激光尾波场加速器产生超短电子束团能量啁啾诊断相关研究

Laser Wakefield Accelerator (LWFA), which is a compact accelerator for charged particles, witness a rapid development in the last decades. But there are still many challenges which hinder the further application of particle beams from a LWFA, for example, the energy spread and the stability of the electron beams from a LWFA are inferior to a conventional accelerator, this is caused not only by the intrinsic instability of laser, electron beams and plasma in a LWFA, but also by the fact that the present diagnostic techniques of the electron beams in a LWFA could not offer accurate description of some important parameters such as the phase space distribution of the generated electron bunch. While the phase space distribution, which determines the electron bunch evolution in plasma and propagation in vacuum, is crucial for parameters optimization and transmission control for a LWFA. According to these research background, we plan to investigate the physics of the interaction between a tightly focused chirped laser pulse and a chirped electron bunch in this project, and diagnose the phase space distribution of the electron bunch from a LWFA. Further experiments to verify this mechanism is included, and optimization of the injection and acceleration processes in a LWFA is designed as well as the electron beam transmission control. These work would lay the foundation for the new type of ultrashort and multicolor beam sources based on plasma, and promote the further development of laser wakefield accelerator.

激光尾波场电子加速是一种全新的紧凑型电子加速方案。虽然激光尾波场加速器在最近十几年发展迅猛，但目前依然面临许多问题，如产生电子束团的能散和稳定性等都不如传统加速器，这极大地制约了激光尾波加速器的许多潜在应用，如自由电子激光。这一方面是由激光、电子束及等离子体的各种不稳定性所致，另一方面也是由针对尾波及被加速电子束团的参数诊断及控制技术的不完善所致，如电子束团的相空间分布，目前还不能获得准确的诊断，而实现电子束团的相空间分布诊断不论是对于电子束团在等离子体内的行为优化还是电子束团的传输控制来说都至关重要。基于以上背景，本项目拟通过啁啾脉冲激光来诊断激光尾波场加速器产生电子束团的能量啁啾分布，进而得到电子束团的瞬时相空间分布，在实验上验证这种诊断方法，实现激光尾波场加速器产生电子束团的品质优化和传输控制，为基于等离子体的新型超短、多色束线源等重要应用提供基础，推动激光尾波场加速器的进一步发展。

为了实现稳定可应用的紧凑型电子加速器及基于此类加速器的小型化次级束线源，如X射线自由电子激光和超快电子衍射，需要对电子束各个阶段的瞬态相空间分布进行严格诊断和控制，但目前为止，此类电子束的瞬态能量啁啾分布尚不能获得有效诊断。本项目针对如何实现超短电子束瞬态能量啁啾重建这一目标展开研究，在理论上基于紧聚焦脉冲激光和电子的相互作用发展了适用于典型线性及非线性啁啾情况下的电子束瞬态啁啾重建方法，并可实现束源间延时的精确诊断，该方案稳健且容易实现，可应用于等离子体加速器的优化和超快电子衍射时间抖动监测，且时间分辨率可达到阿秒级，这使紧凑型等离子体加速器得优化和控制更容易实现，对于加速器物理和超快物理的发展来说都具有非常重要的科学意义；在实验上进一步将啁啾控制的思路运用到高品质及高能电子束的产生过程中，分别得到了千分级能散的高品质和3.2 GeV高能量电子束输出，进一步将产生的高品质电子束运用于次级辐射源的产生实验中，我们验证了基于等离子体加速器的小型化自由电子激光产生的可行性，这为紧凑型X射线自由电子激光及其广泛应用的发展铺平了道路。