Filming molecular reactions
Deep beneath Hamburg, the European X-ray Free-Electron Laser (XFEL) generates intensely bright flashes of X-ray light. Stretching 3.4 kilometers from the DESY campus to the neighboring town of Schenefeld, this international research facility is a record-breaking machine. It produces up to 27,000 X-ray pulses per second, each with a brilliance a billion times higher than the best conventional X-ray sources. The flashes are so short, lasting less than 100 femtoseconds, so they can capture the movement of individual atoms and molecules. scientists create "molecular movies" of chemical reactions as they happen, such as watching proteins at work or observing the formation of new molecules.
To achieve this, electrons are first accelerated to nearly the speed of light within a 1.7-kilometer-long superconducting linear accelerator, the longest of its kind in the world. The accelerator's components are made of pure niobium and must be cooled with liquid helium to a temperature of minus 271 degrees Celsius (2 Kelvin), just two degrees above absolute zero. At this temperature, the niobium becomes superconducting, meaning it can accelerate the electrons with almost no loss of electrical energy. After acceleration, powerful magnets steer the electrons through a slalom-like path, forcing them to emit the powerful, laser-like X-ray flashes.