English: An undulator at the Australian Synchrotron, Clayton, Victoria. The beam of charged particles from the synchrotron passes down the metal box, between the poles of a linear array of permanent magnets with their poles alternating N, S, N, S,. . . The alternating magnetic fields bend the path of the charged particles, causing them to "unudulate" or "wiggle" as they travel. This wiggling causes them to emit electromagnetic radiation (x-rays) which is emitted at the end of the undulator and used for various experiments.