横向聚焦波荡器磁场的计算与分析

横向聚焦波荡器可用于电子束能量较低、函数较小的情况。在现有横向聚焦波荡器设计方案的基础上,通过倾斜磁块端面和磁极面提出了几种不同结构的横向聚焦波荡器方案。利用三维磁场模拟程序Radia,对这些波荡器的聚焦场特性进行了模拟计算,对其聚焦特性与主要参数的关系进行了研究,并与现有其他横向聚焦波荡器的聚焦特性进行了对比。对弱聚焦和强聚焦两种情况,分别给出较好的结构方案。对于弱聚焦,平均聚焦梯度随中心场强的增大而略有增大,变化不明显;对于强聚焦,平均聚焦梯度随中心场强的增大而明显增大,呈高次曲线关系。     

Undulators for the PSI Light Sources

The Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) started user operation in 2001. It has been the first medium energy light source to rely on undulators for the production of X-rays up to 20 keV. For soft X-rays, APPLE II-type undulators, providing full polarization control and quasiperiodic electromagnetic undulators, have been installed. The hard X-ray range has been accessed by the newly developed small-gap, short-period, in-vacuum undulators operated on high harmonics. Based on this, FEMTO, the first hard X-ray undulator source for femtosecond (fs) experiments, started operation in 2006.     

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.     

Optimization of a seeded free-electron laser with helical undulators

Seeded single pass free-electron lasers are promising coherent, short-duration, and intense light sources, from the visible to x rays. Operated with adjustable undulators, they are also a unique device for providing fully variable polarized radiation. We report here the first seeding of helical undulators with a variable polarized source. We demonstrate that the adjustment of the seed polarization and focusing allows the free-electron laser radiation to be optimized in terms of intensity and quality.     

翻转线圈系统在波荡器积分场测量中的应用

 为了更有效地测量用于上海同步辐射光源波荡器的积分场误差,在已有的伸展线磁测系统的基础上研制了一套翻转线圈磁测系统,该系统的运动控制、数据采集和数据分析处理均可自动完成。在利用这套磁测系统测量3.4×10^-6 T·m磁场积分时获得高于1×10^-6 T·m的测量精度,初步的实验结果表明这套波荡器积分磁场测量系统具有测量精度好、速度快的特点,与已有的伸展线磁测系统、平移线圈磁测系统和霍尔点测系统相比,它更适合于测量波荡器的一、二次场积分和多极场分量。     

First results of investigation of radiation from positrons in a crystalline undulator

Radiation emitted by positrons moving in a periodically deformed crystal has been experimentally observed for the first time. Radiation spectra have been measured in a wide energy range. Experimental evidence has been obtained for an undulator peak in a radiation spectrum, which is qualitatively consistent with calculations. Crystalline undulators ensure an equivalent magnetic field of 1000 T and a period in the submillimeter range and can therefore be used to generate x-ray and gamma radiation that is a hundred times harder than radiation in usual undulators.     

A model for analytical description of magnetic field effects and losses in a planar undulator radiation

We analyze the influence of constant magnetic constituents on the radiation of high energy electrons in a planar undulator. Broadening and spectrum shift effect of the constant field is compared with other common spectrum distortions in UR sources. Analytical formulation of the effect of the constant magnetic field enables us to obtain and study exact expressions for the UR intensity. They reveal the possibilities to influence off-axis effects and give practical recommendations for the undulators with radiation properties, best profitable for free electron lasers. Several examples of undulators are considered, recommendations specific for each case are given.     

Recent Advancements of Undulator Technologies

Insertion devices—or more specifically, undulators—play a crucial role in actually producing intense light from a high-energy electron beam in synchrotron radiation (SR) and X-ray free electron laser (XFEL) facilities. Their function is quite simple; i.e., to let the electrons move periodically. Even so, there are many different concepts of undulators, and thus, technologies to realize these concepts are quite diverse. There are a variety of requirements dictated by the experimental users of SR and XFEL, mainly in terms of the polarization and wavelength of radiation. In addition, the specifications of undulators should meet these requirements under the given boundary conditions, such as the minimum operational gap, electron energy, and available area for installation. However, necessity is the mother of invention; undulator technologies and concepts have continuously advanced year by year to meet users' demands.     

X-Ray Free-Electron Lasers with Variable Deflection Parameter of Undulators

Russian Physics Journal - The paper deals with X-ray free-electron lasers (FEL) with the variable deflection parameter of undulators with the electron buncher and harmonic amplifier. The analysis...     

Generating a uniform transverse distributed electron beam along a beam line

It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost uniform transverse distributed(UTD) beam within undulators are required. This study shows that a UTD electron beam can be generated within evenly distributed drift sections where undulators can be placed, by means of octupoles and particular optics. A specific design is presented, and numerical simulations are performed to verify the proposed method.     

Diagnostic technique applied for FEL electron bunches

Diagnostic technique applied for FEL ultrashort electron bunches is developed at JINR-DESY collaboration within the framework of the FLASH and XFEL projects. Photon diagnostics are based on calorimetric measurements and detection of undulator radiation. The infrared undulator constructed at JINR and installed at FLASH is used for longitudinal bunch shape measurements and for two-color lasing provided by the FIR and VUV undulators. The pump probe experiments with VUV and FIR undulators provide the bunch profile measurements with resolution of several femtosecond. The new three microchannel plates (MCP) detectors operated in X-ray range are under development now in JINR for SASE1-SASE 3 European XFEL.     

Radiation from Elliptical Undulators with Magnetic Field Harmonics

Journal of Experimental and Theoretical Physics - We analyze undulator radiation in some multiperiodic magnetic fields. We consider undulators with planar, helical, and elliptical axisymmetric...     

Resonant X-ray magnetic scattering has gone soft

The Linac Coherent Light Source [1] (LCLS) at SLAC National Accelerator Laboratory is preparing for the arrival of its first scientific users in the fall of 2009. LCLS is the world's first free-electron in the spectral range 800?8,000?eV, producing intense, sub-picosecond pulses of Xrays with very high spatial coherence. The accelerator facility has been commissioned in stages, beginning in April 2007 [2] with the injector linac and culminating in December 2008 [3] with the first transport of electrons through the complete beam path. On April 10, 2009, the LCLS Project team was rewarded for years of planning, design, construction, and checkout with a dream-come-true: as undulators were placed on the beam path one-by-one, the laser simply turned on without drama in the course of one hour [4]. First visible evidence of light amplification at 8,000?eV was observed on a fluorescent screen with ten undulators in place, at which point a highly collimated spot of X-rays could be discerned in the center of the spontaneous radiation pattern. After just four days of further checkout, the intensity of this spot increased smoothly and exponentially to the threshold of “saturation” at full power with just 20 of 33 undulators in place. The commissioning team was faced with a mixture of shock and euphoria. The Project team has spent years focused on everything that could possibly go wrong, and what to do about each concern. Speaking for myself, I found I was mentally unprepared for the special case of NOTHING going wrong! In fact, a critical aspect of the FEL performance was significantly better than design goals—the gain length (the distance the electron beam must travel in undulators to increase X-ray power by a factor e) proved to be just 3.5 meters. With this gain length, and room for 33 undulators in the tunnel, we find we have ten more spares! The shutter was closed at about midnight, temporarily preventing the electron beam entering the undulator. At 8:00 A.M. the next morning, the shutter was retracted to reveal the FEL producing an 8,000?eV laser beam without need for operator intervention.     

Undulators and generation of X-ray pulses in free-electron lasers with self-amplified spontaneous emission

The results of theoretical examination and comparative analysis of synchrotron radiation sources (specifically, undulators and X-ray free-electron lasers (FELs)) are presented. The problem of generation of shorter radiation pulses is prioritized; undulator systems and their corresponding FELs, which are considered to be the most promising in terms of generation of high-frequency ultrashort pulses of such radiation (in particular, in the X-ray range) are studied. The possibility of generation of higher harmonics is explored. The advantages and disadvantages of single-pass (with no reflecting elements) and multi-pass (with mirrors) FEL lasing schemes are revealed. The potential to reduce the duration of laser pulses produced by undulators and FELs and use them as sources of femtosecond pulses is investigated. The prospects for further development of X-ray free-electron lasers and the ways to improve the quality of their radiation with the given parameters are discussed.     

Generation of UR Harmonics in Undulators with Multiperiodic Fields

Russian Physics Journal - Undulator radiation (UR) of some elliptical undulators with multiperiodic magnetic fields of sin-sin and sincos configuration is investigated, as is also UR of a planar...     

Analysis of pulsed wire method for field integral measurements in undulators

Pulsed wire technique is a fast and accurate method for the measurement of first and second field integrals of undulators used in free-electron lasers and synchrotron light sources. In this paper, we present a theoretical analysis of this technique by finding out the analytic solution of the differential equation for the forced vibration of the wire taking dispersion due to stiffness into account. Method of images is used to extend these solutions to include reflections at the ends. For long undulators, the effect of dispersion of the acoustic wave in the wire could be significant and our analysis provides a method for the evaluation of the magnetic field profile even in such cases taking the effect due to dispersion into account in an exact way.     

Superconducting Multipole Wigglers for Generating Synchrotron Radiation at the Budker Institute of Nuclear Physics

Physics of Particles and Nuclei Letters - Superconducting multipole insertion devices (wigglers and undulators) used to generate synchrotron radiation significantly increase the photon flux,...     

Hard undulator radiation in an inverse medium

X-ray radiation from fast electrons in undulators filled with an inverse medium is studied. A formula for the spectral density of the number of photons is derived. The intensity zeroth harmonics, as well as the intensity of radiation in zero undulator field, are described by the Tamm-Frank formula for Cherenkov radiation. It is shown that the spectral density of emitted photons in a wavelength range of λ ? 0.4–2.0 Å in such a medium can be increased by four orders of magnitude as compared to the radiation intensity in a vacuum undulator. The energy of emitted electrons in the former case must be in an interval of 5-2 GeV, while electrons with an energy of 14-6 GeV are required in vacuum undulators.

     

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.     

Sm2Co17 magnet blocks for the in-vacuum undulators (IVU20) at the SSRF

The design and development status of Sm<,2>Co<,17> magnet blocks for two in-vacuum undulators (IVU20) at the SSRF with the same hybrid design has been described. By the technological improvement of some processes and comparison with the experimental Sm<,2>Co<,17> magnet blocks for the IVU25A, magnetic properties such as the intrinsic coercive force H<,ci> and the average magnetic moment M are increased, the bend point magnetic field H<,k> value and pass rate are significantly increased, and the magnetic field uniformity of the magnet blocks are significantly improved. The basic developmental method of high uniformity Sm<,2>Co<,17> magnet blocks for IVU20 is presented. The magnetic field qualities of the magnet blocks, including the magnetic property, the magnetic moment distribution, the magnetization deviation angle and the magnetic field uniformity, basically satisfy the specifications of the two IVU20 in-vacuum undulators.