Insertion devices–recent developments and future trends

The first Ultrafast X-ray Summer School, organized and chaired by Nora Berrah (WMU), was held June 18–22, 2007, at the Stanford University's PULSE Center, located at the Stanford Linear Accelerator Center (SLAC). With the advent of 4^th generation X-ray light sources, and in particular, the Linac Coherent Light Source (LCLS) under construction at SLAC, it was timely to begin the process of building a competitive community of scientists. It was also primordial to communicate to everyone the excitement many of us have about these new tools and to help raise awareness of the opportunities in ultrafast X-ray research.     

The fast show with x‐rays and electrons

On October 20–26, 2004, more than 350 people participated in the 31st Annual Stanford Synchrotron Radiation Laboratory (SSRL) Users' Meeting, workshops, and social events. The presentation by SSRL Director Keith Hodgson in the opening session focused on the success in 2004 in getting SPEAR3 and the SSRL beam lines operating and productive. Looking towards the future, he discussed the exciting new opportunities at the Linac Coherent Light Source (LCLS), an X-ray free electron laser. Hodgson emphasized the importance of safety when conducting experiments at SSRL, a point strongly reiterated by SLAC Director Jonathan Dorfan.     

National school on Neutron and X‐ray scattering alumni presentations

The 4th joint Stanford–Berkeley summer school on synchrotron radiation and its applications in physical science was held June 12–17, 2005, at the Stanford Linear Accelerator Center (SLAC). The Stanford–Berkeley summer school is jointly organized by Stanford University, University of California Berkeley, Lawrence Berkeley National Laboratory (LBNL), and the Stanford Synchrotron Radiation Laboratory (SSRL). Since 2001, Anders Nilsson (Stanford/SSRL) and Dave Attwood (UC Berkeley) have been the organizers of this annual weeklong summer school, which alternates each year between Stanford and Berkeley. The summer school provides lecture programs on synchrotron radiation and its broad range of scientific applications in the physical science as well as visits to the Stanford Synchrotron Radiation Laboratory and the Advanced Light Source (ALS), where the students also have the opportunity to experience a beam line.     

Opportunities for resonant elastic X-ray scattering at X-ray free-electron lasers

X-ray Free-Electron Lasers (FELs) are beginning to deliver a revolution in X-ray experiments, thanks to their ultra-bright (peak brightness exceeding 10³³ photons/s/mm²/mrad²/0.1%BW), ultrashort (down to a few fs), spatially coherent X-ray pulses. Presently operational facilities cover wide spectral ranges, from the VUV and soft X-ray wavelengths of FLASH in Hamburg (down to 4.2 nm), to the hard X-rays delivered by the LCLS in Stanford (wavelengths of 0.15 nm or shorter). The basic properties of the new sources are briefly reviewed, and the impact on resonant scattering experiments is discussed. The perspective of investigating ultrafast magnetism, and, more generally, the time-dependent response of strongly correlated electron systems, in a pump-and-probe mode at the L edges of 3d transition metals, would be very attractive. In the hard X-ray range, the very recent proposal of self-seeded X-ray FELs, with 10⁻⁵ intrinsic bandwidth, tunable wavelength, 100 fs pulses and number of photons per pulse of order 10¹² also opens exciting possibilities for resonant scattering.     

Dynamics of Self-Organized and Self-Assembled Structures,by Rashmi C. Desai and Raymond Kapral

The arrival of the first hard X-ray free electron laser facilities promises new advances in structural dynamics and nanoscale imaging that will have impact across the sciences. This introductory review is intended to cover the basic physics behind this potential and illustrate the current state-of-the-art by discussing a number of recent findings from the LCLS facility at the Stanford Linear Accelerator Centre (SLAC). We concentrate on the new science using these light sources rather than the new light source technology itself, although a brief introduction to the operation of LCLS is given. Emphasis is placed upon the new regime of high intensity X-ray matter interaction physics with ultrashort X-ray pulses. We discuss how the unique combination of X-ray parameters will open new opportunities for time resolved structural studies and how the high brightness enables a new class of coherent diffraction X-ray imaging. The potential importance of this new imaging method in the study of nanostructures and biological systems at the sub-cellular and molecular level will be outlined.     

ESRF 11th users' meeting and workshops

More than 90 participants from Europe, the US and Japan gathered from April 27 to 29, 2005, in Zeuthen, near Berlin, to hold a lively international meeting on time-resolved soft X-ray science. The meeting continued the series of preceding workshops held in 2002 in Napa (California, USA) and in 2003 in Montreux (Switzerland). It was organized by the three synchrotron radiation sources BESSY (Berlin, Germany), the Swiss Light Source SLS (Villigen) and the French synchrotron radiation source SOLEIL (Orsay).

The aim of the workshop was to bring together the existing ultrafast laser community and the emerging ultrafast X-ray community in order to discuss recent scientific highlights from both fields and to outline new directions for the application of ultrafast X-rays.     

On the experimental verification of the Landau-Pomeranchuk-Migdal effect

A theoretical explanation is given for the “unexpected” behavior recently observed in the radiation spectrum of ultrarelativistic electrons in a thin layer of matter in an experimental investigation of the Landau-Pomeranchuk-Migdal effect at SLAC [S. R. Klein et al., Preprint SLAC-6378, Stanford (1993); P. L. Anthony et al., Phys. Rev. Lett. 75, 1949 (1995)]. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 11, 837–840 (10 June 1996)     

100 MeV电子直线加速器的物理设计

 能量为100 MeV左右的高性能电子直线加速器是第三代同步辐射光源注入器和自由电子激光注入器的重要组成部分,采用热阴极栅控电子枪、聚束系统和4根SLAC型加速管作为加速器主体结构,一套45 MW的速调管调制器系统和波导系统作为微波功率源系统。设计中,使用了国际通用的模拟软件对加速器的动力学特性进行了数值模拟和参数优化,电子束能量达到100 MeV以上,能散小于1%,归一化发射度小于30 mm·mrad。     

Synchrotron Stories from Stanford—From a Parking Lot to First Beam

Our journey in synchrotron radiation started in July 1972 when we joined a group at Stanford led by Seb Doniach and Bill Spicer to build a “Pilot Project” to test the feasibility of performing X-ray photoemission experiments on the newly commissioned SPEAR storage ring at SLAC. The SPEAR ring was expressly built for high-energy physics using colliding electron and positron beams (ultimately discovering the existence of quarks and garnering two Nobel prizes). As a result, anything we did could not interfere with the high-energy physics experiments.     

Towards one machine, two purposes: using a common SC linac for XFEL and ERL simultaneously

The linac based XFEL and ERL are advanced (or, say, 4th generation) light sources, with different electron beam parameters and different advantages. However, the linac used for XFEL and ERL should provide very advanced beams with high energy, high peak and/or average current, very low emittance and low energy spread, thus making the linac very complicated and expensive. To share the XFEL and ERL advantages and save the construction-operation budget, a proposal of using a common superconducting electron linac for hard X-ray XFEL and ERL is described in this paper. The interactions between the XFEL and ERL beams via the accelerating structure are studied and the result is positive.     

Femtosecond X-rays from relativistic electrons: new tools for probing structural dynamics

Femtosecond X-ray science is a new frontier in ultrafast research in which time-resolved measurement techniques are applied with X-ray pulses to investigate structural dynamics at the atomic scale on the fundamental time scale of an atomic vibrational period (∼100 fs). This new research area depends critically on the development of suitable femtosecond X-ray sources with the appropriate flux (ph/(s·0.1% BW)), brightness (ph/(s·mm²·mrad²·0.1% BW)), and tunability for demanding optical/X-ray pump probe experiments. In this paper we review recently demonstrated techniques for generating femtosecond X-rays via interaction between femtosecond laser pulses and relativistic electron beams. We give an overview of a novel femtosecond X-ray source that is proposed based on a linear accelerator combined with X-ray pulse compression.     

Femtosecond hard X-ray plasma sources with a kilohertz repetition rate

Laser-driven plasma sources of femtosecond hard X-ray pulses have found widespread application in ultrafast X-ray diffraction. The recent development of plasma sources working at kilohertz repetition rates has allowed for diffraction experiments with strongly improved sensitivity, now revealing subtle fully reversible changes of the geometry of crystal lattices. We provide a brief review of this development and present a novel plasma source with an optimized mechanical and optical design, providing a high flux of several 10¹⁰ photons/s at the Cu-Kα energy of 8.04 keV and a pulse duration of ≤300 fs. First experiments, including the generation of Debye–Scherrer diffraction patterns from Si powder, demonstrate the high performance of this source.     

Ultrafast structural dynamics with table top femtosecond hard X-ray and electron diffraction setups

The following tutorial review is directed to graduate students willing to be part of the emerging field of ultrafast structural dynamics. It provides them with an introduction to the field and all the very basic assumptions and experimental tricks involved in femtosecond (fs) diffraction techniques. The concept of stroboscopic photography and its implication in ultrafast science are introduced. Special attention is paid to the generation of ultrashort electron and hard X-ray pulses in table top setups, and a direct comparison in terms of brightness and temporal resolution between current table top and facility-based methodologies is given for proper calibration. This review is focused on ultrafast X-ray and electron diffraction techniques. The progress in the development of fs-structural probes during the last twenty years has been tremendous. Current ultrafast structural probes provide us with the temporal and spatial resolutions required to observe atoms in motion. Different compression approaches have made it possible the generation of ultrashort and ultrabright electron pulses with an effective brightness close to that of fs-hard X-ray pulses produced by free electron lasers. We now have in hand a variety of ultrafast structural cameras ready to be applied for the study of an endless list of dynamical phenomena at the atomic level of inspection.     

PULSE Ultrafast X-ray Summer School

The Third Annual Ultrafast X-ray Summer School (UXSS 2009) was held from June 15–19, 2009, at the SLAC National Accelerator Laboratory (SLAC) and sponsored by the PULSE Institute for Ultrafast Energy Science. The summer school was a weeklong residential event that brought together about 100 students, post-doctoral researchers, and other young and established scientists from diverse backgrounds. Particular emphasis was given to new scientific opportunities enabled by the world's first hard X-ray free electron laser, the Linac Coherent Light Source (LCLS), which underwent a spectacular start-up only months before.     

国际高能脉冲X射线闪光照相加速器的发展综述北大核心CSCD

高能脉冲X射线闪光照相加速器在高性能爆轰流体动力学实验研究中具有重要应用,是牵引高功率脉冲技术发展的重大需求之一。综述了射频直线加速器、电子感应加速器、基于高压脉冲源和高功率二极管的强流脉冲功率加速器3大类、5种闪光照相加速器技术路线的主要特点、代表性装置,对比了几种技术路线的特点,展望了未来发展趋势:一是大力发展共轴多脉冲X射线分幅照相技术;二是采用全固态脉冲功率组件实现加速器紧凑化、小型化和可移动。     

Meeting Report: SSRL School on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences: Theory and Application

Modern synchrotron-based X-ray scattering (SR-XRS) techniques offer the ability to probe nano- and atomic-scale structures, interfaces, and order/disorder relationships that govern the properties of advanced technological and environmental materials. Important materials studied at the Stanford Synchrotron Radiation Laboratory (SSRL) include thin films and interfaces, nanoparticles, amorphous materials, solutions, polymers, and bacteriogenic minerals. Good planning and a working knowledge of beam lines and techniques are required to successfully conduct SR-XRS measurements. This second annual School at SSRL on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences, held at the Stanford Linear Accelerator Center (SLAC) on May 15–17, 2007, provided a practical users' guide to planning and conducting scattering measurements at SSRL beam lines, with an emphasis on information that cannot be found in textbooks. More than 45 researchers, mostly graduate students and postdocs, participated in this crosscutting workshop. Attendees represented a variety of fields including material sciences, applied physics, environmental sciences, and chemistry.     

超快X射线自由电子激光研究进展北大核心CSCD

现代光源的发展不断推动着人们从更深层次上理解物质的基本结构和动力学行为。X射线自由电子激光作为最先进的光源,其超高的峰值功率、超短的脉冲长度和优良的相干性,为人们以原子级时空分辨率探测和操控物质中的超快过程提供了可能。目前全世界已有多个X射线自由电子激光装置建成并投入使用,在原子分子物理、化学、生命科学、材料科学等各学科应用中都显示出了重要价值。同时大量的研究工作也集中于继续提高X射线自由电子激光的性能,包括把脉冲持续时间从fs量级进一步缩短至as量级,这将为超快科学的发展带来新突破。以超快脉冲产生为主线,综述了近年来超快X射线自由电子激光产生方案的研究进展,从产生原理、方案特性、最新成果等方面介绍了各类产生方案,总结对比了各方案的优缺点,最后对超快X射线自由电子激光的未来发展方向进行了展望。     

Ultrafast Dynamics Using Free Electron Laser Sources

As avid readers of SRN know, free electron lasers have recently emerged as important synchrotron-radiation-based tools for a broad range of scientific studies. The combination of their short wavelength (from VUV to hard X-ray) with their exceedingly brief pulses (down to a few femtoseconds), high pulse energy, and coherence makes them particularly useful tools for studying ultrafast dynamics with chemical specificity and atomic-scale structural sensitivity.     

Physics design of a 10 MeV, 6 kW travelling wave electron linac for industrial applications

We present the physics design of a 10 MeV, 6 kW S-band (2856 MHz) electron linear accelerator (linac), which has been recently built and successfully operated at Raja Ramanna Centre for Advanced Technology, Indore. The accelerating structure is a 2π/3 mode constant impedance travelling wave structure, which comprises travelling wave buncher cells, followed by regular accelerating cells. The structure is designed to accelerate 50 keV electron beam from the electron gun to 10 MeV. This paper describes the details of electromagnetic design simulations to fix the mechanical dimensions and tolerances, as well as heat loss calculations in the structure. Results of design simulations have been compared with those obtained using approximate analytical formulae. The beam dynamics simulation with space charge is performed and the required magnetic field profile for keeping the beam focussed in the linac has been evaluated and discussed. An important feature of a travelling wave linac (in contrast with standing wave linac) is that it accepts the RF power over a band of frequencies. Three-dimensional transient simulations of the accelerating structure along with the input and output couplers have been performed using the software CST-MWS to explicitly demonstrate this feature.     

User Training at SSRL: Crystallography,X-ray Absorption Spectroscopy,Small-Angle X-ray Scattering,and X-ray Scattering Techniques

The Stanford Synchrotron Radiation Lightsource (SSRL) is a national scientific user facility at the SLAC National Accelerator Laboratory that provides high-brightness X-ray beams, innovative experimental facilities, and expert scientific support as a resource to study our world at the atomic and molecular level. Operating within this context and being closely associated with a major research university (Stanford), SSRL is strongly committed to providing unique educational experiences, and serves as a vital training ground for future generations of scientists and engineers. As part of this program, SSRL oversees a series of schools and workshops each year which deliver theoretical, experimental, and hands-on training by leading experts in their respective fields. Several of the courses held this year, attended by graduate students, postdoctoral fellows, educators and junior/senior investigators, are described in this report.