An undulator is a machine that is used to generate intense electromagnetic waves, particularly in X-ray and gamma-ray light. Synonyms for the word undulator include wiggler and alternating-gradient accelerator. Another similar device that generates similar electromagnetic radiation is called a free-electron laser or FEL. Undulators are used in synchrotron radiation facilities, which are scientific research centers where beams of charged particles are accelerated to produce a range of light sources, such as X-rays and other high-energy radiation. These beams are then used to study various materials, including DNA, proteins, and other molecules as well as the detailed structures of proteins in order to develop new drugs.