SOLEIL synchrotron. Close-up of the monochromator of the Proxima-1 beamline from the SOLEIL synchrotron facility near Paris, France. A synchrotron is a device that accelerates electrons in a vacuum tube to velocities approaching the speed of light. The electrons are kept in alignment by a series of special magnets. As the electrons travel around in a loop they radiate very bright and intense x-rays. This radiation can be used to study extremely small structures in materials science and molecular biology.