Battle to Become the Next-Generation X-ray Source

It’s crowded at the summit of x-ray science these days. Some 50 state-of-the-art x-ray facilities, called synchrotrons, dot the landscape worldwide. Another 20 are either under development or on the drawing boards. All are stadium-sized rings that produce bright beams of x-rays capable of the Superman-like feat of peering into the heart of matter to see the atomic structure of molecules. Together they’ve produced countless discoveries, ranging from atomicscale maps of proteins that have been linked to disease to insights into the riddle of high-temperature superconductivity. But now, for the first time in decades, x-ray researchers have set their sights on new peaks that promise to raise their science to even loftier heights. Researchers and science funding agencies are pondering a range of new x-ray sources, some of them add-ons to existing synchrotrons, others major new facilities in their own right. If built, these machines will generate much shorter x-ray pulses than top-of-the-line synchrotrons do today. Researchers hope to use those shorter pulses— possibly as short as 10 to 100 quadrillionths of a second, or femtoseconds—as ultrafast strobe lights to see not only the atomic structure of molecules but also the dance of atoms as they make and break chemical bonds. And one class of machines—called free electron lasers (FELs)—promises to give x-ray researchers something they have never had before: powerful beams of coherent high-energy x-rays. Like light waves from the laser at a supermarket checkout stand, coherent x-ray photons would travel together in perfect unison, rising and falling in lockstep. That regular behavior is expected to create x-ray beams billions of times more powerful than those available today, an accomplishment that could make it possible to collect entire data sets with just one blast of photons rather than the hours or days of beamtime needed today. X-ray scientists insist that the new x-ray sources won’t compete with one another. “The ... facilities are complementary in terms of the science that can be done,” says Roger Falcone, a physicist at the University of California, Berkeley. But because money is always tight, proponents will likely have to square off to persuade backers and funding agencies to support their projects. Still, no matter which camp scores first, researchers should gain access to x-ray beams