Magneticresonant three dimensional kinetic theory of the free electron laser with waveguide cavity

Vlasov kinetic theory of the free electron laser employing waveguide frifting tube and helical pump is presented. Distinct from the former theories this theory has (1) taken into account the 3-d structure of the scattering field; (2) applied the plasma kinetic theory, which is more accurate than the other methods, to analysing the effect of the longitudinal. field; (3) taken account of the influence of the annular structure of the beam. The magnetic resonant effect appearing when the cyclotron frequency of electrons approaches the effective frequency of the magnetic pump is analysed and the growth rate formula in the linear regime derived. Results show that on taking into account the 3-d structure of the field and beam, one cannot arbitrarily choose the radius of the hollow beam, or else within certain range the instability may disappear altogether. Lastly, the equation for determination of the optimum beam radius is given and the possibility of raising growth rate by operating in high order modes shown.     

A compact free electron laser investigation

An electron beam source based on pseudospark discharge was successful in operation at the beam voltage of 200keV and beam current of 2kA. The detailed design of a compact free electron laser using an electron beam by a pseudospark discharge is described. The compact free electron laser consists of a smaller Marx generator with 6 capacitors and switches, a water capacitance of 6nF and a beam source with a high brightness of 3×10¹¹ A/(m rad)². The computer simulation shows that an output power of 101MW is expected at a frequency of 38GHz with a beam energy of 300keV, a current of 2kA and a beam emittance of 48mm mraa.     

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

A theory for the two-stream free-electron laser(TSFEL) with a helical wiggler and an axial guide magnetic field is developed.In the analysis,the effects of self-fields are taken into account.An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion.Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields.The stability of the trajectories is studied numerically.     

自由电子激光器谐振腔内电子束和激光脉冲的时间同步

研究自由电子激光器谐振腔内电子束和辐射的时间同步问题.这是激光器谐振腔设计中的一个重要问题.本文讨论了腔内布儒斯特窗片对光路的影响.研制出由微机控制谐振腔的精密微调装置,扫描范围为±3cm,微调精度达1μm.     

Degradation in gain for a free electron laser amplifier due to electron momentum spread

A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)_1/2 = (G_o/248)^1/2 (_o/L), where G_o1 is the gain in db for the cold-beam case, _o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.     

1.19米相互作用长度的喇曼自由电子激光器实验

利用新研制的1.3米双螺线波荡器以及与此相配合的引导场磁体,使自由电子激光相互作用长度从308mm可以最大增加到1190mm.总体实验证明,最大的激光辐射峰值功率达12MW电子转换效率是3.7%.     

北京自由电子激光器的光学速调管结构

采用KMR方程,结合即将运转的北京自由电子激光器总体实验参数,对其光学速调管结构研究.详细分析计算输入功率、电子束能散度、色散磁场、漂移空间长度及位置、以及电子束流等参数对光学速调管增益的影响.基于北京自由电子激光器的振荡器结构,提出一组对电子束能散度要求适中的实用化光学速调管参数.并对其饱和功率、功率谱以及渐变摆动器进行分析.     

自由电子激光器的掠射环形谐振腔

研究一种新型自由电子激光谐振腔结构.采用双曲面-抛物面非球面镜组合的扩束系统,使振荡光束在腔内口径扩大6倍.提高了反射膜层抗激光破坏能力.本文讨论了扩束倍数、非球面参量、谐振腔长度和掠射光斑尺寸等参量对光学系统像差的影响.     

Physical design of a wavelength tunable fully coherent VUV source using a self-seeding free electron laser

In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser (FEL) has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range (70—170 nm). In the light of the users' demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.     

Physical design of a wavelength tunable fully coherent VUV source using a self-seeding free electron laser

In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser （FEL） has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range （70 170 nm）. In the light of the users＇ demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.     

交叉型波荡器软X射线自由电子激光极化控制的影响因素

交叉型波荡器是一种实现软X射线自由电子激光极化控制的有效方式。以自放大自发辐射自由光电子激光为例,采用统计的方法系统地分析了交叉型波荡器软X射线自由电子激光极化控制的影响因素。通过对光场相干长度、光脉冲两分量之间相对滑移长度和光场分量平均功率差异等的分析,给出了优化交叉型波荡器极化控制方案遵循的原则,即：辐射场相干时间尽可能长,光场分量相对滑移长度尽可能短,辐射场分量功率差异尽可能小等。该原则为交叉型波荡器软X射线自由电子激光极化控制方案的优化提供了依据。     

交叉型波荡器软X射线自由电子激光极化控制的影响因素

 交叉型波荡器是一种实现软X射线自由电子激光极化控制的有效方式。以自放大自发辐射自由光电子激光为例,采用统计的方法系统地分析了交叉型波荡器软X射线自由电子激光极化控制的影响因素。通过对光场相干长度、光脉冲两分量之间相对滑移长度和光场分量平均功率差异等的分析,给出了优化交叉型波荡器极化控制方案遵循的原则,即：辐射场相干时间尽可能长,光场分量相对滑移长度尽可能短,辐射场分量功率差异尽可能小等。该原则为交叉型波荡器软X射线自由电子激光极化控制方案的优化提供了依据。     

太赫兹自由电子激光的受激饱和实验

中国工程物理研究院基于半导体光阴极高压直流电子枪和超导直线加速器的高平均功率太赫兹自由电子激光达到了受激饱和,并实现了太赫兹光输出频率可调.在1.99,2.41和2.92 THz三个频率点上进行测试,测得太赫兹宏脉冲内平均功率大于10 W,最高达17.9 W.本文介绍了太赫兹自由电子激光装置的主要组成部分及受激饱和实验的结果.     

Infrared free electron laser measurement of the photon drag effect in P-silicon

We report the use of FELIX (free electron laser for infrared experiments) to study photon drag in p-silicon over the wavelength range 25–80m. Previous spot measurements using a pulsed water vapour laser had indicated high response at 28 and 33m associated with transitions within the valence band. These earlier results have been confirmed and the main futures of the extended photon drag spectrum are also explainable by reference to the valence band structure. A practical outcome of the experiment is the design of a subnanosecond response time detector to observe the 1GHz frequency micropulse output from FELIX.     

X射线自由电子激光晶体学在结构生物学中的应用

X射线晶体学是获得生物大分子三维空间结构最主要的方法。基于X射线自由电子激光的晶体学——串行飞秒晶体学方法的出现,以其独特的优势为结构生物学研究提供了一种全新的研究手段。文章主要介绍了串行飞秒晶体学方法在结构生物学领域的应用及所取得的成果。这些成果表明该方法是在亚纳米空间尺度和飞秒时间尺度、在接近于自然状态下进行生物大分子静态和动态结构研究的强有力手段。     

Investigation of mechanism of free electron laser through spontaneous radiation spectrum

In this paper, the mechanism of free electron laser with a guide magnetic field is investigated by analyzing spontaneous radiation spectrum of electrons. The physical relation between spontaneous radiation and stimulated radiation in FEL with a guide magnetic field is studied. It is found that this relation in FEL is similar to that in quantum lasers. The spontaneous radiation spectrum is discrete. The frequency of stimulated radiation in FEL is oneselected and amplified in the radiation spectrum.     

Effects of self-fields on gain in two-stream free electron laser with helical wiggler and an axial guiding magnetic field

The theory for the two-stream free electron laser （FEL） consisting of a relativistic electron beam transporting along the axis of a helical wiggler in the presence of an axial guiding magnetic field is proposed and investigated. In the analysis, the effects of self-fields are taken into account. The electron trajectories and the small signal gain are derived. The characteristics of the linear-gain and the normalized maximum gain are studied numerically. The results show that there are seven stable groups of orbits in the presence of self-fields instead of two groups reported in the absence of the self-fields. It is also shown that the normalized gains of three groups decrease while the rest increase with the increasing of normalized cyclotron frequency g20. Furthermore, it is found that the two-stream instability and the self-field lead to a decrease in the maximum gain except for group 3. The results show that the normalized maximum gain is enhanced in comparison with that of the single stream.     

Smith-Purcell free electron laser based on the semi-elliptical resonator

A novel Smith-Purcell(S-P) free electron laser composed of an electron gun,a semi-elliptical resonator,a metallic reflecting grating and a collector,is presented for the first time.This paper studies the characteristics of this device by theoretical analysis and particle-in-cell simulation method.Results indicate that tunable coherent S-P radiation with a high output peak power at millimeter wavelengths can be generated by adjusting the length of the grating period,or adjusting the voltage of the electron beam.The present scheme has the following advantages:the semi-elliptical resonator can reflect all radiation with the emission angle θ and random azimuthal angles,back onto the electron beam with same-phase and causes the electrons to be modulated,so the output power and efficiency are improved.     

太赫兹自由电子激光波荡器的设计、测量与优化

波荡器电子轨迹中心偏移和磁场误差对CTFEL装置性能影响很大,通过前期设计和后期测量与优化将其限制在指标要求范围内。在前期设计中尽量避免引入全局性的系统误差：磁结构具有平面反对称结构,保证电子轨迹中心和波荡器磁轴重合;磁结构端部的特殊设计减弱了间隙对出口磁场二次积分的影响;机械系统的大梁和立柱具有良好的刚性,闭环控制系统保证了高的波荡器间隙控制精度,这些措施降低了间隙不一致引入的磁场误差。在后期测量与优化中削弱了磁场的残存全局系统误差和局部随机误差：利用磁场点测台测量了波荡器磁场的纵向和横向分布,通过调节标准单元组件位置对磁场进行了垫补和优化,优化后电子轨迹中心偏移、峰峰值误差、相位误差、好场区及其误差均满足指标要求。