自由电子激光的小型化研究

本文通过对自由电子激光输出波长的分析,指出了自由电子激光小型化的研究方向─-微型摆动器的研究。在分析了小周期摆动器研究现状的基础上,提出了电流摆动器。它不但具有与静磁摆动器相同的效果,而且它的周期可以任意调节。因而,它便于控制。最后,还指出了有待进一步研究的问题。     

Feasibility study on optical vortex generation at Shanghai deep ultraviolet free-electron laser

Coherent light with orbital angular momentum （OAM） is of great interest. Recently, OAM light generation by coupling a relativistic electron beam with a Gaussian mode laser pulse at the high harmonics of a helical undulator has been demonstrated experimentally. In this paper, the possibility of delivering coherent OAM light at the 3rd harmonic of the Gaussian mode seed laser is discussed for the Shanghai deep ultraviolet free- electron laser （SDUV-FEL）. Considerations are given on the experiment setup, the expected performance and the possible measurement method.     

On harmonic operation of Shanghai deep UV free electron laser

By choosing parameters in the modulator, the dispersive section and the seed laser, the spatial bunching of the electron beam can be correlated to the n-th harmonic of the radiator radiation, instead of the fundamental radiation in conventional high-gain harmonic generation （HGHG）. Thus, the radiator undulator is operated at high harmonic mode. In this paper, the possibility of harmonic operation of Shanghai deep ultraviolet （SDUV） free electron laser （FEL） is studied. Discussions on the principle of harmonic operation, the simulation code development, the simulation results, and the proposed experimental procedure for verification of harmonic operation at the SDUV FEL are also presented.     

Modified model for harmonic generation free electron laser

The longitudinal modulation to the electron beam by a coherent seed laser pulse is widely used for generating fully coherent, short wavelength radiation in various harmonic generation free electron laser (FEL)schemes. After introducing the density modulation, mierostruetures down to attosecond scale are produced over the distance of one seed laser wavelength. In order to take into account the mierostructures in the theoretical and numerical analysis, in the frame of undulator period averaged approach, a modified model for harmonic generation FEL is developed in this paper. With the modified model, three harmonic generation FEL examples are investigated by employing Shanghai soft X-ray FEL (SXFEL) parameters. In FEL schemes with ultra-high harmonic generation and ultra-short pulse, the modified model presents some interesting aspects which are helpful for understanding of radiation pulse evolution, bunching efficiency and noise propagation issues.     

X-band technology applications at FERMI@Elettra FEL project

The current activities and future perspectives involving the use of X-band technology at the Elettra Laboratory are presented. These are mainly related to the development of the FERMI@Elettra FEL project, a fourth generation light source facility, now under commissioning in Trieste. The facility, based on a seed scheme, requires sub-ps electron bunches (∼1 kA), with very high optical qualities, at the entrance of the undulator chain. This is achieved by compressing the beam with two magnetic chicanes.A large effort has been undertaken to develop an X-band accelerating structure, to be installed downstream the first bunch compressor, before the magnetic chicane. In addition, we are also evaluating the possibility of extending the FERMI FEL wavelength capabilities beyond the foreseen limit of 4 nm, by increasing the linac energy from 1.5 GeV to 2.4-2.5 GeV, using the X-band technology.     

COMPARISON BETWEEN FEL AND CYCLOTRON RADIATION

In general,in free electron lasers there are two kinds of stimulated radiations:FELradiation and cyclotron radiation.This paper chows theoretically that if the initial transversevelocity of electron beam is large and the selected parameters for FEL are not suitable,thecyclotron radiation will be dominant,especially when the energy of electron beam is low.But thecyclotron radiation does not have double Doppler frequency upshift effect,its frequency is limitedby axial megnetic field,and when the energy of electron beam is high,the cyclotron radiationfrequency will be much lower than FEL radiation frequency.Therefore,in FEL experimentshow to distinguish these two kinds of radiations and to suppress the cyclotron radiation are veryimportant.     

An FEL-based microwave system for fusion

This paper describes designs for 280-GHz and 560-GHz microwave sources based on free electron lasers (FELs). These 10-MW units are based on technology developed over the last 5 years. A first demonstration of high-average-power microwave production with an FEL system is expected in the Microwave Tokamak Experiment (MTX) facility. This paper gives details on the design and construction of that 250-GHz, 2-MW system and discusses specific applications for the Compact Ignition Tokamak (CIT).     

开放式圆柱光栅周期结构的色散特性分析

研究了一种新的开放式圆柱光栅周期结构,该结构可以作为Smith-Purcell自由电子激光和相对论行波管中的慢波结构.采用近似的场论方法,用一系列相连的矩形阶梯来近似代替光栅上任意槽形的槽的连续轮廓,利用各阶梯面上导纳的匹配,以及槽与互作用区的连续和匹配条件,获得了任意形状槽圆柱光栅周期结构的色散方程,并讨论了系统结构参数变化对系统色散特性的影响.利用软件MAGIC对结构的色散特性进行了二维模拟,与理论计算得到的值符合良好.     

Quantum theory for 1D X-ray free electron laser

Abstract

Classical 1D X-ray Free Electron Laser (X-ray FEL) theory has stood the test of time by guiding FEL design and development prior to any full-scale analysis. Future X-ray FELs and inverse-Compton sources, where photon recoil approaches an electron energy spread value, push the classical theory to its limits of applicability. After substantial efforts by the community to find what those limits are, there is no universally agreed upon quantum approach to design and development of future X-ray sources. We offer a new approach to formulate the quantum theory for 1D X-ray FELs that has an obvious connection to the classical theory, which allows for immediate transfer of knowledge between the two regimes. We exploit this connection in order to draw quantum mechanical conclusions about the quantum nature of electrons and generated radiation in terms of FEL variables.     

基于FEL的液压振动台加速度幅相控制

目的针对液压振动台加速度正弦波波形复现、加速度扫频两类试验项目,利用反馈误差学习(FEL)控制策略解决传统三状态控制策略不能解决的跟踪精度低、鲁棒性差的问题.方法利用ADALINE神经网络、归一化LMS算法、结合正弦函数的特点,设计FEL控制策略中的前馈神经网络.结果对于正弦波和扫频信号参考输入,即使在阀控缸系统参数发生变化的情况下,所设计控制器仍然在幅值和相位上达到很高的跟踪精度.结论基于FEL思想设计的幅相控制器跟踪精度高,结构简单,运算量小,能满足对实时性要求很高的液压振动台控制系统的要求,也有利于基于DSPs的嵌入式实现.