Probing nature at the nanoscale with the world’s most powerful synchrotron light source
11 April 2008 (Volume 3 Issue 4)
The RIKEN Harima Research Institute, in Harima Science Garden City near the city of Aioi, Hyogo Prefecture, makes its home at SPring-8, the most powerful source of synchrotron light in the world. The facility’s 1,436 m storage ring encircles a mountain, Mount Mihara-Kuriyama, and within its confines some very exciting science is being done.
Built in 1997 by RIKEN and the Japan Atomic Energy Research Institute, SPring-8 (short for Super Proton Ring-8 GeV) has maintained its leadership position among third-generation synchrotrons for over 10 years, a longevity unheard of in the world of high-energy physics. The ‘number one’ rating, however, is a bit misleading, as Tetsuya Ishikawa, director of the SPring-8 Center, points out. “Because of technological advances made here at SPring-8, for some classes of experiments, synchrotrons don't have to be this big anymore to get the same synchrotron-radiation energy, he said.
The RIKEN SPring-8 Center operates 7 of the 62 beamlines at the facility, conducting research into X-ray spectroscopy, synchrotron-radiation physics, synchrotron-radiation crystallography, structural genomics, X-ray optics and structural biology.
A storage ring works by maintaining electrons in a circular path, close to the speed of light. At this velocity, when the electrons’ path is bent, they emit very intense light, known as synchrotron radiation, made up of radio waves, infrared light, visible light, ultraviolet light and X-rays.
The key innovation at SPring-8 has been the in-vacuum undulator, an array of permanent magnets with alternating polarity, through which electrons run at velocities close to the speed of light. Each period of the magnets bends the electron trajectory to emit synchrotron radiation, which constructively interferes giving it exceedingly high brilliance. Quasi-monochromatic light at specific wavelengths is generated at intensities about a billion times greater than conventional X-ray sources.
“The key advantage of the in-vacuum undulators is that we can make the magnetic period shorter. This makes relatively low-energy electrons emit high-energy photons,” Ishikawa says. He adds, before SPring-8, it was very difficult to deliver 0.1 nm wavelength X-rays using a small accelerator. But now, even a 3 GeV machine can deliver this level of radiation. Such X-rays are also extremely brilliant, and they exhibit a sharp directionality that is superior to laser sources. All of this makes them extremely useful for a variety of scientific tasks.
The facility will soon be getting an upgrade in the form of the XFEL, or X-ray Free Electron Laser. The XFEL is generating excitement in the research community as it promises radiation a billion times brighter than existing X-ray sources, with pulses 1,000 times shorter, a level that will allow real-time observation of objects at atomic-level resolution.
The new laser’s extremely fast femtosecond pulses will permit direct examination of the movements of atoms in motion within crystal lattices, and its ultrashort wavelength will permit observation of individual atoms.
This will allow, for example, close observation of proteins that cannot currently be analyzed. About half of the proteins in the cell membrane have not been analyzed, because for this they must be crystallized, which so far researchers have been unable to do. “We’ll also be able to learn a lot about the structure of viruses and protein complexes by applying the XFEL,” Ishikawa noted.
“With its extremely short pulse duration, about 1 femtosecond, or 10–15 seconds, we will be able to take snapshots of very fast movements. The peak intensity of the XFEL is 109 times that of SPring-8. So it’s going to be a revolution,” Ishikawa said. “The important point here is, no one has ever seen this light or worked with it anywhere in the world. No one knows what will happen with the XFEL’s light, or what it will reveal.”
Excitement is building within the scientific community, and applications are flooding in to SPring-8 to use the new laser, many of them for rather interesting and unexpected investigations.
“Before we built SPring-8, we had discussions for many years about what research we would do with it,” Ishikawa said. “And within two or three years, most of the research we had discussed was complete. Then the really interesting stuff started, after we saw what the light could do. We expect the same to happen with the XFEL.”
SPring-8’s operators are already looking beyond XFEL to consider the facility’s longer-term future. This may include upgrading SPring-8 itself, raising its performance by using the XFEL accelerator as an injector. Plans are already being discussed, with a possible completion date of around 2019–2020.
Watching the motion of atoms
Alfred Q. R. Baron
Associate Chief Scientist, Materials Dynamics Laboratory
Alfred Baron, head of the Materials Dynamics Laboratory at the RIKEN SPring-8 Center, and his team are working to understand the motion of atoms in materials.
X-rays are well known as a tool to investigate the average positions of atoms—their wavelength is similar to interatomic distances, allowing investigation of atomic positions on the same scale, using such techniques as X-ray crystallography and powder diffraction. But given a strong enough X-ray source, SPring-8, for example, it is also possible to directly investigate atomic motions. “If you look on extremely short, picosecond (10 s) and subpicosecond timescales, atoms inside materials are constantly in motion—they never stop moving,” says Baron.
Atomic motions are intimately connected with many physical properties of materials. Many changes in material structure (phase transitions) can be linked with a slowing or ‘freezing in’ of a particular mode of vibration, or phonon. On a more sophisticated level, cooperative effects between atomic and electronic motions drive superconductivity and also, perhaps, more subtle features of technologically relevant materials.
Using the 10 metre inelastic X-ray scattering spectrometer at beamline BL35XU of SPring-8, Baron and his co-workers are investigating new superconductors, liquids, glasses, and other materials to see how their dynamics change under different conditions. The work has yielded some interesting results, including the first-ever observations of changes in atomic dynamics as a liquid metal shifts from conductor to insulator when heated.
Baron is now working on a new, longer beamline, which will be more powerful by a factor of 20 or more. “Building the longer beamline is the right thing to do, and it is uniquely possible at SPring-8,” he says.
A native of the USA, Baron came to Japan 10 years ago, after working as a researcher in the USA and Europe. The time at SPring-8 has been good for him, both professionally and personally, and, if the proposal for the new facility is successful, the project will keep him in Japan for some years to come.
