Introduction

Shanghai Synchrotron Radiation Facility (SSRF) is one of the advanced third-generation synchrotron radiation facilities in the world [1]. Since its official start of operation in May 2009, SSRF has provided user beam time of about 522,820 hours and served more than 40000 users coming from universities, institutes, hospitals, and high-tech companies from home and abroad. Over 10,000 papers have been published based on the experiments conducted at the SSRF.

However, even though a number of beamlines were built in Phase I [2], and even with the addition of dedicated beamlines built subsequently, the SSRF still could not meet the huge user demand. In this context, the SSRF Phase-II Beamline Project proposed building 16 state-of-the-art beamlines, realizing nearly 60 new experimental methods, and equipping them with offline user experimental assistance support [3, 4]. The latest beamline layout of the SSRF is shown in Fig. 1. This new experimental ability is mainly reflected in the following aspects:

Fig. 1Full-screen View

(Color online) Layout of SSRF Beamlines. Phase I beamlines, dedicated user beamlines, Phase II beamlines, and beamlines under construction are distinguished by different colors

● Energy range: Many enhanced photon energy options such as high-brightness infrared for molecular structure analysis, tender X-rays for elemental analysis of P, S, and Cl in environmental science, ultrahard X-rays for structural analysis of aircraft engine materials, and γ-rays for photonuclear physics.

● Spatial resolution from micrometers to nanometers: Enriched beam-size options, such as sub-micrometer X-ray beams for membrane protein structure analysis; spatial resolution of tens of nanometers by X-ray nano-probe or X-ray nano-CT for analysis of elemental mapping, chemical state, and nano-structures in environmental science, material science, and industry applications. Striking examples are lithium-ion batteries or nanoscale semiconductor devices.

● Time resolution from milliseconds, microseconds to picoseconds: Many enriched time resolution options for observing electron/atomic/molecular structures on picosecond, nanosecond, microsecond, or millisecond time scales in the rapid reaction process of a catalytic system to recognize the catalytic active site and selectivity, clarify the catalytic reaction process, and reveal the catalytic mechanism; to observe the microstructural evolution of polymer materials on a millisecond time scale during the impact process; and to investigate the deformation and failure behavior of materials under impact loading and high-speed fuel spray processes of automotive engines by picosecond X-ray single pulse imaging.

● Industry applications: Long beamlines for in situ monitoring of the structural evolution process of polymers in pilot-scale experiments and in situ characterization of engineering materials of large sizes in a serving environment.

● High sensitivity: chemical sensitivity (1ppb) and single-atom-level detection capability for environmental and geological sciences.

● Techniques combining multiple regions of the spectrum: To observe the same dynamic process from different viewpoints by combining complementary synchrotron radiation techniques, for example, the combination of X-rays and infrared (IR) can simultaneously detect the atomic, electronic, and molecular structures, and the combination of hard and soft X-rays can detect the electronic and chemical structures of a film layer by layer.

● Hazardous and radioactive samples: Biosafety P2 protection facilities dedicated to the macromolecular crystal structure analysis of moderate-risk infectious viruses; radioactive protection facilities dedicated to the composition and structure characterization of radioactive materials.  

● User data center: for mass user data storage, real-time data analysis, deep data mining, artificial intelligence, and automation.

Accelerator upgrades

To meet the requirements of these new beamlines in the project, the storage ring has been upgraded accordingly, including the replacement of dipoles with super-bends in two cells, the construction of a 650-W helium cryogenic system, the development of a bunch-length control system, and an upgrade of the beam diagnostics and control systems.

The SSRF lattice was modified with two super-bend-based DBA cells and two straight sections (ID11, ID16) were inserted in a quadrupole triplet so that each creates double mini-β_y optics for accommodating dual canted undulators.

A 3rd harmonic superconducting cavity system was developed and installed to lengthen the bunch in the passive operation mode. A 650-W helium cryogenic system was built to support the 3rd harmonic superconducting cavity and the superconducting wiggler, which can be switched to support the main RF cavities as backup when the phase-I cryogenic system fails. The hybrid filling pattern of the storage ring allows a single bunch current of up to 24.5 mA and a bunch train of 200 mA in the ring with the help of a transverse feedback system and a 3rd harmonic cavity, which can suppress instabilities and stretch the bunch length. This hybrid filling mode provides powerful support for single-pulse imaging and pump-probe transient structure research. The main parameters of the storage ring are listed in Table 1.

New Beamlines

Sixteen beamlines (including one RIXS station) were built in this project, the main specifications of which are listed in Table 2. The photon energy extends to previously uncovered regions, such as the tender X-ray region, super-hard X-ray region, and low-energy gamma-ray region. Beamline design has strengthened support for the industry. In practice, the design and construction of beamlines are extremely difficult. For example, one straight section usually has to consider supporting two beamlines to allow as many beamlines as possible for use, one beamline usually connects multiple end-stations to provide more methodology choices for users, and several experimental end-stations will realize state-of-the-art techniques that combine multiple regions of the spectrum with challenging technical difficulties that need to be solved.

In this paper, a brief description of the new beamlines is introduced, and a detailed description of this special issue can be found.

User Experimental Support

The experimental support for users includes materials laboratories, chemical laboratories, biomedical laboratories, in situ instrumentation pools, and user data centers. They are another essential part of the SSRF Phase II beamline project with the goals of serving users in various aspects and effectively improving the comprehensive experimental capabilities at the SSRF.

(1) The material preparation laboratory satisfies the user requirements for material sample preparation. It provides sample preparation and auxiliary measurements for high-pressure materials, micro-and nanomaterials, etc.

● Powder sample pressing: 5–8 mm

● High temperature treating: 25–1900 K

● Thin film cutting: 0.1–25 mm

● SEM / TEM: 3nm /0.1nm

(2) Chemical and environmental laboratory: Chemical sample preparation and on-site treatment, such as auxiliary component testing and auxiliary structure analysis

● Operating environment: H₂O <1 ppm, O₂< 1 ppm

● Sample storage: – 85 °C ~ –10 °C

● Particle crushing: 40 – 150 µm

(3) Biology and medicine laboratory: provides the basic experimental conditions for biomedical sample preparation on site, auxiliary testing of biomacromolecules and sample preparation, tissue sample preparation, and treatment.

● Slice thickness: 1–100 µm

● Slice temperature: –35 – 0 °C, 5 K

● Freezing rate: 18000 °C /s

(4) In situ instrumentation pool: This provides in situ equipment for the experimental station, such as for changing the temperature, pressure, vacuum, and magnetic field.

● Temperature: 4.5–2600 K

● Magnetic field: 0~8000 Gs

● Vacuum transmission device: 1.0×10^-9 Torr

● Tensile loading: 5 kN

(5) User data center: With 23 PB storage, 11000 CPU cores, 28 GPUs, and 19 edge clusters for beamlines, it provides mass data storage, real-time data analysis, deep data mining, and artificial intelligence and automation. A schematic view of the big data framework in the user datacenter is shown in Fig. 2.

Fig. 2Full-screen View

(Color online) A schematic view of the big data framework in the User Data Centre, encompassing experiments, scientific computing, data acquisition, storage, analysis, management and visualization, aimed at increasing the SSRF users’ scientific productivity, leveraging Big Data, AI, robotic automation, HPC and national supercomputing technologies

● CPU+GPU: Rpeak 967 Tflops

● Store capacity: 23 PB HDD + 100 TB SSD

● Bandwidth to beamline: 40 GB/s

Beamline Technique Support

The beamline technique support supports the construction of optics, mechanical engineering, control and electronics, engineering analysis, and test beamlines. The primary specifications of the X-ray test beamline are listed in Table 3. As an essential part of the SSRF Phase-II Beamline Project, beamline technique support will provide solutions for various key technical issues regarding the development, installation, tuning, and testing of the equipment used at beamlines. In the future, they will ensure the highly efficient operation of the beamlines.

High-performance X-ray optics are the basis and prerequisites for the construction of advanced synchrotron radiation beamlines and experimental stations. Highly brilliant and coherent X-rays are deflected, collimated, changed to be monochromatic, and focused by a series of optical components before being delivered to the sample for scientific experimental research. Therefore, the full utilization of the coherent wavefront and ultrahigh brightness of advanced X-ray light sources depends on the performance of the optical components. Through domestic cooperation and taking advantage of the high-precision optical metrology technology developed by the SSRF, a 1000-mm-long plane mirror with a 0.2-μrad slope error and a multilayer monochromator have been successfully developed.

High-performance key equipment guarantees the construction of advanced beamlines for the project. A series of core equipment was developed to meet the requirements of the beamlines in the SSRF Phase-II Beamline project. For example, the high energy sagittal-focusing Laue monochromator can achieve small radius dynamic bending of ultra-thin crystals, the size of the focusing spot reached 260 µm. The cryo-cooled meridian bent Laue monochromator was first domestically developed and has passed the test acceptance. The plane-grating monochromator realized cryo-cooling of high heat load plane mirrors for the first time. Meanwhile, a number of general key equipment, such as a sub-microradian mirror bender system, a cryo-cooled double crystal monochromator and a precision monochromatic slit have also been developed. The slope error of the mirror bender was less than 0.4 μrad (RMS), and the bending curve resolution and repeatability of the bender was less than 0.5%(∆R/R). The relative stabilities of the first and second DCM crystals were 63 nrad (RMS). The performance of this general key equipment meets the requirements of most beamlines in the project.

The control systems were designed using the EPICS (Experimental Physics and Industrial Control System) [5] and the Bluesky Data Collection Framework. The system supports motion control, detector control, and equipment protection at the beamlines. Hardware for stepper motor control was developed. The synchronization accuracy of the hardware for fly scanning reaches 20 ns, which can meet most requirements for fly scanning experiments. A beam position monitor (BPM) and its current front-end amplifier have been developed successfully with precisions of 1 mm and 1pA, which can play important roles in nanometer positioning feedback control. The control system is equipped with single-pulse timing synchronization control and measurement instruments, such as an event timing system and a streak camera, which can support the timing control of picosecond time-resolved pump-probe experiments. EPICSv7, the most cutting-edge EPICS technology, has been researched and used in a control lab to overcome the bottlenecks of big data communication and enhance the overall performance of the control system.

Conclusion and Perspectives

Since its first operation in 2009, the SSRF has greatly accelerated the development of photon science in mainland China. The completion of the SSRF Phase-II Beamline Project is believed to bring the experimental capability of the SSRF to a new level, with rich and diverse choices in photon energies, methodologies, and in situ conditions, mutual promotion of offline and online experiments, rapid data processing and analysis, and various resolution abilities close to the limit of the third-generation light source. Figure 3 shows the latest bird’s-eye view of the SSRF.

Fig. 3Full-screen View

(Color online) Bird view of SSRF

The construction of the SSRF Phase II Project has been conducted while the SSRF is still in operation, which brought great challenges to project management, installation, and testing. The first beamline, the hard X-ray spectroscopy beamline, was completed and began commissioning at the end of 2018, whereas the last two beamlines, the hard X-ray nanoprobe beamline and the medium-energy spectroscopy beamline, were completed at the end of July of that year. Till the end of 2023, SSRF Phase II beamlines have provided 45,741 h of beamtime and executed a total of 1152 research proposals from 678 research teams, with 368 user papers published, including seven CNS papers [6-12]. The next step is to optimize machine performance for stable operation and to organize and promote large scientific research projects.

To date, 34 beamlines in the SSRF are in operation, and nearly 100 types of advanced experimental methods have been realized. This systematic and state-of-the-art experimental facility for third-generation synchrotron radiation, particularly the SSRF Phase II Beamline Project, is anticipated to contribute significantly to cutting-edge science and technology.