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

这项研究计划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，激光尾流场加速器，它使用激光等离子体相互作用产生高质量的相对论电子束，脉冲持续时间极短，只有几个飞秒（百万分之几的十亿分之一秒），已经显示出巨大的进步。然而，由于表征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是未知的。 这项调查将通过使用额外的激光脉冲，与电子束相互作用的方式，电子的时间分布和它们的初始轨迹的基本信息，可以推导出。实验工作将得到理论工作的支持。低发射度、具有弱相对论束能量的几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趣的。利用激光尾流场加速可以产生这样的脉冲。然而，这种脉冲的全时间分辨的电子相空间分布在很大程度上仍然是未知的。本项目将从实验和理论上研究几兆电子伏级弱相对论电子束的注入过程和特性。低能量束允许使用与较高能量束不兼容的时间诊断。更具体地，将使用通过驻波增强的有质动力散射，该驻波具有实现1飞秒的时间分辨率的潜力。这将与束能谱仪相结合，以确定电子聚束的能量-时间相关性，从而允许对它们的6D相空间密度进行时间分辨的调查。由于聚束没有受到显著的净加速，这也将导致关于电子注入等离子体加速结构的过程的宝贵信息。通过不同的电子注入机制产生的电子聚束的属性将使用此诊断进行研究。预计这些测量将导致对激光尾流场加速背后的物理学，特别是注入过程的重要新见解。这些实验将得到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.