hours of beamtime to public users (i.e. 2000 hours in. 2009 and over 4000 ... strength and pulse delay, and adjusting the kicker tilt by a mechanical adjuster.
● ● Feature Articles
Current Status of the Shanghai Synchrotron Radiation Facility Z. T. Zhao, H. J. Xu, J. H. He, L. X. Yin, W. Z. Zhang, B. C. Jiang Shanghai Institute of Applied Physics, Chinese Academy of Sciences
Abstract The Shanghai Synchrotron Radiation Facility (SSRF), a 3.5 GeV storage ring based third generation light source, became open for user operations in May 2009. The performance of the SSRF complex and its user operation status in the past three years are described in this article. Brief descriptions of the experiments and achievements of some researchers at SSRF are also presented.
An Overview of the SSRF Project The Shanghai Synchrotron Radiation Facility (SSRF) was funded jointly by the Central Government, the Chinese Academy of Sciences and the Municipality Government of Shanghai. They aimed to build an advanced third generation light source of high performance and cost effectiveness, while also providing powerful x-rays for users in China and other parts of the world in various fields of research. A third generation light source was first proposed in mainland China in 1993 and was shaped later as the SSRF in 1995. The SSRF R&D project was carried out from 1999 to 2011. Finally the whole project was formally approved by the central government in 2004, and its groundbreaking was performed on December 25, 2004. Since then, the project construction proceeded very smoothly and quickly. The first synchrotron light was obtained at SSRF within three years, and user operations started in May 2009.
circumference, and seven phase-I beamlines, as shown in Figure 2. The SSRF storage ring was designed to run at a beam current of up to 300 mA with beam emittance of 3.9 nm·rad at 3.5 GeV. With advanced insertion devices, it can provide high intensity x-rays of 1020 photons / (s·mm2·mrad2·0.1%·BW) in the maximum brilliance. In November 2006, installation of the accelerators began with SSRF’s linac. The commissioning of the linac, which started in May 2007, was completed in July 2007 with all the parameters being fulfilled within the design specifications. The commissioning of the SSRF booster started in September 2007 and the commissioning of the SSRF storage ring started in December 2007. The first synchrotron light was quickly obtained at SSRF in December 2007, three months ahead of the schedule. The commissioning of the first beamline started in May 2008. By the end of April 2009, all accelerators and beamlines were tuned carefully and their parameters were measured systematically [1] with the conclusion that “all the design specifications of accelerators have been met and all the beamlines have reached the requirements for user operation.” User operations started immediately afterward. Users pouring into SSRF for experiments marked a happy end to the construction phase of SSRF, while also indicating the beginning of a new phase at SSRF. Since May 2009, SSRF has been fully open to users and many interesting results have been obtained in various research fields.
The SSRF complex consists of a 150 MeV linac, a full energy booster, a 3.5 GeV storage ring of 432 meters in
Fig. 1: Bird’s-Eye View of the SSRF Campus
6
AAPPS BULLETIN
Fig. 2: The SSRF Complex
Current Status of the Shanghai Synchrotron Radiation Facility ● ● The SSRF Accelerator Complex The SSRF linac consists of a 100kV electron gun, a 500MHz sub-harmonic buncher, a fundamental buncher and four sections of three meter-long 3GHz traveling wave accelerating structures powered by two 50MW klystron amplifiers. It has two operation modes, i.e., a single bunch mode with pulse length of 1ns and a bunch charge of 0.2 nC~1 nC (as required for injections), or alternatively the multi- bunch mode with a pulse length of 200 ns and a macro bunch charge above 5 nC [2]. The SSRF booster is a 2Hz electron synchrotron with emittance of ~100 nm·rad at 3.5GeV. It accelerates electrons from the energy of 150 MeV to 3.5 GeV in 250ms. The SSRF injector (including a linac, a booster and two transport beam lines) was designed for top-up injection. The booster lattice is based on a FODO structure with missing dipoles, forming 28 cells with 8 straight sections in 2-fold symmetry. The SSRF booster has been serving as a stable injector for the SSRF storage ring since December of 2007 [3]. The SSRF storage ring is composed of 20 double-bend lattice cells in 4-fold symmetry. Each lattice cell contains two bending magnets, 10 quadrupoles and seven sextupoles. All the ring quadrupoles are independently powered to keep the lattice flexibility. There are 16 standard straight sections that are each 6.5 meters long, and four long straight sections that are each 12 meters long. Three super-conducting RF cavities are located at a long straight section to compensate for the beam energy lost by radiation. Injection kickers and septum have been installed in another long and straight section to minimize injection disturbance. There are 140 beam position monitors (BPMs) and 80 steer magnets distributed along the ring to measure and correct the beam orbit. A bunchby-bunch transverse feedback system with a bandwidth of 250MHz is employed to counteract the resistive wall impedance and fast ion caused instabilities. Table 1: Main Parameters of the SSRF Storage Ring
The performance of the storage ring lattice is determined by the choice of betatron tunes and beta functions in the straight sections. One choice of the betatron tunes is Qx=22.22/ Qy=11.32. The resulting configuration has the natural emittance of 3.9 nm·rad. The main parameters of the SSRF storage ring are shown in Table 1. The storage ring performance has been continuously improved at SSRF, including reducing beam emittance and vertical beam size as well as the transeverse coupling in storage ring. With the SSRF hardware conditions, a lower emittance storage ring lattice has been figured out and optimized using the MultiObjective Genetic Algorithm (MOGA) with the predicted natural emittance 2.88 nm·rad at 3.5 GeV. This ring lattice has been commissioned online and the measured emittance is 2.9±0.2 nm·rad, which well matches the theoretical prediction. The main challenge for such a lattice is beam injection optimization. With great effort, the injection efficiency achieved has exceeded 50% by enlarging the dynamic aperture. The minimum transverse coupling can be corrected to 0.014% by using 30 skew quadrupoles. With coupling of less than 1%, vertical beam size can be controlled to less than 10μ m at the center of the straight section.
Phase-I Beamlines Seven beamlines were selected as phase-I beamlines, the choice of which was made based on extensive discussions which were held in the Chinese scientific community. They were expected to facilitate research in a number of fields, with emphasis on structural biology, materials science, chemical and environmental sciences, condensed matter physics, nano-sciences and biomedical applications. Construction for the phase-I beamlines was on schedule, with the commissioning of the first beamline in May of 2008 and the completion of the commissioning for all the phase-I beamlines in April of 2009. Table 2 lists the main specifications of the phase-I beamlines.
Operational Status and User Experiments Since May 2009, SSRF has provided over 11,000 hours of beamtime to public users (i.e. 2000 hours in 2009 and over 4000 hours both in 2010 and 2011), with an operational availability of 95.7% and 97.6% during the periods for user operation in 2010 and 2011, respectively. User operation availability has improved to 99.4% at the end of the first quarter of 2012. June 2012 Vol. 22 No. 3
7
● ● Feature Articles Table 2: SSRF Phase-I Beamlines*
flux constancy of experiments are greatly improved and increased. Top-up injection was tested and operated from the early commissioning of the SSRF accelerator complex to the later machine conditioning. In order to decrease the injection disturbance on the stored beam, some optimization works have been done, such as scanning the kickers’ strength and pulse delay, and adjusting the kicker tilt by a mechanical adjuster. The amplitude perturbation in both x and y planes is reduced to 20~30μm. At the end of 2011, user experiments with top-up operations were successfully tested [4]. The formal user top-up operations will commence in 2012 after getting the top-up operation radiation safety certificate from the government. A topup operation case at SSRF is shown in Figure 4.
Fig. 4: Top-up Operation Commissioning
In top-up operation mode, slow orbit feedback and RF frequency feedback can keep the orbit distortion within 2μm and 1μm in the horizontal and vertical planes, respectively. The fast orbit feedback system had been tested at the top-up operation condition of removing BPM current dependency. Sub-micron beam stability can be achieved in both horizontal and vertical planes. Seven phase-I beamlines are now in full operation. By the end of 2011, SSRF had received 3,267 user applications with total experiment time requests of 252,624 hours, which is three to four times as much as the seven beamlines can offer. Fig. 3: Operational Statistics
The MTBF (Mean Time Between Failure) increased from 28.3 hours in 2009 to 55.3 hours in 2011. Figure 3 shows the operational statistics for users of SSRF. The use of frequent filling or “top-up” operation is an important characteristic of modern synchrotron light sources. It means that electron bunches can be reinjected into the storage ring while synchrotron experiments are taking data. With a top-up operational mode, the beam stability, integrated photon flux and
8
AAPPS BULLETIN
By the end of 2011, SSRF provided to users 70,403 hours of experiment time for 2,171 peer reviewed proposals and received 3,487 individual users in 8,642 user visits from 224 institutions, including 114 universities, 76 research institutes, 15 hospitals and 19 companies. Based on scientific findings at SSRF, over 400 papers were published, including 10 papers in the three top ranking journals of Nature, Science and Cell, and 14 papers in journals of Nature series and Cell series. SSRF plays an important role in the development of China’s study of structural biology. Its operation brought an immediate change in that scientists in
Current Status of the Shanghai Synchrotron Radiation Facility ● ● mainland China who had utilized mostly foreign synchrotron radiation facilities to study structure biology are now supported by SSRF. They work to explore the frontiers of science and they have made important achievements in the structural studies of membrane proteins, protein complexes and diseaserelated proteins. Numerous important research results were achieved, such as the determination of the crystal structure of CED-4 apoptosome [5], which reveals an octameric assembly of CED-4 and suggests a mechanism for the activation of CED-3 and the initiation of programmed cell death in Caenorhabditis elegans. Other outstanding results include structural insight into brassinosteroid perception by BRI1 [6], the structure of a fucose transporter in an outward-open conformation [7], the structural basis for site-specific ribose methylation by box C/D RNA protein complexes [8], the structure of MyTH4-FERM domains in amyosin VIIa tail bound to cargo [9], and the structural basis for sequence-specific recognition of DNA by TAL effectors [10 ]. In materials science, the SSRF users carried out a number of studies on the structure of new materials and property modification of materials, including ferric superconductors, hydrogen-storage material, magnetic semiconductors, piezoelectric/ferroelectric material, crystalline material, and polymeric material. Some of the achievements raise interesting prospects for broad and important applications, e.g., graphene chiral liquid crystals observed in the world for the first time [11] and the re-emerging superconductivity at 48 kelvin in iron chalcogenides under high pressure [12] .
In environmental science, geo-archaeology and biomedicine, many experiments with particular features have been conducted by SSRF users and many interesting results have obtained. Among them are the research of the distribution and transport mechanism of toxic elements and chemical compounds in rice and vegetables. Others include the oxygen-carrying mechanism of suspended particles in polluted water, cardiocerebral vascular and tumor imaging, and the observation of differentiation of ancient embryos in fossils. So far, about 700 research groups across the country have performed various research projects at SSRF. How to do better work utilizing SSRF has become a key issue for improving the scientific competitiveness with high-level research. Over 10 enterprises have utilized SSRF for their R&D activities in order to further develop pharmacy, chemical engineering or appraisal techniques.
Table 3: New Beamlines Under Construction at SSRF
The research of nano-catalysts is another active field at SSRF. Understanding and controlling chemical reactivity by catalysts at the scale of atoms and electrons has a profound impact on chemical energy conversion and utilization. By using both in-situ and ex-situ XAFS and XRD experimental methods, scientists in China have made significant progress on the research of novel nano catalysts, which can be used in chemical production and other industrial applications. As a prominent example, a user group confirmed the presence of coordinative unsaturated sites confined in nano-sized catalysts, which have been proposed to be the main active centers in many catalytic reactions [13]. Other important results include the confirmation of isolated single Pt atoms anchored to the surfaces of iron oxide [14] and the characterization of the sub-nano Au catalyst supported on TiO2, which is an efficient heterogeneous catalyst for direct synthesis of quinolines from nitroarenes and aliphatic alcohols [15].
June 2012 Vol. 22 No. 3
9
● ● Feature Articles New Programs for SSRF
References
To meet the strong demand from the Chinese user community, new programs for more beamlines have been initiated. As shown in Table 3, six new beamlines are under construction, and among them, five beamlines are dedicated to protein sciences within the program of National Facility for Protein Sciences at Shanghai. Another beamline is a user funded soft Xray beamline with very high resolution for ARPES and PEEM. These six beamlines are scheduled to be completed in 2013.
[1] Z.T. Zhao H.J. Xu and H.Ding, Proc. PAC09, Vancouver, May. 4-8, 2009. 55-59.
The program to build a big bunch of new beamlines at SSRF, the so-called SSRF Phase II project, now ranks as one of the top priorities according to an extensive survey of the scientific community. It is aimed at covering a very wide range of synchrotron radiation techniques and research fields in order to provide strong support for the development of science and technology in China. After a series of user workshops and review meetings, the formal proposal of the SSRF Phase-II project is in preparation and will be soon submitted to the government for approval. In addition, about five user funded beamlines are in the design stage and are waiting for approval. Furthermore, a soft X-ray FEL facility will be built adjacent to SSRF in the campus. By 2020, there will be about forty beamlines at SSRF in operation together with the FEL facility, which will form a world-class photon science center.
[2] M.H. Zhao et al., Proc. EPAC08, Genoa, Italy, 3649-3651. [3] D.M. Li et al., Proc. EPAC08, Genoa, Italy, 2189-2191 [4] Z.T. Zhao et al., Proc. IPAC2011, San Sebastián, Spain, 3008-3010. [5] S.Q. Qi et al., Cell, 141(3): 446-457. [6] J. She et al., Nature, 474(7352):472-476. [7] S.Y. Dang et al., Nature, 467(7316):734-738. [8] J.Z. Lin et al., Nature, 469(7331);559-563. [9] L. Wu et al., Science, 331(11):757-760. [10] D. Deng et al., Science, 335(6069):720-723. [11] Z. Xu and C. Gao, Nature Communications,2:571. [12] L.L. Sun et al., Nature, 483(7387):67-69. [13] Q. Fu et al., Science, 328(5982):1141-1144. [14] B. Qiao, Nature Chemistry, 3:634-641. [15] L. He et al., Angewandte Chemie, 123 (43):10398 -10402.
Erratum: Anglo-Resolved Photoemission Spectroscopy Study on Iron-Based Superconductors Yan Zhang is a Ph. D student in the group of Prof. Donglai Feng at Fudan University. His research interests focus on the angle-resolved photoemission spectroscopy study of strongly correlated materials. Donglai Feng is a professor of Fudan University, and obtained his Ph. D at Stanford University in 2001. His research interests are focused on the electronic structure of highly correlated electron systems: hightemperature superconductors, Mott insulators, magnetic materials, low dimensional systems, etc., He is interested in developing high-resolution spectroscopies, VUV, x-ray, vacuum and synchrotron radiation instrumentation in searching for and understanding new materials. This article of the April issue contains erroneous author information which has been now replaced with Yan Zhang’s photo and CV. The error has been also corrected in the online version of the article available at www. aappsbulletin.org.
10
AAPPS BULLETIN
