Spontaneous emission and spectral properties of radiation by relativistic electrons in a gyro‐klystron and optical‐klystron undulator

In this paper spontaneous emission of radiation by relativistic electrons in a gyro‐klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non‐resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron‐type modulation as compared with a conventional gyrotron‐type device driven by cyclotron maser interaction. It is shown that the klystron‐modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro‐klystron is discussed.     

Undulator beamline optimization with integrated chicanes for X‐ray free‐electron‐laser facilities

An optimization of the undulator layout of X‐ray free‐electron‐laser (FEL) facilities based on placing small chicanes between the undulator modules is presented. The installation of magnetic chicanes offers the following benefits with respect to state‐of‐the‐art FEL facilities: reduction of the required undulator length to achieve FEL saturation, improvement of the longitudinal coherence of the FEL pulses, and the ability to produce shorter FEL pulses with higher power levels. Numerical simulations performed for the soft X‐ray beamline of the SwissFEL facility show that optimizing the advantages of the layout requires shorter undulator modules than the standard ones. This proposal allows a very compact undulator beamline that produces fully coherent FEL pulses and it makes possible new kinds of experiments that require very short and high‐power FEL pulses.     

有轴向磁场的平面摆动器自由电子激光的自发辐射

研究了电子在有轴向磁场的平面摆动器中的辐射，得到了一个较普遍的自发辐射谱表达式，谱线的形状也是由函数ｓｉｎｃ（ｕ）决定，当电子的能量较高或者没摆动器轴线观察时，辐射是满圆极化的，数值分析表明，在平面摆动器中附加适当的轴向磁场，可以提高各次谐波辐射的强度，对于基波和较低次谐波，提高更明显。     

A simple optical system delivering a tunable micrometer pink beam that can compensate for heat‐induced deformations

The radiation from an undulator reflected from one or more optical elements (usually termed `pink‐beam') is used in photon‐hungry experiments. The optical elements serve as a high‐energy cutoff and for focusing purposes. One of the issues with this configuration is maintaining the focal spot dimension as the energy of the undulator is varied, since this changes the heat load absorbed by the first optical element. Finite‐element analyses of the power absorbed by a side water‐cooled mirror exposed to the radiation emitted by an undulator at the Advanced Photon Source (APS) and at the APS after the proposed upgrade (APSU) reveals that the mirror deformation is very close to a convex cylinder creating a virtual source closer to the mirror than the undulator source. Here a simple optical system is described based on a Kirkpatrick–Baez pair which keeps the focus size to less than 2 µm (in the APSU case) with a working distance of 350 mm despite the heat‐load‐induced change in source distance. Detailed ray tracings at several photon energies for both the APS and APSU show that slightly decreasing the angle of incidence on the mirrors corrects the change in the `virtual' position of the source. The system delivers more than 70% of the first undulator harmonic with very low higher‐orders contamination for energies between 5 and 10 keV.     

THz自由电子激光波荡器工程设计

根据波荡器物理参数的要求,主要设计了磁块与磁极的尺寸公差、装配方式、永磁性能指标及永磁测量系统。束流方向上磁块与磁极尺寸公差分别为0.05 mm和0.02 mm,磁块与磁极独立装调,利用亥姆霍兹线圈和磁场积分法测量磁块性能。最后设计了机械与控制系统。其中,横梁与支架形变分别为1.5 m和7.5 m。间隙调节范围18~32 mm,调节精度和锥度分别为0.01 mm和0.015 mm。     

用模拟退火法进行纯永磁波荡器磁块组合优化

纯永磁波荡器由多个磁块组成,磁块的剩磁离散性会引起波荡器磁场误差,从而影响储存环工作状态和自发辐射谱质量。在波荡器磁块安装之前,使用模拟退火法对磁块进行组合排序优化,可以使峰值场强误差降低到10-4量级以下,磁场一次积分降低到10-6 T·m量级,二次积分降低到10-6 T·m2量级,优化结果不依赖于初始状态的选择。给出优化的详细过程,提出了根据磁块剩磁快速计算波荡器峰值场强误差和积分场的方法。     

真空波荡器楔口机构结构分析与优化

为了满足物理设计要求,楔口机构被应用于真空波荡器机械系统设计中。利用有限元分析软件ANSYS Workbench对上海光源真空波荡器的关键部件——楔口机构进行了线性静态分析,得到了该关键部件的变形和应力分布情况及它们对外大梁变形和滚动角的影响,采用补偿弹簧系统并进行参数优化减小了影响,使之满足工作中的高精度需要。分析结果在真空波荡器调试过程中得到了验证,与实际情况基本吻合。     

储存环光学速调管磁场分析

在合肥国家同步辐射实验室的储存环上,插入件光学速调管已安装完成,对光学速调管的磁场分布进行了一些附加测量,分析了横向磁场的空间谐波分量;测量了积分场的分布,对积分场变化的原因作了一定探讨。还测量了磁场横向分布的均匀度,为将要进行的相干辐射和自由电子激光研究提供实验数据;最后用实测的磁场对光学速调管自发辐射进行了数值模拟,结果表明这个光学速调管基本上满足实验要求。     

兼用FEL光学速调管的同步辐射波荡器的设计

介绍了合肥800MeV储存环 FEL光学速调管改造成同步辐射波荡器的设计与计算过程,给出了改造方法,计算了波荡器的光通量与亮度并给出了先通量与亮度曲线。计算结果表明,改造后的波荡器可以将目前辐射亮度提高两个多数量级,使许多目前光源亮度下无法开展的研究工作得以进行。     

Fast continuous energy scan with dynamic coupling of the monochromator and undulator at the DEIMOS beamline

In order to improve the efficiency of X‐ray absorption data recording, a fast scan method, the Turboscan, has been developed on the DEIMOS beamline at Synchrotron SOLEIL, consisting of a software‐synchronized continuous motion of the monochromator and undulator motors. This process suppresses the time loss when waiting for the motors to reach their target positions, as well as software dead‐time, while preserving excellent beam characteristics.