SACLA X-ray Free Electron Laser FacilityScience Technology
The X-ray free electron laser facility at the Riken Harima Institute in Hyōgo Prefecture has produced an X-ray free electron laser beam with the shortest wavelength in the world. This SPring-8 Angstrom Compact Free Electron Laser (SACLA) facility, completed in March 2011, produces the XFEL using electron beams generated by an electron gun. The XFEL is a new type of light that will allow researchers to study, at the atomic level, the structure of matter and the instantaneous changes to this structure. The facility is now conducting test operations so that necessary adjustments can be made, and it should be ready for public users from Japan and overseas by March 2012.
The Light Beam “Sees” Momentary Atomic Changes
The wavelength of an XFEL and of an X-ray are in the same range. An X-ray has a short wavelength and a great capacity for penetrating solid matter; while in the case of a laser, used in applications such as high-speed optical communications and DVDs, all the individual waves of this strong type of light are perfectly aligned. The XFEL, by combining the outstanding properties of both an X-ray and a laser, is a billion times brighter than a ray from existing X-ray sources and has a shorter wavelength than those in conventional lasers. This means that the laser beam can be used to conduct minute observations at the level of atoms and electrons . One possible XFEL application would be the analysis of the individual cell membrane structure of protein molecules, which will benefit the development of pharmaceutical drugs because 60% of those currently available act on membrane proteins. Moreover, because XFELs flash for an exceptionally brief time (around 10 trillionths of a second) they can be used like an ultra-high speed photographic flash to capture images of momentary atomic changes or extremely fast chemical reactions. Researchers will thus be able, for the first time ever, to observe the momentary changes of the infinitesimally small atomic world.
A Compact and Energy-Efficient Facility
The long, narrow SACLA facility consists of an accelerator building, an undulator building, and an experimental facility, all joined together in a straight line that only extends around 700 meters in length. The electron gun at the mouth of the accelerator generates an electron beam, which is accelerated to nearly the speed of light by the 400 m accelerator. In the undulator building, XFELs are produced from the electron beam by the undulator, a device made up of a number of powerful magnets arranged next to each other. The force of the magnets causes the electrons to move in an undulating path. At the exit of the undulator, the generated XFEL is processed by the beamline so that it can be tailored for use in specific experiments.
There are only two XFEL facilities in the world, one in the United Stated and another one is SACLA. Efforts are underway to generate the XFEL in Europe as well, but a particular feature of SACLA is that it is both compact and energy efficient. The newly developed accelerator has twice the accelerating capacity of existing ones, so its accelerator tubes can be shorter. Moreover, its undulators use a technology known as “in-vacuum” that allows them to produce the XFEL using a lower energy electron beam than those used at other facilities. As Ishikawa Tetsuya, director of the Riken Harima Institute, explains, “Bringing together Japan’s unique technologies made it possible for us to build a facility that is just a quarter the size of facilities located in the United States and Europe.”
Technology Paves the Way for New Research
SACLA is a facility that is sensitive to the minutest changes in conditions. When the undulators which produce the laser were installed and aligned, for instance, even the curvature of the Earth had to be taken into account to ensure that the light traveled along an absolutely straight path. Thanks to this tiny modification, the axis of the beam deviates from its true path by no more than 0.1 millimeters over the 120 m distance of the lined-up undulators. SACLA has been brought to completion through these sorts of minute adjustments. But there is no room for complacency, as one of the developers explains: “We are now coming to the crucial time because when the facility becomes operational we may encounter unexpected phenomena.”
It took five years to complete the facility, and apparently some initially wondered whether it was truly feasible. Now that the facility has been completed without any mishaps, and the laser successfully generated, there is an excited feeling of anticipation among both the researchers who plan to use the facility and those who built it. The potential users view it as just the sort of facility they have been waiting for, while the developers hope that as many researchers as possible will make use of the new technology.
On July 13 an XFEL beam with the shortest wavelength in the world, a mere 0.08 nm (1 nm = 1 billionth of a meter) was confirmed. “By adjusting the beam,” Director Ishikawa says with pride, “we will be able to produce an even shorter wavelength.”
For its future data analysis, the facility plans to team up with the world’s leading next-generation supercomputer, “K computer,” located in Kobe at the Riken Advanced Institute for Computational Science. Director Ishikawa has ambitious plans, hoping that the collaboration will “open up new horizons for science.”
Overcoming the limits of existing technology has cleared the way for ground-breaking research such as explaining the structure and function of membrane proteins, which is essential for the development of pharmaceutical drugs and ultra-high precision micro-processing technology. In the years to come we can look forward to such practical applications from research conducted at the SACLA facility.
(Originally written in Japanese by Satō Narumi, freelance writer. Photographs by Hans Sautter.)