高品质激光尾波场电子加速器

激光尾波场电子加速的加速梯度相比于传统直线加速器高了3—4个量级,对于小型化粒子加速器与辐射源的研制具有重要的意义,成为当今国内外的研究热点.台式化辐射源应用需求的提高,特别是自由电子激光装置的快速发展,对电子束流品质提出了更高的要求,激光尾波场电子加速的束流品质和稳定性是目前实现新型辐射源的首要障碍.本文归纳整理了中国科学院上海光学精密机械研究所电子加速研究团队十年来在研制台式化激光尾波场电子加速器过程中采取的方案和取得的进展.例如率先提出了注入级和加速级分离的级联加速方案,通过实验获得了GeV量级的电子束能量;基于级联加速方式利用能量啁啾控制,实验获得世界最高品质的电子束流;通过优化激光系统稳定性和特殊的气体喷流结构,获得稳定的高品质电子束流输出等.这一系列实验结果有利于进一步推进激光尾波场电子加速器的应用.

High-quality laser wakefield electron accelerator

The acceleration gradient of laser wakefield acceleration is 3–4 orders of magnitude higher than that of state-of-the-art radio-frequency accelerators,which has unique advantages in the field of electron acceleration.With the development of application fields,higher requirements are put forward for the quality of electron beams.Achieving high stability,high energy,high charge,narrow pulse width and low emittance is the direction of long-term efforts in the field of electron acceleration.This article mainly summarizes the achievements of the relevant research teams in electron acceleration from Shanghai Institute of Optics and Fine Mechanics in recent years.The energy of the electron beam based on the acceleration of the laser wakefield is mainly limited by the dephasing length and the laser pumping loss length.Aiming at the problem that the two stages of laser wakefield acceleration cannot be controlled independently and the plasma density is difficult to balance,a cascaded acceleration scheme where the injection stage and the acceleration stage are separated is proposed.The injection stage has a higher plasma density and the acceleration stage has a lower plasma density.The acceleration stage with lower density has a longer dephasing length,so that a higher acceleration can be obtained without affecting electron injection.Finally,the electron beam energy of the order of GeV is obtained in experiment.In order to obtain a higher-quality electron beam,a low-energy-spread electron beam is obtained experimentally by using energy chirp controlling.The six-dimensional phase space brightness,which simultaneously characterizes multiple qualities such as electron beam emittance,charge and pulse width,is introduced.It is hard,with high quality only,to achieve long-distance transmission of electron beams and to generate free electron lasers.For the development of free electron lasers,the transmission and modulation of the electron beam are equally important.Taking into account the need to further optimize the acceleration of electrons from generation to realization of active control,higher quality and higher stability,it is necessary to monitor the interaction process between laser and plasma in time to obtain parameter through diagnosis.We have designed and optimized a variety of diagnostic solutions suitable for electron acceleration in the laser wakefield to achieve single-shot measurement of electron beams at different positions,such as using Betatron radiation inversion to measure ultra-low emittance.The effect of laser multifilament on the quality of the generated electron beam is also discussed.