TW Laser system for Thomson scattering X-ray light source at Tsinghua University

A TW (Tera Watt) laser system based on Ti:sapphire mainly for the Tsinghua Thomson scattering X-ray light source (TTX) is being built. Both UV (ultraviolet) laser pulse for driving the photocathode radiofrequency (RF) gun and the IR (infrared) laser pulse as the electron-beam-scattered-light are provided by the system. Efforts have also been made in laser pulse shaping and laser beam transport to optimize the high-brightness electron beam production by the photocathode RF gun.     

TW Laser system for Thomson scattering X-ray light source at Tsinghua University

A TW (Tera Watt) laser system based on Ti:sapphire mainly for the Tsinghua Thomson scattering X-ray light source (TTX) is being built. Both UV (ultraviolet) laser pulse for driving the photocathode radio-frequency (RF) gun and the IR (infrared) laser pulse as the electron-beam-scattered-light are provided by the system. Efforts have also been made in laser pulse shaping and laser beam transport to optimize the high-brightness electron beam production by the photocathode RF gun.     

Preliminary experiment of the Thomson scattering X-ray source at Tsinghua University

The X-ray source based on Thomson scattering of ultrashort laser pulse with a relativistic electron beam is a means of generating a tunable, narrow bandwidth and ultrashort pulse of hard X-rays. Such a sub-picosecond hard X-ray source is proposed at Tsinghua University, and a preliminary experiment with a 16 MeV Backward Traveling electron linac and a 1.5 J, 6 ns Q-switched Nd:YAG laser is carried out first. A 6 ns pulse X-ray with a peak energy of 4.6 keV and an intensity of 1.7×104 per pulse is generated successfully in the experiment. The experimental setup, result and discussion are reported in this paper.     

汤姆逊硬X射线源中锁模脉冲激光稳频方法

 汤姆逊硬X射线源中，光阴极微波电子枪要求触发激光脉冲与腔中微波场相位的精确时间同步。理论分析了锁模脉冲激光器相位噪声，探讨了对激光脉冲相位探测和控制的方法，并通过实验构建了激光相位抖动测量系统和锁相环稳频回路，用基频鉴相信号驱动压电陶瓷晶体改变谐振腔长，实现了从开环3.42 ps到闭环1.46 ps的均方根相位抖动的测量和控制。     

清华大学汤姆逊散射超短脉冲X射线源研究

 介绍了清华大学加速器实验室近年来关于汤姆逊散射超短X射线源的研究工作;研究了在任意散射角度下电子束参数和激光束参数对散射光子参数的影响,给出了散射光子的参数如光子产额、脉冲长度、时间抖动等与电子束参数、激光束参数和散射角度的关系;利用实验室已有的16 MeV反波行波加速器与中国工程物理研究院激光聚变研究中心提供的ns调Q激光搭建了汤姆逊散射初步实验平台并开展了实验研究;加工了1.6-cell光阴极微波电子枪,搭建了高功率实验平台,对产生的电子束参数进行了初步测量;对汤姆逊散射超短X射线源进行了设计并开展了相关的平台建设工作,对产生的X射线脉冲参数进行了模拟。     

激光同步辐射作为阿秒X射线辐射源的特性研究

 研究了逆流相对论电子与激光脉冲相互作用获得激光同步辐射的频率上移、微分散射截面等特性。发现逆流相对论电子与短脉冲激光相互作用，可以获得阿秒X射线辐射脉冲。短脉冲激光条件下得到的后向散射光的频率上移与长脉冲激光条件下得到的后向散射光的频率上移是完全一致的，同时发现随着入射电子初始能量的增加，散射光的准直性越来越好，后向散射光脉冲的脉宽越来越短。     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough.A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform.In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance.With the uniform driving laser and the unbalanced RF gun,the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm.mrad.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that ...     

A simulation study of Tsinghua Thomson scattering X-ray source

Thomson scattering X-ray sources are compact and a?ordable facilities that produce short duration, high brightness X-ray pulses enabling new experimental capacities in ultra-fast science studies, and also medical and industrial applications. Such a facility has been built at the Accelerator Laboratory of Tsinghua University, and upgrade is in progress. In this paper, we present a proposed layout of the upgrade with design parameters by simulation, aiming at high X-ray pulses flux and brightness, and also enabling advanced dynamics studies and applications of the electron beam. Design and construction status of main subsystems are also presented.     

电子束放射照相的特性与参数优化

短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点, 在放射照相诊断中具有独特作用. 本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟, 研究了100 keV到几百MeV能量电子束对有厚度起伏或存在界面的靶的透视, 并与质子、X射线束透视结果比较, 给出了电子束放射照相的特性与参数优化: 基于电子在材料中非弹性散射或能量损失, 选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性; 基于电子在材料中的弹性散射, 选用射程超过靶厚度的电子束来诊断靶界面.     

汤姆逊散射X射线源初步实验中电子束参数测量及其对X射线性能影响的研究

为了准确计算和分析汤姆逊散射X射线源初步实验中产生的X射线参数, 对实验中所用的16MeV返波行波加速器产生的电子束参数进行了测量. 并通过模拟程序计算和分析了在该参数下初步实验中产生的X射线的参数.     

基于汤姆逊散射的X射线光源的物理问题研究

针对汤姆逊散射X射线光源,推导了任意散射角下出射X射线的时间结构、产额,分析了位置和同步偏差、发射度、能散等非理想因素的影响.     

基于激光尾场加速的自反射式全光汤姆孙散射的参数优化

基于激光尾场加速的全光汤姆孙散射能够提供高质量X射线束并大大减小装置的尺寸.与分光式相比,自反射式的构架可以降低实验的时空同步难度,但是由于激光尾场电子加速和汤姆孙散射过程耦合, X射线优化难度大,目前缺乏参数优化的相关报道.本文用数值模拟修正解析理论的方法,定量分析了激光尾场电子加速和汤姆孙散射过程中激光和电子束的焦斑、脉宽、能量等参数变化情况,并给出了激光在等离子体镜上的反射率,从而实现了用解析公式计算而非数值模拟跟踪参数变化,在保证精度的同时节约了计算时间.另外,利用修正后的公式优化了给定激光条件下的自反射式全光汤姆孙散射X射线,通过改变等离子体密度和等离子体镜位置这两个参数给出了最优X射线亮度和光子产额,该方法为将来结合人工智能优化控制全光汤姆孙散射光源提供了理论基础.     

上海激光康普顿散射伽马源的发展和展望

激光康普顿散射(Laser Campton Scattering, LCS)光源,是一种基于相对论电子束与激光光子相互作用的新型X-ray或Gamma-ray光源。它具有能量高、波长短、脉冲快和峰值亮度高的特性,已成为国际先进光源技术的重要选项之一。本文介绍了激光康普顿散射光源的产生原理、国内外发展现状以及目前国际上运行和在建的激光康普顿散射光源装置,其中重点介绍了上海光源二期正在建设的上海激光电子伽马源(Shanghai Laser Electron Gamma Source, SLEGS)装置,以及在这一光源装置上可以开展的核物理、核天体物理、核废料处理及核医学应用等研究。随着上海软X射线自由电子激光试验装置(Soft X-ray Free Electron Laser, SXFEL)升级为用户装置,以及未来十三五国家重大科技基础设施-硬X射线自由电子装置(Shanghai HIgh repetition rate XFEL aNd Extreme light facility,SHINE)的建设完成,基于直线电子加速器(LINear ACcelator, LINAC)的康普顿散射光源的伽马能量将会达到GeV量级的高能量。超短脉冲、高极化度、高通量的激光康普顿散射光源将迎来新的发展机遇,基于康普顿伽马光源的核物理、天体物理、粒子物理及应用基础研究也必将迈上一个新台阶。     

紧聚焦激光束作用于电子实现单个阿秒脉冲输出

研究了电子在聚焦的圆偏振高斯激光束中的非线性汤姆孙散射过程，在此基础上提出了实现单个阿秒脉冲输出的新机理.通过计算机模拟，发现利用紧聚焦的激光脉冲可以有效地增大辐射脉冲链的最高峰和次高峰的峰值强度比即信噪比，从而将阿秒脉冲链变为单个阿秒脉冲输出.紧聚焦情形下，随着驱动激光强度的增大，辐射信号的脉宽变短，信噪比变大；同时当减小激光束腰半径时，辐射信号信噪比也能得到有效改善.研究还发现，利用几个光周期的极短激光脉冲与电子的相互作用也能实现单个阿秒脉冲输出. 关键词： 阿秒脉冲 紧聚焦 信噪比     

全光汤姆逊散射X光源数值模拟

 使用蒙特卡罗数值模拟程序研究了不同电子束和激光强度下,尾场电子束与超短脉冲激光发生汤姆逊散射获得的X光子能谱、角分布等,初步探索了180°散射下高质量X射线光源所需要的电子束与激光强度。数值模拟结果显示,为了尽量提高光子产额并抑制非线性效应,激光归一化强度应为1的量级。为了获得方向性和单色性好、亮度高的X射线脉冲,需要较高的电子能量和较小的电子能散,电子束脉冲尽量短,且发散角尽量小。     

RF deflecting cavity for bunch length measurement in Tsinghua Thomson scattering X-ray source

An RF deflecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source.The cavity is a 2856 MHz,π-mode,3-cell standing-wave cavity,to diagnose the 3.5 MeV beam produced by photocathode electron gun.With a larger power source,the same cavity will again be used to measure the accelerated beam with energy of 50 MeV before colliding with the laser pulse.The RF design using MAFIA for both the cavity shape and the power coupler is reviewed,followed by presenting the fabrication procedure and bench measurement results of two cavities.     

Thomson scattering from ultrashort and ultraintense laser pulses

The Thomson scattering in an ultraintense ( approximately 10(18) W cm(-2)) and ultrashort (20 fs) laser field is calculated that demonstrates different characteristics from those of the low-intensity field case. The electron trajectory no longer conforms to a figure-eight pattern, and the spectra demonstrate complex shifting and broadening to suggest that Thomson scattering can be used for characterizing pulsed lasers. The initial phase at the electron entrance of the field can critically affect the Thomson scattering, but its effect is weighted by the intensity profile of the field. As a result, the fourfold symmetry of the radiation pattern breaks down when the electron enters the field closer to the pulse peak. The relationship between the Thomson scattering and Compton scattering in the high field is analyzed.     

SASE自由电子激光

 SASE自由电子激光可以产生短至0.1nm的高亮度（峰值亮度比当前的第三代同步辐射高10个量级;平均亮度高3~5个量级）、短脉冲（脉冲长度小于2个量级、达到亚皮秒水平）硬X射线相干光。因而被称为是继第三代同步辐射之后的第四代光源。SASE依据的是高增益自由电子激光原理,利用了光阴极微波电子枪技术和电子直线加速器技术。综述了SASE的历史发展、基本原理、基本结构、主要物理特征和对电子束的要求。     

Increasing the RF energy per pulse of an RKO

The Air Force Research Laboratory RKO source has recently demonstrated the ability to convert electron beam power to RF power until the termination of the electron beam pulse, achieving a power of 1.5 GW at an energy of 170 J. These results represent an increase in power of 25-30% in power and energy extracted from this source. This paper discusses the principal research areas encountered in lengthening the RF pulse (FWHM) from 50 ns to the present 120 ns and the associated increase in the RF energy