Linac Coherent Light Source: Probing the Ultra-Small and Capturing the Ultra-Fast

One of the most spectacular new applications of accelerator science in recent years has been the X-ray free-electron laser, or XFEL. It combines the penetrating power of X-rays, whose wavelengths are thousands of times shorter than those of visible light, with advanced accelerator technology that forms those X-rays into laser pulses 10 million times brighter than any X-ray source available before. These ultrafast X-ray pulses are used much like flashes from a high-speed strobe light, enabling scientists to take stop-motion pictures of atoms and molecules in motion. The first of these machines, called the Linac Coherent Light Source (LCLS), opened for experiments in 2009 at SLAC National Accelerator Laboratory; since then a second one has opened in Japan, and three more are under development in Europe and Asia.  

Those advances would not have been possible without pushing accelerator technology to new frontiers. While X-rays were discovered in 1895 by German physicist Wilhelm Conrad Röntgen and quickly began to play an important role in medicine and other fields, it was not until the early 1970s that scientists discovered how to harness X-rays given off by electrons circling in a particle accelerator – initially a nuisance byproduct of particle physics experiments­ – into powerful beams of X-rays for research. Over the years, researchers discovered how to intensify the X-ray beams from these synchrotron light sources by sending the accelerated electrons through “undulators,” which force them to wiggle back and forth and emit more X-rays. Today these beams reveal atomic structures, help make new drugs, investigate the structure of matter, develop new materials and follow chemical reactions in time and space on a molecular level.

The LCLS and other XFELs are the next step in this evolution, accelerating electrons along a straight line and through undulators to produce an even more intense, rapidly pulsed X-ray laser beam.

This talk will describe how the demand for more intense X-rays perfectly intersects with improvements in  accelerator science and technology to deliver steady and sometimes revolutionary advances in our ability to explore the realm of the very fast and the very small. It will also make a plead to continue to dream of the next generation of accelerators, because it was always the research with respect to these dreams that created them -- and the wisdom of the funding agencies to actually support it – even though it was not always clear where it would go.