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.
A legacy of discovery
The DESY campus has a long history of fundamental physics research. Before the European XFEL began operation in 2017, the site hosted a series of powerful particle accelerators. One of the most significant was the Positron-Electron Tandem Ring Accelerator (PETRA), a 2.3-kilometer ring that began operating in 1978. In 1979, experiments at PETRA provided the first direct evidence for the existence of the gluon, the elementary particle that "glues" quarks together to form protons and neutrons. This discovery was a cornerstone in establishing the theory of the strong nuclear force, known as quantum chromodynamics.
From 1992 to 2007, DESY operated the 6.3-kilometer Hadron-Electron Ring Accelerator (HERA), the world's only lepton-proton collider. HERA smashed electrons into protons to probe the proton's inner structure with unprecedented precision. Today, the historic PETRA ring has been repurposed. Now known as PETRA III, it is one of the world's most brilliant storage-ring-based X-ray sources, generating highly focused X-ray beams for materials science, medical research, and nanotechnology.