X-Ray Laser on Course

The Linac Coherent Light Source (LCLS) undulator system, which will be the first x-ray free-electron laser, is on course for completion in March 2009, said Argonne National Laboratory, a partner lab in the project.

The laser, which will operate at the Stanford Linear Accelerator Center (SLAC), "will be the first x-ray laser to combine the brilliance of laser sources with the penetrating power and atomic sensitivity of x-rays," Argonne said in a statement.

The project is also the first time such ultraprecise undulators were mass-produced in America by nonspecialized small businesses, said Emil Trakhtenberg, Argonne senior mechanical engineer at the Advanced Photon Source (APS), the electron accelerator and storage system that are the first steps in producing the high-energy x-rays .

The diagram illustrates the path of electrons through the Linac Coherent Light Source and the resulting x-ray beams. The linac (linear accelerator) accelerates a linear beam of electrons that pass through undulators, which force the electrons to oscillate back and forth. The oscillations produce large amounts of x-rays. These x-rays interact back on the electrons and force them to bunch at x-ray wavelengths. When this occurs, the electrons emit their light coherently, causing a large gain in radiation power that raises the x-rays' intensity. The result, when the LCLS begins operations in 2009, will be x-ray beams one billion times brighter than can be produced by any other x-ray source. (Image courtesy LCLS)

"Argonne was tapped to participate in this project due to the expertise demonstrated with the APS undulator systems," said J. Murray Gibson, associate laboratory director of Argonne's Scientific User Facilities. "An x-ray laser such as LCLS will open up new scientific frontiers and represents an immense technical achievement for the United States."

Argonne LCLS Project Director Geoff Pile said the last of the 40 LCLS undulators was assembled and accepted by Argonne late last month, on time and within budget, from Hi-Tech Manufacturing in Illinois and Metalex Manufacturing in Ohio.

Isaac Vasserman (left) and Matt Kasa of Argonne's Accelerator Systems Div. prepare an undulator for magnetic tuning and verification. (Image courtesy LCLS)

The LCLS project is funded by the US Department of Energy and is a collaboration of six national laboratories and universities, including SLAC, Argonne and Lawrence Livermore National Laboratory. Argonne is responsible for the 130-meter undulator system, including magnets, support structures, beam diagnostics, controls and vacuum systems.

Undulators are the heart of the LCLS free electron laser, providing a precise magnetic field through which an electron beam will travel. The undulators' magnetic fields force the electrons to oscillate back and forth and produce large amounts of x-rays. These x-rays interact back on the electrons and force them to bunch at x-ray wavelengths. When this occurs, the electrons emit their light coherently, causing a large gain in radiation power that raises the x-rays' intensity.

Detail of a completed undulator. (Image courtesy LCLS)

Each undulator comprises a precision-tuned array of ultrastrong neodymium-iron-boron permanent magnets and vanadium permendur magnetic poles. The magnets and poles are mounted in aluminum structures bolted into a 3.4-meter-long titanium strongback. The strongback secures the magnet and pole assemblies, counteracts the very high magnetic forces between the upper and lower magnetic arrays, and is critical in determining the thermal and mechanical stability of the undulator. Precision and stability requirements for the LCLS devices far exceed those for existing undulators at the Advanced Photon Source and other light-source facilities, Argonne said.

The pulses of x-ray laser light from LCLS, a fourth-generation light-source, will be shorter and a billion times brighter than any that can be produced by x-rays sources -- now or in the near future, the lab said.

"These advanced characteristics will aid scientists in discovering and probing new states of matter, understanding and following chemical reactions and biological processes in real time, imaging chemical and structural properties of materials on the nanoscale, and many new and exciting discoveries we cannot even imagine today," said Marion White, senior physicist at APS.

For more information, visit: www.aps.anl.gov/cgi-bin/lstat. The Linac systems status is updated every two minutes at www.aps.anl.gov/cgi-bin/lstat.