谱仪相结合，以确定电子束的能量-时间关联，从而允许对其6D相空间密度进行时间分辨研究。由于束团没有受到显著的净加速，这也将导致关于电子注入到等离子体加速结构的过程的宝贵信息。利用这种诊断方法，我们将研究通过不同的电子注入机制产生的电子束的特性。这些测量有望对激光尾迹加速背后的物理原理，特别是对注入过程有重要的新见解。这些实验将得到细胞内粒子模拟的理论支持。

This research project will measure some of the most important attributes of relativistic electron beams produced by interactions between a laser and a plasma. Novel laser-driven electron accelerators have the potential to become an essential part of future accelerator technology. In particular, laser-wakefield accelerators, which use laser-plasma interactions to produce high quality relativistic electron beams with an extremely short pulse duration of only a few femtoseconds (a few millionth of a billionth of a second) have shown tremendous progress. However, because of the exceptional challenge of characterizing these extremely short electron pulses that move with velocities close to the speed of light, their exact properties are still widely unknown. This investigation will be accomplished through the use of additional laser pulses that interact with the electron beam in such a way that the essential information about the temporal distribution of the electrons and their initial trajectory can be deduced. The experimental work will be supported by theoretical efforts.Low-emittance, few-femtosecond electron pulses with weakly relativistic beam energies are highly interesting as injectors for future electron accelerators or for ultrafast electron diffraction. It is possible to generate such pulses using laser-wakefield acceleration. However, the full time-resolved electron phase-space distribution of such pulses is still largely unknown. In this project, the injection process and properties of laser-wakefield accelerated electron beams with weakly relativistic beam energies of a few megaelectronvolts will be studied experimentally and theoretically. The comparably low beam energy allows the use of a temporal diagnostic that is incompatible with higher-energy beams. More specifically, ponderomotive scattering enhanced through a standing wave that has the potential to achieve a temporal resolution of 1 femtosecond will be used. This will be combined with a beam energy spectrometer to determine the energy-time correlation of the electron bunches and thus allow the temporally-resolved investigation of their 6D phase-space density. Because the bunches have not been subject to a significant net acceleration, this will also lead to invaluable information on the process of electron injection into the plasma accelerating structure. The properties of electron bunches generated via different electron injection mechanisms will be investigated using this diagnostic. These measurements are expected to lead to significant new insights into the physics behind laser-wakefield acceleration and in particular into the injection process. The experiments will be theoretically supported by particle-in-cell simulations.