The Investigation of Thermal Plasma-Loaded Free-Electron Laser: Linear Analysis

The dispersion equation of thermal plasma-loaded FEL is derived employing linear fluid theory. The characteristic of this thermal plasma FEL is analyzed in detail. FEL growth rate varying with plasma density and plasma temperature is investigated. We find there is an optimum plasma temperature where FEL growth rate can be enhanced considerably. The FEL growth rate is decreased accompanying plasma density raising.     

填充等离子体的切伦柯夫自由电子激光的理论分析

本文用磁流体理论研究了柱形波导填充等离子体的切伦柯夫自由电子激光器，表明该系统比普通切伦柯夫自由电子激光具有更高的工作频率和线性增长率。发现在入射电流和波导结构一定时，该系统和普通切伦柯夫自由电子激光器的增长率并不是随随电子束与介质的间距的增加而减小，而是存在一个最佳值。     

带Wiggler场平板型部分填充介质CFEL的切仑柯夫自由电子激光的动力学耦合模理论

用二维波动力学耦合模理论研究了带Wiggler场平板型部分填充介质的FEL。研究结果表明,该系统可用低能电子束产生对介质厚度无特殊要求的短波长FEL。适当选择参数,可使其增长率和效率高于普通自由电子激光和切仑柯夫自由电子激光,并证明本系统超辐射放大的工作主模应是纵向截面电场模。     

Echo-enabled谐波放大自由电子激光参数

通过数值模拟,结合解析计算分析,研究了Echo-enabled谐波放大自由电子激光对装置参数和主要束流参数变化的独立敏感性,给出了谐波聚束因子和饱和功率随参数变化的数值模拟结果;对色散段由相干同步辐射效应引起的能散和发射度增长进行了估算和数值模拟。结果表明:相干同步辐射效应引起的切片能散和切片发射度增长在5%以内,对最后辐射影响不大。     

Effects of Background Plasma on Free Electron Laser with Planar Wiggler

Dispersion equation of planar-wiggler free-electron laser with background plasma is derived using linear fluid theory. The characteristic of this plasma FEL is analyzed in detail. It is shown that reasonable background plasma density tends to improve FEL growth rate. We also find there exits a critical plasma density for FEL operating. When the background plasma density is higher than critical density, the FEL can no longer be excited.     

Effects of self-fields on dispersion relation and growth rate in two-stream electromagnetically pumped free electron laser with axial guide magnetic field

A theory for a two-stream free-electron laser （FEL） with an electromagnetic wiggler （EMW） and axial guide magnetic field is developed. In the analysis, the effects of self-fields are taken into account. The growth rate is derived. The characteristics of the growth rate are studied numerically. The dependence of the normalized wave number, which corresponds to the maximum growth rate, on the cyclotron frequency is presented. The comparisons between the normalized maximum growth rate and its corresponding wave number normalized by employing the axial magnetic field, for the cases with and without self-fields in the two-stream FEL are studied numerically.     

Linear Theory of Free Electron Laser with a Plasma-Loaded Cylindrical Waveguide

The dispersion characteristics of plasma–loaded free-electron laser has been analyzed using linear fluid model. The device under consideration consists of the cylindrical metallic waveguide, completely filled with background plasma and a relativistic electron beam which passes through a helical wiggler magnetic field. The result predicts that reasonable plasma density tends to improve the growth rate of the low-frequency optical wave of FEL and causes an shiftup in the operating frequency, However it has little effect on the growth rate of the high-frequency wave. In the plasma–loaded FEL, for the FEL oscillator, it may be tuned by varying the plasma density; and for the FEL amplifier, the wider frequency bandwidth is gained. A critical density n ^c _p for the background plasma density is found.     

曙光一号自由电子激光装置的设计研究

曙光一号自由电子激光装置(SG-1 FEL)是一台高功率毫米波段自由电子激光放大器,它由3.5MeV直线感应加速器、电子束调制系统、变参数摇摆器和微波种子源等部件组成。本文扼要叙述了SG-1 FEL的物理设计和主要技术参数,并重点分析了各主要部件的实验研究、计算模拟,以及物理设计和结构的特点。     

Performance study of a soft X-ray harmonic generation FEL seeded with an EUV laser pulse

The performance of a free electron laser (FEL) using a low-power extreme ultraviolet (EUV) pulse as an input seed is investigated. The parameters are appropriate for 30 nm seeds produced from high-power Ti:Sapphire pulses using high harmonic generation schemes. It is found that, for reasonable beam parameters, robust FEL performance can be obtained. Both time-independent and time-dependent simulations are performed for varying system parameters using the GENESIS simulation code. A comparison is made with a two-stage harmonic FEL that is seeded by a high-power Ti:Sapphire pulse.     

Instability of Two-stream Free-electron Laser with an Axial Guiding Magnetic Field

A model of two-stream Free-Electron Lasers (FEL) with an axial guiding magnetic field (AGMF) is proposed and investigated in this paper. The dispersion relation is derived employing linear fluid theory. The characteristics of dispersion relation are analyzed in detail by numerical solutions, which show that the growth rate can be considerably enhanced and the operation frequency is significantly broader with the suitable of AGMF, separation velocity and beams’ relative density factor, and the occurrences of two-stream instability in FEL are stronger due to the presence of AGMF.     

磁压缩对高频稳定性的要求

 曲柄式磁压缩系统是北京大学SASE自由电子激光装置中非常重要的部分，通过其对电子束团的压缩为扭摆器提供高流强、短脉冲的电子束，使电子束在扭摆器内较短的距离实现饱和出光。曲柄式磁压缩需要利用偏离高频峰位的加速相位使得电子束产生能量-位置关联，主要讨论高频相位抖动与能量-位置关联的相互关系，高频相位抖动使得束团的能量-位置关联不同，即束团内电子能量随位置分布不同。进而研究其对磁压缩性能的影响，即能量-位置关联不一样会导致磁压缩得到的束团长度出现涨落。     

稳定波长反馈引起的失谐对自由电子激光的影响

 利用修改的一维非定态程序,基于美国杰弗逊实验室（JLab）Demo自由电子激光装置的参数,对高功率自由电子激光振荡器稳定波长的反馈系统进行了数值模拟。电子微脉冲为高斯型分布,每个纵向网格中取16个模拟宏电子,不考虑电子束的能散度。结果表明：当无反馈时,腔内光功率和波长都可以在一定范围内稳定;加入反馈后,由于电子束能量的变化所引起的等效失谐对整个系统有着重要的影响,甚至可能导致电子和光场失去相互作用,从而使得装置不能工作。提出应该在光场达到饱和以后再启动稳定波长反馈系统。模拟结果证明,该实施方案是合理有效的,可以避免其对FEL运行的严重影响。     

基于超导直线加速器的XFEL初步方案

基于超导直线加速器的X射线自由电子激光(XFEL)是自由电子激光领域未来发展的一个重要方向。介绍了国际上Euro-XFEL及LCLS-II等超导XFEL装置的设计建造现状。在此基础上提出基于一台7GeV超导直线加速器的超导XFEL初步方案,给出主要设计参数,并讨论实现100~1000GW量级峰值输出功率的技术路线,包括提高峰值流强、采用波荡器磁场渐变技术等。     

激光电子散射中的最大可能增益

借鉴自由电子激光(FEL)发展之初Madey对自由电子激光器中受激辐射引起的增益的讨论,通过在激光场中的量子电动力学(QED)的模型中引入激光电子系统初态态密度以及由不确定的系统初态到确定光子末态的跃迁速率,推导了激光电子正碰过程中受激辐射至单一电磁模式产生的最大可能增益。采用成功得到X射线或γ射线光子的三个激光电子Compton背散射实验的实验参数计算了激光电子散射过程中的最大可能增益,与第一台X射线自由电子激光(XFEL)中的最大可能增益作比较,进而对激光电子散射作为激光光源的可行性进行评估。计算结果表明,现有的能够得到X射线光子或γ射线光子的激光电子散射实验中的最大可能增益远低于第一台XFEL中的。本工作未能找到合适的激光电子参数以获得比第一台XFEL中更高的最大可能增益,但是在入射电磁波位于射频波段范围内找到了能够实现较高增益的参数组合。     

Three-dimensional simulation of long-wavelength free-electron lasers with helical wiggler and ion-channel guiding

A three-dimensional simulation of a steady-state amplifier model of a long-wavelength free-electron laser (FEL) with realizable helical wiggler and ion-channel guiding is presented. The set of coupled nonlinear differential equations for electron orbits and fields of TE 11 mode in a cylindrical waveguide are solved numerically by the Runge-Kutta algorithm with averages calculated by the Gaussian quadrature technique. Self-fields and space-charge effects are neglected, and the electron beam is assumed to be cold and slippage is ignored. The parameters correspond to the Compton regime. Evolution of the radiation power and growth rate along the wiggler is studied. Ion-channel density is chosen to obtain optimum efficiency. Simulations are preformed for the FEL operating in the neighborhood of 35 GHz and 16.5 GHz for the electron beam energies of 250 keV and 400 keV, respectively. The result of the saturated efficiency was found to be in good agreement with the simple estimation based on the phase-trapping model.     

耦合太阳能和地热能的冷热电联供系统优化

天然气和可再生能源互补是一种并行解决环境污染和克服可再生能源不稳定的有效方式,本文提出一种耦合太阳能和地热能的混合冷热电联供(CCHP)系统。基于以电定热(FEL)和以热定电(FTL)运行策略,提出了地源热泵出力比依照逐时电价和季节而变化的运行模式;以一次能源节约率、费用年值节约率以及二氧化碳减排率为目标函数,建立CCHP系统优化模型,运用多目标遗传算法对系统配置及运行策略进行了寻优求解。结果表明:该混合CCHP系统在FEL模式能够实现最优的综合性能.     

自由电子激光中电子与辐射波相互作用有效时间的分析

利用已获得的大信号自由电子激光增益公式,导出了激光平均增长率表达式,分析了自由电子激光中电子与辐射波相互作用的有效时间,讨论了其主要物理参量对相互作用有效时间的影响 关键词：     

Three dimensional study of harmonic operation at the Shanghai deep ultraviolet free electron laser

With the right choice of parameters in the free electron laser (FEL) scheme, the undulator can be primarily operated at high order harmonic modes and the harmonic radiation is expected to be significantly enhanced. Recently, the possibility of proof-of-principle harmonic operation experiments on the basis of the Shanghai deep ultraviolet (SDUV) FEL test facility has been studied. In this paper, the principle of harmonic operation, three dimensional numerical approaches, and detailed performances of proposed harmonic operation at SDUV FEL are presented.     

FEL光学速调管的升级性能分析

通过三维磁场的有限元计算,给出了自由电子激光（FEL）研究用光学速调管升级后的磁参数。国家同步辐射实验室合肥光源（HLS）电子储存环能量可以日常运行在200～800 MeV间,为了与电子储存环能量匹配,并在较高束电子能量下进行实验和得到较多的相干辐射光子,光学速调管从原来的对称结构升级成非对称结构,用于HLS储存环谐波产生FEL实验。给出了升级后非对称光学速调管的几组匹配磁参数,用于在HLS储存环注入能量和可以运行的最高能量下进行谐波FEL实验。初步计算表明,HLS 储存环电子束性能优越,能散很低,FEL实验用最高能散仅为2.05×10-4,相应FEL辐射的能散修正因子在0.96以上,可以忽略不计。     

自由电子激光放大啁啾脉冲的数值模拟

 利用1维非定态程序对单程自由电子激光(FEL)放大器放大线性啁啾脉冲的过程进行了数值模拟,得到了不同啁啾参数的脉冲通过FEL放大器的增益曲线,计算了不同啁啾参数的脉冲被单程FEL放大器放大后的腔外压缩情况。通过对数值模拟结果的定性分析得出：影响输出脉冲宽度和峰值功率的主要因素是FEL放大器的增益线宽和啁啾参数,并以此说明,通过先使用FEL放大器放大啁啾脉冲、然后再将其在腔外压缩的方法产生超短脉冲FEL是可行的。