Magnetic design and modelling of a 14 mm‐period prototype superconducting undulator

The magnetic design of a ten‐period (each period 14 mm) prototype superconducting undulator is reported using RADIA. The results of modelling the magnetic flux density are presented in an analytical formula. The dependence of the field integrals and phase error on the current density and undulator gap has been calculated, and temperature curves are determined for the models and are compared with earlier reported Moser–Rossmanith fits.     

Analysis of undulator radiation with an electromagnet undulator

In this paper we discuss the theory of undulator radiation in an electromagnet undulator. We discuss the spectral properties of undulator radiation when electrons are injected off the undulator axis. This paper highlights the distinctive features of the radiation spectrum from electromagnet undulators, as compared to PPM undulators.     

Condenser for Koehler-like illumination in transmission x-ray microscopes at undulator sources

We report on a novel condenser for full-field transmission x-ray microscopes that use synchrotron radiation from an undulator source. The condenser produces a Koehler-like homogeneous intensity distribution in the sample plane and eliminates object illumination problems connected with the high degree of spatial coherence in an undulator beam. The optic consists of a large number of small linear diffraction gratings and is therefore relatively easy to manufacture. First imaging experiments with a prototype condenser were successfully performed with the Twinmic x-ray microscope at the Elettra synchrotron facility in Italy.     

混合型波荡器的3维优化

 以波荡器辐射波和共振电子能及混合型波荡器的解析计算为基础，通过3维磁场的有限元计算，在欧洲光源横向优化基础上，给出了同步辐射和自由电子激光用混合型波荡器纵向优化参数，进而给出了用于DUV FEL混合型波荡器的设计计算参数。加侧位和顶部永磁块后，峰值磁场分别提高到0.722T和0.773T，辅助以1μm量级分辨率的磁间隙调节机械系统，磁场分辨率好于10^-4T量级。     

Design,construction and characterization of the compact ultrafast terahertz free-electron laser undulator

A compact ultrafast terahertz (CUTE) free-electron laser (FEL) is being developed at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. The undulator required for the CUTE-FEL has recently been developed. We have designed, built and characterized a variable gap, 5 cm period, 2.5 m long pure permanent magnet undulator in two identical segments. The tolerable error in the magnetic field was 1% in rms, and we have measured it to be 0.7%. The obtained rms phase shake is around 2°. To ensure that the trajectories do not have an exit error in position or angle, corrector coils have been designed. Shimming coils have been applied for both the undulator segments to reduce the amplitude of the betatron oscillations in the vertical trajectory. Details of novel corrector coils and soft iron shims are given and their performance is discussed.      

强聚焦混合型扭摆器的优化设计

扭摆器是自由电子激光装置的一个核心部件.强聚焦混合型扭摆器具有结构紧凑等一系列优点,但其结构复杂,技术难度很高,在国内还没有成功研制的先例.本文描述该类型扭摆器研制的一个基础而关键性的工作:一台10周期的强聚焦混合型扭摆器的优化设计     

Investigation of a method to calculate spontaneous radiation spectra from relativistic electrons in undulators

Undulators are key devices to produce brilliant synchrotron radiation at the synchrotron radiation facilities.In this paper we present a numerical computing method,including the computing program that has been developed to calculate the spontaneous radiation emitted from relativistic electrons in undulators by simulating the electrons' trajectory.The effects of electron beam emittance and energy spread have also been taken into account.Comparing with other computing methods available at present,this method has a few advantages with respect to several aspects.It can adopt any measured or arbitrarily simulated 3D magnetic field and arbitrary electron beam pattern for the calculation and it's able to analyze undulators of any type of magnetic structure.It's expected to predict precisely the practical radiation spectrum.The calculation results of a short period in-vacuum undulator and an EllipticaUy Polarized Undulator (EPU) at Shanghai Synchrotron Radiation Facility (SSRF) are presented as examples.     

双波荡器自由电子激光理论

给出了双波荡器自由电子激光器的通用理论.在双波荡器自由电子激光器中,引入了一个周期长度非常接近主波荡器中电子束感应加速振荡周期的附加波荡器.推导出了一套自治方程组描述双波荡器中自由电子激光场演变过程,并分别给出了低增益、高增益和饱和三种情况下的解析解.研究表明,适当选择附加波荡器的参数,可以提高自由电子激光器的增益或转换效率     

Characteristics and developments of quantum-dot infrared photodetectors

Quantum dots infrared photodetectors (QDIPs) theoretically have several advantages compared with quantum wells infrared photodetectors (QWIPs). In this paper, we discuss the theoretical advantages of QDIPs including the normal incidence response, lower dark current, higher responsivity and detectivity, etc. Recent device fabrication and experiment results in this field are also presented. Based on the analysis of existing problems, some approaches that would improve the capability of the device are pointed out.     

远红外自由电子激光器的性能和可能的应用(英文)

本文提出了远红外自由电子激光器(FIRFEL)的现实优点:对电子束质量要求不太苛刻;比较经济;对远红外区的非线性和相干性研究是唯一的合适的光源。分析了自由电子激光器增益与电子束和摆动器参量的关系,指出对给定的发射度存在一特定的波长,当波长比特定波长短时,增益将急骤下降。概述了远红外区的重要物理现象以及远红外自由电子激光器的可能的应用,预期这些研究对THz电子学发展是很重要的。     

Influence of a constant magnetic field on the radiation of a planar undulator

The influence of a constant magnetic field on the radiation of a planar undulator is studied analytically with the use of generalized Bessel functions. The behavior of on-axis radiation intensity in the undulator and the influence of a magnetic field on off-axis radiation are investigated. The critical magnitude of the constant component of the magnetic field, which has a significant effect on the motion of electrons in the undulator, is calculated analytically. The examples of several planar undulators are discussed, and the influence of the Earth’s magnetic field on their spectrum is evaluated.     

Efficiency and sideband observations of a Raman FEL oscillator witha tapered undulator

Power and spectral measurements are reported from the Columbia Raman free-electron laser (FEL) oscillator experiment. High-power radiation pulses (~12 MW, 100 ns) are generated at a wavelength of ~2.5 mm, using a 750-kV electron beam injected into a helical undulator. The undulator is made up of a 40-cm long constant-period (1.45 cm) section followed by an equal length of tapered undulator. The period is decreased by 7.6% in such a way that the on-axis field remains constant. It is reported that the taper allows an increase in total power efficiency from ~4 to ~12%. Most noteworthy is that the tapered undulator reduces the sideband radiation compared with a constant-period undulator FEL which is studied in the same configuration. The power was measured calorimetrically and compared with the results of a 1-D Raman code. The reduction of sideband power observed in the experiment was consistent with computational results obtained with a 2-D sideband code     

Calculation and analysis of the magnetic field of a linearly tapered undulator

There is an empirical formula describing the relationship between the peak magnetic field and the undulator structure parameters for a uniform-parameter hybrid undulator.In this paper, we investigate the relationship for a linearly tapered undulator through numerical calculation by using the code RADIA, and check it with the empirical formula.The results imply that this empirical formula is also effective for linearly tapered undulators at a big enough scope for the requirements of normal FEL experiments.Therefore, for a linearly tapered undulator,we can use the empirical formula to design the variation of the undulator gap.For the tapering rate demanded by normal FEL experiments, the gap of a linearly tapered undulator increases almost linearly, and the tapering rate will keep constant while adjusting the undulator gap with the same variation for each undulator period.     

SXFEL阻抗壁尾场对束流相空间畸变的影响

X射线自由电子激光器（FEL）由于其超高亮度、超短脉冲等特点,在世界范围内得到广泛应用。 基于尾流场理论,我们计算了上海X射线自由电子激光器（SXFEL）中从直线加速器出口到波荡器末端,束流在245 m不锈钢传输线和波荡器中的阻抗壁尾场。通过对两种不同的阻抗壁尾场的叠加,发现将导致束流纵向相空间的畸变。在SXFEL上进行束流物理的实验,并得到与理论预测非常吻合的实验结果。 结合之前对主要直线加速器部分的详细模拟和实验研究,为后续FEL整体束流优化提供了参考。     

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·m ²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。     

In situ characterization of undulator magnetic fields

A new in situ method is proposed to characterize the peak magnetic fields of undulator sources. The X‐ray beam emitted by the HU52 Apple‐2 undulator of the DEIMOS beamline of the SOLEIL synchrotron is analyzed using the Bragg diffraction of a Si(111) crystal. Measurements over the undulator gap range in linear horizontal polarization are compared with simulations in order to rebuild the Halbach function linking the undulator gaps to their peak magnetic fields. The method presented also allows information about the electron beam to be obtained.     

Real-space calculations for electron transport properties of nanostructures

Recent developments in the fabrication and investigation of conductors of atomic dimensions have stimulated a large number of experimental and theoretical studies on these nanoscale devices. In this paper, we introduce examples presenting the efficiencies and advantages of a first-principles transport calculation scheme based on the real-space finite-difference (RSFD) formalism and the overbridging boundary-matching (OBM) method. The RSFD method does not suffer from the artificial periodicity problems that arise in methods using plane-wave basis sets or the linear dependence problems that occur in methods using atomic basis sets. Moreover, the algorithm of the RSFD method is suitable for massively parallel computers and, thus, the combination of the RSFD and OBM methods enables us to execute first-principles transport calculations using large models. To demonstrate the advantages of this method, several applications of the transport calculations in various systems ranging from jellium nanowires to the tip and surface system of scanning tunneling microscopy are presented.     

Mini‐beam collimator enables microcrystallography experiments on standard beamlines

The high‐brilliance X‐ray beams from undulator sources at third‐generation synchrotron facilities are excellent tools for solving crystal structures of important and challenging biological macromolecules and complexes. However, many of the most important structural targets yield crystals that are too small or too inhomogeneous for a `standard' beam from an undulator source, ～25–50 µm (FWHM) in the vertical and 50–100 µm in the horizontal direction. Although many synchrotron facilities have microfocus beamlines for other applications, this capability for macromolecular crystallography was pioneered at ID‐13 of the ESRF. The National Institute of General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA‐CAT) dual canted undulator beamlines at the APS deliver high‐intensity focused beams with a minimum focal size of 20 µm × 65 µm at the sample position. To meet growing user demand for beams to study samples of 10 µm or less, a `mini‐beam' apparatus was developed that conditions the focused beam to either 5 µm or 10 µm (FWHM) diameter with high intensity. The mini‐beam has a symmetric Gaussian shape in both the horizontal and vertical directions, and reduces the vertical divergence of the focused beam by 25%. Significant reduction in background was achieved by implementation of both forward‐ and back‐scatter guards. A unique triple‐collimator apparatus, which has been in routine use on both undulator beamlines since February 2008, allows users to rapidly interchange the focused beam and conditioned mini‐beams of two sizes with a single mouse click. The device and the beam are stable over many hours of routine operation. The rapid‐exchange capability has greatly facilitated sample screening and resulted in several structures that could not have been obtained with the larger focused beam.     

Comparison of calculated brightness and flux of radiation from a long‐period wiggler and a short‐period undulator

In this article the calculation of brightness and flux for two insertion devices of the 2.8 GeV X‐ray storage ring at the NSLS is discussed. The radiation properties from the X25 linearly polarized wiggler and the new X25 short‐period undulator are compared at a fixed photon energy (11.3 keV) corresponding to emission from the fifth harmonic of the short‐period undulator. For this computation, three commonly available synchrotron radiation programs are used. The capabilities of each of these codes are briefly discussed, and their range of applicability are commented on. It is concluded that special care is needed when modeling the radiation of the classes of insertion devices considered here.     

摆动器场误差对自由电子激光器自发辐射谱的影响

在考虑平面型摆动器（Ｗｉｇｇｌｅｒ）场误差△Ｂ（ｚ）的情况下，求解电子在磁场中运动的洛仑兹（Ｌｏｔｅｎｔｚ）方程，得到场误差对电子横向速度的改变，然后作傅里叶变换即为电子自发辐射谱的改变，并讨论了各种场误差对自由电子激光器自发辐射谱的影响，选择北京自由电子激光器（ＢＦＥＬ）参数，进行模拟，最后确定出各种场误差的可接受条件。